What's wrong?

[67weimann]

Someone please help. Motor is a 327 SBC and when I cruise around 3200-3800 RPM it runs fine and then it goes duh-duh-duh then runs fine for a little longer and then duh-duh-duh. When it is doing this, if I open it up all the way, it doesn't do it. I've had the distributor curved, and it did it before and after the dist. work was done...:confused:
What do you guys think it could be?

[wickedfab]

duh duh duh as in missing????
or running out of fuel
or???

[maddad]

Duh duh duh?
Sounds like somethings retarded.
:D

[Jetaholic]

Duh duh duh?
Sounds like somethings retarded.
:D
Duh duh duh...:D

[67weimann]

Duh duh duh?
Sounds like somethings retarded.
:D
Damn, I knew that was coming. For a lack of a better way to describe it.
It may be fuel, but what get's me is if it is doing it I can gas it and it goes faster, just cruising, it does it. It slows down a little when it does it then picks back up. I think it is ignition related but maybe fuel...I don't freakin know. It's hard to describe but the motor sounds different when it does it. I also don't notice it till I've ran it for a bit...:confused:

[wickedfab]

if it only does it when warm i would think its fuel related. pull the plugs and see what they look like. if they are hot i would go up 4 jet sizes in the primary just to see if anything changes. even if the plugs look perfect i would change something to determin what its not

[67weimann]

So, it could be carb related? Maybe, I bumped the jets up 2 sizes already, I guess I'll try to fatten it up more and then check the plugs...

[Fiat48]

Start with new sparks plugs and check all spark plug wires and connections.
Try it again.

[thatguy]

Is there a vacuum advance diaphragm on the distributor?

[ghittner]

Try changing the coil, it can fool you and it is a classic heat related Duh Duh Duh deal.....All joking aside, I've had this stump me before as the boat warmed the thing ran worse and worse. Coil.

[IMPATIENT 1]

Start with new sparks plugs and check all spark plug wires and connections.
Try it again.
sounds like a broken down plug wire/cracked cap/cracked plug to me too.

[IMPATIENT 1]

hope your not feeding it to much timing, that noise could be detonation:sqeyes:

[Fiat48]

Spark plugs and connections would be the easy quick thing to eliminate. Also that vac advance....depending on how the dist was curved could be a player but....he says it did this before dist was curved. Miss goes away under full throttle....could be a part throttle lean condition.
But I would get plugs in it first. Fresh plugs fire easier. Process of elimination.

[DMOORE]

Try changing the coil, it can fool you and it is a classic heat related Duh Duh Duh deal.....All joking aside, I've had this stump me before as the boat warmed the thing ran worse and worse. Coil.
The only thing , is that he said it clears out when he goes WOT. Every bad coil I've seen gets worse with more RPM, as it's breaking down.
Darrell.

[SmokinLowriderSS]

The only thing , is that he said it clears out when he goes WOT. Every bad coil I've seen gets worse with more RPM, as it's breaking down.
Darrell.
Thast has been my experience with bad coils too. Starts with a full throttle miss/colapse, that clears lower, then the bad RPM point gets lower and lower.

[ghittner]

The only thing , is that he said it clears out when he goes WOT. Every bad coil I've seen gets worse with more RPM, as it's breaking down.
Darrell.
Agreed, Thank you.

[67weimann]

Timing is set at 10* BTDC and I believe it has 25* advance. It has the vacuum advance, but I don't have it hooked up since it was curved.
I have had coil probs before and it doesn't come and go. Like was said before, coil probs are in the top RPM range and get progressively lower. I will start with new plugs, wires, cap and rotor and see what happens. I'm gonna try one at a time to see what the hell it is...:D After new plugs, I'll take a plug reading and see if it needs to be fattened up. Now reading a plug for the correct mains should be done by running wot and turning the engine off before letting of the gas, correct?

[67weimann]

I was just thinking, I've heard of the older Holleys (which I have) blowing out power valves upon a backfire. Before my distributor was curved, the mech advance setup inside the dizzy was loose and wouldn't hold the timing it was set to. It backfired a couple times through the carb before I fixed it. Could the power valve be blown out and causing this problem???

