Vacuum secondaries won't open

[captainblye]

I recently had my pump blueprinted and now the engine will only rev to 4200 rpm. The engine doesn't sound as if it is under load and the secondaries on the holley 850 cfm doesn't sound as if they are opening up. Do I need to change the spring on the vacuum secondary diaphragm spring?
My theory is that when I had the pump blue-printed that it changed the load characteristics on the motor and is causing the vacuum secondaries from opening up. I think I need to go with a lighter spring.
Has anyone else ever encountered this problem?

[SmokinLowriderSS]

first, what was it spinning before?
Second, just how loose was the wear ring clearance that is now tight?
third, the only way to KNOW what the seccondaries are doing is to let someone else drive and you watch the carb.
fourth, if you can "feel" the seccondaries opening up, they are mis-timed. It should be a smooth and seamless change aas the engine winds up under load. They will not open up without a load if the engine is simply rev'd.

[Jim Hall]

I have been battling the same problem! It falls flat on it's face after 4,000 rpm. I have changed base plate because throttle shafts were worn and installed extended jet's thinking it was starving itself and still works exactly the same.This past weekend I had the opportunity to watch carb while under full throttle and secondaries were not opening.When I opened them manually it was like a shot of nitrous and gained an easy 1000 rpm's.I am going to try some different springs in diaprahm and see if that works unless somebody has a better tip.

[sdba069]

You can check the things that Smokin mentioned, but I'd take that vacuum secondary carb and sell it to some street car guy and buy a good 850 double pumper. There's not a jet boat alive that, in my opinion, benefits from a vac secondary carb. Fuel economy may be the exception on that.

[Squirtcha?]

While I agree with Garry on the mech vs. vac sec, have you checked the diaphragm itself? It might be torn or not sealing around the edges of the pot? One little leak will render it useless. As a test, you can disconnect the linkage for the vacuum pot, push on the little brass rod thereby compressing the diaphragm, hold your finger over the hole and release the rod. It should stay compressed. If it doesn't, it's not sealing.
If you stick with the vac sec carb and replace the diaphragm, it's one of the trickiest things on a Holley rebuild. The screws for the pot cover try to grab the rubber and spin it up which will tear it. I found that just a little grease on the screws helps to keep it from grabbing the rubber when you go to put the cover back on.
If nothing else that's the beauty of the double pumper carbs. No diaphragms to mess with.

[GUGS102]

I recently had my pump blueprinted and now the engine will only rev to 4200 rpm. The engine doesn't sound as if it is under load and the secondaries on the holley 850 cfm doesn't sound as if they are opening up. Do I need to change the spring on the vacuum secondary diaphragm spring?
My theory is that when I had the pump blue-printed that it changed the load characteristics on the motor and is causing the vacuum secondaries from opening up. I think I need to go with a lighter spring.
Has anyone else ever encountered this problem?
See if you can borrow a 800/850 DP to try out, you'll put that vac secondary up for sale.
As far as fuel mileage goes, depending on the amount of vaccum your motor pulls, you can have the secondaries cracked and not realize it. I like the DP because I know exactly how much throttle blade is open, not to mention the hit when you open er up.
After checking all the mentioned areas/springs etc. At 4200 you may not have enough vaccum to fully open the secondaries. What's the rest of the combo?
Gugs

[sdba069]

Damn good tip on the diaphragm rerplacement with the grease. The way I check to see if I'm getting secondary oening is have someone driving the boat in a straight line at full throttle, then I check to see if they are opening or how much, by simply reaching back and trying to open the secondaries further. This will tell you if they are opening or how much thet are opening, but not why they may not be operating properly. And no, simply flashing the throttle open while on the trailer and out of the water will not open the secondaries unless you hold it wide open long enough to grenade the engine.

