Dual 450'S Part Dux

[tittyman]

So I changed out my 660'S for 450'S...BBC, 12:1, tunnel ram, radical cam, mag..Before I installed the carbs I changed out the PV to 2.5 from the original 8.5. Heres the problem..In order for the boat to sort of idle I have the idle speed screws almost maxed out, maybe 1/2 turn left. Mixture screws are all set at 1 3/4. When running, the boat is very snappy, no bog during acceleration. Does not want to idle (normally needs to idle at 1200) just fades away to stop, sometimes idles a little too fast then fades away to stop. If you turn the key off before it stalls it starts right up. If it fades away it's hard starting and sometimes backfires. Secondary throttle plates are in original location, almost closed. Still has original jets (58). Plugs are brown after idle. Did not check after WOT..there are no vacuum leaks...how do I get this thing to idle..thanks again for all the good advise..

[Blown 472]

You have the curb idle cranked? then you are into the transition slots, you may have to drill holes in the throttle blades to get more air into the motor.
What was the problem with the 660's??
Did you read any of that stuff on the holley web site?

[tittyman]

Yes..I read it..Holley tech clown said go with 450's..got the 660's to run great, The problem is where we launch and have to boat to camp and ski is about a 15 mile boat ride..I would run out of fuel coming back with the 660's..Going to keep them for short hot rodding days...So tell me more about drilling these holes..how big..do I also need to open the rear throttle plates more? Any other solution other than drilling?

[Blown 472]

Yes..I read it..Holley tech clown said go with 450's..got the 660's to run great, The problem is where we launch and have to boat to camp and ski is about a 15 mile boat ride..I would run out of fuel coming back with the 660's..Going to keep them for short hot rodding days...So tell me more about drilling these holes..how big..do I also need to open the rear throttle plates more? Any other solution other than drilling?
I would start with the rear throttle blades, if there is a screw to open them do so, but only expose a lil bit of the transition slot, if alot of it is exposed it will start to draw fuel. If you get the rears open you can close up the fronts. How much of the mixture screws do you have out? 2 turns from closed? make sure there is no crap plugging the air bleeds on the top of the carb throttle body.

[tittyman]

Just got off the phone with the Holley tech guy again..he said just crack open the secondary throttle plate on the front carb maybe 1/2 turn..see how it runs..if still no idle crack open the secondary throttle plate on the rear carb 1/2 turn. Do not crack both those rear plates open more than 1/2 turn max..See how it runs..if still no idle start drilling the front carbs primary idle plate with 1/16 drill..if still no idle then go the the rear carb and drill those out 1/16..if still no idle then go to 1/8 and drill...he said once you get the air right they should be fine and I should be able to set my curb idle screw way back down again...

[AzMandella]

Personally I think two 450's is too small.I have talked to Holley tech before and think they are a little nuts.Give Marvin a call at Quick Fuel Tech.He was a head engineer at Holly for 30 yrs.He and the VP of marketing at Holley left and started their own buisiness.He is very informative and won't steer you wrong wether you buy anything from him or not.
http://www.quickfueltechnology.com/home_2.htm
Marvin Benoit
270-793-0900

[tittyman]

These are bought and paid for...so I got to do my best to dial them in..I know a lot of guys here are running dual 450'S..Doesn't starting to drill 2 holes 1/16 of an inch sound like it's a little to small to begin with? Also holley recommended that I just drill the front plates first and then give it a try and see how it idles..wouldn't it bet better to drill all 4 so the air flow is equal or does it matter..if that's not enough air then go back and drill at least the front 2 to 1/8" and then see how that works..what are your thoughts on that...thanks again guys...

[tittyman]

Guy's..give me some help here..do I drill the holes? Just got off the phone again with the Holley clowns and now they don't know for sure..should I start by drilling the four 1/16 holes..then if that doesn't work go to drilling four 1/8 holes or what...really appreciate some help..The Holley clown just said those carbs should work period.....

[AzMandella]

Like I said give Marvin at Quick Fuel a call and talk to him.He knows more than the tech guys at Holley any day. But here is my 2 cents. Usually when you start drilling holes and modifing a carburator is because you have the wrong carb. I know others are using 450's on their big blocks but most are mild engines(i.e. low comp. mild cams) In my opinion those carbs will not work very well with your combination. I run dual 750's vac. secondaries on my BBF514.I too wanted beter fuel milage when towing the kids on a tube etc.BUt the way I have them tuned they will also run liked a raped ape when I put my foot into it.