[justfloatn]

I don't think it would be plugs or wires. They show up on acceleration when the load is increased.
I think your float level in the primary bowl is too low or something is clogged causing a lean condition on primary only. You stated you changed jets once allready. I had a similar problem on my hydro. It ran fine when I hit the throttle, pump shot, spit and sputtered on the pull and took off on full throttle. I found one of the carbs primary bowls had a sticky needle and seat that would not let the fuel in fast enough.
Fuel delivery would also show up on the big end.
It could be the power valve too

[VDRIVERACING]

Really sounds like you're running lean/out of gas at mid-rpm.
I wouldn't suggest you start changing jets yet, or before you know it you won't know what you have. I presume it ran before with the same jets, yes?
I agree on some plugs, but beyond that before you start changing all kinds of parts, you may want to check for air leaks(manifold or carb), fuel restrictions(fuel filter, debris in carbs or pump), or even a bad batch of fuel.
I have had all the above at one time or another, and it's usually the most basic thing.

[67weimann]

I don't think it would be plugs or wires. They show up on acceleration when the load is increased.
I think your float level in the primary bowl is too low or something is clogged causing a lean condition on primary only. You stated you changed jets once allready. I had a similar problem on my hydro. It ran fine when I hit the throttle, pump shot, spit and sputtered on the pull and took off on full throttle. I found one of the carbs primary bowls had a sticky needle and seat that would not let the fuel in fast enough.
Fuel delivery would also show up on the big end.
It could be the power valve too
See the problem is, is that it isn't consistant. It comes and goes. Not like everytime I'm taking off or anything. It will run fine for a while at mid RPM and then act up for 10 seconds then run fine for another 30-45 seconds then act up for 10 seconds and so on...

[67weimann]

Really sounds like you're running lean/out of gas at mid-rpm.
I wouldn't suggest you start changing jets yet, or before you know it you won't know what you have. I presume it ran before with the same jets, yes?
Yes, but did the same thing and lots of people said it sounds like it was lean, so I pulled plugs and checked...Yeah it was a little lean, so I fattened it up two sizes, took a reading and seemed ok to me. I'm not an expert though. It still did excatly the same thing with bigger mains...

[Moneypitt]

Now reading a plug for the correct mains should be done by running wot and turning the engine off before letting of the gas, correct?
NO!!! You'll totally wash the cylinders down with liquid fuel and wet all the plugs. After a hard run back it down, close the carb, and then click it as soon as it is safe to do so. I always tried to turn away from my wake, Killing a speeding jet is a good way to swamp it from the rear. You will never be able to click it the way you would in a car. WHAT IS THE FUEL PRESSURE???....... I honestly don't think a jet number or two is going to make any difference at all in the quest to solve your problem. Imagine a couple of decades ago when all cars had carburators. We drove from sea level to the mountains all the time without changing jets. Sure the engine ran better at sea level if that is where it was set up for, but it also ran OK up to about 6000 feet. Not as good, but OK without any real stalling or stumbling. Holley will tell you not to exceed 4 jet sizes in either direction. If you still can't dial it in you have the wrong size carb. All that said, you may have a fuel delivery problem, either hanging needle, as mentioned, a kink in a hose, a SS hose that is breaking down inside and collapsing, (suction side), or the little bronze filters in the inlets.......Could also be the air bleeds, those tiny little orfaces, 4 primary and 4 secondary, or just a gummed up internal passage from drying up the fuel last winter. Before I went nuts with ignition parts I would strip and dip the carb, blowing out all the passages real well, then re assemble with a new kit. If you're not experienced with carb rebuilding reach out to your buddies here in HB and find someone in your area that is, buy the kit and some beers and make an afternoon out of it....I'm in eastern Ventura county, bring it over, I've got the dip and the air, and I drink Coronas w/ lime.............MP
PS: After re reading from the top I think it may be a secondary drip. Meaning the secondaries are dripping. What type F/pump do you have? If a needle was overpowered by high fuel pressure it could cause a flooding condition which WOT would cure. Also, what type exhaust? Too much back pressure could put the vacuum impulse into a spasum, causing the carb to go blind as to what to deliver. If WOT cures it, it is too fat at that throttle opening....Not to lean.....MP

[67weimann]

Carb was rebuilt end of last summer. and hasn't sat more than a month tops without being used. So, I should pull it apart and make sure everything in there is good? As for the fuel delivery to the carb...new tanks, new SS lines new electric pump, etc...everthing to do with the fuel was replaced the same time the carb was rebuilt.

[Moneypitt]

Carb was rebuilt end of last summer. and hasn't sat more than a month tops without being used. So, I should pull it apart and make sure everything in there is good? As for the fuel delivery to the carb...new tanks, new SS lines new electric pump, etc...everthing to do with the fuel was replaced the same time the carb was rebuilt.
OK, but it has backfired since the carb was rebuilt, right? Replace the power valve. You may be fat as I said at that particular throttle opening due to a blown power valve, more air at WOT can use the extra fuel. ........Did it have this problem with the old tanks, pump, carb?......MP
PS which carb is this? Vacuum or mech secondaries........