[Jim Hall]

I just went and bought secondary diaprhragm spring kit and the instructions outline a few things but one that pertains to my situation is carburator restriction affecting vacumm signal.I went from having a spark arrester in an enclosed engine compartment to an open engine configuration with headers and snorkel type scoop that encloses the entire carb. Before I throw carb away I think the spring kit would be worth a try. my $.02 worth

[Hallett19]

I have a vac secondary on my boat and I like it, however after it was rebuilt, I get a loud, and I mean LOUD hissing sound around 3500 RPM's, and it doesnt go away unless its under or above 3400-3800, it will hiss all day if you keep it around those RPM's.... sorry to hijack the thread, but if anyone could help while we are on the topic I'd greatly appreciate it !!
What should I look at to see whats causing it, the operation of the carb by the way is flawless, all 4 open just fine and seamlessly.

[SmokinLowriderSS]

I'm willing to bet the hiss is right at the opening point of the seccondaries. Open far enough and the engine volume as well as larger opening masks it. Reduce revs and it closes, and stops.
I also agree about a preference for a DP carb, I run a 4150 style, 700 CFM, and she runs hard as a lake-boat. Personally, unless you have a LOT of motor, a 750 would be much prefeable to an 850.

[sdba069]

Unlike with a car, we've found that you ALMOST can't over carb a jet boat. Using a CFM requirement formula, I've found that jet boats like anywhere from 150 to 200 CFM more than that formula will show. Smokin, if you have access to an 850, give it a try and I'll bet, if the carb is good and is jetted correctly, you will see a performance gain. Also, any of you guys running vac secondary carbs, give a DP a try and see what happens. Make sure the carb is at least as big as the the vac carb you pull off. Once again, make sure the carb you try is in good condition and has the correct jetting.

[bakerjet]

sounds like a simple fix with the vacume kit and spring choice.
i just sent back a 850dp it had a bad metering plate and it took me a while to figure it out with alot of phone calls during which i spoke with the guys at bigs carbs a couple times, anyway they said this, if your gonna go with a big carb buy the hp 950dp not the 850 because the venturies in the 850 are 1''9/16 with butterflies at 1''3/4 almost a straight shot as compared to the 950 which is 1''3/8 with butterflies at 1''3/4 giving good response on the bottom end as well as the top. maybe that is why summit does not sell the 850dp in the HP? now i dont ''jack'' but i'm gonna try it. :rollside:

[Hallett19]

I'm willing to bet the hiss is right at the opening point of the seccondaries. Open far enough and the engine volume as well as larger opening masks it. Reduce revs and it closes, and stops.
Now, how can I get rid of this sound, it is so high pitched, it hurts your ears !! Thanks for any help :D

[jtmarten]

I recently had my pump blueprinted and now the engine will only rev to 4200 rpm. The engine doesn't sound as if it is under load and the secondaries on the holley 850 cfm doesn't sound as if they are opening up. Do I need to change the spring on the vacuum secondary diaphragm spring?
My theory is that when I had the pump blue-printed that it changed the load characteristics on the motor and is causing the vacuum secondaries from opening up. I think I need to go with a lighter spring.
Has anyone else ever encountered this problem?
I've just gone through this with a brand new 750 vac sec Holley (I should've gone DP!). I've got the lightest (white) secondary spring, and they'll open almost immediately if I hammer it, but they don't want to open if I gradually get on it.
To test your diaphragm, remove the housing from the main body, push the diaphragm rod up and put you finger over the vac port. If the rod stays in place you don't have a vac leak there, if it doesn't hold, replace the diaphragm. While the vac housing is off, make sure the port through the main body is open by squirting some carb cleaner through it. You should see it spraying out of both the primary and secondary venturi.
I agree the best way to tell if they're opening is to have someone else drive while you watch.

