Fouling Plugs
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Pro
Joined: Mar 2009
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Fouling Plugs
Should I expect to foul plugs on a fairly stout performance motor with large cam if I frequently start the motor up for only a few minutes at a time? For example, I may not drive the Vette for 2 weeks straight but I always have freinds or customers stop by the shop that want to hear it rumble so I start it up for a few minutes and then shut it off well before its warmed up.. The motor I recently installed was tuned and dynoed and when I received it the plugs looked great but after starting it a handfull of times now they are totally fouled out and today it ran really rough until it warmed up... Just wondering if thats expected or if I should try leaning the idle mixture screws?
Burning Brakes
Joined: May 2008
Posts: 1,165
Likes: 24
From: Boston MA
I would think adjusting the idle would have no effect on the higher rpm bands...I would think...at least with the tweaking I have been doing on my car that seems to be the case...i did have to put one size larger shooters when I realized the idle was obscenely rich, and leaned it out to an acceptable level.
Le Mans Master
Joined: Nov 2008
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From: columbus oh
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Everything is brand spanking new, including the carb and there are no leaks.. I can also see the float level is good through the clear sight plugs.. I didnt have any backfires so I would assume the power valve is good but tomorrow morning when its nice and cold again I will fire it up and lean out the idle mixtures and see what happens. Hopefully that will also help clean the idle up too because I'm tired of having to feather it until it warms up, even with an electric choke hooked up, which is operating just fine.
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Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
if the plugs are fuel fouled you may have to replace them for starters, if you are running a vac adv.be sure the diapharam is ok....if you replace the plugs and get it started, then let it warm up throughly before you adjust the idle mixture,shut it down to see if you are ok....sounds like something is amiss though......check timing and vac adv if equipped.....good luck
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
The black choke housing can be rotated to richen or lean out the mixture. Loosen the three screws and rotate the housing, usually one or two index marks will make enough difference.
There is also a fast idle screw that you can use to raise the rpm when the choke is operating. It works on a stepped cam that moves as the engine warms. As the idle speed increases, kick the throttle and it should step down. These two adjustments work together, so you may have to make go over it two or three times to get it right. It can be time consuming because you have to start with a cold engine each time.
Your idle adjustment will have to be made with the engine warmed. When that is right, then the choke adjustments can be done on a cold engine. Hope this helps!
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
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Take your buddies for a ride and get it warmed up and keep the plugs clean.
Yes they will foul if you keep doing that. Nasty hot rod motors aren't real smooth until the intake/heads etc get some heat in them. They miss and burble with a big cam when cold....but they sure sound cool! When cold you're getting lots of unburned fuel and it's going to kill plugs eventually.
I'd quit doing it. You're doing the worst thing you can do. You've always heard that startups are the hardest on a motor since oil isn't everywhere yet. Plus you're adding tons of unburned fuel to the oil and lots of condensation that never gets burned off. Your ol is going to get pretty acidic.
Fire it up and go riding!!
JIM
Yes they will foul if you keep doing that. Nasty hot rod motors aren't real smooth until the intake/heads etc get some heat in them. They miss and burble with a big cam when cold....but they sure sound cool! When cold you're getting lots of unburned fuel and it's going to kill plugs eventually.
I'd quit doing it. You're doing the worst thing you can do. You've always heard that startups are the hardest on a motor since oil isn't everywhere yet. Plus you're adding tons of unburned fuel to the oil and lots of condensation that never gets burned off. Your ol is going to get pretty acidic.
Fire it up and go riding!!
JIM
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
Take your buddies for a ride and get it warmed up and keep the plugs clean.
Yes they will foul if you keep doing that. Nasty hot rod motors aren't real smooth until the intake/heads etc get some heat in them. They miss and burble with a big cam when cold....but they sure sound cool! When cold you're getting lots of unburned fuel and it's going to kill plugs eventually.
I'd quit doing it. You're doing the worst thing you can do. You've always heard that startups are the hardest on a motor since oil isn't everywhere yet. Plus you're adding tons of unburned fuel to the oil and lots of condensation that never gets burned off. Your ol is going to get pretty acidic.
Fire it up and go riding!!
