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airman_turtle 07-03-2005 12:26 AM

Runs Rough when Cold
 
I have been wondering lately, when i start my car in the morning after it sat all night, or at night when it sat all day it runs rough. I dont mean cold outside, i just mean when the engine is cold. It has been 70s-80s lately in the morning so its not cold by anymeans. So in the summer, i keep my choke fully open, to a point it doesnt shut at all.

could this rough idle and wanting to stall be that? should i still have the choke somewhat engaged? If i let it warm up for a few minutes by holding the gas down it runs just fine, its just that first start after a night or day of not running.

I dont think i need all my specs for this one, its probably a basic carburation answer im looking for.

thanks

DoubleVision 07-03-2005 12:34 AM

As you know, I run a road demon jr. and it runs like crap when the engine is cold, always runs super rich and will only stay running if I keep the rpms to around 1200 or better, it doesn`t have a choke, and a choke would likely only compound the problem. I`ve just lived with it even so I could live without it. When I drop in the new engine i`m going back to a Q-jet, I don`t like the downleg boosters on the primary side of the demon, it`s been a great carb other than that though. The only time it`ll start with the engine cold and idle fine is when the car has sat in the sun in 90 degree temps.

TurboS10 07-03-2005 06:38 AM

Hmm....I missed where he has a demon. I did not see what kind of carb we are talking about.

As a general rule, the engine needs to be much richer when it is cold than after it warms up. The good thing is that an engine will idle with a wide range of AFR. I never realized this fully until I started fooling with EFI. I just checked my warmup enrichment on my turbo engine. At 80 degrees I run 40% more than the normal amount of fuel at a warm idle. My engine idles at 13.8 AFR because it just seems to like that. That puts the AFR in the 9:1 range when I first crank it at 80 degrees ambient. Keep in mind my CR is around 9:1, cam is 230 dur @ .050 with 114lsa, which all can affect cold start enrichment(choke position for you).

Point of my ramblings is that an engine likes a very rich mixture when it first cranks up. This is what the choke does for you. If the mixture is right without choking then it is WAAYYY too rich when it gets up to temperature.

Just food for thought.

Chris

airman_turtle 07-03-2005 10:06 AM

well I have a speed demon and my cam is 236 duration. It really doesn't bother me, but I just wanted to make sure that this is normal..or not a bad thing at that. I can deal with holdin' the gas down until it warms up. I'll just leave the choke open like I have it.

airman_turtle 07-21-2005 11:21 AM

ok then no worry,i got an LM-1 and when i have it idle at 13.5-14:1 when it is warmed up its like 11:1 when its cold...if thats how its supposed to be then im ok with it. My only question is...is this couple rich minutes, bad enough to foul plugs?

Tech @ BG 07-21-2005 11:35 AM

Quote:

Originally Posted by airman_turtle
ok then no worry,i got an LM-1 and when i have it idle at 13.5-14:1 when it is warmed up its like 11:1 when its cold...if thats how its supposed to be then im ok with it. My only question is...is this couple rich minutes, bad enough to foul plugs?

Rasing the fast idle RPM may help this situation, but 11:1 should not foul your plugs out if it's only doing this when you're warming the engine up.

TurboS10 07-21-2005 01:25 PM

Agreed with BG. I run about 10 or 11:1 if I remember right while it is cold. That will not foul the plugs at all.

Chris


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