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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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#5 ·
It does have a new 12 gauge wire running from the box to the HEI. When I first installed it and went to start it, the key was dead. Someone pointed out that one of the old wires had to be tied into this new 12 gauge wire. I can't recall exactly where it goes, but I believe it went to the starter which makes sense. After that it fired right up. Should this wire maybe be connected somewhere else so that the HEI gets its own wire not shared with anything else?

I can get under there and sort out where it comes from and maybe get some pics if you guys need.
 
#6 ·
well, there is an old school possibility; the float sticks. It would make sense after RPM ( higher PSI from pump), and even high idle ( cold pump, moderate rpm) or that could be the choke pull off. A restart would fix it, as fuel PSI drops to zero; the float falls back down.

I've recently become re-acquainted with Qjets, they are VERY sensitive to fuel pressure, and the float settings are really finicky.

Fuel PSI too high, float level too high ( or both in combination) .


PS. EXACTLY what type of distributor are you buying and EXACTLY where is the wear? w/o data, I suspect you may be dealing with cheap offshore pig iron. Buy GM.
 
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#7 ·
Would there be a difference between high RPM idling in park or high RPM while driving? That is something that always confused me about this - I can rev it quite high in park while checking timing and these issues don't happen, just when driving...

I will see what I can figure out about a possibly sticky float.

I do still have the old carb. It seemed to work fine other than the problem where those plugs at the bottom leaked fuel when hot and flooded the engine making hot restarts tricky. I could always throw that back on and see if it happens with it too. That would at least narrow it down to the carb or eliminate it as a problem.

I didn't see the last part of your post. It is a Pertronix Flamethower D1100. I also suspect that these are cheaply made. The first one I tried was a Summit brand and it didn't work right out of the box. It would idle not bad, but once in gear the slightest touch of the gas would bog the car and almost stall.

The Pertronix was better where it worked out of the box, but would end up running just like the Summit one. Whether it took weeks or in one case a few months, they all ended up like that. When idling roughly I could pull plug wires off, some with little effect, others with no effect. Oddly enough, from day to day the plugs that made a difference were not the same.

I do have an original out of a 1976 custom cruiser. Everyone says the originals are best in terms of reliability. I replaced the cap and coil and pick-up. Other than that it was just stripped down, cleaned up and re-greased. Oh, I also put on a new vacuum advance. If this Pertronix fails I will be throwing that one in and see what happens...
 
#8 ·
From a past post checking fuel pressure:

"I had the gauge connected from the cold start (had to re-fire once) to operating temp. It was basically at a bouncy 5.5 PSI the whole time. When reving it went up slightly maybe close to 6 PSI and was still bouncing. The bounce was about 0.3 PSI. Not sure if the bouncing is normal or even if the reading itself is decent. It seems to me that the pressure should go up more than 0.5 PSI under load versus operation to keep the bowl full, no?"

It was then explained that a fairly consistent pressure is normal and the bouncy needle is just from how the pump works.

The fuel pump is new from a year or so ago. But when changing an intake manifold gasket I tried to take the fuel line off but it was stuck on good and while turning slightly twisted/wrinkled the top of the pump where the line connects. There is no visible damage and the test results are from after that so I think it is ok. I do have a new one so I can change if need be.
 
#9 ·
Well, not sure if this makes sense to anyone, but here was my lunch hour:

I figured now that the voltage situation I was having was fixed with a new solid state regulator I would recheck the idle fuel mixture and check the timing. Not much changed. I turned the fuel screws in about half a turn. Timing was set at about 14* base with 7* vacuum from the distributor. Looked to top out around 36-38* around 2500RPM. I may revisit that a little and play with the distributor springs but for a stock (nice weather) daily driver that is probably fine.

The only thing I did change the vacuum source for the distributor. The car came with it connected to the carb, but it was suggested that going directly from the manifold works better or at least idles better, so I did and that is where it has been for the last couple of years.

I figured I would try going back to the carb and see if it idled different. It really didn't seem to make a difference other than showing 14* timing at idle from the carb, or 21* from the manifold. It ran fairly smooth either way. I again checked where the timing came in with it off the carb and it still seemed to be roughly the same. So out for a test drive I went.

It actually seemed like it had a bit more pep at lower speeds and RPM's like when you are rolling off a side street onto the main street. Just overall smoother. Then once driving I tried to get on it a little without the kick down. After a few pulls like that I pulled over to see how it was running. All seemed good. So I went back out and kicked it down a gear (does that ever sound and feel nice, lol) and then took it home. It was fore sure not in high idle, but was idling slightly higher than before and maybe a little bit rough. I hooked the timing light up and it was about 800RPM. I shut it down, fired it back up and it was back to smooth at 750RPM.

