RazorN8

1987 carbed camaro w/ 350. Main components of the ignition are stock replacements that have been replaced within the last 6 months (dizzy and coil). Wires are 1 week old 8.5mm summit brand. Plugs are NGK These.

Anyways, the car was running great at the beggining of the week this week. About wednesday, the car starting stumbling and misfiring some times when I gave it light gas from a stop, but if I gavce it more gas it smoothed out and accelerated well. Today the car started backfiring through the exaust this afternoon when I tried to give it more gas to smooth it out. The car will all but stall then it will accelerate. Its kinda like quadrabog but with som loud bangs from the tail pipe.

I checked everything I could think of. Vacuum was at 19 in of Hg steady. All cylinders were 165-170 psi compression. The plugs showed a rich condition so I swapped in my spare carb to see if that was maybe the problem. It wasn't. The way I see it, sooty plugs tells me that either my carb is set too rich or my sparks are weak sauce or both. I found 1 cracked plug and replaced it. I pulled the valve covers and looked for broken valve springs (kinda taken stabs in the dark at this point).

I'm lost at this point. Where do you guys think my problem is? I'm thinking ignition myself, but I don't know how to test this theory. Any thoughts.

PLEASE HELP. i'm stuck driving my sunfire turd till this is fixed.

bradley23150

iTrader: (10)

My engine was backfiring pretty bad from the exhaust, and it turned out to be the timing. Put a timing light on your motor, and see what it says. Your distributor clamp could be a little loose causing your distributor to have turned slightly.

Im just throwing an idea out there, heh.

Good luck!

RazorN8

Yeah, I forgot to mention that. I checked timing and it was steady at 5*. Right where I left it. Good thought though.C'mon guys. I need some ideas here

RazorN8

bump. i really need some ideas here guys

RazorN8

Update:
I worked on it a bit today. I double checked that all of the wires are on the dist cap in the right order and made sure they were attached to the spark plugs tightly. That was all good. I realized that I had never set the secondary spring tension on my back-up carb. That is definately part of my problem now. I will swap back to the other carb one of these days when I find time. Other than that all seems perfect. It starts right up but still stumbles its way up to 1700rpm with the choke closed. I think there is definately still a problem.

Is there any way to test a distributor to see if its bad? How about a coil? I found some mention of this in old threads but the instructions were sketchy at best "ohm it and see if its good". If you guys would give me some detailed instructions I would really appreciate it. "Check resitance from pin a to pin B, it should be between 8ohms and 10ohms" type instructions would be hugely helpful.

Thanks Guys

RazorN8

Ideas PLEASE.

johnny89345

play with the timing i beleive if it back fires out the exhaust timing may be retarded....play with it see what rpm it does it at and when like my car only has a backfire at 3000-2800rpm under deceleration.

JakeJr

Did you disconnect thje EST before setting the base timing?

If so, did you reconnect it once you were finished? Did you disconnect the battery for 30seconds or so to clear the stored code?

It should be 6 degrees Before Top Dead Center (BTDC) if you're using the stock setting.

Jake

RazorN8

The timing is where I want it, but I didn't reset the codes. Would that really make a difference? I may kick the timing up to 8* BTDC though. I will definately reset the codes

bcmag

generally speaking a weak spark will cause pop thru intake not exhaust.go to autozone etc. buy an adj spark tester($10) set it to 30kv and you should get a nice fat blue consistant spark.if not youve found your issue.i usually find bad switching transistor in icm to be the cause.

RazorN8

Bad switching transistor in the icm? Yhe ignition control module is only about a year old at most along with the rest of the distributor. I will do the test though. i ran to napa and grabbed one of those spark testers a couple of days ago. I had the same thought you did. Do you usually attach the tester between a plug wire and ground or the coil wire and ground? I haven't had time to work on it yet, busy week.

bcmag

start at spark plug end and if results are no good go to the coil wire and check it there if ok at coil..rotor leaking voltage to shaft if not ok at coil icm, coil,power or ground issue etc.

bcmag

only other thought i have is maybe a stretched chain?but that wouldnt explain plugs carbon fouled.keep us posted.

RazorN8

Thanks, I appreciate that. It's always good to know how to use my tools.

RazorN8

I checked the spark at the plugs today. I get a thin bluish white spark every once in a while (every 5-10 revolutions of the engine). I checked the coil and i got a huge blue spark consistently. Bad distributor, rotor or cap? please advise quickly, I have very little time to work on the car, exams next week.

bcmag

try turning the adj. on tester in until you get a fairly consistant spark.if its anything below 20kv i think a cap and rotor are in order.you can test rotor for leakage but its easy to get zapped.im kinda used to it but rotors are cheap enough that i wont get into procedure.lemme know what you find.oh obviously you will get more sparks at coil than at an individual plug but 4-5 revs in between is too much and you should pretty much have that big fat blue spark at plug that your seeing at the coil.

