I recently replaced the 2 barrel on my 81 GMC with a Holley carb and Edel. manifold. It runs awesome most of the time, but on the way home tonight, I couldn't get it to idle. I was thinking it may have been building up ice on the carb. I read about it in a 4x4 magazine once, and it is snowing like a mother out tonight. That's the only thing I can think of. I'm running a 1/2 inch phonelic spacer under the carb, and the engine never gets over 190*, and most of the time it rides the thermostat at 180. When I stop, it idles for a minute, and then cuts off. I have it idled down pretty low, but it runs great all other times. Has anybody else had this happen or know what else it may be?

 

It's hard for me to say..I've never had an icing problem. You can alwasy try taking out that phenolic spacer. The carb will stay warmer, and if the problem goes away you know that was it.

 

I'm going to try adjusting the float level. When I run it and then let it sit for a while, it acts like it's flooded. It takes a few seconds of cranking and blows some smoke. I looked back at the tail pipe today when I took it out, and there was black smoke coming out. It may be jetted too rich, also. It has the factory 65 (?) jets. It ran so good, I didn't mess with that, just the idle mix. If it matters any, it was tuned at 65-70* and it is now 20*.

 

It must have been the weather, cuz I've driven it in cold, dry weather before, and it was fine. It got back up to the forties today, and it runs great again. I'm still going to check the float level and do a better job of tuning it to see if I can improve the mileage. It's an otherwise stock 305 2bbl truck motor that used to get 15 mpg. The only mods are carb and manifold (Holley 600VS and Edel Performer). Now it gets 10, maybe. That sucks. If anybody has any suggestions, I'd appreciate it.

 

Carb icing happens the worst in damp weather from 45* down to about 25*. Start up and it'll run fine at first. But in 2-3 minutes the idle slows and gets rougher. Keep going at the engien can die completely at idle. But restart a few seonds alter and it'll run fine for another few minutes before the same thing happens.

If you don't have a hot air source going to the carb this can continue for up to 20 minutes after a cold start!