Help diagnose new 1st gen
 

HI! I picked up a CLEAN 83 GS on monday. Car ran really good (as described by seller) when he bought it. It needed brakes. He let is sit for ~2 months, wouldn't start...

I brought the car home, immedaitly did a few things;

New batt cables, Optima red top, new plugs, drained and refilled gas tank (NASTY)
Car had sat for ~7 months.

I diagnosed no spark on leadings, switched coils and fired just the trailings... idles OK, but any amount of accel pedal and it dies. Once it shot a flame about 2 feet
out of the carb....

I'm pretty convinced the carb needs a thorough rebuild. I've tried to manually move the throttle plates open, they are pretty hard to move. I've DL'd the carb manual, and I'm reading the FAQ's etc...

Obviously I need to get a new ignitor, or convert to direct fire. Right now I'm trying to get it on the road as cheaply as possible, but I DO have an MSD laying around.


What do you guys/gals think might be the issue(s)?

Thanks in advance!

sounds like the carb to me because the ignition shouldn't cause it to die just off idle.

something you can try just for shits and giggles is check the + side of both coils for power and if you pull the leading ignitor off you can check the pickup resistance to see if it's ok. if you think the ignitor is bad and have more time than money (like me) and have the parts laying around you can rig a early 70's GM 4 wire HEI module to the coil and pickup to see if it will fire.

Actually, this could be directly related to ignition issues, so I'd start there. Even if it doesn't fix the original problem, at least you know the ignition is working correctly. Plus, with BOTH trailing and leading firing, you'll get best fuel economy.

You mentioned that it will idle just fine; this seems to indicate that you're getting spark to the trailing without a problem. Off idle, it dies - this could be caused by the increased engine speed triggering the ignition advance on the Leading side, which isn't firing. In this case, the engine will attempt to speed up, not have enough Leading spark to fire the mixture, and stop.

Trailing plugs firing are to aid in complete burn of the fuel and also add a bit to overall torque. Leading plugs firing are required for high-speed operation, and the advance designed into our cars helps the engine to accelerate quickly and maintain clean, powerful burning even at high rpm.

You stated the leading ignitor is bad - swap it for the trailing ignitor and see if you have the same problem. If so, you're looking at cap/rotor/wires/plugs - in that specific order. Have a look at these components and see if there's anything amiss.

Ignitors are pretty easy to come by at your local pick-a-part, but can kill performance and gas mileage when they go bad. As long as your car is an 81-85, you should be able to swap these easily right on the dizzy with 2 screws and the wiring harness.

Good luck, and give that a shot,

DO NOT and I repeat DO NOT just drive the car on trailing ignition. The car will have zilch for power, and then after about ten minutes take a look at your exhaust and watch the pretty orange glow comming from it.

I blew out my leading ignitor once, and I had to limp the car home by only driving it a minute at a time and waiting another 10 for the exhaust to stop glowing

Fix the ignition first. Try swapping the ignitors, the trailing doesnt add that much power, and it really helps clean up emissions as well provide a signal for the tach.

I can guarntee 90% of your problems are right there.

I wasn't clear in my origional post.

It idles shitty, won't stay running. Right now I'm really confused as well, after swapping coils and wires..

A series of questions:

Front ignitor is for leading?
Coil most forward is for leading?

Last night I ran the rear coil off the rear ignitor, and swapped the coil wires. I obtained spark on the leading plugs, but obviously that was out of time which would account for the backfiring out of the carb (fire)

Tonight I swapped ignitors, and swapped back the coils, as well as the coil wires. For some reason, it was firing the trailings only again?!?! So I think I've got something backwards somewhere!

Also, I have continuity on the rear ignitor on both wires of the coil. Perhaps the wiring harness is screwed up? I don't have a diagram and the service manual hasn't been located yet.

Please help!

leading igniter faces forward and the trailing should be facing the alty.if you have a look at the uncovered part of the wires on both the trailing and leading coils/igniters, the following places for the wires go:

from negative on leading coil to the negative lead on igniter- wire is yellow/blue

from neg. on trail coil to neg. on trail igniter- wire is yellow and green.

black/white wire from the positive terminals on both coils should go to the appropriate igniter(leading/trailing)

after you are sure the wiring is correct, I would switch the leading with the trailing igniter(As far as I know they are the same) to obtain leading spark. once you have done the and provided it is idling check the timing(just to be sure). Next I would then move on to the carb if your problems aren't fixed. Move on to the carb next for an initial inspection or the butterflies and such. personally I would just rebuild the carb if you can, it won't take you more than a day and you can get a reasonably cheap one from napa usually. hope some of my ramblings have helped!

I did swap the ignitors around, except I simply left off the trailing one as it is "bad".
I'll double check the neg wires on the coils.

