Hi guys, I have a 1970 LT1 that I frame off restored last winter and Top Flighted with a 98.1 score last spring. The car is 100% restored and original with smog pump TCS etc... All wiring has been replaced along with new TI ignition etc... (All from Lectric Limited) The car runs absolutely fantastic until it has been driven about a half hour. After a half hour of driving and getting warm it will start to get finicky about idling at stop lights and once it stalls is very hard to re-start. Sometimes I have to pull over and lift the hood to let cool for 10 minutes or more and then I can restart by mashing / holding down the accelerator.

I have been fighting this problem all summer. I have changed the coil adjusted the fully rebuilt original carburator by lowering the float bowls, added thicker spacer gasket under carb, changed fuel pump etc.... (I even tried another carburator and had same symptoms!)

The symptoms have lead me to believe it is a fuel vapor lock issue etc., but when this symptom happens I have immediately removed the air cleaner and have not noticed any fuel boiling over into the bowls and if I move the accelerator it instantly squirts fuel into bowl, which leads me to believe it cannot be a vapor lock issue. So could it be something electrical!! Any suggestions at this point would be so greatly appreciated!!!

I recently read up on the TCS System and how it works. I thought I had determined the problem. As I understand it the Transmission Controlled Spark selonoid shuts off vacume to the distributors vacume advance when the car is in first, second, nuetral or reverse. It allows advance in only third and fourth gears. It also has a 20 minute delay when you come out of third or fourth gear when engine is at normal operating temp.. So my plan was to keep the car in third gear at stop lights when hot and shift into first just prior to the light turning. This seemed to be working last night and was certainly increasing the idle when in third gear (TCS is definitely working), but I think I was fooling myself because I only drove the car about 20 minutes. Tonight after about a half hour the problem developed again and shifting into third gear did not help!!!

 

John, you may have a leaking carburetor well plug or some other internal leak in the carburetor. This will leak fuel into the intake manifold causing it to flood out. You can't see it. That's why you have to hold the pedal to the floor to start it. Q-Jets were known to do that back in the 70's. Your Holly may have a similar problem.

 

Hello John, I have read that running with the TCS system can give you problems. My '70 LT1 runs great and I can only tell you what I have done. I run the vacuum line direct to my vac advance from the 4 port connector instead of to the TCS solenoid and I plugged the TCS port meant for the vac advance. In addition I have the vanes removed from my smog pump, plugs in my exhaust manifold smog tubing and the vacuum line from the 4 port connector to the diverter valve plugged internally. So, I do not have a functioning TCS nor smog, but it all looks good. In addition I am running a new 4555 Holley and have my original 4555 on the shelf. Good luck, Lenny

 

If the answer isn't in the TCS:

Sounds like you're lean to me. When the car is cold, the choke is masking the condition; when the choke comes off, the engine is starved for fuel. That can be caused by a vacuum leak or improper tuning, but I would lean toward the former to start.

Timing issues can also cause your problems. What advance are you running? Factory was something like 4*, which today is likely too low. I have a 1970 L-46, which also had 11:1 compression, and it will barely idle at 4*. I have it set to about 12* initial.

 

Thanks Lenny, What a beautiful engine compartment!! Great attention to detail!! I love it!! I notice you have a bracket coming off of the carb mounting stud holding the fuel line. I have never seen that before is it stock? Looks like you have Marlborough Maroon like my car. Is it a roadster or coupe? I tried by-passing the TCS by connecting direct vacum to the distributor but symptoms still persisted. I still wonder if the smog system could be causing the problem. It just seems that something is getting hot in the engine compartment and causing the problem. Car will run flawlessly for about 30 minutes then the problem starts. I feel it must be fuel related because even if I start the car for only 5 or 10 minutes I always have to mash the pedal to restart. (acts like it is getting flooded).

 

Lenny, One more question. What kind of fuel are you running. Cam2 or any type of octane booster. I have been running 92 octane pump fuel in this car. Seems to run fine with no pinging but have thought that maybe I should try putting 5 gallons of Cam2 race fuel in with every fill up??