[captainblye]

first, what was it spinning before?
Second, just how loose was the wear ring clearance that is now tight?
third, the only way to KNOW what the seccondaries are doing is to let someone else drive and you watch the carb.
fourth, if you can "feel" the seccondaries opening up, they are mis-timed. It should be a smooth and seamless change aas the engine winds up under load. They will not open up without a load if the engine is simply rev'd.
The motor was spinning high 4800 rpm with an aluminum impeller. I don't recall the size impeller, but I believe it was the stock impeller that came with the pump. I reused the stock impeller was blueprinted and reused in the pump. The tolerances on the wear ring are set tight, because I told the shop that I primarily boated on lakes.
I plan on taking the boat out to Elsinore and letting someone else drive while I check to see if the secondaries are opening. Before the pump blueprint I could definitely tell when the secondaries opened because the carb would let out a loud hiss. When the secondaries came in it was smooth and seemless.
I've purchased a Holley Vacuum Secondary Spring Kit and a Holley Quick Change Cover for Vacuum Diaphragm Springs. Hopefully this fixes it.

[captainblye]

first, what was it spinning before?
Second, just how loose was the wear ring clearance that is now tight?
third, the only way to KNOW what the seccondaries are doing is to let someone else drive and you watch the carb.
fourth, if you can "feel" the seccondaries opening up, they are mis-timed. It should be a smooth and seamless change aas the engine winds up under load. They will not open up without a load if the engine is simply rev'd.
The motor was spinning high 4800 rpm with an aluminum impeller. I don't recall the size impeller, but I believe it was the stock impeller that came with the pump. I reused the stock impeller was blueprinted and reused in the pump. The tolerances on the wear ring are set tight, because I told the shop that I primarily boated on lakes.
I plan on taking the boat out to Elsinore and letting someone else drive while I check to see if the secondaries are opening. Before the pump blueprint I could definitely tell when the secondaries opened because the carb would let out a loud hiss. When the secondaries came in it was smooth and seemless.
I've purchased a Holley Vacuum Secondary Spring Kit and a Holley Quick Change Cover for Vacuum Diaphragm Springs. Hopefully this fixes it.

[SmokinLowriderSS]

You could loose 400+ RPM from the impeller to wear ring clearance being way too wide. If it happens, the high pressure water behind the impeller blows into the intake stream which both lowers the pressure in the bowl (which lets the engine wind higher trying to build it back) and blows a hard spray into the intake causing bubbles/cavitation, which lets the engine wind higher.
Do you have any idea what cut size impeller you are running? IMO, it may easilly be 1 to 2 sizes too large holding you down all the way to 4200 RPM.
An impeller can be cut smaller, easilly.

[1968Droptop]

I've purchased a Holley Vacuum Secondary Spring Kit and a Holley Quick Change Cover for Vacuum Diaphragm Springs. Hopefully this fixes it.
I think you'll be happy with the spring kit cptn. I just performed a spring change and was happy with the results. I don't feel them 'hit' when I roll into it, but you can kind of here when they open. I put in the white (lightest pressure) spring per ***boat mag article a couple of months ago. I'm running a 750 VS currently, and have never had a DP on it. I've heard DP is an improvement, but no on hand experience here. I do like the idea of crusing along w/o the secondaries open, may save a little fuel ? Don't know how much it saves, or if the HP loss/gain is worth it, but the 750 VS was on the boat when I got it.
Hallett19: Can you have a buddy drive it and hit that noisy spot in the rpm's while you hold a rag in different area's around the carb to try and define exactly where the sound coming from ? That is an odd one for sure, and I'm sure quite irritating as well.

[SmokinLowriderSS]

As far as cruising on the seccondaries, you better confirm that one. At least with a DP, the seccondaries being closed or open can be assured of. On a Vac Secc, is entirely up to the carb and engine load. If you happen to know what rpm they crack open at (or can hear them) then please disregard the above. :)
On mileage, this is about to be apples/oranges, but, In my youth I owned a '74 Camaro Z-28, SB 400 I built into it. 600CFM Vac Secc Holley, and I bought the spring kit, and normally ran the lightest spring, which had the seccondaries cracked some at highway speeds/rpms.
I did a test one weekend. Drove about 160 miles on a family visit, white spring in, refilled car, drove back home next day, black (heaviest) spring now installed, same route thru Flint Hills in Kansas. Got BETTER mileage with lighter spring in. Engine ran weaker and required larger throttle inputs to make the hills with the seccondaries effectively closed, so used MORE gas.