I've got an MSD sitting around here, I'm really thinking about just triggering it off the leading mag pickup, and seeing if that will fire it up.

The ignitors go out it usually will only run on one rotor, take it very easy driving if this happens or things can get really hot. There's all kinds of things that can go wrong with those carbs with all that emissions garbage on them.

OK update.

I've double checked everything wired in the correct order. Something funny though, the leading coil is picking up continuity from both ignitors, both side?!?! Perhaps something is screwy with my meter, as it beeps and then quits, off and on, almost like a bad contact. Although it does the exact same thing if I simply touch the leads together.. ????

Motor seems like it's TRYING to start...it's popping like it's running a very slow idle while I'm cranking, but quits as soon as I stop cranking.

I verified spark on leading plugs from leading ignitor/coil, so it's wired correctly. I'm not sure if there is something wrong with the wiring... although last night when I had the leading plugs firing on the trailing coil it at least idled...barely...


Let me recap:

Wired correctly, verified color at ignitor plugs.
I only have the leading ignitor installed, the other one is bad
I verified spark on leading plugs
If I pump the gas while cranking, it will occasionally backfire out of the carb
it tries to run, but quits as soon as I stop cranking.

Damn, what am I doing wrong?

Update - If I continue this attempt to start...it eventually floods out.

VERY frustrating....last night it at least idled for a few seconds, now, nothing :(

Could my plugs be toast? Only other thing I can think of... What plugs do I get?

Just did a compression test with a traditional tester.

Holding in the schrader valve, I get even 30 psi "bounces" on all three faces, front and rear. I think the high number was ~90psi, but I don't remember exactly. It took a few turns to get to a "high" number.

Keep in mind this is after the motor has been flooded a few times tonight in efforts to start it.

Are these numbers acceptable, or should I pull this thing out and rebuild it?

Get NGK plugs, im sure that yours are fouled, but, unfortunately, I doubt that will end your troubles. Im sorry i cant be of much more help, but i say definately check your plugs and wires once more...

30 psi is not good at all. What you may have to do is look into the exhuast ports to see if there is any damage to the apex seals. Try dumping some auto tranny fluid into the motor and turn it over a bunch, maybe stuck seals? You should see around 90-125 PSI on a usable engine. Holding the schrader valve isn't going to get you a good reading either, remove the plugs and turn the engine over-simply listen to it...does it have a smooth rythm or a compression stroke and a miss or 2?

the motor may be flooded badly, sometimes they take a long time to unflood.

Have you reset the timing yet? Turn the motor to top dead center and pull out the dizy. Theres a mark on the gear and a mark on the housing, align the two up and stab the dizzy back in. once you get the motor fired up, fine tune the timing with a timing light.

If you have leading spark keep it that way. again make sure that leading spark is firind on TDC.

you can run some wiries to the coils and ignitors temporarily if you think they are screwed up. Just take 4 positive wires and run them to both coils and both ignitors, then ground the coils to the other terminal of the appropiate ignitor.

The motor is probably flooded too, pull the plugs out and turn it over to spray the fuel out. make sure the fuel pump is off when your doing this.

While your turning it over, listen for the pulses from the rotors. If you hear a "PUFF PST PST" from a rotor thats a blown apex seal, if its a "PUFF PUFF PST" thats a blown corner seal.. id try using MMo to free up carbon before you try ATF.

Did you read my post? It was 90 or so odd PSI total buildup pressure. 30 psi was with the schrader held in, and it was pulseing three even times per rotor.

when attempting to "un-flood" the motor, I get 3 good pulses per housing. It sprays fuel out of the plug holes with authority on each pulse, and they all sound even. The 30psi bumps on the compression gauge indicate to me that they are even as well.

Nope, something I didn't do. I will go out and re-set the timing now, as that is probably WAAY out of whack. Sounds like it is when it's "trying" to start.

What exactly is MMo. I see it mentioned on the site alot, but can't figure out what exactly it is.

Marvel Mystery Oil, found in most auto parts stores. It is a goo dthing, as it is an oil, which is meant to be burned (unlike ATF) and also has cleaning agents in it to clean carbon deposits and such. Read the bottle, it explains better than I can. Its also relatively cheap.

sounds good to me. I'll go pick some up + fresh plugs and see.

Now I'm trying (and can't) to find the TDC mark on the front pulley. Nothing really there :(

Other ignitor went bad??? THis AM I didn't have any spark on leadings now...

I said fuck it, installed MSD direct fire. It lit off on first rotation..

It idles now if I give it a shot of gas (accel pump). Carb def needs rebuilding, but at least I know the motor is ok now:)

Off to buy electric fan, new rad hoses, another coil, plugs, wires, cap, rotor, oil/filter, and fuel filter.