[67weimann]

It sat for a few years before I did all the new tanks etc...
It's a Holley 600 CFM Vac secondary

[Moneypitt]

It sat for a few years before I did all the new tanks etc...
It's a Holley 600 CFM Vac secondary
OK, has someone stuck a screw in the secondary link?.......

[67weimann]

OK, has someone stuck a screw in the secondary link?.......
As in, to keep it from opening? Not sure what you mean...

[Jordy]

It sat for a few years before I did all the new tanks etc...
It's a Holley 600 CFM Vac secondary
Can you watch the linkage for the secondaries open and close when you're going across the water??? On my Schiada jet, with a 750 and vacuum secondaries, it was doing pretty much what you're describing and the secondaries weren't opening like they should. Turns out the diaphragm was in bad shape, combined with the little seal that goes between the main body of the carb and the vacuum pot. Worth a look.

[Moneypitt]

As in, to keep it from opening? Not sure what you mean...
Some guys used to add a screw in the link "arc" to pull the secondaries open. It doesn't work......But now we can address the vac sec carb. It sounds as though the stumble, duh duh duh, is around the transistion from pri only into pri and secondary operation. When you mat it, the problem goes away. There is a real fine line here to make everything happy at the same time, and part of that line involves the power valve. Also critical is the secondary spring, the one that holds the secondaries closed until XX amount of engine vacuum pulls them open. Right there you are dealing with the pri mains, the power valve, and the partial open secondaries pulling on the sec main jets. As you can see this is a tight area of tuning. When the motor duh duh duhs, it could be the fuel is slow coming to the sec venturi, the duh duh duh affects the vacuum and keeps the carb confused until you whack it and the vacuum levels out. If you really want to dial this thing in you will need a vacuum gauge and an observer riding on the motor to see when the sec opens, and/or stumbles. Go to the Holley site and look at the vacuum sec spring assortment, buy it. Then using the vac gauge and the observer, increase or decrease the spring until you get a smooth transistion into all 4. Remember, secondary opening should not be a "bog" and recover, it should be a smooth transistion , a steady acceleration. I really think this is the critical area where the carb is confused. The vac gauge can be a tool type, temp hook up (to manifold vacuum) where the observer can watch it and the secondary linkage at the same time.......The spring kit is color coded, so you can find instant improvement if you have the data to work from.......Then you can get fancy and work on fuel economy........MP

[bwillieb]

............Remote possibility?...........but I've had the same symptoms from picking up small amounts of water in the fuel............dosen't cost much to throw some of the green stuff in your fuel tanks.................

[justfloatn]

See the problem is, is that it isn't consistant. It comes and goes. Not like everytime I'm taking off or anything. It will run fine for a while at mid RPM and then act up for 10 seconds then run fine for another 30-45 seconds then act up for 10 seconds and so on...
That is consistant with a mild lean condition. It leans out causing a few intake backfires, duh,duh,duh, this gives the carb a few seconds to catch-up when the vacuum falls off. The the boat runs for a few seconds more untill the bowl runs dry and duh,duh, duh again. The cycle will repeat forever depending on vacuum and fuel flow. Plus it goes away when you open it up and the secondarys come in which requires more fuel eliminating fuel filter or pump problems. It costs nothing to check for a sticky needel and seat or improper float levels. good luck.

[Some Kind Of Monster]

Ryan,
I never heard all weekend that you were having a problem. I brought a virtual parts store to the lake. I had carb rebuild kits, caps & rotors, pumps.. anything you could want except a gm in tank fuel pump... We could have worked out your problem on the water!

[roostwear]

Holleys use a transition slot to (oddly enough) transition from the idle circuit to the main circuit. the unfortunate part is, the slot is susceptible to carbon buildup, essentially creating a lean spot in the the transition between circuits. I wouldn't lean toward the secondary diaphragm merely becuase it normally creates a bog, not a lean misfire. It could be a TON of different things (or a combination of them), but first, I'd pull the carb off and do a thorough inspection looking at passages and slots, air bleeds (if equipped), gaskets, etc. Eliminate one thing at a time..... shotgun repairs are often expensive.