JIM
Yes they will foul if you keep doing that. Nasty hot rod motors aren't real smooth until the intake/heads etc get some heat in them. They miss and burble with a big cam when cold....but they sure sound cool! When cold you're getting lots of unburned fuel and it's going to kill plugs eventually.
I'd quit doing it. You're doing the worst thing you can do. You've always heard that startups are the hardest on a motor since oil isn't everywhere yet. Plus you're adding tons of unburned fuel to the oil and lots of condensation that never gets burned off. Your ol is going to get pretty acidic.
Fire it up and go riding!!
JIM
......and if the above advice doesn't solve the problem, "read" your plug carefully....you may need a slightly hotter heat range; especially if most of your riding is short street trips.
Melting Slicks
Joined: Jul 2004
Posts: 2,577
Likes: 2
From: Long Island New York
Take your buddies for a ride and get it warmed up and keep the plugs clean.
Yes they will foul if you keep doing that. Nasty hot rod motors aren't real smooth until the intake/heads etc get some heat in them. They miss and burble with a big cam when cold....but they sure sound cool! When cold you're getting lots of unburned fuel and it's going to kill plugs eventually.
I'd quit doing it. You're doing the worst thing you can do. You've always heard that startups are the hardest on a motor since oil isn't everywhere yet. Plus you're adding tons of unburned fuel to the oil and lots of condensation that never gets burned off. Your ol is going to get pretty acidic.
Fire it up and go riding!!
JIM
Yes they will foul if you keep doing that. Nasty hot rod motors aren't real smooth until the intake/heads etc get some heat in them. They miss and burble with a big cam when cold....but they sure sound cool! When cold you're getting lots of unburned fuel and it's going to kill plugs eventually.
I'd quit doing it. You're doing the worst thing you can do. You've always heard that startups are the hardest on a motor since oil isn't everywhere yet. Plus you're adding tons of unburned fuel to the oil and lots of condensation that never gets burned off. Your ol is going to get pretty acidic.
Fire it up and go riding!!
JIM
100%
Thread Starter
Pro
Joined: Mar 2009
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Is there anything I can do to at least minimize this without having to drive it every time I start it? I keep the Vette in the back of the shop and there are also alot of times where I have to just move it to get it out of the way, which means another cold start.. I checked the idle mixture screws yesterday and they are already with-in 1/2 turn of being all the way in.. Would a hotter plug help and if so what is a good choice if I'm curently using the ngk bkr6es?
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Your problem sounds more like a "choke" adjustment problem than an idle adjustment issue. If it idles well [and doesn't run 'rich'] when it warms up, then your choke is closed off too much when the engine is cold. That limits the air to the intake and you are likely fouling your plugs at cold start-up. The Chevrolet Chassis Service Manual has all the info you need to properly adjust a stock carb. Contact the carb manufacturer for instructions on setting the choke properly on an aftermarket carb.
Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
If you start it......., drive it until it's fully warmed up. If you have to move it...., push it. If you have to start it to show off to your friends how "cool" it sounds..... don't. If you follow these three things your plugs will be clean and your motor oil won't be diluted with raw fuel. Cars were made to be driven not stored or started for a couple of minutes at a time !! Heat it up and drive it.......
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
You can get a block heater to keep it plugged in all the time like it was winter time. That would help a lot. You already have some pretty toasty plugs. Do you have an MSD? They help keep them clean a lot.
JIM
JIM
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Pro
Joined: Mar 2009
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I dont have an MSD, I do have a Mallory HEI with high output coil though.
Race Director
Joined: Nov 2002
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From: Taylor Michigan
I have no idea what engine your using but universally across the board many are guilty of using spark plugs way too cold. Performance enhancements does not systematically mean to use cold plugs for every application. Some engines never see a track.....
Thread Starter
Pro
Joined: Mar 2009
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Your problem sounds more like a "choke" adjustment problem than an idle adjustment issue. If it idles well [and doesn't run 'rich'] when it warms up, then your choke is closed off too much when the engine is cold. That limits the air to the intake and you are likely fouling your plugs at cold start-up. The Chevrolet Chassis Service Manual has all the info you need to properly adjust a stock carb. Contact the carb manufacturer for instructions on setting the choke properly on an aftermarket carb.