Engine stutter/misfire under load
 

First post for me, yes I have searched to no avail.

My car has recently started to develop what I think is misfiring. It's a 1983 gsl with a 12a and 144k on the original motor and I'm afraid the seals are starting to go. I recently had the carb off to remove the shutter valve, anti-afterburn valve #2, and replace the accelerator pump. It idles fine, I have it at about 850rpms. When I start it with the choke engaged it runs very rough sounding like it's misfiring which it didn't do before I had the carb off (idled rough but no misfire sounds). Without the choke it revs out fine in neutral, and idles normally.

Problems start between 3000 to 5000rpms in 3rd-5th gear (never experienced in 1st or second). The car starts to get jumpy under throttle and feels like it's misfiring and losing power completely in pulses. I can usually get it to stop by downshifting, revving it out, and getting a large backfire. It also sounds horrible like it's groaning. During one of its moments it also died today. Cold and hot start are a little hard and require some accelerator to start.


What could be causing this?

did the car do this before or after you did the carb work?
If you happened after then you'll have ti go back and double check your work.

It only happened a couple times before, it's much more frequent now which is why I'm worried the engine's about to go

Have you looked at the fuel pickup in the tank? I would. It gets blocked over time, and will deliver enough to run thru 1st and 2nd, but will struggle with 3rd.

I have not. How does one go about that?

Like the other posters stated, this sounds like a fuel issue. It sounds like it is flooding out, like when a muscle car goes from idle to wide open and coughs from having a carb that is way too big.


I know it might be a pain in the ass for you to do, but I would try to either return your carb to stock, or get a stock carb and rebuild it with a stock rebuild kit and no mods. If your ride still acts up with a stock carb setup, then yeah you might be experiencing a tired motor or a fuel pump or tank issue. But I would try that first, just cover your bases. A 12a should last you a few dozen more thousand miles as long as it was taken care of.

you would need to drop the tank for that. it does sound like a fuel delivery issue. i would lean toward a lean condition, myself though (see what i did there? :)).

anyway, you can check the plugs after a decent run where it behaves like you describe and see what that tells you. speaking of plugs, what plugs are you running? also, when was your last tuneup? if not recent, then you may want to look into doing it.

I have br8eq-14s in all 4. They're just over 1k miles old. The wires looked fine so I didn't change them. What would I be looking for on the plugs, unburned fuel and/or burned tips? Last tune-up was... We'll haven't had the car long enough, what's in a full tune up for a rotary?

That's why I'm worried, I really don't know for sure. I can tell you I have found some interesting things held together by wire...

bare minimum, you will want to change the oil and filter, cap and rotor, fuel filter and clean the carburetor. check the MOP function as well, make sure it's working as it should. i would call that bare minimum. wires can be bought cheap, so you should probably do those, too, but if adequate sparks are getting to the plugs, then you can call it for yourself.

for the plugs you want them to be a brownish/tannish color and fairly free of carbon. anything else would indicate an issue, so yeah, you don't want them wet or burned.

I did a compression test and got ~80-90 on all faces of both rotors so my engine should be ok for a bit. I pulled the leading plugs for that, the rear was fine, the front had some unburned fuel on it and was pretty black. I leaned out the mixture screw but I haven't gotten to test it out too much. What does the front plug condition tell me I should check?

it means tune the car up. :)

it means that plug wasn't lighting the mixture. you can check the cap. you could also swap another plug and/or plug wires (not both at the same time) to L1 and see if the unburned fuel shows up somewhere else.

I figured it out! Put a carter fuel pump and holley fpr and it solved my problems! Only thing is my gauge sucks and reads 0. Anyone know of a good gauge fuel gauge for low pressure applications?

That's good to hear, better than having to deal with rebuilding an engine.