[Captain Assin' Off]

I run two 660 Center squirters, and there is a definite throttle position that hisses loud.I can drive through it, but the linkage on the 660 is progressive, so I think the hiss is from the secondary position and air rushing past the plates. I know of no cure. Drive through it, or below it, if it's right at cruise speed, change carbs for a different CFM.

[captainblye]

1968Droptop - In what issue of ***boat was the article?
I am running an 850 cfm carb on, what I believe to be, a stock 1988 Hardin Marine 454 with log manifolds. That might be too much carb for the motor. I recently pulled out a spark plug and it didn't look that bad, just a very light coating of carbon. The motor has 150 hours on it and I think it still has the original AC Delco MR24T spark plugs. The plugs are 18 years and have 150 hour of use on them and only a light carbon deposit, so it doesn't seem like too much carb.
The distributor on the motor is a mallory that has points. So, once I resolve the issue with the vacuum secondaries, I'm installing an HEI Distributor with a 50,000 volt coil. Hopefully, the hotter spark will take care of the carbon on the plugs.

[captainblye]

You could loose 400+ RPM from the impeller to wear ring clearance being way too wide. If it happens, the high pressure water behind the impeller blows into the intake stream which both lowers the pressure in the bowl (which lets the engine wind higher trying to build it back) and blows a hard spray into the intake causing bubbles/cavitation, which lets the engine wind higher.
Do you have any idea what cut size impeller you are running? IMO, it may easilly be 1 to 2 sizes too large holding you down all the way to 4200 RPM.
An impeller can be cut smaller, easilly.
The cut of the impeller is what ever size came in the from the factory with the Hardin Marine/Berkley Jet Drive. The motor is spinning at 4200 RPM effortlessly. I never hear the secondaries open. Its like the motor never wakes up. I'm almost positive its some issue with the secondaries. I suspect that there is more rev left in the motor.
If it were the tighter tolerances or the size of the impeller wouldn't the motor at least be straining in an attempt to spin the impeller faster?

[1968Droptop]

1968Droptop - In what issue of ***boat was the article?
I am running an 850 cfm carb on, what I believe to be, a stock 1988 Hardin Marine 454 with log manifolds. That might be too much carb for the motor. I recently pulled out a spark plug and it didn't look that bad, just a very light coating of carbon. The motor has 150 hours on it and I think it still has the original AC Delco MR24T spark plugs. The plugs are 18 years and have 150 hour of use on them and only a light carbon deposit, so it doesn't seem like too much carb.
The distributor on the motor is a mallory that has points. So, once I resolve the issue with the vacuum secondaries, I'm installing an HEI Distributor with a 50,000 volt coil. Hopefully, the hotter spark will take care of the carbon on the plugs.
I just got my new issure earlier this week, so counting that one it was 3 ago. Like stated earlier, boat engine seem to like to be over carbed. An 850 VS doesn't sound like to much to me. The plug color sounds fine as well, but I'd pony up the few bones and do a complete tune up, 18 years is a LONG time. Maybe drop that HEI in as well, then work on your secondaries. This will help eliminate any other possble trouble spots while dialing in your carb.

[sdba069]

Even if the carb is slightly larger than what you need, you can rejet to help correct the carboning problem. A daily driver type jet boat will most likely show a little rich on the plugs and that's fine. You should have the tune up a little on the rich side for everyday use, not ridiculously, just a little.

[captainblye]

Will I be alright with the white spring in the secondaries on an 850 cfm carb?

