[gto4evr]

I figured I'd start a new thread here about my quad problems I apologize this is on a 68 olds cutlass supreme rather than a pontiac but I figured that wouldn't matter much.

Original issue was a bad accelerator pump. I bought a kit from CliffR and we disassembled, cleaned and reassembled it yesterday. Ran smooth, and was pretty happy with the results other than some dieseling when we'd shut it down. I chased around online this morning and read that was because of the idle mixture screws being too rich -- I didn't have time to play with those adjustments yesterday by the time we got the car together but I'd reset them exact number of turns that they were when I pulled the carb off (1-3/4 on the left one and 2 turns on the right one) So the plan was to adjust those today, but never got there because I get a call from my dad at work that the car's running like hell and keeps missing. I also figured out I'd put the acc pump rod in the wrong hole comparing it to other pics online.

So I get home tonight, he gets the car over and we pull the carb back off. I take it all back apart, clean everything again, shoot carb cleaner into the passages and blow them out with air. Put it back together the right way and reinstall it. Same results. The engine will run smooth for 20 seconds, then stumble, then almost stall, then smooth out. Giving it slow acceleration it will start to climb clean on rpms for a bit, then starts to miss and stumble. If I start revving it it will take it initially, hold a high rpm clean for a few seconds, then start missing again and will occasionally backfire. Always diesels when you shut it off. Let it sit and no gas fumes, nothing looks like it's leaking out of the primaries and the plates are dry. I've had my share of carbs with stuck floats flooding and you can see/smell the gas, this thing's dry. I've sprayed carb cleaner around the base looking for vac leak and no changes. it will idle forever with the constant coming and going of the stumble and miss but never enough to kill the motor. it's sitting around 1100 rpm and the stumble drops it down into the 700'ish range, then back up to 1100.

I almost feel like maybe it's electrical and the back fires and stumbles are no spark situations and the fuel loads up then fires off? I changed points a month ago and threw the meter on it tonight. point dwell is steady at 30 degrees and does not move even when the motor's stumbling.

I popped off a wire at a time and didn't see any difference in the way the motor was running and I can hear the snap of spark when I put the boot close back to the plug. Timing doesn't really change during the stumble that I can see either. Changed out the cap and that didn't help. started it up just now in the pitch black and no arcing on any of the wires.

Any ideas of what I should be chasing here? It definitely wasn't doing this before the carb cleaning, yet it's been apart twice now and still doing the same thing and I can't get past the fact that yesterday after the carb went back on, that motor ran like a dream for the half hour we drove it around. This all started this morning.

Thanks in advance for any advice on this!
Dennis

[Buford T. JuSStice]

First things first... what is the compression ratio of your engine, and what octane rating are you running? How old is the fuel that is in your tank?

[many birds]

Check the timing with and without the vacuum advance.. In the early nineties, I had a ‘75 TA 455 do the exact same thing. Turned out vacuum can was bad and timing was fluctuating all over the place causing surging, misfire and backfire

[unruhjonny]

if this is "new", as in post carb rebuild, the only way to 'keep it simple' is to look at the carb;
if something is causing gas to leak into the engine, that might explain the deiseling...

many birds has a great idea, if you have a decent timing light, hook it up, and leave it hooked up long enough to go through one of the coughing fits...

but my hunch is to look closer at the carb...

[george kujanski]

Dieseling usually occurs when the engine is hot and throttles not closed enuf or getting air some other way...vacuum leak?

George

[gto4evr]

thanks for jumping in here guys, this'll be tomorrow's project as I have the day off for this long weekend (and wasn't planning on it being sucked up by this!)

Buford: I haven't checked compression, but this is a completely original motor, never been opened up and has just turned 39,000 miles on it. Running 91 octane and, up until recently, we had a source for the non-ethanol but Noco got bought out and the new speedway wasn't carrying the non corn crap gas so he filled it with91/10% ethanol about two weeks prior. I did think possibly fuel but like I said, it was running like a top for a half hour yesterday on the same gas it's on today. Before the carb rebuild the motor ran fine other than the missing shot of the accelerator pump so you had to feather the acceleration to get over the quick miss but beyond that the car was fine. I guess it's possible he got a bad tank of gas and it's working it's way into the system - I could probably disconnect the fuel line and gravity feed it from another source and let the fuel pump fill up a container to see if what's coming out has any water in it.

many birds: I had a timing light on it and it was around 10 degrees. The vac advance was working when I tested it during the points replacement a month or two ago. I didn't notice any change in rpm when I disconnected it from the port on the carb. I also don't see the timing change during the stuttering. When I flash the light it seems like I can see a gap in the frequency of flashes that coincides with the miss but since the light's off, I'm not seeing the timing mark change. I tried the light on a few plug wires just to see if the stumble matched the lack of flash on multiple wires and it does seem to be on all the wires which was leading me back to thinking it's an electrical problem. I moved the timing up to 12 degrees and the rpms increased but no reduction in the occasional stutter and stumbling at idle.