So I think I am basically there. Does any of that even make sense? I will let it cool off and go try to repeat the experiment just to make sure it wasn't a fluke. The car rarely gets driven hard so if this is as good as I can get it I can live with it. I am interested to see tomorrow morning how it starts from cold.
 
#10 ·
For me,,,,,,,,, I had a " Super Duper " Alum. Dist from Advance (off Shore) Dam near needed a roll back on SPEED DIAL! After a few modules and another Super Duper Alum. Dist. I went to kenny ross Chevrolet and bought a
G.M. = H.E.I., This was 35/40.000 miles ago.
I still have(under the pass seat) the TOOLS to change a module. I got real good at it. The word for the G.M. HEI.......... " Bulletproof " comes to mind! Is the 12 Vts. to your H.E.I. a direct source and NOT using any old factory wiring? I ran a wire from my fuse box that is hot on " Crank & Run".
If you need a Super Duper-Alum. H.E.I., I have one at the man door of my garage. I use it for a " DOOR STOP ".
Bob
Good parts aint cheap, And-Cheap parts aint good..........:thumbsup:
 
#11 ·
Good to know. I hope I have the car good now with the vacuum line switched around and the voltage situation sorted out. If this Pertonix model fails again it will be the last. I will try the 1976 with new parts that I have ready to go next and if that doesn't work I will try a new GM one. On the plus side I am very good at changing distributors now, lol.

Wiring to the HEI is a brand new 12 gauge wire directly from fuse box to HEI. I can't recall what spade it connects to but it was the one that all the instructions said to use.
 
#12 ·
So if I understand correctly -
Regarding your vacuum advance, you moved the vacuum source from full manifold to ported?
I’ve always ran my VA off full manifold, in most situations I believe that is the correct way. On full manifold vacuum it’s possible that your springs were too light, bringing in your advance too early at a lower rpm.

Regardless, there is no one size fits all and it sounds like you have made some progress.
Good luck
 
#13 ·
That is correct, went from full manifold to ported on the carb. I think stock is at the carb and that is how the car came. Most were telling me that the car runs better and smoother on manifold so that is where i had it, but I really don't see a difference in idle and it really seemed to drive better with ported. Like you said, maybe it isn't a one size fits all thing. I will keep it like this and see what happens in the next few days.
 
#15 ·
How much vacuum do you have at idle?

I suspect what may be happening is that when you are running full manifold vacuum to your distributor, your vacuum advance unit is not being pulled fully open at idle.

Then, when you are cruising about, you raise the vacuum and get more of a pull on the vacuum advance unit, which causes your RPMs to go up, which causes your vacuum to go up, which keeps you at that higher idle.

By shutting the car off and on, you reset the feedback loop until you raise the vacuum enough to get back into that loop.

By moving to ported vacuum instead of manifold vacuum, you have eliminated the feedback loop at idle because vacuum drops to 0 to the distributor vacuum advance which fixed the symptoms you were seeing.

Thus, your vacuum advance unit is not setup correctly for your car's idle vacuum.
 
#16 ·
Interesting. I have about 17" at idle. I have been told that is low and have been through the whole car. I am fairly certain I don't have any leaks, and someone on the oldsmobile forum actually posted some literature from an original manual showing that the 35 olds engine from these years was only around 16.5 to 18 new so I think I am ok there.

What you described about the vacuum advance above makes sense. I am just glad to be on the right track finally.
 
#17 ·
I think your vacuum level is fine at 17".

So, the other thing is that it could just be a bad vacuum advance unit that gets stuck periodically, and until you get it back to 0 vacuum on it, it is pulling advance when it should not be. If that is indeed it, by moving to ported vacuum, you masked the problem. The same was happening with manifold vacuum and by shutting the car off, you sent it back to 0 as well.
 
#18 ·
That makes sense to me. I will see how it starts and runs tomorrow but I think that is likely the issue. Maybe depending on what happens with the test I will try the other distributor or just a new vacuum advance if I can find a good one and try manifold vacuum again since that seems to be the preferred way to do it and see what happens.

Thanks for all the help and explaining what is likely going on. I am glad to be making progress on this issue.
 
#20 ·
How many degrees of timing does the vacuum advance add to the initial timing when the V/A hose is plugged into full manifold vacuum (DO NOT USE A DIAL BACK TIMING LIGHT TO CHECK THIS SETTING).