[1968Droptop]

Will I be alright with the white spring in the secondaries on an 850 cfm carb?
I think you'll be just fine. But even if your not, it's a quick and easy change. Maybe your engine will like a different spring (I think there's 5 in a pack ?), you'll need to do some test and tuning with it.

[Jim Hall]

I put the purple spring in mine and sure enough that is what my problem was! Man,what a difference when everything is working right.Have you had a chance to see if the white spring took care of your problem?

[Cas]

In your first post you mentioned you had an 850 but I don't think Holley has an 850 vs? I'm assuming you have a 750 vs or maybe it's something else?
Is there a list # on the airhorn to make sure what carb you have right now?
Many of the stock engines came with a Holley 715 vs, a 750vs and some had the 780 vs. I've also seen a few with 650's.
When the pump was rebuild you can bet the clearances were tightened up. In doing so the engine may not have enough power to turn it to the 4800 rpms that it was able to when the pump was looser.
What intake manifold do you have on the engine? still stock?
I'd also think a good tune-up is in order, plugs, wires, cap, rotor or just go with the HEI now. You might as well do the tweeking with all the parts you are going to run.

[Cas]

In regards to the carb size discussion, this is what I found to be true on my very mild BBC in a boat I had a few years ago. The engine had log exhaust with OT pipes and an Edelbrock Torker intake then changed to an Air Gap. The distributor was a Mallory dual point then changed to a Mallory Unilite. The cam was relatively mild with .515 intake lift and .525 exhaust, 234 duration and 112 lobe center. The boat was a 21' Tahiti with a Panther pump...the impeller is similar to a Berk B.
The first carb I had on it was a Holley 780vs that was in pretty rough condition that came with the boat. 2nd carb I tried was a used Edelbrock marine 750. 3rd carb was 750 vs that I purchased from Bigs Performance and then I tried an 850 dp.
With the 780, the engine would turn the engine to about 4400 rpms with fairly decent gas mileage. The Edelbrock had pretty much the same results as the 780. I'm pretty sure both of those carbs could have done a lot better with a good rebuild. Both carbs used with the Torker and dual point.
I then changed the intake to the Air Gap, changed out the distributor and installed the 750vs. The engine went from 4400 rpms to 4900 and it was able to run about 7 hrs on 24 gals of gas. Went from about 54 mph to 59 in the 21' boat.
The next carb was the 850dp. I saw 59.8 on the gps but went from being able to run for 7 hrs down to maybe 3. Since the boat wasn't going to be a speed burner, .8 mph wasn't anywhere near as important as losing 4 hrs of run time. I then went back to the 750vs, did a little tweeking with the jetting (78 pri/ 82 sec) rebuilt the pump and got the boat to just under 62 mph before I sold it.
I am changing my current set-up on an engine with quite a bit more power. It had a Weiand Team G single plane intake with a Bigs built 750 dp and it now has an Edelbrock Air Gap and another Bigs 750vs built to the specs of this engine. I have yet to run it to find out if there's any difference in performance but will do so this coming weekend. Prior to this change, the boat ran 71.8 @5000 rpms...oh yea, it's an 18' Bahner open bow (Roger's bottom) with a 20 year old Berk pump/ A impeller.
I've been real happy with the performance but I'm making the change purely to get some better gas mileage. Even though I've been told to the contrary, I just don't think the top end will suffer all that much....we'll see.

[1968Droptop]

I put the purple spring in mine and sure enough that is what my problem was! Man,what a difference when everything is working right.Have you had a chance to see if the white spring took care of your problem?
It's amazing how long that purple spring is. I couldn't believe it even was possible to open the secondaries with it in.

