# 455 won't idle



## 66lemansgto (May 31, 2020)

i have a 66 lemans with a 455 has a mild build by Previous owner. Lately it won't idle runs fine at high rpm. If you take the egr hose off the front of the carb it sticks air but runs better. Carb smokes badly after it shuts down. I thought to much fuel pressure so i installed a regulator got the pressure down to 4psi from 8. Still acts the same way. 
Has a brand new edelbrock avs2 carb. Floats are correct but acts like it's flooding badly. Can't start it unless it is floored. 
Any suggestions or similar issues that have been resolved?


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## Lemans guy (Oct 14, 2014)

Is this cold? If cold is your choke set correctly,? Should start and idle higher, like 1200 to 1400 Rpm for a minute as car warms and choke opens...then you can kick down the pedal

is tat all correct?


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## 66lemansgto (May 31, 2020)

No it does it when it's warm also. If it's not running 2500rpm it won't run. When the hose is off for the egr it will run about 1800 rpn but if you try to lower the idle even a little it just dies slowly.


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## Lemans guy (Oct 14, 2014)

Could be the idle circuit adjustment, and it was running good before it did this?

One possibility if your base timing is too retarded when you get the rpms up to 2500 it adds timing from the centrifigal weights,......then then added timing will allow it to run, but not at idle

recheck your base timing, if the distributor clamp bolt loosened or moved it could have moved the timing to retarded.

idle circuit may need readjustment on carb from baseline, .....PCV hose should be attached and PCV valve should be working...it does effect the mixture, the vacum leak from the PCV is smalll at idle but still there and effects the adjustment so have it in and clear.

also check your plug gap, plugs wear to a wider gap and can make a engine hard to idle if gap gets too wide...

a carb leaking fuel into the intake can cause the mixture to be overly rich, say at idle, when you open the throttle although more fuel goes in so does more air so it runs...

make sure that your power valve is not leaking fuel into the Mixture and making it flood and later smoke, fuel bowl gasket as well....


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## Mine'sa66 (Oct 30, 2019)

Everything you describe indicates a rich condition. Good thing about carburation is it's in there. Bad thing is you have no electronic diagnosis available. My guess from 1000 miles away is that you have a blown out power valve in your carb.


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## 66lemansgto (May 31, 2020)

Carberator is brand new. Also tried another carb of a vehicle that runs good just to check. They both ran the same. I am really lost I've sent through timing, plugs, cleared the fuel line and return line. Getting nowhere.


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## Lemans guy (Oct 14, 2014)

if it is not the carb, are you sure of the base, centrifigal and vacumn timing settings? Is dist hooked to full manifold vac or ported? try unhooking andp luging that and see if there is any change.

also throttle linkage can make you run too fast, weak or too strong throttle spring setup can do this as well.


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## Mine'sa66 (Oct 30, 2019)

OK, you take off the EGR hose? You are running an EGR valve on this engine? When you say the carb smokes badly, you mean when you shut down, there's smoke coming from the carburator itself? Is it white like steam? Not much more it could be than gas running into the engine and being boiled. Which points back to the carb, but a different carb is the same. Does the test carb "smoke" when shut down as well?


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## 66lemansgto (May 31, 2020)

Pcv valve sorry for the confusion. When it is unhooked and open it runs better but still not good. After shut down white smoke rolls out of carb. Did it with both carbs. 
I will try moving the vacuum advance to full manifold but i don't see it making that much of a change. 
Timing i set at 32 degrees at 3000 rpm can't idle it down low enough to check initial timing because it won't idle down


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## RMTZ67 (Mar 12, 2011)

Have you already checked for vacuum leaks with some sort of spray?


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## 66lemansgto (May 31, 2020)

I did. Checked all around manifold and hoses. No signs of a leak anywhere.


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## PontiacJim (Dec 29, 2012)

If you pulled the PCV valve and it got better, that to me would indicate you are may be introducing additional air to the mixture, changing the A/F ratio.

Things to check. Did you verify that the throttle blades are closed with the carb off - visually checking?

Is the idle screw fully backed out and not holding the primary throttle blades cracked open?

What are the settings on your idle mixture screws on the primaries? Did you gently turn them in, then back them out a few turns for your initial settings?

Did you try a different spring for the power valve on the AVS? If you have a healthy cam, you may not have enough vacuum to pull the power valve down which will add additional gas into the engine. You may need a weaker spring.

Did you verify that the carb gasket you are using fits both the carb & intake opening. If the wrong match is used, you may be allowing air in under the carb/manifold.

I agree with the others, sounds like it is flooding. Whatever the factory drop is for the AVS, I would go a little tighter so the float does not raise as high and see if that helps.

Have you read the online AVS pdf and followed their tuning/problem adjustments?


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## Lemans guy (Oct 14, 2014)

Well, all of your timing may be coming from your centrifigal advance, I have seen a lot of distributors like that they have 30,34,36 degrees of timing....

you have 32,... but it may be all centrifigal....and no base...if your vacumn advance is on ported Vac it pulls no timing at idle......but if you put it to full manifold it will pull some timing...depending on the can......if it idles then you found the problem.....so it is just for atest a chance...

