not exactly sure if this is the problem but wen i go to turn car off its as if the carburetor is sucking too much air wont allow me to turn car off unless i tap gas a little or i have to try to get it ti idle very low before attempting to turn off and it will shut off fine also seems as if car is getting a little hot is was told that these probs have to do wit car or carburetor are sucking too much air. its an 87 TA 4bl carb 5.0 Any help and suggestions is much appreciated

 

what is idle speed? what is idle timing? Are the idle mixture screws set properly?


PS...until you get it all fixed you can shut it off in gear and that will kill the motor, then just put it in park to remove your keys.

 

not sure about mixture screws but ill check on that but it idles just above the 1 when its already warm and running. when its cold about half way between 1 and 2. also sometimes when im in drive and stopped like at a light or stop sign when i go to take off to hit gas its as if it chokes abit almost giving u the impression that it will shut off but it wont. its like a split second thing

 

turn the idle down!

once warmed up it should be idling around 700rpm. When the idle is set too high it allows alot of fuel and air to get past the throttle blades and cause the 'run-on' like you describe.

 

on a stock engine with a stock cam the engine could idle as low as 500 or so in gear, so you definitely can lower that speed until the motor chugs then raise it another 100 or so. My engine idles at 800/850 in gear and it has a much larger cam than yours I'm sure.

 

Yah, I had the same problem with my warmed up 355 with 305 ported heads. Comp. is around 10.3 (92 oct.) so if my idle is to fast the engine will run on when it is at normal (200* to 220*) operating temp. What I did was add another solanoid (see pic) next to the A/C sol. The second sol. is used for engine idle only so I backed the idle speed adj. screw all the way off. When I shut off the engine the idle sol. loses power and the return spring closes the throttle plates complety so no A/F mixture gets by. The engine shuts down right away. No run on.

Auggie

 

Did you do something to the carb or make any other changes to the car? This could also happen if you retarded the timing too much... or it could be electrical problems.

 

Nothing has been done to the car. Nothing has been upgraded. I just got the car about two months ago after selling my 82 firebird. It was my dads and had been sitting for about two-three years ( was in minor car accident. Was sitting because needed new front bumper,hood, and windshield). Could sitting for 3 years have caused whatever is wrong with it? My dad said hes not sure what it is. He messed around with the timing to see if that would help. Helped a bit, not really though. The car wasnt doing that before it was sitting for those few years. He thinks the timing is off and the carb needs to be adjusted. I work alot so we havent had much time to look at it because I take the car to work about 40min away from my house. Like I said car runs fine for the most part aside from this. We are prob gonna mess around with it tommorow morning. Aside from the timming what are things that could contribute to this that I should check for?

 

I have a pretty large cam as well, high comp pistons, but not so much heads. My effective compression is just shy of 10:1. I like to idle my car at 1000, usually just above when its cold, and usually just below when slightly warm. I realize, 1000-1200 is on the high side, but i need a new transmission and stall converter, the stock 900 stall drops the revs quite a bit in gear.

My point is, 1000-1200 is a high idle, BUT it will not cause run on, unless you have some serious carbon build up goin on in your cylinders. My car idles sometimes all the way up to 1500, but when the key goes off, so does the car, no hint of run on.


Does your car burn oil? (black smoke out the rear, and smells like burning oil). Pop the hood, get a torqs bit on the end of a screwdriver, and turn the idle screw down. Takes a couple seconds. Then shut off the car, but i have a feeling theres a bit more to this, then just high idle run on.


Few more questions, what he described in the original post, doesnt say anything about run-on. When you say it doesnt shut off, describe what it does. ie: Your turn the key off, and it keeps running normally, as if u didnt do anything? OR You turn the key off, and it fires a couple cylinders here and there, struggling very much, and not sounding like a running car at all?

Also, he mentioned the car is running hot??? Too much air would mean a lean mixture, and a lean mixture has the opposite effect. May your just running it in traffic alot or something.

However, your mixture is definately off, that would also explain the bog. Carbs have to be fine tuned, and you'll notice they wont run the same on a rainy cold day, as they would on a really hot day.

 

When turn the key for the car to turn off, the engine shuts off it seems, but the carburetor starts like choking. Sometimes while its like stalling or choking it shoots out like vapor or fumes and does a truck sounding noise before it stops. Im sure it has more to do than the car simply idling high. When I had first got my 82 firebird v6 carb 2.8 (sold it) it idled high before I adjusted it, but never did this.

 

That sounds like dieseling to me. I think the first thing to do would be to snag a timing gun and set the timing back to the factory setting. If it still continues to happen then we can go from there knowing that timing wasn't the problem.

 

Yea ok, thats exactly LIKE dieseling/ run on, now were getting somewhere. LIKE a bad mixture would totally influence it, but not LIKE effect it. LIKE your timing is probably really off, and LIKE your idle is also too high.

However, i think you may also have some carbon deposits in your cylinders. If its been sitting for that long, your gaskets have probably taken a toll, and if youre burning oil, that would build carbon in the cylinders. When carbon deposits build up in your engine, they glow red hot, and will continue to ignite whatever little mixture is getting into the cylinders. My buick did this because the oiling ring were fried.

EVERY time you shut it off like that, you are making it worse, because youre basically choking the car to shut it off, and that fouls your spark plugs badly.

Until you get around to fixing the problem, shut the car off IN GEAR with your foot on the brake. The dieseling cant over power the brakes, and you wont be choking the car each time u need to shut it off.

 

Online170, don't you mean Dynamic compression ratio? Effective C/R is calculated when the intake valve closes and a good street eff. C/R would be like 7.5 to 1.

Auggie

 

No i didnt mean dynamic CR, i have a terrible DCR at low revs, its a 112 or 110 LSA or so. I have 11:1 TRW pistons, and a 70cc chamber, so its not the highest CR, and probably near high 8 or so for DCR.