My '76 has a hot start problem. On cold start, it starts right up, high idle for a few minutes until I kick down the choke, then it idles fine. If I shut it off and start it within 10 minutes or so, it starts quick and idles fine. It I let it sit for 1/2 hour, it starts hard and doesn't want to idle. The issue is only on idle. Once I get going it runs great, no hesitation. I have checked for vacuum leaks, timing, cent. advance, vac advance, and replaced the carb with a Jet quadrajet. I have also adjusted the idle screws on both carbs. What next?

 

Check the connections on the starter. Make sure they are good, and as far away from the exhaust as possible. There is a wire (on my 72 is yellow cloth covered) that goes to the coil. It's purpose is to provide extra to the coil during startup. But heat=resistence, so if the wire gets too hot from either a frayed connection, or being too close to the exhaust, it can create extra resistence on your coil.

 

So, you're saying that the wire provides voltage to the coil, increased resistance reduces the spark available at the plugs?

 

A 76 has a completely different ignition system from a 72 - if stock. Bad current to the distributor would get even worse as the RPM rises, you say the problem is only at idle. The 76 HEI ignition module can have heat problems, but usually would not be just at idle. Same problem with two carbs. What kind of fuel pump do you have? Using fuel pressure regulator? Have a fuel return line?

Reason I am asking, sounds like fuel percolation (boiling in the fuel bowl)

 

That makes sense. It appears to be a stock pump, with a return line and no pressure regulator. The fuel filter has the check valve. I do notice gas fumes on the air filter. I have the thick gasket under the carb. Should I try a carb spacer?

 

I would look into it. The factory even came out with an aluminum shield that extended out under the fuel bowls. Many use a shield of this type or a phenolic/plastic (less heat conductive) spacer. I also block off the heat riser passage under the intake, but I live on the Gulf Coast. If you drive in the winter (my wife grew up on Grand Island) you may want to leave it. Todays fuels dont help, and if you have a leftover tank of the winter blend fuel, it's just asking for trouble.http://paceperformance.com/i-6250300...jet-carbs.html

 

Thanks for the info. I'm going to try a spacer. (I've tried everything else). I'll post the results!

 

Please post your results. I am having the same problem with my 78. Cranks and cranks spits and sputters a few times before it starts. Annoying when out running around town. Look forward to seeing if it helps.

 

Will do. Just to note, it only happens on a hot start. Starts hard, sputters, won't idle. After 5 minutes on the road, it returns to normal.

 

Ditto to only hot starts. Fires right up on first start in the morning

 

Might want to check (if you still have one) your heat riser valve to make sure it is opening.

 

Have you tried the spacer yet? I'm having the same issue with my 79. I can start it cold perfect. Restart it right away after getting gas or quickly getting something from a store. But 20-45 minutes and it's really hard to start. I was thinking of trying a spacer.

 

I had the hot start problem also, i used a 1" spacer, from summit i think.
I does help, trying to keep the heat away from the carb. About $30 i think.

I have an L88 hood so lots of room. I also had the aluminum spacer but that didn't work to good.
My problem was just starting after sitting 1/2 hour, gas sitting in bottom of manifold. Once it started it was ok.

 

I was going to get a spacer but it turns out I don't have the clearance on my stock hood. Only have about a inch tops. I ordered a Mr. Gasket 86B Quadrajet Heat Dissipator on Amazon for about $26. It's 7 layers consisting of aluminum and the fiber gaskets made specifically to keep heat from the carb. It's only 1/2 inch if you install all layers but you don't have to. Hopefully it works. I'll post my findings when I install it.

 

I put on the mr gasket heat dissipation gaskets but still no good after a really hot drive. Its only .5 inches so I might try to see if I can fit the inch spacer under my stock hood. Not sure what to try after that.

 

Just read this on the summit racing site about the spacers Guess I should have looked into this more before buying the aluminum pancakes and taking my car apart.

Aluminum*is the worst insulating material of the bunch, with a thermal conductivity rating of 1,665.1. It does offer three advantages—it’s very durable, are easily altered to help tune the intake charge, and is the only spacer material allowed by many racing sanctioning bodies.

Phenolic Resin*has a thermal conductivity rating of 2.01. While not as good an insulator as wood, it is far more resistant to fuel and chemicals, making a resin spacer more durable.

Polymer*is less expensive than phenolic resin. But with a thermal conductivity rating of 3.90, it does not insulate as well. Some polymers have been developed that insulate nearly as well as phenolic resin, so it pays to do your homework before you buy.

 

I tried

 

Ok. I got my parts in and after having a hell of a time putting everything back together twice (I put a gasket on backwards, made a horrific sound when I tried to start it. ) I think I have something that works good.

So here is my setup now. Manifold, gasket, ACDelco aluminum heat shield, gasket, .5 inch plastic spacer, gasket, carb. Total height less then 3/4 an inch. I have a stock hood so not much space.



The ACDelco heat shield comes with a thin top and a thick particle board like gasket stapled to it but to save a little bit of room I removed those gaskets an added some better Mr. Gaskets that I had. I also had to take a Dremel tool and cut out room for the EGR valve and a few more things on the passenger side.

Because of the extra space now I had to buy larger bolts. I used two 5/16-18 x4.5 and two 5/16-18x2.25 with some washers.

I also figured out that the person who had the car before me must have broken the fuel line a some point and replaced it with just a rubber fuel line that sat between the manifold and the heater hose. I replaced it with another rubber hose but now I have an insulated cool tube around the fuel hose that will deflect up to 500 degrees.

If I can give any tips from this post it would be to buy some 5/16-18 threaded rod and use that to line up all of the gaskets before you put the carb down. If I had done that in the first place I would have saved a ton of time. I just went to home depot a bought one long threaded rod and had them cut it for me there. That was also when I bought my new carb bolts.

In the end I drove my car around for about 30 minutes on the freeway and then lifted the hood and I was able to lay my hand right on my chrome air filter cover and it was barely warm. I was even able to put my hand right on carb and it wasn't really hot at all. I then tried to touch that aluminum shield which end up being hotter then the sun. It works great. Hope this fixes my issue.

Sorry for the long post but I hope it helps others.

 

Sounds like you are indeed flooding due to boiling in the bowl. I have tried almost every hot start fix, electrical and fuel related. I have headers and here is what helped me most.

1. Insulate the fuel lines along the frame rail BEFORE the fuel pump. They run right past the headers and the fuel boils before it gets to the pump. Vapor lock. I also insulated the fuel line after the pump.

2. when you turn the car off listen to the carb for a boiling sound, look down the throat for fuel squirting down the intake. Now here is what also helped, lowering the float level a little.

3. I run 14* initial advance, cooler

4. Idle mixture is rich like 12.5-12.8, cooler.

5. 180* thermostat and running temp

The also sell wood spacers. Get a spacer for sure but it may take a combination of things to resolve the issue. Do what you can to keep things cool.

 

What would you say this whole set up ran you?