[AzMandella]

http://i5.photobucket.com/albums/y189/AzMandella/Boat/carb003.jpg http://i5.photobucket.com/albums/y189/AzMandella/Boat/carb002.jpg well I have no problems using vacume secondaries on my 12:1 comp. 514 that sees the 7000 range.Plus I do get great mileage out of it when skiing and tubing.And when its time to do a little racing they work as good or better than a set of mechanicals.It took alot of testing but figured out the best combination for my boat.I find the purple spring works the best and a secondary metering block conversion kit.Using secondarys in racing is nothing new.In the 60's Ford used them on their 427 sideoiler cobras.http://

[Sticky Fingers]

Ran 750dp, 850dp, 1030 3 barrel & 780 vacuum secondary. After spending way too much time tuning each one found all turned boat same rpm. Double pumpers fuel circuits setup richer to run on race oriented motors, while vacuum secondaries setup for street. Definately got way better fuel consumption with vacuum sec. 460 in jet got crap mileage any way you stack it. Guick way to check vacuum secondaries it to blow compressed air through venturi that has vacuum pickup in it. If they open your workin, no leaks, just maybe different springs for proper opening time. You can make anything "work" but don't buy into dual 660's or a 850dp on a boat that turns under 5000 thinkin your gonna pickup "BIg" rpms. Unless you have money and fuel to burn. Just my .03 cents.

[captainblye]

In your first post you mentioned you had an 850 but I don't think Holley has an 850 vs? I'm assuming you have a 750 vs or maybe it's something else?
Is there a list # on the airhorn to make sure what carb you have right now?
Many of the stock engines came with a Holley 715 vs, a 750vs and some had the 780 vs. I've also seen a few with 650's.
When the pump was rebuild you can bet the clearances were tightened up. In doing so the engine may not have enough power to turn it to the 4800 rpms that it was able to when the pump was looser.
What intake manifold do you have on the engine? still stock?
I'd also think a good tune-up is in order, plugs, wires, cap, rotor or just go with the HEI now. You might as well do the tweeking with all the parts you are going to run.
The carb has 850 stamped in the main body. I went to holley's website and was unable to find a 850 vs. I was thinking that maybe at one time holley made a 850 vs and discontinued it. Am I looking in the right place for the carb size? When I get a chance I'll post some pics of the numbers on the carb.
I am running the stock intake manifold. I am considering an upgrade to a edelbrock performer or rpm performer.
Just installed a HEI distributor w/ 50000 volt coil, fresh plugs, and MSD plug wires. I haven't put the boat in the water yet.
By the way, I also replaced the spring in the vacuum secondaries. The VS had the heaviest yellow spring installed.

[captainblye]

In regards to the carb size discussion, this is what I found to be true on my very mild BBC in a boat I had a few years ago. The engine had log exhaust with OT pipes and an Edelbrock Torker intake then changed to an Air Gap. The distributor was a Mallory dual point then changed to a Mallory Unilite. The cam was relatively mild with .515 intake lift and .525 exhaust, 234 duration and 112 lobe center. The boat was a 21' Tahiti with a Panther pump...the impeller is similar to a Berk B.
The first carb I had on it was a Holley 780vs that was in pretty rough condition that came with the boat. 2nd carb I tried was a used Edelbrock marine 750. 3rd carb was 750 vs that I purchased from Bigs Performance and then I tried an 850 dp.
With the 780, the engine would turn the engine to about 4400 rpms with fairly decent gas mileage. The Edelbrock had pretty much the same results as the 780. I'm pretty sure both of those carbs could have done a lot better with a good rebuild. Both carbs used with the Torker and dual point.
I then changed the intake to the Air Gap, changed out the distributor and installed the 750vs. The engine went from 4400 rpms to 4900 and it was able to run about 7 hrs on 24 gals of gas. Went from about 54 mph to 59 in the 21' boat.
The next carb was the 850dp. I saw 59.8 on the gps but went from being able to run for 7 hrs down to maybe 3. Since the boat wasn't going to be a speed burner, .8 mph wasn't anywhere near as important as losing 4 hrs of run time. I then went back to the 750vs, did a little tweeking with the jetting (78 pri/ 82 sec) rebuilt the pump and got the boat to just under 62 mph before I sold it.
I am changing my current set-up on an engine with quite a bit more power. It had a Weiand Team G single plane intake with a Bigs built 750 dp and it now has an Edelbrock Air Gap and another Bigs 750vs built to the specs of this engine. I have yet to run it to find out if there's any difference in performance but will do so this coming weekend. Prior to this change, the boat ran 71.8 @5000 rpms...oh yea, it's an 18' Bahner open bow (Roger's bottom) with a 20 year old Berk pump/ A impeller.
I've been real happy with the performance but I'm making the change purely to get some better gas mileage. Even though I've been told to the contrary, I just don't think the top end will suffer all that much....we'll see.
Sounds like you've got a pretty nice setup.
I here you on the gas mileage thing. I'm probably going through 40 gallons og gas in 3-4 hours. I'd trade a smaller carb for the performance gain.
I want to build a new motor. Ideally I'd like to build a 555 cubic inch BBC with a single carb pumping out 700+ horsepower, and it all fits under the motor box.

