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Never Enough
07-14-2008, 10:33 AM
Team:

My 1991 Tristar 351 Indmar has always run great. It starts fairly well but idles in "surges" or "chugs". I have cahnged the fuel filter and adjusted the idle speed up a bit but it still doesn't idle very well. It runs great at high RPM. Any ideas? I don't want to lose 2 weeks in the shop at this time of the year. :confused:

Gonzo
07-14-2008, 10:42 AM
Mine was doing this just last week and it was running too fat, I leaned the mixture with the screws on the side of the bowls and then upped the idle a little. Per a friend I need to fatten the mixture up a bit because as lean as I have it I may burn up the cylinders but it wont be nearly as fat as the PO had them. One of them was almost all the way out. Here is a PDF on your carb, it has all the adjustment info.

http://www.tmcowners.com/teamtalk/showthread.php?t=24873

O and welcome, hang out here and do some searching, there is awesome information.

JimN
07-14-2008, 11:00 AM
If idle speed was never a problem before, it won't fix the problem you're having. How long since the last tuneup? Has the flame arrestor been cleaned recently?

Never Enough
07-14-2008, 11:30 AM
JimN:

Thank you for your comment. The problem started a couple of weeks ago. It was never a problem before. I have never had a tune up done. (it only has 400 hours on it). I changed the spark plugs about 10 years ago. The flame arrestor is clean.

JimN
07-14-2008, 01:21 PM
You think a car would run well if it had a tuneup 10 years ago and hardly ever ran?

TMCNo1
07-14-2008, 02:12 PM
Poor Idle on 1991 MS 351 Indmar
Team:

My 1991 Tristar 351 Indmar has always run great. It starts fairly well but idles in "surges" or "chugs". I have cahnged the fuel filter and adjusted the idle speed up a bit but it still doesn't idle very well. It runs great at high RPM. Any ideas? I don't want to lose 2 weeks in the shop at this time of the year. :confused:


I would like to see some pics of this 1991 MariStar TriStar, if that's what your referring to. It has to be one or the other, but not both! TriStar model from 1987 to 1991 and MariStar from 1989 to today.

learjet2230
07-14-2008, 06:48 PM
You wont burn up cylinders with a lean idle. It just wont run as well.

Never Enough
07-15-2008, 10:00 AM
It is a Tristar

fletch_n_me
07-15-2008, 10:29 AM
I always did plugs every year. I think she just needs a tune-up per JimN's recommendation. They do a lot of sitting around and I would bet you have some fouled plugs by this point. The carb shouldn't just go out of adjustment like that. I woould just swing by autozone and grab some plugs - also check your cap, rotor and wires - make sure the rubber bushings haven't dried and cracked. My 2 Pennies...

Storm861triple
07-16-2008, 05:28 PM
You wont burn up cylinders with a lean idle. It just wont run as well.
I agree. You won't even "burn up cylinders" at WOT, running lean on an engine that makes 41 hp/liter.

OP; the symptoms that you're describing are indicative of an improper air/fuel ratio at idle. While you can adjust the idle mixture screws as described and probably solve the immediate issue, I agree w/JimN that the engine is overdue for a "Tune up", which would include adjusting the idle mix adn idle speed...among other things.

JimN
07-16-2008, 06:14 PM
"You won't even "burn up cylinders" at WOT, running lean on an engine that makes 41 hp/liter."

Then, how does this happen to people's cars when they're bone stock?

Storm861triple
07-16-2008, 07:15 PM
Who says that it does? I've never seen it happen. (bone stock). In fact there were factory cars in the 70's that (bone stock) were engineered and sold, configured to run as lean as 18:1 A/F ratio. They didn't "Burn up". Any leaner than that, and you lose so much power, and begin to misfire, that you'll "burn up" nothing anyway. The real "danger zone" under heavy load is 14.5:1 to ~16:1 IMO. Leaner than that, and the engine is "falling off" in a big way.

Years ago, I had a TBI Trans Am. I ignorantly installed used injectors from a 2.8L TBI engine, ASSuming that all GM TBI injectors were the same adn the programming was the difference. As you can imagine, a 5.0L engine ran pretty lean on 2.8L injectors! It idled like crap, but actually ran "O.K." on the highway. I ran it like that for at least 6 months before I committed enough time to figure out my error. No "burned up" anything. When I got the correct injectors in it finally, it ripped (for what it was) and more importantly, was no worse off for the incident.

Later, same car, I installed a 6.6L engine, but ran it w/the same ECM, programming and 5.0L injectors initially. It ran fine. So fine, that I though that it was "fine", until I took it to the drag strip and ran about 2 seconds slower than it should have. It was way too lean, on the 5.0L injectors. I installed a bigger fuel pump, bigger injectors, and promptly dropped ~2 seconds off the 1/4 mile times. Unfortunately, the time frame for those fueling changes was another several months due to "life". No damage, no "burned up" parts. Nothing. Just a lack of power that the old SOTP meter didn't identify.

I'd love to see a stock or even stick-ish car, that is 50hp/liter or less, that burned a piston due to a lean mix, and no other extenuating or contributing factors.

Never Enough
07-16-2008, 11:21 PM
Thanks guys. I will try to make a tuneup my weekend project - now that I smashed my baby into my dock after it died on me (I was coming in too fast as my wife always tells me). Now I need to find some platinum colored gelcoat and learn how to repair fiberglass.