Hi All,

I have run out of ideas as to why my Corvette will now not start. I would appreciate some assistance because I have hit the wall. Here is the back ground to this very frustrating tale…

I have a 1970 LS5 powered Corvette. On returning from a recent trip the car unexpectedly stalled just as I turned into my street. I took the air cleaner off, and found no fuel when I actuated the throttle. There was fuel in the filter, and about 10 gal of fuel in the tank. I took the carburettor off (Holley 750 vac-sec). I pulled it apart and found some corrosion in the primary bowl. It appears water got into the carburettor while it was in storage on the shelf. My thinking was that some corrosion particles got into the fuel circuits and blocked them. So I cleaned and put a new kit through the carburettor and refitted it.

The car started but did not run well at all. It was backfiring through the exhaust and kept stalling. I pulled the carburettor and checked that I rebuilt it correctly, matched up the new gaskets with the old, and everything seemed okay. I fitted the carburettor back on, and tried again.

This time the car would not start at all (just cranked over) and backfired through the exhaust. I decided that maybe I had more that a fuel problem! I was running an older GM HEI distributor, and when I tested a few spark plug leads, the spark seems dim and erratic. Along with this, I noticed my tacho (VDO electronic) was bouncing around and not reading correctly. I decided to fit a new distributor, and bought a new MSD HEI unit.

I fitted it and found it made no difference; the car still would not start. Grrrr! I pulled the drivers side valve cover and turned the engine by hand to ensure I fitted the new distributor correctly, TDC piston #1. Re-checked the firing order. Now I’m running out of ideas. It has spark, it has fuel. What the?

After a search on the forum I tried a few suggested from other posts. I cleaned the battery ground to chassis and the engine to chassis ground. No difference. I drained the fuel and put some new stuff in. No difference. I jumped the +12V from battery to HEI to eliminate a faulty ignition switch. No difference.

Please help ☹

BB

 

about the thing you have not done is replace the plugs...its possible all that cranking and fuel fouled the plugs...a fresh set might help with no other ideas......

 

Backfiring through the exhaust? Crank the engine while spraying some starter fluid. If the engine backfires it's not because of the carb but the spark timing.

 

Sounds like the next step to me!

 

Change the plugs. Do a compression test. Be prepared to go after the timing chain and gears.

 

Thanks for the responses guys,

I did pull all the plugs. They were still wet from fuel. Cleaned and regapped them. The engine only has a few thousand miles on it, so the plugs are still new. Not to say one might have gone bad, but plug quality is pretty good these days! Will try anyway.

That is a good idea for eliminitating fuel versus ignition. Will try it tonight and report back.

The engine only has a few thousand miles on it, so I am not expecting a dead cylinder (I hope!). I know the timing chain and gears are fine, because I cranked it over by hand with a valve cover off and watched the rockers move. Cam lobe maybe?

It still seems electrical to me, but maybe I'm just praying that is the case, because the alternatives are ugly

Any other suggestions?

Cheers, BB

 

plug wires all in the right place.

 

I did check and double check this, firing order 1-8-4-3-6-5-7-2. The leads are new reproduction Corvette ones from Ecklers (Packard brand), with the metal radio shielding on the outside like OEM. Just a thought, this wouldn't interfiere with the HEI? I think these types of leads were standard only on the points type distributor!

Cheers, BB

 

Not good enough. Either replace the plugs with new ones, or at least check each plug with a good ohmmeter on the highest scale. They can foul with very little mileage on them and look great, but will not function properly.

 

Good point. I will get a new set of plugs and try them out.

Cheers, BB

 

Full credit goes to longbros, finally got a chance to put some new plugs in and she finally fired up again. Set the timing and adjusted the carb, and it it drives much better. Thanks for all your suggestions.

Cheers, BB

 

Check connection on and in starter.

 

Thanks, but it was a group effort. Glad you have it back on the road. Wish I still had my 70 LS5. Bought and sold it when I was in my 20's, I am in my 60's now. Have fun!

 

At this point since its running, I would wait until dark then run the engine at idle and look for shorting / gounding of the ignition wires which you should be able to see readily if it occurs . Move each wire around where it lays against anything metal like your valve covers as you watch. During the daytime, at idle, id run some SeaFoam thru the carbs venturis SLOWLY and put some down each bowl vent as well as the little air vent screws for the primary and secondaries --- I do this regularly on my 1970 built LS5 and it does a great job of cleaning out the carb (which is a Mighty Demon 800) .