[Cas]

The carb size probably won't be stamped on the carb itself unless someone added it. The carb # is found on the airhorn and then you will need to cross referrence it on the Holley website or on Mortec.com. Personally, I found the RPM Air Gap to be the better choice for an intake manifold plus it's cooler looking than the Performer :D
I'm sure you're going to find the boat will be easier to start and run better with the new distributor and coil. I know switching out the dual point on my boat made a big difference.
My set-up isn't anywhere near what most of the people have around here. In comparison, it's a pretty mild build with somewhere around 500hp but thanks for the compliment. I'll be taking a couple of pictures of it today now that the new look is complete. I decided I'm really tired of keeping up on the polishing of all the aluminum so everything has been painted. I made the decision a little late for powder coating so that's going to happen this coming off season.

[captainblye]

I used the white spring for the vacuum secondaries and now they work fine. I also dropped in a DUI HEI distributor, MSD Plug Wires, and a new set of plugs. Now she accelerates like a bat out hell. But I am disappointed with the top end speed of 53.5 miles per hour (gps) spinning 4400 rpm. My boat feels faster on a lake then on the river. Its time to make some mods. I'm considering replacing the stock hardin intake manifold for an edelbrock. I'm also considering replacing the log manifolds with a set of lighting headers. What should be my next mod?
What mod will provide the most bang for the buck?

[SmokinLowriderSS]

I used the white spring for the vacuum secondaries and now they work fine. I also dropped in a DUI HEI distributor, MSD Plug Wires, and a new set of plugs. Now she accelerates like a bat out hell. But I am disappointed with the top end speed of 53.5 miles per hour (gps) spinning 4400 rpm. My boat feels faster on a lake then on the river. Its time to make some mods. I'm considering replacing the stock hardin intake manifold for an edelbrock. I'm also considering replacing the log manifolds with a set of lighting headers. What should be my next mod?
What mod will provide the most bang for the buck?
It's always a combination of things. Would sure be nice if I could find the likely cam specs on that motor. What vintage is it? I am assuming it is as-orriginal (stock). Sometimes I tinker in Desktop Dyno WAY too much. LOL
My 1978 454 was IMO really hampered by the iron dual-plane manifold and what turned out to be a .460/.472" lift stock cam (chevy factory hi-lift hydraulic). I installed a much improved cam setup and Performer RPM Air Gap manifold. About $700 there gained me about 60 to 70HP.
That left me with the Niccson logs & snails being my choke-point now. I just put Lightning headers on and 4" outlets. $1500 (used, new outlets) netted me 40 to 50 HP.
That leaves my factory 353049 heads with small valves (2.06/1.73") being the choke point now. Local shop will get those about October for a stage 1 and new valves (2.19/1.88" manley pro-flow reduced stems) Gonna run about $1500 for 100 or so HP there.