Johnny : agreed, that's why I pulled the carb back off and went through it again because it just wasn't running like this before the carb cleaning. One problem is I can't get a real answer out of my dad about how "it was running rough" before I decided to do the carb. We identified the lack of acc pump early this spring but have basically ignored it as it didn't really affect him just driving it around basically to and from the Thursday cruise in we go to. He doesn't really drive the car much beyond that so it wasn't a big deal. I drove the car last week after putting new mufflers on it and it seemed fine to me minus the acc pump issue. But...now he's saying it was running poor before the carb deal and I can't really give me a good explanation of what that means. He definitely feels it wasn't running like THIS before. So, it really seems it's a carb thing however I just can't get past the fact that yesterday after the carb, it ran great for 30 minutes blasting it around everywhere (except the dieseling after shut down which it hadn't been doing to this prior)

george: I sprayed around the carb base with carb cleaner and didn't see any differences in sound or rpm. would a vac leak really matter much at WOT? it's got the stumbles even wound up to high rpm and after kicking it up that high, it's now occasionally back firing out the exhaust when you come back down to idle.

would sporadic points still give a rock solid 30 degree reading on the dwell meter? is it possible they're missing occasionally and it's too quick for the meter to dip? any way the coil could be at fault?

[Buford T. JuSStice]

Yeah, if the gas is good and it was running fine on that same octane then at least that's something we can possibly eliminate. I'm honestly not sure if that ethanol content would have an effect, but I wouldn't rule it out. Maybe something cheap to try would be a gas treatment, or trying a slightly higher (93) Octane. With 91 Octane I would guess that your engine is probably in the 9-10:1 compression ratio range, but that is just a guess!

If it turns out that your throttle flaps are staying open, then one solution if you don't already have one, might be to try installing an "anti-dieseling", or "idle stop" solenoid. It's a very simple electric solenoid which takes a single wire connector that goes to an circuit that is on whenever the ignition is on. When it has power going to it, the solenoid retracts the plunger away from the throttle linkage. When power is cut off from it, the plunger goes back out and pushes on the linkage, ensuring that it closes fully. Most Quadrajets have accommodations for these to be installed, and many came with them standard from the factory.

Again, this is one thing to TRY, but I think these other fellas might be on the right track. There are obviously other things to look at and test in order to get to the source of the problem. Good luck!

[242177P]

Originally Posted by gto4evr

any way the coil could be at fault?

Yep, layer shorting. Had it happen with a Blaster2 coil. Swapped it out, and everything was fine. In my case, the coil body was HOT to the touch.

[TAQuest]

If what you did with the carb was the line between 'running like a top' and acting like it's got a problem then it's what you did with the carb.

It seems you messed up the float set up. Easy to do while changing out the accel pump. It has to be something like that. Look very closely at how the float is working.

Take it back apart and find what you messed up. Or switch on a different carb to troubleshoot.

Pretty straight forward solution.

[HO Kenny]

Things I would look at:
- Replace the plugs. Today’s crappy gas fouls old car plugs. I’ve seen it way to many times.
- burnt or broken spark plug wire
- mechanical advance stiff or hanging up.
- worn distributor bushing
- worn cam lobe.
- cracked/burnt valve
- water in fuel
- triple check the firing order
- timing light advance/ retard dial bumped off of 0. It Seriously messed me up for a while.
Is it backfiring through the carb or out the exhaust?
Is it possible it’s carbond up?

[gto4evr]

well, that was quick fix....thanks to all with the advice.

I fired it up this morning, same issue cold. Decided to start with the simple basics and changed the points. Problem solved. I don't get it. The points were new about 8 weeks ago and he's put decent mileage on it since then. They're not burned and they look fine, continuity tests fine but for whatever reason, installing new ones took away the miss and we just drove it hard around town and it's running great.

Trouble shooting sucks when a new problem happens at the same time as a major change! I would have chased that carb to oblivion. my next step was to swap carbs with my GTO and then I'd have been even more pissed when it didn't solve the issue and have two cars down.

[carbking]

"but like I said, it was running like a top for a half hour yesterday on the same gas it's on today."

This to me eliminates, or at least minimizes, a carburetor issue.

Most carburetors have no personality (well Rochester type B one barrels, maybe).

