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Odd running condition..

3K views 36 replies 14 participants last post by  1972ChevelleMalibu 
#1 ·
Hi,

This will probably be a strange one, but I have a 1971.... Oldsmobile Cutlass. The reason I wanted to try the question here is because Chevrolet and Chevelle specifically seem to be a lot more common so more eyes might mean more possible solutions. I have tried the Oldsmobile forum too but can't quite seem to zero in on a cause. I do realize that a Chevy 350 is different than an Olds 350 but in terms of overall systems there are similarities so I am just curious if anyone here has encountered a similar issue.

So with that said, it is a 1971 Cutlass, 350ci, 4 barrel Rochester, 350 turbo trans. Basically all stock. Trans rebuilt last year. Bought it with the points ignition and switched to Flamethrower HEI. Single exhaust replaced with Flowmaster dual exhaust. Carb rebuilt professionally by Everyday Performance. I think that is basically the highlights.

Now, the issue is that under light driving it seems to work fine. But if I get on it a little bit, not even enough to kick it down a gear it seems to run rough when returned to idle. But, simply shutting it off and restarting (not touching the gas pedal) it seems to get it smooth again. Even more strange - if I get on it hard enough to kick it down a gear it seems to be stuck in high idle after. Again, shutting it off and restarting it without touching the gas seems to fix it. As far as I can tell nothing in the choke or throttle linkage is hanging up, and it just doesn't make sense to me that a simple restart would fix these things.

One more thing to note, my car tends to eat these new HEI distributors. Not the module, I have changed that roadside and it makes no difference. I haven't tried changing a coil or pick-up so maybe it is on of those, but since the unit was under warranty I always just got it replaced. I have recently changed to a solid stat voltage regulator and tested everything in terms of volts at the battery and the alternator and all seems good there now. Perhaps that was killing these, perhaps this issue is related to the driving conditions. One other thing that might give a clue is when started cold, it jumps into high idle as expected, but then after about 3 seconds bogs down or flat out stalls. After it bogs down it climbs back up into high idle or if it stalled, another pump of the gas and it fires back up into high idle. Not really a big inconvenience, just want to mention in case it ties into this.

Anyway, sorry for the long post and wrong car, lol. Just desperate to figure this thing out.
 
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#29 ·
I have thick skin, bring on the knowledge as aggressively as required, lol.

I did actually buy a piston stop tool to verify TDC, it was out by maybe a degree, and that could have been due to me never using the tool before. I tried it twice and got the same spot. I keep hearing a lot of people say to hell with timing lights, they just keep adding timing till it pings then back it off a bit. Maybe the 14* I have isn't enough, but I just can't bring myself to do it that way.

He actually just emailed me a wealth of information so I am going to take some time going through that - thanks Dave, much appreciated.

I will take a look at the weights hot and cold for comparison. I did check them today right after running it and they seemed fine, but its still worth a look.
 
#30 ·
OK, lets take a look at what I just read, "I was just noting the base timing with the vacuum advance disconnected and plugged, then using the allen wrench to adjust."

In looking at the above, "then use the Allen wrench to adjust"

Does this mean the vacuum advance is one of the adjustable types, ones that can have the vacuum rating set by an Allen wrench in the hose nipple???? And, that you are using that Allen wrench to set the degrees given??? Most adjustable types, save Crane, tell you to use the Allen screw to set the degrees stop, but, they don't tall you that down around 10 or so degrees, the vacuum rating is about 25 in/hg operating vacuum. Way past most engines use.

If so, that ain't the right way to do it, but, most adjustable vac adv's tell you to do that. Problem is, that Allen screw sets a spring seat that is adjustable, TIGHTER, for vacuum pull to match the engine. Tight enough, and the advance stops working. So, turning the screw tighter does reduce the degrees the advance gives, while ALSO jacking the vacuum operation rate sky high. Crane has a plate in their kits, and stand alone that can be fitted to the advance correctly, to separate the Allen wrench degrees stop, from the vacuum pull rate adjustment, making the vac adv totally separately adjustable for vacuum pull, and degrees given.

The Crane stop is also a stand alone part, 99619-1, and fits adjustable, and stock vac advances, one screw hole, 8/32 threaded ole, hex head stainless steel screw and number 8 stainless flat washer, and it is done, under 5 bucks.