Did you install a degrees stop plate to the vacuum advance, and set it for the correct amount of degrees? Did you ask for the right way to do it from my instructions, they are free, no ads, only info on how to do it right.

gmvacuumadvancemodifications@gmail.com
 
#21 ·
I don't believe I have a vacuum advance stop plate... It was the one that came on the distributor and thought that it listed a max vacuum, I just don't recall what it was. I had it set where it was only adding 7* at idle when connected to manifold vacuum. I checked this by doing the base timing with the vacuum advance disconnected and plugged, then with it set at 14* reconnected the vacuum advance and noted that it went to 21*. Is there a better way to do it? Seems like most say it should be adding 10*. If that is correct I can make that adjustment. Thanks for the advice.
 
#22 ·
Yeah, ask for my instructions, set the plate to give 10 degrees, plug it into full manifold vacuum.

As far as vacuum advance vacuum ratings, there are about 20 stockers each for points and large HEI. They all have different vacuum operating levels, and degrees added. Figure out the vacuum the engine has, select the correct advance with the workable vacuum level, add the degrees stop plate, and set it to give the correct amount of degrees, done.

Or, the best way, Crane adjustable vacuum advance full kit, 3 pairs of mechanical advance springs, adjustable vacuum diaphragm, degrees stop plate, you get all 20 advances, and everything in between them to work with, unless you set it up wrong, no way to not get it to work great.

99600-1 for large coil in cap HEI
99601-1 for points distributors

Mount the degrees plate as outlined in the instructions I offer, NOT as Crane says to do.
 
#23 ·
So with the vacuum advance connected to carb port, it still did that thing where it starts in high idle for a few seconds, died, restarted and ran in high idle like normal, but this time after about a minute when I kicked it out of high idle it died. After a restart it would barely run. So I switched the line back to manifold vacuum and then it ran fine while it warmed up. So, back to manifold vacuum for me, lol.

Thinking that the vacuum advance seemed to have something to do with the RPM increase after the kick down acceleration when I got it back to the garage and it was idling at 1350 rpm I tried pulling the vacuum line off the distributor hoping that would drop the RPM like the restart does, but no difference. I again made sure choke was fully off, throttle linkage was resting against the set screw, secondary plates... at least the top ones... were closed... now that I think about it, I should have checked to see if the actual throttle blades were closed. I am sure I checked this last year but just want to be sure.

I did the test again today because I figured I might as well try to disconnect the vacuum line to the trans but that didn't work either. I am just trying to think of what is different when in gear and under load that wouldn't be an issue while idling in park. It just seems so strange I can rev it as high as I want for timing and tuning in the garage but when revved up on the road it has this issue. My last two things I can think of would be a stuck float in the carb or the weights in the distributor sticking. I did have the cap and rotor off today and the weights seems to move freely. But even the float and weights I would think would be an issue in the garage in park same as one the road

I also adjusted the vacuum advance to be at 10* now so 14* base timing and when vacuum connect sitting at 24*.

I think I am just going to have to swap the old carb back on and try that. If it doesn't change the carb can be eliminated as an issue. Then I will try another distributor and if that doesn't work... I don't know what next.
 
#24 ·
Just how are you "adjusting the vacuum advance"???

If you are resetting the screw inside the vacuum hose with the Allen wrench to change the total number of DEGREES, YOU ARE DOING IT WRONG. If you have some sort of serrated stop plate MOUNTED ON THE VACUUM ADVANCE END SCREW, PUSHING THE PULL PIN INTO THE DIAPHRAGM, YOU ARE DOING IT WRONG.

Please advise.
 
#25 ·
Are the mechanical advance weights sticking and not returning to their off position ? Like where they should be at idle
 
#26 ·
I was just noting the base timing with the vacuum advance disconnected and plugged, then using the allen wrench to adjust. It has 14* base timing with it disconnected and 24* with it reconnected....

The weights seemed to move fine with no hard or rough spots. They smoothly moved all the way out and the spring back to where they started.
 
#27 ·
72CheBu.. works got me like a fart in a hurricane.. but glad to see the Team has assembled upon you....

Dave Ray is much like my dad ( RIP) the old OSS solider who was very direct, very precise and no BS. HE is also an expert, so you are in the best hands here with Dave the NCOIC.

Hey , not to throw a wrench in the worx, but the old G2 soldier says check all assumptions... sir... have you verified TDC on the balancer. Just to confirm your timing readings are what the engine is indeed seeing.

You are almost there... to the PERMANENT satisfaction of gaining control of the beast....!

Dave's going to come back and rip you one for doing it the wrong way I believe ( out of my wheelhouse it is, but he told me allen wrnech no go.) No matter "grasshoppper", accept and gain knowledge from the sensei.

( it doesnt sound like the engine is seeing anything like 14 or 2x TDC at idle is why I ask to question all assumptions)
 
#28 ·
Perhaps the weights only stick when the distributor is hot? Would be easy to check-see what the timing is doing when the engine is not hot and not misbehaving, then check again when it is misbehaving.
 
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