 

Thanks John. Yes it is maroon and it's a roadster. My car actually starts better and runs great when hot. It ran good when I got it, but the original carb is on the shelf. I bought this carb from Camaro Central and it ran perfect right out of the box. http://www.camarocentral.com/1970_Ho..._p/enc-538.htm
"New correct design holley carb for your camaro. Exact for all 70 small black Z28 and 350 high performance models. 780 cfm delivers the needed fuel to give optimum response to your ride. Features original GM part number 3972121 and holley list number 4555 on the front air horn, just like originals. This is a brand new in the box holley carb. Gold iradite plating as factory units. Correct for automatic and four speed transmissions. Fresh to date technology with the right old school look. Tested and guaranteed, ready to rock!"
I use ethanol free 91 octane and it runs fine, in fact I bought home 5 gal. today for the car. No additives or octane booster used.
When I ordered the smog set-up, I requested the smog pump be de-vaned and I plugged the smog tubes and vac line when I installed it; mostly so I would not heat damage all those nice components. Yours' functioning could be part of the problem.?
My car was very original when I got it and that fuel line bracket was there. Looking at the AIM and the Prince book it is not shown. The Dobbins book shows a '70 LT1 engine without it, But look at this site showing a 1100 mile Z28; at least 3 pictures show the same bracket. http://www.1970z28camaro.com/engine/ My car is 1889; a Jan. '70 with a Dec. '69 engine stamp. Maybe used on early cars? I do not know. (that pump spacer should be orange)

 

Hi Lenny, Thank you for all the tips. My car is 5128 late Feb. 1970 car. I have tank sticker, protecto plate, original sales invoice, GMAC finance contract and photos of car when new along with original registrations. I got very lucky and was able to find the original owner after I purchased the car. Car has very few options. Standard black vinyle interior, FM radio, and alarm system.

 

Yes John mine is close to being a twin. Like yours' standard black vinyl interior, only fm and white letter tires as options, but no alarm. I have the tank sticker and POP verified by NCRS, but no original docs beyond that. What you have is above and beyond what the most demanding owner could hope for. They are so valuable and almost required for a safe/smart purchase. Mine was not judged and I probably will not have it done in the future. I did use a service offered by Drew Papsun who is a NCRS master judge and Bloomington gold judge to verify the car and all the mechanical components. I to dug up the original owner; spoke to him 3 times and sent him pictures twice. Fun, friendly conversation between us; I asked him to send me a short letter, he said he would, but never got anything.
Good luck finding that gremlin and enjoy that beautiful car. Lenny

 

Sounds like ruptured or perforated power valve in the carb?

This will cause a rich condition and will get worse as the car warms up.

You can't see a power valve leak down the throat of the carb because it leaks through the base plate.

I was fighting a terrible rich conditon in my car and found two things. My fuel pump diaphragm was cracked all over and leaking
and my power valve was dry rotted as well.

May not be your issue but if I stopped for gas and tried to restart the car was flooded. New power valve and I'm golden... I also replaced all component that had rubber in the car.

Eldelbrock fuel pump tech told me to run 6oz of marvel mystery oil in each tank full to keep pump diaphragm from drying out and carb components from drying out due to sitting to much.

Look at my accelerator pump etc... Again may not be your issue but sounds like the power valve. A back fire in old holleys can blow them as well... Newer holleys like mine have blowout preventers.

 

I'll give you my take on things as I've struggled with a similar problem with a Holley equiped car.

Our current fuel has different additives to give you the same octane rating as our old fuel. These additives make for a lower boiling point of our current fuel.

What happens is the following : when you shut down your car, your ventilator doesn't turn and there is no fresh air supplied to the space under the hood. The engine block and exhaust start to heat up the air. This hot air rises and creates a pretty high temp below the hood, exactly where your carb is. This gets so hot your fuel starts to boil/vaporize. The fuel starts to expand which causes it to drip from the main boosters into your engine. The vapors go through the vents and end up in the air filter.

Once you start your engine you have a flooded engine.

The fuel we have today is meant to be used with FI where the fuel is under pressure constantly.

After I went to efi my issues were over.

There is only one fix that I know of and that is an electric ventilator of sorts to keep blowing air through the engine bay. Good luck.