pcguy2u

Yesterday I was getting the 350 ready for Sonoma Raceway's last test and tune of the season tonight and again encounter a nagging timing issue.

In the past, I have been unable to get the all in timing to the mid 30's, off and on, and never could understand that.

Then yesterday I was putting some finishing touches on the tune and found the same problem. Then later the "all in" worked like it should have.

Then it got confusing because at the very end, when all should have been perfect, I had to increase the idle with the idle adjustment screw.

OK, so it seemed like I should take it for a test drive and find out if I was going to the track or not. Drove about 10 miles round trip and nothing seemed out of order and the temp was running at about 195.

At the very end of the trip, the temp started climbing to 225 and I parked it half into the garage. I have an aux fan that I can run while the engine is off and I ran that for a few minutes after which I restarted the engine to circulate the cooler fluid.

At that point, when the engine started the idle was way too high and I had to lower it again.

It seems that all of this (including the temp rise) could be explained by a defective vacuum advance, however, the vacuum to the advance was disconnected and this morning I pulled the advance and it test perfectly.

So what is going on here - the only other component that could be causing this seems like it could be the magnetic pick-up, but I'm out of my league on that one???

Any help will be appreciated.

RonSSNova

Sounds as though the advance weights are sticking. Sometimes advanced, then you reset the timing, then they relax all the way and you are retarded. Not you, the timing.

Have you messed with the springs at all? Do the weights move freely?
I have found that the stock weights are usually light enough to advance quick, they just advance too far. There is an easy way to limit the advance and set these up.

If the weights appear to be sticking, you may have to disassemble the whole distributor and lube the main shaft where the reluctor goes. That can get gummed up and stick.

Ron

pcguy2u

Have experienced this problem off and on from the beginning, even before changing the weights. Have now removed the dist from the engine and it's on the bench - I believe the reluctor the very bottom circular device at the very lowest part of the mechanism and the part that is moved by the vacuum advance. I'll check that and report back.

pcguy2u

Disassembled the entire dist and didn't find much of anything, except that one of the two posts that the weights swing on was bent slightly - though not enough to cause a noticeable binding of any kind. I also recall that there was a little rust in the area of and on the swing posts as well as the raised metal area that the weights rest on (no plastic rests on this dist.).

I also recall now that every time I encountered some difficulty obtaining the “all in” advance of 35+ degrees at 2800 rpm, the timing light showed the max advance to be 25 degrees – basically this boils down to shooting at a moving target which is what I described in the opening post in this thread. I suspect that whatever the underlying cause for all this boils down to, has ultimately caused me to unknowingly set the timing incorrectly at times – perhaps retarded and at other times accurately. If I managed to happen to set the timing correctly (and vice versa) and the problem becomes evident because of the underlying/random cause, resetting the timing becomes fruitless.

So much for the possibilities of how all this seems to work and on to what is the cause.

I did some Google searches on HEI modules and found numerous references which suggest that of the 7+ different 4-pin to 8-pin variations, some actually use 10 degrees as a fallback or startup setting depending on engine conditions at the moment. Unfortunately this is a 4-pin module and I found no such reference for this module.

In any case, does anyone know if there is some kind of fluctuating power condition that might cause the 4-pin to exhibit that 10 degree retard symptom? Or perhaps one that is on its way out?

Short of that I have sparingly lubed the weight mechanism in the hope that will cure the problem. Of course, only time will tell with this one.

pcguy2u

This morning I reinstalled the distributor to find that the engine seem more stable at idle that it had been in any of my previous attempts to isolate this - even the timing seemed rock solid at any given rpm, ie not moving around 4+- degrees. The all in was 32 degrees which seemed appropriated for two intermediate springs - while the dist was out, I changed from one intermediate and one loose to two intermediate.

The only problem I encountered was that the idle was too high (1100 rpm) and there was no additional adjustment available from the idle adjustment screw, ie the butterflies are now the limiting device. Incorporating the vacuum advance only, as I eventually hope to do, only exacerbated the problem.

Don’t know that I have cured the advance/retard issue, but now, how do I deal with the idle adjustment screw limits? Maybe I need to retard the initial to less than 14, which is where I set it??? I chose 14 because the cam is a bit over the top, you know, kind of lumpy.

RonSSNova

What carb?

If a Holley, and it's idling with the butterflies closed, perhaps the secondary butterflies are open too far? There is an idle circuit there, it just isn't adjustable. Mess with that little screw on the secondary stop.

pcguy2u

Stopped at Pick n Pull yesterday and stumbled on a near new HEI with cap and rotor - it was lying on the ground if you can believe that. Spent an hour last night going through it, cleaning mostly and I noticed a couple of things.

The most significant differences are in the centrifugal advance system:

Old one has heavier weights and has no plastic buttons on which to slide, although it never seems to hang up and always snaps back.
New one seems to glide easily over plastic buttons and when it snaps back it seems more posiitive.

In retrospect, the old distributor in the engine looks like an original GM that was rebuilt with aftermarket parts.

I'll be installing the replacement today and will start with everything but the cap and I'll let you know.

pcguy2u

Replace the distributor yesterday but did not make any progress and pulled off to watch football and search the internet for an answer to this problem and I may have found it. Still haven't pulled the carb to adjust the secondary idle setting and have not applied the concept that is suggested in the both of the threads linked below. I believe that the suggestion is that using the proper vacuum advance for the amount of HG your engine produces at idle will result in your engine idling smoother and running cooler.

http://www.chevelles.com/forums/arch.../t-329862.html
http://forums.corvetteforum.com/c1-a...hat-to-do.html

Hopefully I can get the idle under control without attempting to fill the two holes drilled in the primary butterflies. Just in case, anyone have a suggestion about how to easily/safely fill the holes.

More to follow.

pcguy2u

Pulled the carb and found the high idle problem - the spring in the vacuum diaphragm for the secondaries was weak. Tensioned it and all is well on the idle. Also found a leaking diaphragm in there at the same time, just installed with part of the edge not clamped down so the secondaries should open now.

Connected the vacuum can and timed the engine with 15 initial, 35 with the vacuum at 1000 rpm and all in with no load at 3000 rpm, it was 51 with the vacuum and 36 with the vacuum advance plugged.

Also, it appears that all this cured the high temp issue - the highest temp I saw was 185ish. Perfect for a 57 degree day. Running a 160 thermostat and an extra 2500 cfm (7 amp) aux electric fan. The aux fan never came on except when I tested it in manual mode.

This looks like the end of this project, sans a couple of wiring changes. Race Sonoma closed for bracket racing and I was never ready for the last day a week ago, so I won't be running this one in the spring – will be detailing this and will put it on craigslist in a couple of weeks. Hopefully by spring I will be on my way to building a 40X50 barn and building what I really want to run, an LS3 late 60's Camaro with a tune and mild cam. The Vega was a test project to see if I really wanted to commit to the LS conversion. Would have loved to put an LS in the Vega, but I believe the frame and suspension needs way to much work.

Many thanks for all the help,
Nick