For a completely FREE info packet with both text, and pictures on ow to do it, send email to: gmvacuumadvancemodifications@gmail.com It ain't hard to do. The result is, a better vacuum advance, and engine operation. Don't care to do it, keep fumbling around, your choice, no skin off my 6, enjoy.
 
#31 ·
Correct, it is one of the adjustable types, but based on your explanation of how it works and what the adjustments actually do I have some work to do. You did email me a nice email with a lot of attachments that I think covers this in great detail. I will go through it tomorrow and see what I can do.

I do actually have an HEI from a 1976 Custom Cruiser that I took apart, cleaned up and changed the coil, cap, rotor, pick-up, re-greased and changed the vacuum advance to a Crane 99600-1. Since my car kept eating HEI's I wanted something different to try if it fails again. I do have a parts order from Summit I should place soon so I will add a Crane 99619-1 to that order.

I will for sure look through your email package and take any information you or anyone else is willing to give me. I have always loved muscle cars, Chevelles specifically, but until recently couldn't really afford them. I know a fair amount about them and have no issues getting in there and working on them, just lack the in depth knowledge needed to sort out issues like these. Last winter I dragged the TH350 to my basement and rebuilt it (first one ever) to fix my no third gear situation. Up next I am going to tackle a quadrajet rebuild. Not cause I need it, there is a new rebuilt unit on there now. I just have my old one laying around and a rebuild kit is so cheap I figure why not... at the least I walk away with a much better understanding of how they work and I will have a spare.

Thanks for the help, especially considering I don't really have the right car to be here, lol.
 
#32 ·
Please stop the madness and put the stock points system back in. There is nothing wrong with it.. It is better then what you replaced it with.. If you want more power, use the points to trigger a MSD6AL CD box..

These aftermarket companies and the people they pay on these boards, have you guys brainwashed thinking that HEI stuff is better, its NOT!
 
#33 ·
I was strongly considering going back to the points, but at least through all this I found a voltage issue I was having. Hopefully that fixes my HEI issues. I also swapped the old carb back on today, and it runs better, I have a higher vacuum reading up to about 18" now, the idle fuel mix screws are happy about 3.5 turns out where they used to be about 6 with the "new" carb. Best of all, I can drive it as hard as I want and the RPM doesn't hang up anymore. So something in the carb appears to have been the problem.

Now that I have that fixed, I can get to work reading through and understanding all the information that was sent over. I think I have some parts to order and maybe I can get this car running even better! Thanks everyone!
 
#34 ·
"These aftermarket companies and the people they pay on these boards, have you guys brainwashed thinking that HEI stuff is better, its NOT! "

WHAT A FULL LOAD OF HORSE HOCKIE. YOU are the "madness". Both points, and HEI work well, when they are set up correctly, which you consistently insist on not doing.

YOU have constantly posted erroneous info to anyone with an ignition system all along, so don't blame others, you have no clue for a street driven engine. Maybe your BS works in a boat, but it just does not work for 99 - 44/100ths percent of street driven engines,
 
#35 ·
Jeff, can you name a person who is getting paid (by anybody) to post stuff on here?

meanwhile, WHAT A FULL LOAD OF HORSE HOCKIE.
 
#37 ·
Everything seems clear with the air cleaner on. With the old carb back on the issue where it would start from cold in high idle, then die after a few seconds is gone too. Went out and kicked the transmission down a few times and the RPM issue is gone. So it appears most of these issues were carb related.

The car always seemed to run fine with the old carb, but there was just an issue where after it was hot and sat for a little while it was very hard to start. I was told this was likely because the quadrajet had an issue of the plugs leaking and basically flooding the engine even though the gas pedal wasn't touched. After it was good and hot yesterday I parked it for an hour. Went out and without touching the gas it fired right up. Got it good and hot again and left it for two hours, fired right up again. I am going to try 3 and 4 hours today.

I am wondering if the difficult hot start issue when we first got the car was actually vapor lock. It seemed to be running lean when we got it, and ran very hot. I have been told lean can cause excess heat. I put a gauge set in mainly for the coolant temp, but got oil pressure and voltage too. On hot days sitting at long red lights it would creep up into the 230's sometimes. Now tuned better and with a new thermostat it never seems to get higher that 190 to maybe 200. I don't know the exact scenarios where vapor lock likes to happen but maybe that was the issue and the old carb is fine.
 
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