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-   -   Holley tuning question (http://www.clubcobra.com/forums/holley-tuning/120197-holley-tuning-question.html)

PeteF 04-16-2013 12:06 PM
Holley tuning question
 
Holley experts: Should putting your finger over the bowl vents (either one) at idle cause the engine to die out quickly? Mine does this. This implies to me that the engine is breathing through the bowl vents, which I think it should not do. Carb is a model 4160/3310, 750 cfm vac secondary about 4 years old. I developed a bowl leak after coming out of winter hibernation, and installed new (Holley blue) gaskets. The metering block is flat and no contamination found anywhere. I didn't change float settings, but did adjust idle mixture screws. Engine runs fine otherwise, idles around 800 rpm and 15 inches vacuum. Any advice appreciated, thanks

patrickt 04-16-2013 12:41 PM
Quote:
Originally Posted by PeteF (Post 1240152)
Holley experts: Should putting your finger over the bowl vents (either one) at idle cause the engine to die out quickly?
Yes. By sealing off the tube with your finger there is no longer a pressure difference which "pushes" the fuel out through the carb. If the car runs well, and does not leak fuel, then it's time to leave the carb alone.;)

Gaz64 04-16-2013 02:25 PM
Correct. All carbs will do that, nothing to worry about.

zrayr 04-21-2013 06:13 PM
Quote:
Originally Posted by PeteF (Post 1240152)
Holley experts: Should putting your finger over the bowl vents (either one) at idle cause the engine to die out quickly? ....."
have you ever filled a drinking straw with Coke or any other liquid, held a finger over one end, then lifted it up out of the glass ? The liquid doesn't flow, or barely flows, right ? Same thing. Without air flowing into the carb, gas cannot, and will not flow properly.

at the other end of your car, stick a potato up the exhaust pipe(s). See how long the car runs.

Free flowing rules.

Z.

domenic saia 12-29-2013 08:38 AM
help! my 4150 double pumper shoots fuel right out of the secondary bowl vent right off idle...am I looking at to much fuel pressure? just replaced the needle and seats and have the yellow plastic floats...it's a 650 on a 289 hi-po...regards domenic. thanks guys for any input!

patrickt 12-29-2013 09:26 AM
Quote:
Originally Posted by domenic saia (Post 1277668)
help! my 4150 double pumper shoots fuel right out of the secondary bowl vent right off idle...am I looking at to much fuel pressure? just replaced the needle and seats and have the yellow plastic floats...it's a 650 on a 289 hi-po...regards domenic. thanks guys for any input!
Check your fuel pressure, but this is usually a needle and seat not sealing off problem. The fact that you just replaced the needle and seat means you probably have it out of whack or a chunk of something in there holding it open. If you take out the sight plug on that side you're going to have a gusher coming out, so don't do it on a hot engine.

domenic saia 12-29-2013 12:37 PM
Patrick, I will remove the sight plug and take a look , possibly remove the needle and seat but first I have a new fuel pump laying around. I will replace it and see what my fuel pressure is. hopefully around 5psi ?

patrickt 12-29-2013 12:51 PM
Quote:
Originally Posted by domenic saia (Post 1277693)
Patrick, I will remove the sight plug and take a look , possibly remove the needle and seat but first I have a new fuel pump laying around. I will replace it and see what my fuel pressure is. hopefully around 5psi ?
5 to 7 psi. By the way, if you have an in line liquid filled fuel pressure gauge like mine, DO NOT RELY ON IT. You have to measure your pressure with an external, known to be reliable, gauge.

http://www.clubcobra.com/photopost/data/500/blue001.jpg

domenic saia 12-29-2013 12:57 PM
Patrick, should I use just a hand held pressure gauge and start the car let it run with the fuel left in the carb or just crank it over and check the pressure? domenic

patrickt 12-29-2013 01:07 PM
Quote:
Originally Posted by domenic saia (Post 1277696)
Patrick, should I use just a hand held pressure gauge and start the car let it run with the fuel left in the carb or just crank it over and check the pressure? domenic
For a mechanical pump, if plumbing it in is too tough, you can just run it for a short while on the gas that is in the float bowl. I think your fuel pump will probably be OK, but you always have to check it first.

domenic saia 12-29-2013 01:16 PM
thanks Patrick, I will get back to you!

RallySnake 12-29-2013 01:28 PM
I had the same problem a while back. It was caused by a Carter electric fuel pump. The internal regulator failed and it was putting out 12 psi instead of 5.

Also, try lightly tapping on the end of the carb near the needle/seat. Sometimes that seats the needle.


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