RazorN8

I replaced the rotor and now I'm getting a consistent, thin, bluish white spark. I think I will replace the cap tomorrow just to be sure. The cap looks fine though (no carbon or cracks). I took it out for a test drive and it runs pretty good until I get into the secondaries, then it runs rough and surges at idle. I took it into the garage and reved it until the secondaries opened. It backfired through the intake pretty bad the first time and then wouldn't repeat the backfire. Any ideas on this?

bcmag

now it sounds like lean missfire.no more backfire out exhaust?what carb u using?might be time for carb tuning or rebuild.

game1939

sounds like a carb adjustment is nessassary, try bumping timing to 6" at idle, hows the timing curve? you know timing changes from idle to wot, for the simple fact when motor spins faster, it hits the combustion points quicker, therefor spark has to come quicker to, my car although a 383, runs at about 12 at idle and between 32 to 34 at wot, running a msd probillet with mechanical advance, yours wont be that extreme, but 5 is a little low at idle, also check at wot........

RazorN8

its a stock setup. I set it to 8* at idle last night with the 3 wire (I think, the one closest to the firewall) distributor plug unplugged. Then when it is plugged in I would say that idle timing is around 16* BTDC at idle.
The carb is a stock quadrajet that I rebuilt about a year ago. The carb ran great on this engine before I did a cam and heads change. The only thing that I can think of is that the secondaries don't completely close after they have been opened. What tuning would you suggest? I think I'm going to pull my Plan B carb out of the garage and get it all cleaned up and ready to run and try that one.
Oh, and no more backfire from the tailpipe that I can tell.

RazorN8

I got it to backfire through the carb again this morning. In fact, it does it on a regular basis now. I replaced the dist cap, no major changes in spark intensity. I think that the spark is ok now. I'm getting kinda frustrated with this backfire issue though. I can't think of anything in the carb that would cause this. The carb is still freshly rebuilt. Dwell checks well as does all of the other idle stuff. This is not an idle issue though. I'm running cc rods on a G hanger in the secondaries if that helps any.

RazorN8

Any ideas guys

JakeJr

I realize you posted you checked the spark plug routing, but I'm still concerned about that. Soice the problem began so close to the time you changed plug wires, I'm suspicious about that.

5 & 7 and 2 & 4 are the ones most often swapped.

Even a genius like me (LOL) inadvertently swapped 2 & 4 when I first fired my 388. Go back to when the problem first began; what change was made JUST BEFORE the problem started? Many times it's the simpliest things.

Jake

RazorN8

The plug routing is correct. I checked that probly 4 or 5 times in the last week. The problem didn't start right after the wire change, it was a couple days later. I'm thinking now that I need to increase the spring tension on my secondary air valves. the backfire only happens the instant that the secondaries open.

singledad1972

might be running to lean

RazorN8

That's what I'm thinking. The plugs were caked with carbon from running rich, but I think that the instant the secondaries kick in, I think it goes lean just for and instant. that's why I think that if I tighten the AV tension, I will solve my problem.

MI ROC-Z

Just a thought... Have you verified that the distributor was stabbed with #1 at TDC. Sounds like you're distributor is trying to play catch up with the timing.

JakeJr

Okay, since that's your leaning, give it a try and see what the results are.

Keep us posted.

Jake

RazorN8

If I stabbed the distributor in the wrong spot, wouldn't the timing light show my mistake. The timing mark wouldn't show up in the right spot, right?

Jake, sounds like you don't think that the secondary AV is my problem. Is there a reason for that? Any other ideas?

I'm rebuilding my backup carb right now. It should be done by friday (waiting on parts). I'll let you know if the carb is the problem at least.

RazorN8

I fiddled with the car a bit today to get out of the house (not exactly the happiest week of the month around here). I found that the hook bent into the AV tension spring had unbent effectively reducing the tension on the flaps. I'm really hoping this is my problem, but I won't know until I get the other carb on the car or change out the spring with one of the others I have laying around. I tried bending the hook back in there, but when opened the flaps again, the hook just unbent again.

RazorN8

I put the qjet that I just rebuilt on the car. She runs like a top. I'm not totally sure if all my problems were due to the AV, but they must have mostly been in the carb. I guess I will take my other carb apart and see if I find anything obvious.

Goany

i didnt bother reading the whole forum but that is caused by sparkplug wires against heads or exhaust manifolds pull em back tie em up you should be good

RazorN8

The wires are pretty much brand new and they are in looms. There are no wires contacting any hot metal or any metal at all.