won't run right under 2500rpm!?

tfritz · 01-07-09, 12:56 AM

I found my ‘catch’ in the linkage problem (there was a slight bend) but it didn’t solve all of my problems. Now it won’t run under 2000rpm, I can feather the throttle to try and keep it running at most rpms between 2k and 900rpm. If I try to hold a steady throttle at any particular rpm in that range it either proceeds to die or the rpms climb rapidly until I stop them by letting off the gas completely at 3500rpm then the rpms fall and it proceeds to die again unless I feather the throttle. I can set the choke to hold the rpm at anything over 2k but if I try to go under it spits and sputters until I feather the throttle. Over 2k rpm with the choke or just using the gas pedal it runs good and smooth. I checked the spark plugs, cyl. 5 & 6 were wet, and all were worn so I replaced them. I cleaned out the distributor. I checked the timing, it is very close –I didn’t have a timing light, but I set it to TDC and the rotor pointed to plug wire #1. I have rebuilt the carburetor, changed out the bad gas, and run lots of sea foam and carb cleaner through it without any change. None of the adjustment screws seem to do anything. I left the idle mix screw alone as it was capped off and assumed it didn’t need adjusting if nobody changed it. Anybody have any ideas??? I am lost I spent most of the day working on it with little improvement I am frustrated to say the least.

inkpot · 01-07-09, 02:36 AM

Howdy! What year is it, and is it stock/desmogged? I would first guess that you have a big vacuum leak. Check all the hoses and fittings around the carb and intake manifold. John

NocalFJ60 · 01-07-09, 04:35 AM

Sounds like your carb settings are all messed up now or a big vacuum leak.

Like John said about checking all your vacuum lines for a leak.

Did you remove the plug over the idle mixture screw or was it already gone when you rebuilt it?
How was the mating surface on the manifold when you installed the carb?
Did you use the rubber gasket with no paper?
Have you checked that the choke flap is open all the way when the choke is pushed in all the way?

grant5127 · 01-07-09, 05:45 AM

Symptoms of idle solenoid malfunction...... got voltage? got ground? little o-ring on the tip replaced during rebuild?..........

tfritz · 01-07-09, 11:55 AM

its a '87 and its all stock

the choke appears to be adjusted correctly, it is all the way closed when pulled out and all the way vertical when pushed in

the idle mixture screw hasnt ever been uncapped, it is untouched.

I haven't checked power to the idle selenoid, I am sure I replaced the o-ring...

Now I have some more things I didnt think of to go back and check!!! thanks guys I will keep you posted.

szester · 01-07-09, 04:36 PM

Quote:

Originally Posted by tfritz

I found my ‘catch’ in the linkage problem (there was a slight bend) but it didn’t solve all of my problems. Now it won’t run under 2000rpm, I can feather the throttle to try and keep it running at most rpms between 2k and 900rpm. If I try to hold a steady throttle at any particular rpm in that range it either proceeds to die or the rpms climb rapidly until I stop them by letting off the gas completely at 3500rpm then the rpms fall and it proceeds to die again unless I feather the throttle. I can set the choke to hold the rpm at anything over 2k but if I try to go under it spits and sputters until I feather the throttle. Over 2k rpm with the choke or just using the gas pedal it runs good and smooth. I checked the spark plugs, cyl. 5 & 6 were wet, and all were worn so I replaced them. I cleaned out the distributor. I checked the timing, it is very close –I didn’t have a timing light, but I set it to TDC and the rotor pointed to plug wire #1. I have rebuilt the carburetor, changed out the bad gas, and run lots of sea foam and carb cleaner through it without any change. None of the adjustment screws seem to do anything. I left the idle mix screw alone as it was capped off and assumed it didn’t need adjusting if nobody changed it. Anybody have any ideas??? I am lost I spent most of the day working on it with little improvement I am frustrated to say the least.

Mine was doing the exact same thing, just got done putting new vac lines on it and now all is well.

tfritz · 01-07-09, 10:51 PM

I bought all new ones today so I am going to try replacing them ALL tomorrow wish me luck guys

Michael Hanson · 01-10-09, 05:45 AM

Check EGR pipe for clogs. Mike

tfritz · 01-11-09, 05:45 PM

all vacuum lines have been checked and replaced to their proper locations

egr valve has been tested and its good

but it still doesnt run any better!!!

It still acts like a vacuum leak -shoot carb cleaner in the carb it revs up. The timing is advanced about 40 but you cant change it much without it running worse at the higher rpms. I am not getting anywhere :( any other ideas? Im going to pull the carb again and check all the gaskets and look over the intake manifold wish me luck

Richmond · 01-11-09, 06:15 PM

Check your carb gasket, spray some cleaner around the base of the carb and if it revs up then you have a bad gasket, same goes for intake gasket and a lot of other stuff on top of the engine. Just go lightly with the spray and don't let it pool up anywhere.

tfritz · 01-13-09, 01:13 PM

it wasnt really running well enough to narrow it down using carb spray nor propane

I did however find the problem!

I took the carb off for the 176253rd time and made a plate to go over the opening in the intake and threaded an air hose fitting onto it. I fed around 5-10psi in the mainfold listening for leaks, I then dumped water all over it and it began bubbling all along every intake port. I rechecked the torque values and they were good, looks like I'm getting a new gasket. I it was however a pain in the ass to get the manifolds off!!

daviesl · 01-13-09, 03:27 PM

just in case the new header gasket doesn't solve the problem remember to check the heat riser flap's condition and the intake manifold (just under the carb) for cracks, it's a common problem causing backfiring through the carb (black soot on the engine side barrel) and idle probs. Also, just to make sure add a ground line from the green wire going from your idle solenoid to part of the frame, Richard at K&H showed me that trick. cheers (I'm in the process of doing the same on my fj60, ended up taking buying the overhaul gasket kit and taking off the head too, figured while i had everything off I might as well make more work for myself.)