[Squirtcha?]

That leaves my factory 353049 heads with small valves (2.06/1.73") being the choke point now. Local shop will get those about October for a stage 1 and new valves (2.19/1.88" manley pro-flow reduced stems) Gonna run about $1500 for 100 or so HP there.
No offense intended here, but I just have to ask................With the prices on aluminum heads what they are, why not go with something that works as well or better and saves ya 70 lbs of unnecessary weight?
As you may or may not know, I had a go round with a set of reworked iron heads. Larger valves, ported, studs and guide plates installed, new valve guides, etc. etc. I paid just a little over a grand for all that and they took a shit on me. Both heads cracked right in the middle at a valve guide. Had I known then what I know now, I would've never even messed with that crap.
Bought the Edelbrocks complete with valves, springs etcetera for $1600 delivered to my doorstep. Literally just bolted em up and ran the piss out of em for the past 5 seasons.
Never again with the iron head thing.

[Scotte28516]

Why not just ditch the POS Holley for an Edlebrock or Carter, which are much better carbs?

[SmokinLowriderSS]

No offense intended here, but I just have to ask................With the prices on aluminum heads what they are, why not go with something that works as well or better and saves ya 70 lbs of unnecessary weight?
As you may or may not know, I had a go round with a set of reworked iron heads. Larger valves, ported, studs and guide plates installed, new valve guides, etc. etc. I paid just a little over a grand for all that and they took a shit on me. Both heads cracked right in the middle at a valve guide. Had I known then what I know now, I would've never even messed with that crap.
Bought the Edelbrocks complete with valves, springs etcetera for $1600 delivered to my doorstep. Literally just bolted em up and ran the piss out of em for the past 5 seasons.
Never again with the iron head thing.
Mainly, I never really gave it much thought squirtcha. That dollar figure is a lot lower than I have seen (but I believe it as I have not searched everywhere to see what I can find), and my ported figure is including about $300 of valves from Manley as well.
I've already got the upper hardware I need (springs, ratainers, polylocks) and will this way buy the valves I want (Manley Pro Flow's severe duty, in the large stock sizes (2.19/1.88)). Just what I need is more extra parts laying arround LOL
Thx for the info tho Squirtcha, as I get down to it, I may rethink. :)

[SmokinLowriderSS]

Why not just ditch the POS Holley for an Edlebrock or Carter, which are much better carbs?
POS?
Ho hummmm.
Holley vs. Edelbrock, Ford vs. Chevy, more of the same.
Edelbrock fans hate Holleys, say they are junk. Holley fans wouldn't touch an Ed. without a BFH in 1 hand, oh well.
POPCORN!!!!!!!!!!!!!!!!!!!!!
My 700CFM 4150 Holley has run perfectly for 28 years. The only time it didn't was every 6 years or so from being wintered-up before the invention (and discovery in the midwest) of Sta-Bil. No sta-bil, and 6 years of crap varnish. Bet it'd jack an Ed or Carter (ed) too. Oh well.
He needs a Mighty Demon he does AAARRRHHHHHHHH!!!! :rolleyes:

[YumaBiesemeyer]

The carb has 850 stamped in the main body. I went to holley's website and was unable to find a 850 vs. I was thinking that maybe at one time holley made a 850 vs and discontinued it. Am I looking in the right place for the carb size? When I get a chance I'll post some pics of the numbers on the carb.
I am running the stock intake manifold. I am considering an upgrade to a edelbrock performer or rpm performer.
Just installed a HEI distributor w/ 50000 volt coil, fresh plugs, and MSD plug wires. I haven't put the boat in the water yet.
By the way, I also replaced the spring in the vacuum secondaries. The VS had the heaviest yellow spring installed.
Holley does make a 850 v.s. It comes on the 502 crate motor. They also sell it as a 870 Avenger.