If the carburetor ran like a top yesterday for 30 minutes, it should do so today, and tomorrow. Carburetors fail over decades.

On the other hand, ignition systems fail in the blink of an eye; and certainly have a personality.

EDIT: your post with the fix beat my typing by 2 minutes. Glad you found it. Another "carburetor" issue solved.

Jon.

[unruhjonny]

Originally Posted by 242177P

Yep, layer shorting. Had it happen with a Blaster2 coil. Swapped it out, and everything was fine. In my case, the coil body was HOT to the touch.

I had that happen too.
I spent what little money I had on one, and shortly after swapping it, the car ran like turd, so after thinking about it, I swapped the older regular coil, and low and behold that was it.

I took it back to the shop i bought it from and they basically said "tough deal";
I have NEVER been back to them for not standing behind their parts.

I didn't suggest anything ignition related, because I didn't recall reading that anything ignition related was changed, and I try to use this old addage;
Keep
It
Simple,
Stupid
So, if it ran fine beforehand, only look at what was changed... otherwise this kind of stuff can be a quick way to go bald from pulling out your hair.

I am glad this was fixed!

Next time, can I suggest only doing one thing at a time, then test driving it before doing the next change?

[steve25]

You moved things in changing the points, like the ancient wire that runs under the breaker plate and sheds off its insulation and then causes mayhem!

I would not call it fixed until you pull the Dizzy and check that wire if you have not done so already.

[carbking]

Quote "I spent what little money I had on one, and shortly after swapping it, the car ran like turd, so after thinking about it, I swapped the older regular coil, and low and behold that was it.

I took it back to the shop i bought it from and they basically said "tough deal";
I have NEVER been back to them for not standing behind their parts."

Around here, the standard rule on electrical parts is: if the seal on the box is broken, the part is not returnable, whether the part has been used or not. All parts houses adhere to the rule.

Jon.

[Chief of the 60's]

Put a Holley on it. Problem solved.

[unruhjonny]

Originally Posted by carbking

Quote "I spent what little money I had on one, and shortly after swapping it, the car ran like turd, so after thinking about it, I swapped the older regular coil, and low and behold that was it.

I took it back to the shop i bought it from and they basically said "tough deal";
I have NEVER been back to them for not standing behind their parts."

Around here, the standard rule on electrical parts is: if the seal on the box is broken, the part is not returnable, whether the part has been used or not. All parts houses adhere to the rule.

Jon.

well for the former version of myself who had barely enough money to cover bare necessities, this was an expense that wasn't taken lightly;
I was hoping for something of a warranty - I would have pleased to have received a replacement - I had my bill in had from probably less than a week earlier...
I know that the warranty that MSD had printed on the packaging should have made an exchange for the shop to be a no biggie - but they had ZERO interest in maintaining me as a customer.

Before I replied, I checked MSD's warranty (which probably hasn't changed in twenty plus years):

MSD LLC. Limited Warranty
MSD Performance is a company built on Customer Satisfaction and Service. That is why all MSD products go through regimented test procedures before they are ever packaged and shipped. MSD stands behind our products for one full year after purchase and has an excellent repair department. Terms of Warranty and Service are as follows:

Limited Warranty
MSD, LLC warrants MSD products to be free from defects in material and workmanship under normal use and if properly installed for a period of one year from date of purchase. If found to be defective as mentioned above, it will be replaced or repaired if returned prepaid along with proof of date of purchase.

The shop still exists;
They were an authorized dealer, and this was clearly a defective part.

I have gone a step further in the years since then;
If an authorized dealer for their parts will not stand behind parts with an expressed warranty, why in the world should I bother to even consider buying any of their products.
No MSD for me.

[steve25]

You know it's a very funny thing that in the mid 80s when dodge / Mother Mopar could not get Thermoquads from Carter to satisfy production needs in trucks anyway, they sourced Q jets from Rochester , and I would assume had they liked Holleys better they would have used them as a supplier , so in short its high time to stop kicking the Q jet around ias far as I am concerned!

[TAQuest]

Originally Posted by gto4evr

I changed points a month ago and threw the meter on it tonight. point dwell is steady at 30 degrees and does not move even when the motor's stumbling.




Dennis

This is the part that puzzles me.

[carbking]

Originally Posted by steve25

You know it's a very funny thing that in the mid 80s when dodge / Mother Mopar could not get Thermoquads from Carter to satisfy production needs in trucks anyway, they sourced Q jets from Rochester , and I would assume had they liked Holleys better they would have used them as a supplier , so in short its high time to stop kicking the Q jet around ias far as I am concerned!

Those that throw rocks at the Q-Jet own stock in Shell Oil

Jon