[bp]

my suggestion (and it's only that) is to close off the mixture screws to 3/4 turn each. as 472 said, and your tech guy said, you don't want to set the butterflys open too far, because the transition slot will be too exposed, then you end up with a bog.
you can do this in your driveway (with pump disconnected of course:) ). after getting each of the idle mixture screws at 3/4, start the thing and see if it will idle. then check each float bowl, make sure the levels are correct. if not, adjust them (loosen float adjusting screw/big flat screwdriver, while holding adjusting nut with 5/8. lower float level [clockwise] or raise [counterclockwise] one flat at a time, snug holding screw and watch level rise/fall). before running the boat and setting the floats, make sure the boat is level side to side (floor jack works), and the bow raised so that the attitude of the boat is the same as it is in the water (if you adjust the floats with the boat exactly level, they'll be off in the water). float level can affect idle.
with the bowl levels adjusted to the overflows, and the idle mixture screws at 3/4, you should be able to get the thing to idle (if it ever will). once there, you can open the idle mixtures 1/8 turn at a time (each one), until the engine slows down from too much fuel, then close back off. you could also go it the other way, closing off 1/8 at a time until it's getting too lean.
the issue is that there is way too much fuel going in through the idle circuit with the butterflys closed, and the mix screws at 1 3/4. holley recommends setting the mixture screws at 1 1/2, based on one carb. but that's theoretical, and you don't have much, if any, more air going in there than 1 carb would allow. this is also why your plugs are shiat brindle brown after idling around.:)
if this doesn't help, and you still can't get it to idle with the butterflys set as you previously described, go with 5/64 holes, two in each primary butterfly. but unless you're engine is pumped up pretty good, like a fairly high lift/duration cam, it should idle just fine without drilling the holes. getting the right a/f mixture at idle is key, and you got too much on the /f side... good luck with it.

[tittyman]

Here is the latest..took the 450'S off and made sure they were both adjusted the same. Closed the secondaries back down to the original position. Some wanted me to drill holes in the primaries and some didn't...I drilled four 3/32 holes. Got it to idle with problems. I can get it to idle between 1200-1300 just like when I had the 660'S on. But after about 1 to 2 minutes it wants to fade and stall out. It will hold idle without any stall from say 1500-2000. I cracked open the secondaries about 1/2 turn. I still have a little ajustment left in my curb idle screw. My mixture is at 1 1/2 turns. If I try and reduce the mixture it wants to stall after I get about half way done. My plugs are now light gray and so is are the headers. My floats are set correctly. I know if I put the boat in the water and put some load on the pump I will have to set the idle up..don't have much left..should I drill the holes a little larger or set fire to the boat or what...thanks again for the help..thanks to the guys who sent me PM'S...just don't know where to go from here....

[tittyman]

Come on guys..need some help..should I drill the holes 1/16 larger..If I do that will I get more curb idle adjustment..will I be able to lean out the carbs more if I drill the holes larger?

[sandwindersandcars]

this might be a stupid question but, have to checked timing,and compression on all cylinders, also made sure all cylinders are firing, it is alot of work for an engine to idle if one or two cylinders are dead, also needs enough timing to idle. this just seems insane that your engine wont idle, unless the idle stop screw is turned in to far and the plates are so far open they are exposing the transfer slot, but even this usually makes is slobbery rich and it gets pretty obvious.
so in answer to your question, if all is correct, all cylinders hitting, decent compression, no vacuum leaks, not even leaks on single cylinders, and you have enough advance in it, and the idle set screw is just starting to open the throttle plates, and you cannot get it to idle with the mixture screws,and the fuel is indeed good, then yes, drill the holes larger.
the idea of the holes is to allow enough air to bypass the plates for the engine to idle without having to turn the idle screw in and mess up the relationship between the throttle plate and the transfer slot.
but i still think something else must be wrong, because with two carbs,with both idle set screws turned in slightly, there should be plenty of air to get the engine to idle.

[tittyman]

My compression is good, checked that, my ignition, timing is good..Another thing I don't think I mentioned earlier is that before I drilled the holes my plugs were brown from just idle and so was the exhaust color on the headers. Now they are more light gray. I know it's not the fuel pump because it's a Holley Blue with a reg. and it was working with the other carbs. I'm going to drill these holes out to 1/8..if that doesn't work I'm going to push the boat off a cliff! Still can't figure why it will idle for a minute or two then wants to fade and needs more fuel, then idle for a minute or two and then wants to fade again...thanks for the reply and help..I know this thread is getting boring..