72millemigliacoupe

My 72 has a problem where if I've been cruising around at low speeds on hot days (or in stop & go traffic), after a while (after it gets nice and soupy hot in the engine compartment), when I accelerate from a dead stop it miss-fires and hesitates, etc until I get up some speed. If I let it cool off or get on the open highway at higher speeds the problem goes away.

Just so you know what I've done (or had done in some cases):

* Installed new radiator (Dewitts aluminum)
* New water pump
* New thermostat (engine stays right on 180 to 190 even in the heat!)
* Had carb rebuilt by a very good Corvette mechanic (he did put in a nice thick gasket between the carb and intake manifold)
* Had new fuel pump installed (getting around 7 to 8 lbs of pressure now)

I thought all that would fix the problem, and dangit! The other day it happened again.

Any suggestions?

Twin_Turbo

Do you have a bypass regulator and a return line???

72millemigliacoupe

Well, I plan to check the return next. Want to make sure that:

A. The fuel pump has a return outlet
B. The mechanic hooked up the return
C. The return is not clogged

Also, I noticed that the fuel line running from the pump to the carb is contacting the radiator hose. I think that is the "cool" side of the radiator (return to engine), so I don't think that would be the problem though.

Twin_Turbo

that cool side ain't exactly cool

72millemigliacoupe

Agreed. I will move it off that hose (if possible) just to be safe.

76REDSTINGER

hot fuel......vapor lock like symptom

72millemigliacoupe

Yep, that's what I'm thinking too. Just checking to see if anyone else had any ideas. I'm zeroing in on the return line, if that checks out, I'll be coming back to the forum for other ideas.

Thanks guys! Will post results back either way.

Rolm

I had the same problem on my sons MX6, After a few weeeks of hell and spending $300 at the dealer. I finally fix the sucker by removing the Bosch platinum plugs and installing the stock NGK plugs.

72millemigliacoupe

Wow, sparkplugs huh? Funny you mention it, I did put in some of those Delco performance plugs (the kind with the longer body). Could that really be a possible cause of these symptoms?

I'll try switching back to stock type, thanks for the tip!

carriljc

Mine used to do that a long time ago...I kept thinking vapor lock and all kinds of stuff. When it would start missing, I'd open the hood, and I could never find anything...seems that when I opened the hood, the coil would cool off, and it would quit missing....

I happened to find this one late evening when I was looking at my timing, I was tired and it wasn't running right, so I was just sitting there watching the timing light blink, and blink, and blink....so as I'm sitting there spacing out I notice that every once in a while it skips a beat...hmmm, I slapped my old datsun's coil in it and WOW! It ran smooth....
It used to really annoy me on a hot day, when it would start running rough, or almost quit, I thought I had vapor lock....so then when I opened the hood and looked around...get back in and it would start. Bothered me for a couple of years. I used to have a Mallory coil on the firewall when it did this...I just put in a standard GM coil after that and never had THAT problem again.

72millemigliacoupe

You guys are really giving me some ideas here. I've been focused on a fuel problem, but between the plugs and the coil sounds like it could be more fire related. I had also put in a fancy coil, so I wonder if I just switch back to a stock coil and plugs?

Thanks again!

bqce

First thing I thought about was distributor cap possibly being cracked. It does sound like some kind of electrical thing associated with the spark.

Steve Grodin

Try replacing the coil.

72millemigliacoupe

Well guys, the forum has saved the day once again! I replaced that Accel coil with a stock Delco and what do you know? It fixed it!

Took it out this afternoon (95 degrees and full sun) and took it on a nice slow cruise. After about 45 minutes I declared victory (previously it was stalling out after about 20 minutes in the heat).

Thanks again, if it weren't for this forum I would probably sell that Vette. Otherwise, I would be spinning my wheels on this kind of thing all the time. I hope some day I can contribute back to the forum with knowledge gained.

Steve Grodin

Glad you were able to solve the proplem. Thank you for posting the results of your trouble shooting.

martinsw

i have been having total cut out (three times last two 100 mile drives) - only when hot and usually giving a bit of fuel. I was thinking vapor lock, but also suspect my accel hei coil. Think I will buy the Delco coil and give it a shot (first autozone coil I put in was not putting out enough voltage - only about 15000 volts - shouldv'e put back in Delco, but tried the accel).....
maybe it will be party time for me to (and I can get on with new carpet, rear brakes, paint, etc......)