My new to me for about a few months 1983 Z28 with carbureted 305 has started acting up this week!
I have had the car for a couple months. It has only 6800 miles on it and is bone stock.
It had been running perfectly for the first two months. No issues starting and idled fine.
Sunday, my wife and I went out to take care of a few things nearby so we jumped in and took it for a spin. It ran well for about 30 minutes and the first few stops. The third stop I decided to wait for her while she went into the grocery store and grabbed a few things. I waited underneath a parking area with shade but kept the car running with the A/C on. I live in Florida and it was 99 degrees out. Everything fine, idling well in park, A/C cold.
When she got in the car I shifted to Drive and that’s when it started. The car stumbled and almost stalled, the choke light flashed on and off a few times. I had to give it a little gas to keep it from stalling. Drove away and it stumbled a bit but eventually got up to 45 MPH. Even though it was running ok then when I went to accelerate I could feel a stumble.
Got home and parked in garage. Let it sit for a couple hours, started back up(hard to start) and it again flashed the choke light and tried to stall.
I left it for the night. Started it the next morning, drove it a mile or so and all good. Great! This afternoon, went to lunch. All good on the way out, no problem. After lunch (car sitting out in heat) started and the infamous choke light flashed and it tried to stall again. Same exact thing like last time. Also, this may be unrelated but the A/C blew only very hot air until I got moving, then it cooled down a bit.
not sure what direction to go with this. I have searched the forum and plenty of info on the alternator causing the choke light to come on. I haven’t found anything like my issue, where the choke light comes on (intermittent) and there is an actual issue with how the car runs.i guess the choke light is just coming on because as the engine tries to stall, the alternator is not spinning fast enough to provide enough voltage to the choke (alternator) circuit? This I guess would mean I don’t have a choke problem but some other issue with air/fuel? Sure does seem to be related to heat, though.
I should mention that I did install a subwoofer last week but the only connections that were made were at the battery positive and the rear sail panel speakers. No other wiring was touched or disturbed.
I’m not a big believer in coincidence, but I can’t think of anything I could have done to inject this issue, especially since it does not have the issue all the time. I checked the belts and they are fine.
Any suggestions or advice?
thank you!

 

Ignore the "Choke" light. While it's somewhat involved with the choke, it's REALLY the alternator light. What it's ACTUALLY telling you is that the alternator isn't working, most likely because, at those particular times, the engine RPM is too low because the motor is about to stall. It's a symptom of the problem, not the problem itself, and not related to the problem except as I just described. Not a useful troubleshooting fact therefore.

I'd almost be willing to bet (butt I'm not a betting person, so there is that) that the problem is the fuel in the carb boiling. I'd suggest that you replicate the problem, which most likely can be accomplished by letting it sit and idle with the AC on; maybe, block the radiator a bit with a piece of cardboard or something, so that the underhood temps get REAL hot (no need to overheat the motor though); then try to take off IN A SAFE PLACE. Like, I'd suggest doing this out in a LARGE parking lot somewhere, with no other cars around and not blocking anything no matter where you're going to go, so that you don't become a traffic hazard or whatever. In other words DO NOT try this on a public street!!!! When it does it, IMMEDIATELY stop, shut the key off, take off the air cleaner, and see what there is to see. My bet would be that there will be fuel EVERYWHERE; spewing out the top of the carb, running into the throttle bores, dripping all over the manifold, etc.; accompanied by a strong odor of fuel. You didn't mention it butt I'd ALSO be willing to bet that there was just such an odor when this happened before.

Reason for the fuel boiling is that it's getting too hot. (duh) Reason for that is heat from the engine heating up the fuel pump, the carb, or both. In my experience it's usually the FP butt it could be the carb. Solution is a phenolic spacer to isolate the FP from the block, and/or one to isolate the carb from the intake. I'd recommend the FP one first and then if and only if it doesn't take care of it, use one under the carb. The carb already has a real thick gasket that acts as quite an effective heat insulator as well so that [should be taking care of its temp.

https://www.summitracing.com/parts/ctr-85-000

It replaces the steel plate between the FP and the block, thereby insulating the pump.

