Good evening! I have posted in this forum before with issues on the same vehicle. I have a 1959 GMC 150 with a Chevy 350 that seems to have carburetor issues, but I'm starting to have my doubts if that's really the issue. I recently got it running after it sat in the shed for 10 years. I got it started and it ran, but only on half choke. If I pushed the choke in so it was off it would spit, sputter and die. It wouldn't even try to start after about 4-5 hours of sitting. Then I go to start it again and it would repeat itself, so I thought it might be the old gas in it. I drained the tank to find that the gas that was in was horribly varnished. I got busy and didn't touch it until last week. I went through the whole fuel system last week. I rebuilt the carburetor (Which is a Holley 4412 2 barrel since I forgot to mention it.), put new fuel lines on, installed a new fuel pump, and drained the gas tank of the old gas that was in it. To my surprise, that didn't fix it. It did the same thing that it did before, but this time it ran for a shorter time. When I went to restart it after it died, it tried and tried and tried and tried to run, but it would only spit and sputter. I started to smell gas coming from the carb, so I thought I flooded it. Sure enough, it was. Could my carburetor issues not be carburetor issues at all? Could it be the distributor, points, or coil? Could the engine only wanting to run on half choke be an ignition issue? I just don't think it's a fuel issue anymore since I've worked on everything that has to do with fuel. Before you think it's a vacuum issue, it's very unlikely. I checked for that already, and even put a new gasket where the carb bolts up to the block. I apologize for writing a book, but I thought it might be more helpful to explain the issue as best as I could so you guys could have better luck helping me diagnose the issue. Thanks a million, Tex
Yes, it could be ignition problems. It could also be stuck intake valves, they tend to do that when exposed to varnished, old, fuel. Gotta start at the beginning...compression test, then check for good spark (make sure it can jump a 1/2" gap), see if the plugs are fouled, and replace with new ones if they are, check ignition timing, etc. If it's a point ignition system, you might want to replace the condenser if it's still having problems.
Tex....absolutely...many a carburetor issue is ignition...throw a set of points and a condenser in it...hopefully not Chinese made...and see if there is an improvement. Since you addressed the fuel system...I think its a fair bet in your case...
Yeah, not a fan of the Chinese made points. I've had a set on an old farm truck before, they ever worked worth a darn. I'll try the points and condenser, see what happens. If that doesn't work, I'll do a compression test as Squirrel suggested.
Use an old junk box condenser if you have one laying around. Clean the points if it's been sitting for ten years. Squirrel hit all the points. If you're wondering about the ignition, check for spark. A fat blue spark is best, that snaps in the air. A red or yellow spark in open air, won't be able to jump the plug gap when installed and under compression. If plugs get fouled bad enough, they can turn to permanent duds supposedly. With all that said, with a new fuel pump check the fuel level in the bowl. The float height may need to be adjusted up or down so it maintains the proper fuel level at all times. Too low and it will lean out on the highway and too high it will flood.
You may have ignition issues, but you may still have carb issues . You could still have blocked passages in the carb. I got a 39 Willys sedan out of long term storage and it would not run without some choke. Turns out the idle circuit was plugged even after soaking the carb for 2 days. Took some fine wire and a lot of carb cleaner and air pressure to finally get the car to idle without choking it.
I don't know if this makes any sense or not, but it won't even run with the choke off while I'm giving it throttle, it just dies... I fixed a '68 Ford pickup with the same issue. It would idle with the choke on but it would die if it didn't. If I gave it some throttle and let off the choke it would still half ways run, so I cleaned the carb like 3 times and it finally ran without choke after that. Nonetheless, carb still can't be ruled out on the GMC. I will mess with the ignition then take the carb off again if points and condesnor don't fix it.
Got a vacuum gauge? Sounds like a big vacuum leak if it won't run unless the choke is artificially richening the mix.
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