czl6lx

I have a 1969 L71 and after driving the car for an hour or so the idle wants to drop to the point where if I do not give it gas it dies. Once it dies the starter becomes inoperable due to being too warm I am assuming, the starter does have a heat shield installed. If I let the car sit I can get the starter to engage again. So I have 2 issues, engine idle dropping after car is warm and starter not engaging once car is driven for a while. The temp gauge indicates the car is in normal operating range. I have had the TI system and distributor rebuilt last year (by TI Specialties)and coil checked out fine.

Any ideas where to start to try and diagnose?

toobroketoretire

Does your engine still have it's original three 2 barrel carburetors? What is your HOT idle speed in neutral? It should be around 750 to 800 rpm. The "hot starter" is a ridiculous urban myth with no truth to it so ignore it but solenoids can quit working if their internal ground wire is broken (like mine just did earlier this week). The problem is the spot weld that fastens the ground wire as it can be too much which makes the wire paper thin and breaks. When its cool the wire makes contact and when its HOT the wire lifts slightly and fails to make contact.

czl6lx

Yes the car has the original tri-power (rebuilt by Holley about 2 years ago) and hot idle is at 750 in neutral. When you say internal ground wire in solenoid, you actually mean inside the solenoid? Never had one apart so not familiar with them. The starter is a rebuilt original from John Pirkle also about 2 years ago. So can the solenoid be disassembled and checked for issue you suggest? Thanks - Jeff

toobroketoretire

Yes, you can remove the black plastic solenoid end cap by removing the two large stud nuts and the nut on the "S" terminal. Pivot the cap over to one side and notice the small copper ground wire that is spot welded to the housing. That wire can break where its been spot welded because its so thin. I brought this up because my solenoid failed a week ago and when I opened it up I found that wire was fractured.

When that little wire breaks the solenoid won't make any noise; no click at all. Just nothing. Then maybe 30 minutes later it'll start working until it gets warmed up again.

Big2Bird

Yes and no. Chevy had a service bulletin back in the day. The solenoid spring gets weak when warm The "cure" was a high temp solenoid with a brown cap. It had a stronger spring.

1Fordman

Have a 68 with an L-71, mine cold high idles at 1200 and when warmed up idles at 850. You may need to raise the hot idle speed up. How do you set the idle mixture, by the tach method or vacuum gauge method? I use the vacuum gauge method and find it to be more accurate for me.

I ditched the original Delco starter and put in a hi-tork gear reduction starter to put an end to the heat soak no start issues.

If you want to keep the starter original, the advice above is excellent about the solenoid.

gungatim

these are the bulletins...

REELAV8R

Hmm...perhaps a re-phrase is in order.

gungatim

no, well sorta maybe... heat soak is real but not the way people think. it's a solenoid issue, not a starter issue. That is the confusion people have, going out and buying mini-starters and such. it is also pretty rare, as the solenoid design has been improved years ago. you'll also note that it is prevalent in motor homes, no mention of vette's...

If you read through it all, heat soak is the last thing to check, as the grounds and connections all play a significant part.

I had a 421 tripower super duty Pontiac that had this issue. special manifolds tight around the starter, solenoid on top, and original casting nla, meaning a special starter was made for those GP's and racing with an alternate solenoid location. had lots of problems until I read up on the bulletins and learned exactly how a solenoid works and what it does. it's does more than just engage the bendix...

MelWff

In reference to your starting problem, what is your initial timing set for with the vacuum advance disconnected?

REELAV8R

Right. But rather than stating it's an urban myth it might be more helpful if it were explained that in addition to the heat there may be other issues.

Check connections and battery cables, and then if the problem still exists try replacing the solenoid as that in fact is or can be affected by the heat.
I know guys go out and buy new mini starters to combat this problem. That's their choice.
If it were explained how heat may or may not be a factor they may opt to fix it rather trying to combat an "urban myth" by purchasing a new starter.

Our battery cable runs on the C3 are relatively long and voltage drop can occur in that length, particularly if someone has replaced it with the wrong gauge cable sometime in it's past. That combined with the increased coil resistance in the solenoid due to heat may present a minimum voltage problem. It's at least worth checking out.

czl6lx

I took the solenoid apart and the wires that you spoke of are intact and have no breaks. I was really hoping that this was the issue. This was the first thing I looked at since your description of the no start condition was exactly what I have. Just to be clear though I get no noise at all from starter or solenoid or bendix when the condition presents, it's kind of like trying to start the car without the clutch pushed in, just dead silence but I have power, 30 minutes later it starts. Thanks for your advice.

Big2Bird

1)You can try and find a brown cap solenoid, but I have no source.

2)You can try a heat shield, sometimes it is enough, sometimes not.

3)Install a mini starter.

It's a PITA when a car won't start.

toobroketoretire

Its just the ground wire that I am referring to; the bare wire that is spot welded to the case. To check it for breaks you have to physically put sideways pressure on it to see if its still in one piece because you can't tell by looking at it. Mine looked fine UNTIL I gave it a small sideways shove and found it moved (uh oh). Sure enough it was broken and was the cause of my solenoid only working after it cooled.

czl6lx

I did look at it with a magnifying glass, I'll yank it again and try to bend it to see if it is broken.

74modified

Here is what I would do before tearing anything else apart or replacing stuff. From what you describe, it is a problem with the solenoid either not working (bad), or not getting enough power to operate. If it was working, you would hear the click of the contacts coming together.

First check basic things like battery and cable conditions. If you cannot jump the solenoid, then the solenoid is bad - whether you can see it or not. If good, then start at the wiring to the solenoid and check for power, then work back thru the system. The wiring, to the firewall connector, the clutch/neutral safety switch, and ignition. Any and all of these things could cause the no start. It can happen, check this thread. https://www.corvetteforum.com/forums...ease-help.html

"Heat soak" is not a myth, heat can cause resistance to go up and parts getting hot can expand and move around. I saw Chevy mechanics install the parts from the TSB mentioned above in the late 70's. In fact, I have used the same sort of system (with a Ford solenoid) on all of my Chevy "heavy use" vehicles, and it works. You can even buy kits with the components. After 40 years, resistance can build up in connections and components and using this "extra" solenoid allows full voltage and ample current flow (through larger wiring) to the starter.

The solenoid spring mentioned above should actually be a weaker spring. The weaker spring makes it easier for the solenoid to actuate - it has to push against the spring - then the spring pushes the solenoid back open when you release the key - that is a good change as well. I just don't know where you can find one nowadays.