I've been experiencing some drivability issues after a few hours driving at lower speeds, back roads. It will sputter sometimes pulling out from a stop light. I can usually clear it by revving the engine. Other times it seems to lose performance, sounds like it's not firing on all cylinders. It did this yesterday, cleared up after I took it on the highway and let it rev for a while.

I have two carbs, one setup by Cliff Ruggles, the other by Lars. The problem has appeared with both to varying degrees. I doubt it's a carb defect.

The coil is new. Car idles great, runs pretty well until I've been out for an extended period.

I'm wondering about the exhaust crossover. Maybe the carb is being overheated after long runs? Did the LS5 have a restrictor installed, intake manifold? If so, it could be missing. My heat riser operates freely.

I had a hard time getting it restarted once with one of the carbs. This was listed as one of the symptoms.

It seems to me the exhaust crossover system should work fine so long as all the parts are installed correctly. I'm reluctant to remove the heat riser, could be another problem. The problem appears after the car has completely warmed, seems to be heat related.

I do have a thick gasket installed between the carb and intake.

Thoughts?

 

What do you mean my "exhaust crossover"? This is on your 1970 LS5 right?

 

70 LS5. I am referring to the passage in the intake where exhaust is passed from the right side to left, meant to warm the carb and choke. The heat riser directs exhaust to this passage when cold.

 

Consider fuel percolation. Lars states that it occurs in the fuel pump input side. Does your pump or fuel line have a return line that is operating properly?

 

It has a return line, new lines, new tank. I assume they're working properly. Another item I noted yesterday was when I stopped to buy gas, took off the cap, it sounded like there was either a vacuum or pressure. This is a vented cap. I know the 70 usually has a non vented cap. Thought it curious I would hear this, expected the vented cap to let off pressure or vacuum. This car doesn't appear to ever have had a charcoal canister. I see no evidence one was ever installed. The car was built on March 3, 1970, early 70.