Really sounds more like a fuel mixture problem, because when you pull off the PCV it runs better. The PCV is mostly closed at idle the vacumn pulls against a spring, when you accelerate and vacumn drops the spring takes over and opens the valve to clear out the crankcase fumes. It is not solid shut at idle but much less.

when you take it off and introduce more air it runs better. So when you lean it out it runs better, like PJ, meme and RM said maybe too rich.

is your exhaust clear, no sticking heat riser valve? Choking it out....Is your linkage ok, you said you swapped carb and checked fuel pressure......

make sure that you take the cap off the dizzy and the rotor and look at the weights and springs, and they stuck, move freely, springs on?an easy look....

recheck spark plug firing order as well, rough running could indicate a miss,, it will run with a plug out of sync, but mayrun rough or not idle like you have....just verify plug wires synced and on tight.

of course could be internal mechanical as well, but check these other things that are ez, then you may need to do a compression test and or leak down test.


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## 66lemansgto (May 31, 2020)

Thanks for all the responses. I'm gonna take a day this weekend and try some of the ideas. Hopefully i can get it cruising soon.


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## Lemans guy (Oct 14, 2014)

Things that make your car run too rich,...fuel pressure too high, floats too high, leaky accelerator pump, leaky carb gasket......

.OR a restriction in air flow, like a clogged air filter, a real strong throttle spring that close the throttle place so tight it restricts the air flow ( some air goes thru idle circuit, but plates have to be set right as well)...Idle mixture screws set wrong...

so just remember that restriction in “air flow” also cause a rich mixture....just like too much fuel.....


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## Mine'sa66 (Oct 30, 2019)

Lemans guy said:


> Things that make your car run too rich,...fuel pressure too high, floats too high, leaky accelerator pump, leaky carb gasket......
> 
> .OR a restriction in air flow, like a clogged air filter, a real strong throttle spring that close the throttle place so tight it restricts the air flow ( some air goes thru idle circuit, but plates have to be set right as well)...Idle mixture screws set wrong...
> 
> so just remember that restriction in “air flow” also cause a rich mixture....just like too much fuel.....


2 different carbs do the same thing.
Really tricky. Steaming unburnt gas after shutdown, from both carbs.....
Somethings making them both rich, you say you lowered the fuel pressure from 8>4. Did you do that after you tried both carbs? Too high fuel pressure could have bent the float arms causing similar symptoms to stuck/sunk float.


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## 66lemansgto (May 31, 2020)

Yes regulator was installed and turned down before second carb was tried out. When i checked the floats on the original carb they were a little out of spec but not much. I adjusted them to correct height. I'm gonna get to it this weekend. Try to lean it out every way i can see what happens.


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## Montreux (Mar 8, 2009)

You’ve replaced carbs—what about the rest of the fuel system? What fuel filters are you using? Are you pumping trash into the needle and seat?


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## 66lemansgto (May 31, 2020)

New fuel filter and pressure regulator installed


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## Mine'sa66 (Oct 30, 2019)

66lemansgto said:


> New fuel filter and pressure regulator installed


What are you getting for engine vacuum? There's not a heck of a lot the car can do to the carb. Fuel pressure/foreign material. Throttle linkage, engine vacuum. Vacuum issue (low or high) causing secondaries to hang open a little?
Down to spitballing here....


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## Lemans guy (Oct 14, 2014)

had an engine act like this years ago, it was a cracked block at one cylinder. The coolant was getting into the engine and that was the white smoke at shutdown.

It would not idle but would run, found it with compression and leak down test. A leaky head gasket could do the same by putting coolant into the cylinder and messing up the mixture. when you open the throttle it has enough air and fuel to overcome the coolant leak. when you shut it off, then white smoke pours up the intake from the cylinder.

So don't despair as your engine may be new and not doing this. but after you check ignition, timing, fuel pressure, carb and vacumn leaks. then you have to check cylinders with compression test, leak down test and or even for byproducts of combustion in coolant with the liquid and syringe thing at the radiator cap. If it turns color then you have combustion byproducts in the coolant, and that only gets there with a head gasket leak, or a cracked block or head.

so let's hope the timing is off!


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## Mine'sa66 (Oct 30, 2019)

Lemans guy said:


> had an engine act like this years ago, it was a cracked block at one cylinder. The coolant was getting into the engine and that was the white smoke at shutdown.
> 
> It would not idle but would run, found it with compression and leak down test. A leaky head gasket could do the same by putting coolant into the cylinder and messing up the mixture. when you open the throttle it has enough air and fuel to overcome the coolant leak. when you shut it off, then white smoke pours up the intake from the cylinder.
> 
> ...


Yes, let's hope for the OP's sake that isn't the case!
Should be pretty easy to tell even without a block tester....
What's the white "smoke" smell like?
Evaporated gas or evaporated coolant each can be pretty easily identified via odor.


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