[Moneypitt]

Holleys use a transition slot to (oddly enough) transition from the idle circuit to the main circuit. the unfortunate part is, the slot is susceptible to carbon buildup, essentially creating a lean spot in the the transition between circuits. I wouldn't lean toward the secondary diaphragm merely becuase it normally creates a bog, not a lean misfire. It could be a TON of different things (or a combination of them), but first, I'd pull the carb off and do a thorough inspection looking at passages and slots, air bleeds (if equipped), gaskets, etc. Eliminate one thing at a time..... shotgun repairs are often expensive.
If it was an off idle stumble I would agree, but this is in the mid range. The transistion into the secondaries from what I can deduct. The duh duh duh he has described sounds more like a flat spot in the exhaust, rather than a lean intake bark. My son has a jet with dual vac sec carbs and it has this also, but is easy to drive through it. And as with his, once you mat it it clears right up and gets crisp again. Does the mid range use anything else besides the vac diaphram to transistion into secondaries?? I feel if it was a double pumper this problem wouldn't happen...........MP
PS: What about a lazy exhaust lifter? Kinda like a part time flat lobe on the cam..........That could upset the vacuum in the intake...and give the duh duh duh he is hearing if it is coming from the intake.

[roostwear]

If it was an off idle stumble I would agree, but this is in the mid range. The transistion into the secondaries from what I can deduct. The duh duh duh he has described sounds more like a flat spot in the exhaust, rather than a lean intake bark. My son has a jet with dual vac sec carbs and it has this also, but is easy to drive through it. And as with his, once you mat it it clears right up and gets crisp again. Does the mid range use anything else besides the vac diaphram to transistion into secondaries?? I feel if it was a double pumper this problem wouldn't happen...........MP
PS: What about a lazy exhaust lifter? Kinda like a part time flat lobe on the cam..........That could upset the vacuum in the intake...and give the duh duh duh he is hearing if it is coming from the intake.
I didn't get the impression from his posts that he mashes it, just that he has to get it into the main circuit to clean it out. Rpm really isn't as important (in the lower ranges) as it's the vacuum (load) and throttle angle that determine the transition characteristics. If he's past the transition when it duh-duh-duh's, I'd look into the secondaries next. Before I threw parts at it, I'd want to see at what vacuum it's occurring.
Why do I keep wanting to say "dee-dee-dee"?:D

[VDRIVERACING]

You didn't mention a fuel filter... Have one?
I recently ran into a fuel delivery problem and found tiny pieces of aluminum stuck in the needle seats and in the fuel pump. No idea where they came from, but it was just after we installed a new in-line filter and larger SS fuel lines. Probably during the course of making the plumbing and mounting we got sloppy and some shavings got in a line.
I think MP is on the right track. Might be time to tear down the carbs and inspect and blow them out; then work you way back to the tank to eliminate the possibility of restrictions.
I wouldn't change anything until you verify a distinct problem, or you could end up masking the original one.

[steve d]

Shot in the dark here. Had several condensers go bad. Seemed to always run
great cold. When it got hot it did everything from sputter, hiccup, run great to quit. Finally grounded it, hung it in the breeze. Hadn't had a problem since. Not too familiar with the new stuff but heat can't be a solid state ignition's friend.....Steve

[Sandbar Mike]

Sounds like water in the fuel. Do you have a water fuel seperator that may be loaded up?

[67weimann]

Sounds like water in the fuel. Do you have a water fuel seperator that may be loaded up?
Yes, I have a fuel filter/water seperator. I'll pull it and see what it looks like. It isn't that old. Maybe 10-15 tanks through it...

[67weimann]

Also, It isn't a lean condition bark, more like a miss or something... I'm gonna go tear into it and see what things look like. Camera in hand...I'll post up later...
Hey Billy, I didn't want to bother you guys with it. I don't want you guys to have to wrench on my shit cuz it isn't running right. I want you to enjoy your time on the water, besides, you had enough to worry about...:D

[bwillieb]

...............If you pull the dashpot that controls the secondaries and there is a check ball in line, you could remove it and give it a try.( it does restrict the amount of vacuum available to begin opening the secondaries) ergo a lean condition could be occuring if you are not getting enough vacuum to open the secondaries when needed.........I had a "not opening at the right time secondary problem" with a Holley replacement for a Quadrajet on my day cruiser, removed the checkball, not a stumble since(it does make the carburator feel more like the secondarys are mechanical)...............Also what kind of distributor are you running? If it's a point type, and you do ( isolate the problem to the distributor, you could buy a Petronix electronic conversion ( not the cheap one) and their high output coil...............At a minimum use a curved HEI........Not a Rocket Scientist, but water in the fuel and the above, are scenarios I have been through............

