Carb prob??? - Team Camaro Tech
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post #1 of 12 (permalink) Old Jan 31st, 10, 04:54 PM Thread Starter
 
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Carb prob???

i have a 72 camaro with 402 that's been bored 30 over, 10.5:1 compression, 113 cc oval port heads, lunati solid lift cam (kit), msd ignition, victor jr intake, 750 holley carb., 350 auto trans w/ 3500 stall & 4.10 gears.

when the car is cold it will fire right up with a little pumping of the gas pedal. when the car gets up to operating temperature and i drive it and shut it off (or don't drive it and shut it off), then try to fire it back up it will, fire up cut off, fire up cut off, fire up cut off (almost like it is out of gas). after about 4 or 5 times like this it will finally fire up and idle. i have a full tank of gas.

any ideas is greatly appreciated.

thanks in advance.
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post #2 of 12 (permalink) Old Feb 1st, 10, 06:12 AM
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Re: Carb prob???

clogged filter
or crap in fuel tank clogging the sock filter in the gas tank.


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post #3 of 12 (permalink) Old Feb 1st, 10, 06:42 AM
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Charlie
 
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Re: Carb prob???

When you say fire up, do you mean it will fire up and run, then stall or do you mean it will ignite for a split second then shut off? I ask because it sounds like you may be experiencing fuel percolation. This occurs when the fuel in the bowl gets heated to the point where it expands out and into the intake. Try this the next time. After she heats up and you know the issue will be present, push the pedal to the floor and hold it there while you turn the key. What this does is allows a large amount of fresh air into the system and flushes out all that fuel in the intake. Do not pump the pedal, simply hold the pedal to the floor and turn the key. If this solves the issue, it will help to place a phenolic or plastic spacer between the intake and carb. DO NOT use an aluminum spacer as aluminum is a conductor of heat and will only exacerbate the problem.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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post #4 of 12 (permalink) Old Feb 1st, 10, 06:36 PM Thread Starter
 
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Re: Carb prob???

new gas tank, sending unit, sock filter, new in line filter. seems to be smoke coming from the carb when i shut it off. and yes when i fire it up it cranks for a split second and shuts right off. today it didn't even get warmed up and i tried it after a few seconds of idling and it still did the same thing (fire up shut off). did this like 4 times and i held it to the floor and it fired up and idled rough.

thanks for the help so far.

let me know whaat you think.
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post #5 of 12 (permalink) Old Feb 2nd, 10, 06:17 AM
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Charlie
 
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Re: Carb prob???

I think it is fuel percolation. The fuel is heating up and expanding out of the bowl and into the intake. Try my suggestion and see if it will fire up and stay running. Push the pedal to the floor and hold it there. Turn the key. Once it fires up and begins to run, you will know when to take your foot off the pedal.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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post #6 of 12 (permalink) Old Feb 3rd, 10, 03:37 PM Thread Starter
 
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Re: Carb prob???

tried what you were talking about. still did the same thing except this time it backfired through the exhaust. sounded like a shot gun. talked to the guys at summit and they say timing or ignition. timing is set just like lunati says it should be. ignition is msd 6a system. put the carb on another engine (496) just to see if it could be the carb. the 496 ran good. gonna try the spacer this weekend. i'm hoping this is the problem. let you know what the verdict is as soon as i try it out. thanks for the help.
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post #7 of 12 (permalink) Old Feb 3rd, 10, 03:58 PM
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Alan
 
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Re: Carb prob???

If it is percolation, would he be able to hear/feel the fuel boiling in the bowl when the car is hot and shut down?

alan
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post #8 of 12 (permalink) Old Feb 3rd, 10, 04:15 PM
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Re: Carb prob???

As a bove pumping will only flood an engine...hold the throttle down till fires...u are pumping all the excess raw fuel out....then back fires...yes can happen...espec if exhaust if....all the raw fuel mixture in the exhaust explodes.

So after this happened , and did not pump the gas again, did it backfire again?

When an engine is cold it requires a very rich mixture to start...pumping, hence starts fine

Now lets assume the issue is carb..hot firing no pumping, slow to fire...generally could be float levels too high,leaking fuel raw fuel into the engine.

Old school rule of thumb "many a carb been tunes by changing the spark plugs"
Speaking figurativily...spark plugs= timing HT leads stuff like that.

What is the intial timing without vac and with vac Advance?

Does it spin over easy on the atarter motor before firing or sort of huh--huh .huh .huh fire?

I doubt perculation thry heat...back in the old days..real old days it was a common issue modern engines 40/45 yrs old rare enough to be discounted.

My Spelling is not incorrect...it is creative

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post #9 of 12 (permalink) Old Feb 4th, 10, 06:48 AM Thread Starter
 
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Re: Carb prob???

engine spins fast (gear reduction starter). total timing with the cam is set at 32 degrees. i will check timing with and without vac this weekend as well. i will also adjust float levels lower than what they are now. i may even jet down the carb just to see if this will help. really hoping the spacer is the fix tho.

thanks

let you guys know what happens.....
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post #10 of 12 (permalink) Old Feb 6th, 10, 10:28 AM
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Re: Carb prob???

A spacer should not fix the problem unless the carb is running rich. I would start with the timing. Its free and easy to do. Loosen the distributor clamp bolt and move the distributor in one direction. Shut the engine off and try to restart it. Keep doing this in increments. First one direction then the other. If this does not solve the problem. I'd then move to the carb.
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post #11 of 12 (permalink) Old Feb 6th, 10, 11:01 AM
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Re: Carb prob???

Quote:
Originally Posted by 67CamaroRS/SS View Post
When you say fire up, do you mean it will fire up and run, then stall or do you mean it will ignite for a split second then shut off? I ask because it sounds like you may be experiencing fuel percolation. This occurs when the fuel in the bowl gets heated to the point where it expands out and into the intake. Try this the next time. After she heats up and you know the issue will be present, push the pedal to the floor and hold it there while you turn the key. What this does is allows a large amount of fresh air into the system and flushes out all that fuel in the intake. Do not pump the pedal, simply hold the pedal to the floor and turn the key. If this solves the issue, it will help to place a phenolic or plastic spacer between the intake and carb. DO NOT use an aluminum spacer as aluminum is a conductor of heat and will only exacerbate the problem.
Also check your float levels and when you shut it off look down into the carb to see if it is dripping fuel down the inside of the carb. It could be fuel pressure, high float bowl levels, percolation, bad coil or a bad vented gas cap.

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post #12 of 12 (permalink) Old Feb 6th, 10, 05:29 PM Thread Starter
 
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Re: Carb prob???

Fixed!!!! first off i tried the timing, it was fine. second i checked the float levels, it was fine. checked the volts coming into the msd ign, it was weak. rewired the msd ign along with a couple other items that was a drain on the electrical system. hit the swith and vroom on the first hit. let it idle up to operating temp and shut it off. immediately hit the swith and again it fired up and idled no prob. cleared out the carb and shut it down. fired it up again and all was good. everything is great now. even pull it down in gear and it idles (which it hasn't done in quite a while). heck i can even stand outside the car hit the swith and it fires right up with no problems.

thanks to everyone who has helped me out with the ideas for the fix. cool thing is i have a carb spacer that i was ready to use and now i don't think i need. i may hang on to it and add it anyway cause i hear it helps out with hp anyway.

again thanks to everyone who helped out.
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