302 idle when cold
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Senior User
Joined: Aug 2007
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302 idle when cold
Heres the problem-
When cold (morning) starts fine idles high(fast idle) then as the choke opens up starts to die. i have to give it gas to keep it running till the engine gets up to tempature. Ive tried adjusting the choke to stay closed longer (lean it out?) helped a little but as its gotten colder here it has gone back to the same. Its a 74 302 with a edlebrock 600 cfm carb. im not rulling out plugs, but they are relatively new(replaced in sept along with coil, dizzy, etc). Also when this happens i can smell the gas fumes coming from the exhaust(why i tried leaning it out to begin with) ive got good vacum, around 20 when at temp, havent checked when cold. i dont have egr or any of that, ive checked for vacum leaks and couldnt find any. any ideas?
When cold (morning) starts fine idles high(fast idle) then as the choke opens up starts to die. i have to give it gas to keep it running till the engine gets up to tempature. Ive tried adjusting the choke to stay closed longer (lean it out?) helped a little but as its gotten colder here it has gone back to the same. Its a 74 302 with a edlebrock 600 cfm carb. im not rulling out plugs, but they are relatively new(replaced in sept along with coil, dizzy, etc). Also when this happens i can smell the gas fumes coming from the exhaust(why i tried leaning it out to begin with) ive got good vacum, around 20 when at temp, havent checked when cold. i dont have egr or any of that, ive checked for vacum leaks and couldnt find any. any ideas?
Elder User
Joined: Sep 2004
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From: midwest
my big block did this when it was real cold out. i believe the problem is the intake and fuel is so cold it just puddles and doesnt atomize like it should. i think the only fix would be to get a heat riser tube from the exhaust manifold to the air filter just to help warm the fuel up thats goin into the intake. stock they have them but we tend to throw them out when they get old and we do a carb swap. should be able to rig up one though. i think you can buy a universal heat riser from the local auto parts
Cargo Master
Joined: Dec 2004
Posts: 2,232
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From: NE Texas
Closing the choke does NOT lean it out, it richens it up. Having the choke open a little longer should have helped the situation, however.
I would have to see how the fast idle works on that setup, but I would think that you could run the fast idle up a little as long as it doesn't interfere with warm idle.
I would have to see how the fast idle works on that setup, but I would think that you could run the fast idle up a little as long as it doesn't interfere with warm idle.
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ok, so i did a quick search on a few parts sites for a heat riser and looks like i need a vacum canister. now i had one of those at one point in time, but i took it out when i put in the intake and got rid of all the old emission gear. Do all of them require a canister? and if so would i just buy one and hook it up to the vaccum tree? Also i have true duel exhast with an x-pipe installed is the heat riser going to be affected by that? or is the engine going to be? and would having headers effect this?
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one other suggestion i got was to try a different heat range spark plug? Anyone have any experiance with this? i know it can be done, but have never looked into it.
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Joined: Mar 2008
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From: Hanford Ca.
yes i did on my 69 mustang i put spacer plates in also add 2in volosty stacks to it and ran the choke as open as need but also i changed my fuel metering rod by one so it wasnt so agresive
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Elder User
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From: midwest
all you need for a heat riser is a tube from a header pipe to your air filter. just something to add some warm air to the intake charge that will help the fuel atomize. you shouldnt need a vacuum canister. they are more effective with a snorkel type air filter but you could get one to work with an aftermarket filter and just take it off when the weather is warm.
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makeing the carb more rich dosent make much sense to me as im already smelling gas fumes even when the engine is running fine. do i have the wrong idea here? i would assume that making the carb burn richer would in turn cause more problems?
Post Fiend
Joined: Nov 2005
Posts: 7,437
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From: Charles Town, W bygod Va
It keeps it on fast idle longer. When you smell gas is it blowing black smoke? The fast idle is adjustable, but mine was doing that minus the gas smell and my choke opened too fast not letting the fast idle cam hold the throttle open at all. Going towrds rich made the choke open slower. The vacc. canister is just a reservoir so when you go full throttle you dont lose vac. to the heat riser flap in the air cleaner, so it would work well enough without it
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well i adjusted the choke, put it more rich this time. and seemed to help with the idle at start up and getting to temp. now though when i give it gas going down the road, it bogs down. just one thing after another with old trucks/cars i guess. but im not to worried about that really, so long as i dont get on it to much it drives fine and im happy with that. still going to look into the heat riser, but wife lost her job last week so looks like ill be putting alot of things on hold till summer time.
Post Fiend
Joined: Nov 2005
Posts: 7,437
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From: Charles Town, W bygod Va
Sorry to hear about the wifes job. Make sure your choke opens all the way when it warms up, otherwise you'll be sucking lots of fuel. The edelbrok owners manual has some pretty good info, its on their website