[67weimann]

Yes, there is a check ball in the sec. dashpot. It wasn't in there untill I took it to a shop and they put it back in there.
It is a curved GM HEI dist.
I pulled the water sep/fuel filter canister off and dumped the gas out that was in it. I noticed a bunch of crap in there that I can't explain like sand. I'll replace it tomorrow. Pulled all the fuel lines and blew them out. I pulled the carb apart and found a piece of AL shaving stuck in the sec. metering plate. Blew out all the passages in the carb. Nothing was blocked other than that metal shaving. I noticed the sec dashpot linkage was a little bent and hitting on the carb body, possibly preventing it from opening. Bent it back straight.
I checked the plugs and they were showing lean conditions in the front half of the motor and good color in the back half:confused: ...not real bad but could be better. Any suggestions on the plug I should use. I have standard autolite plugs from Checker in there now?
Looked at plug wires and seemed ok...noticed the dist hold down came a little loose. Enough I could move the dist...not good. I'll re-set timing and see how it does...
Is it possible to get a sec metering plate that is larger, as in bigger jetting, for the vac sec Holley. As it is, the sec are smaller than the primaries?
Thanks for all the help

[Some Kind Of Monster]

Hey Billy, I didn't want to bother you guys with it. I don't want you guys to have to wrench on my shit cuz it isn't running right. I want you to enjoy your time on the water, besides, you had enough to worry about...:D
So.. You sat there and watched me go through some $100 in gas when we could have been working on your boat for free? How dare you!
Just messin buddy. If my boat wasn't running right, you would have known about it. My boat ran so good that it took off in the middle of the night while we ere sleeping ;) We are all there to help each other. Sometimes it's easier to work on the boats on the water where you can check your results.

[Some Kind Of Monster]

Yes, there is a check ball in the sec. dashpot. It wasn't in there untill I took it to a shop and they put it back in there.
It is a curved GM HEI dist.
I pulled the water sep/fuel filter canister off and dumped the gas out that was in it. I noticed a bunch of crap in there that I can't explain like sand. I'll replace it tomorrow. Pulled all the fuel lines and blew them out. I pulled the carb apart and found a piece of AL shaving stuck in the sec. metering plate. Blew out all the passages in the carb. Nothing was blocked other than that metal shaving. I noticed the sec dashpot linkage was a little bent and hitting on the carb body, possibly preventing it from opening. Bent it back straight.
I checked the plugs and they were showing lean conditions in the front half of the motor and good color in the back half:confused: ...not real bad but could be better. Any suggestions on the plug I should use. I have standard autolite plugs from Checker in there now?
Looked at plug wires and seemed ok...noticed the dist hold down came a little loose. Enough I could move the dist...not good. I'll re-set timing and see how it does...
Is it possible to get a sec metering plate that is larger, as in bigger jetting, for the vac sec Holley. As it is, the sec are smaller than the primaries?
Thanks for all the help
I think you found about 10 things that were definitely not helping your problem.

[Moneypitt]

I think you found about 10 things that were definitely not helping your problem.
Yes, what he said..........Before you go changing metering plates, try that one with the clean up you've done. I have a feeling your problems are over......MP

[VDRIVERACING]

Yes, there is a check ball in the sec. dashpot. It wasn't in there untill I took it to a shop and they put it back in there.
It is a curved GM HEI dist.
I pulled the water sep/fuel filter canister off and dumped the gas out that was in it. I noticed a bunch of crap in there that I can't explain like sand. I'll replace it tomorrow. Pulled all the fuel lines and blew them out. I pulled the carb apart and found a piece of AL shaving stuck in the sec. metering plate. Blew out all the passages in the carb. Nothing was blocked other than that metal shaving. I noticed the sec dashpot linkage was a little bent and hitting on the carb body, possibly preventing it from opening. Bent it back straight.
I checked the plugs and they were showing lean conditions in the front half of the motor and good color in the back half:confused: ...not real bad but could be better. Any suggestions on the plug I should use. I have standard autolite plugs from Checker in there now?
Looked at plug wires and seemed ok...noticed the dist hold down came a little loose. Enough I could move the dist...not good. I'll re-set timing and see how it does...
Is it possible to get a sec metering plate that is larger, as in bigger jetting, for the vac sec Holley. As it is, the sec are smaller than the primaries?
Thanks for all the help
The old "aluminum shaving in the carb trick." Chances are you will also find crud/particles in your fuel pump too. If its the kind that can be disassembled, it would be a good idea to do that before you put everything back together. That's where I found the majority of AL pieces.
I'll be surprised if the things you are correcting do not make a world of improvement. By the way, how old is the gas?

[67weimann]

By the way, how old is the gas?
Not old at all. Couple weeks...
I'll pull the pump apart and clean it too. It's a Holley red. I believe it disassembles...

[squirt'nmyload]

nice.....sounds like you found your possible problem....see ya sunday:)

[tx-19]

check ur gas for water.