 

Thank you responding so quickly. I actually was doing some more reading in the meantime and I had gone back and edited my post as I realized the light was probably due to the alternator spinning down and that I had some other test issue. We were taking at the same time.
thanks for the link. I’ll try this. Hey, did you ever see the optional blower fan that went in the side of one of the fenders that routed “cool” air to the carb?
If you did, did those help?
it’s strange, I had this exact same car (not literally the same vehicle, but exact car back I. The 80’s in god awful hot south Florida and never had this issue…

 

Sofa, also yes, you are correct I forgot all about the smell. It was pretty bad, smelled almost like the egg smell of a catalytic converter..
I ordered the spacer. Does this take the place of a standard gasket or does it go directly against the block?
thanks

 

You still need gaskets. Stock, there's a steel plate that looks exactly like the Canton part ... except of course the steel/phenolic detail. The block looks like this.



The fuel pump has a much smaller flange and bolts on with only the 2 larger upper holes. Replace both gaskets, plate to block and pump to plate, obviously.

Note in that pic that there's a bolt hole circled. MAKE SURE there's a SHORT bolt in that hole, if the bracket isn't there anymore. If you look into that hole you can see the FP drive rod, and if there's no bolt there, it will leeeeeeek oil SHAMELESSLY at high (pretty much anything above idle) RPMs, which will then get slung by the crank damper and coat the ENTIRE pass side of the engine down low, and the underside of the exhaust, with oil. If you have that going on, put a SHORT (like, ¾" or shorter) bolt in there with a drop of sealer on the threads.

Might also be a good opportunity to replace the FP drive rod since it will fall out during all this. Get a lightweight one such as this. https://www.summitracing.com/parts/sum-250025 The FP is a spring-loaded diaphragm, which when the cam eccentric pushes the drive rod down on the little arm thing that works it, draws fuel into itself; then, when the cam eccentric allows the rod to retract, the spring pushes the diaphragm back, moving fuel toward the carb. Problem (ahem: [corporateAmerica] opportunity for a solution [/corporateAmerica]) is, the spring ALSO has to push the drive rod back up, and at higher RPMs, it can't return that big heavy-a$$ thing back up into there fast enough, which makes the carb run out of fuel after awhile. Old round-track racer's trick to allow a stock FP to support sustained high RPMs when the stock FP is required by the class rules to be retained.

 

BTW, never saw one of those silly little fans. My late little bro did in fact work at a GM stealership back then though, so he showed me the diagram in the TSB they circulated about it when it came out. We got a good laugh out of it.

Fuel has changed ALOT since these cars were new. Not surprised that you didn't have that trouble before, esp if it was a long time ago. I never really had it until, I guess it was, the mid/late 90s sometime. Sorry I can't recall the exact year let alone the date, butt at the time I was also living in the deep South, and had this happen to my car. (83 L69)

Also note that if you put a bolt that's too long in that hole, it will clamp down on the FP drive rod, and the FP won't work at all. You can take advantage of that while changing out the FP in a small block Chevy by putting a longer bolt in there temporarily, FINGER TIGHT, to hold the drive rod up from falling out, thus making it less difficult (not that it's all that hard to begin with) to put a new FP on.

 

Thank you!

 

Thank you for all the info! Two more questions:
- should I try to isolate the fuel pump bolts as well?
- I figured I may as well replace the pump since it’s no more effort and it’s the original one. Any recommended pumps? I see several options. Some are “CARB” compliant, should I avoid those?

thank you!

 

You could I suppose; wouldn't be that hard. Acoupla large nylon washers and a regular flat washer under the bolt heads should do the trick. Not sure it would make all that much difference in the grand scheme of things though; the pump flange is probably 95% of the total contact of the pump to the engine, meaning the bolts have little effect, comparatively..

No. That just means they're street legal as stock replacements.

Just yerbasic good quality parts store replacement should be fine. Be EXTREMELY careful not to damage the steel fuel line though. Use a tubing wrench, or line wrench, whatever the particular mfr calls it; looks like a crow's foot, contacts all 6 corners of the nut. Size is 5/8". Put a bit of anti-seize on the nut threads and the place where the nut seats against the flare, to make it less of a PITA next time. Don't tighten it too terribly tight.

 

Thanks. I’ll tackle this over the weekend. Looks like fun getting to it with the pump right near it.

 

re-installing the hard line to the pump can sometimes be a challenge. it will likely have some tension on it as installed

best to try to install it to the pump before bolting the pump all the way in place, in more difficult instances you may need to release it from the fitting at the carb to get some play in it at the pump

 

Just a quick follow up. I ordered the fuel pump phenolic spacer but in the meanwhile I filled the car a couple times with non ethanol gas. That alone seems to have cured the problem. I’ll still install the spacer but thought this was interesting.