Carbed Horizon Misses

[1986GLH]

My 87 Horizon misses between 2k-3k RPM. It is a 2.2 carbed 5 speed car, it was originally an auto and still has the auto computer. The power loss light has not come on. After about 3000 RPM it seems to run better and will pull all the way to 6000 fine.

Tried putting a different carb on it and didn't help so switch back to the original. Tried diferent wires and rotor, the cap looked fine. Spark plugs look decent. I'm running out of ideas. It has the air pump removed and the holes welded shut, but I don't think that would have anything to do with it.

I need to get this problem fixed so I can park my GLH before it snows to keep it rust free.

Thanks in advance for your help.

Justin

[85boostbox]

have you checked timing. when was the last time the Fuel Filter was replaced. i would check those two and check back.

[1986GLH]

Quote:

Originally Posted by 85boostbox have you checked timing. when was the last time the Fuel Filter was replaced. i would check those two and check back.

The base timing is set at 12* which it should be. As for the fuel filter, it runs fine in the higher RPMs so I would think that is fine.

[1986GLH]

Any other ideas?

[NAJ]

I will try to help but it has been over 20 years since I actually diagnosed or worked on a carbed Mopar FWD.
Is there any backfire(exhaust or intake), surge, loss of power or is it just dropping a cylinder?
Will the problem occur in park/neutral or only when driving under load?

[84omni]

when it acts up it lacks power and is hard to keep speed. And the problem occurs only when driving but dont have to be accelerating for it to miss. Didn't hear any backfiring either.

[NAJ]

Refresh my memory.
Feedback or non-feedback carb?
Spark control or standard ignition system?
OE exhaust with Cat?

[1986GLH]

The car has its OE exhaust with cat, its a feedback carb and I believe it has electronic spark control. The car is mostly stock, just has a 5 speed swapped in instead of the auto.

Actually Jason I did back fire while coming to a stop, not loud because it has the muffler but there was a plop sound from the rear. It did backfire out of the intake once when I pulled into the shed. It also diesels once and a while when it is warm.

Thanks everyone for your help so far.

[NAJ]

All systems operate the same, fuel, air, ignition, compression so it is a matter of isolating the system creating the problem.
Start by tapping into the O2 sensor signal line with a digital voltmeter and see what the O2 is doing at idle and while cruising and then under load.
Carburators are not as efficent as EFI but the voltage should still be crossing above and below .450 volts. If it is latched below .450 volts you have a lean/misfire condition, if it is latched above .450 volts you have a rich/incomplete combustion problem.
Also have you checked Cam timing?
Also remove the O2 Sensor and see if the problem goes away, that will eliminate a restricted exhaust as the problem.
Your dieseling problem is related to incorrect idle speed, advanced ignition timing, you are still pulling fuel from the carb after shutting off and engine heat is producing combustion. One of the things I do remember is Chrysler used 4 different PCV valves and if the wrong one was used on a carburated car it allowed additional fuel under the throttle plate which lowered the idle then someone would turn the idle screw up causing a throttle plate opening that was too large without enough air flow so the carb would drip and everyone would replace the carb which did not correct the problem because the wrong PCV valve was the problem.

[1986GLH]

Thanks for the help NAJ, I'm about 100 miles from the car so maybe I might drive home tomorrow and try some of this stuff. I haven't check the cam timing, so I will have to check that. I wouldn't think the exhaust would be the problem because it runs normal above 3000 RPMs, but I will check that anyway.

I bought this car for a winter car to park my DD 08 Focus becuase I didn't want to buy tabs. So I ended up driving my GLH becuase it is my only legal car to drive that will make it anywhere, I just hope it doesn't snow soon.

[NAJ]

Like I said it has been a really long time since I diagnosed a carbed car so I will do what I can. I probably forgot most of the problems I used to run into with these cars but I will help as much as I can.

[1986GLH]

NAJ any help is appreciated this is the first carbed car I've ever purchased. Carbs are just foreign to me, the concept behind them is simple but tuning them looks like a nightmare.

I just want it to make it through the winter. I am thinking about either swapping it to MPI or turbo next summer.

[NAJ]

Chrysler had so many problems with thier carbed cars that when they finally went to fuel injection they used high pressure tbi and went overkill to be sure all the problems were corrected before they went to low pressure tbi.
All of my original training was on Chrysler, GM and Ford feedback carbs back in the mid 80's but like anything else, use it or lose it, it was actually this site that refreshed my memory on TD's, other than mine I have not worked on one in 15 years or so.
Keep me posted on your results and if something pops into my head I will post it.

[84omni]

Did some testing on the horizon today and at a cruse or accelerating the volt meter was at .001 to .008 and did not accelerate at all but when it would go above 3000rpms the meter would read around .450 to .850 and at idle it was at .850

[84omni]

also when taking off from a stop it would buck and jerk while accelerating