I'm working on an O/T truck. It sat for over 12 years. It'll fire up ok but that's it. When I hit the throttle I can see the butterflies open but there's no change in RPMs. I want to get feedback as to if this sounds like just in need of a carb rebuild, replace or if it's unrelated to the carb.
Hmm.... I'll have to check. When it comes to carbs I tend to get foggy. Always been that way. I've done all aspects of engine work but carbs remain a mystery to me.
air comes in the top hole, fuel comes in the little hole where the fuel line is. Air/fuel mixture comes out the bottom, where the throttle blades are. It's simple, but it is indeed magic. Sitting for a long time is bad for carbs, but they can usually be fixed by cleaning very thoroughly, and replacing the "soft" parts, that come in a carb kit. Overhauling a carb takes patience, and knowledge, you can screw stuff up if you're not careful. I was lucky, I started when I was a kid.
Ya gotta start somewhere. When I put the first carb I rebuilt on my car (which was running poorly), I couldn't get it to even start. It was only then that I did a little research on carburetors, the circuits involved, and how they work. I'm doing a lot better these days.
Check for mouse nests, just in case. But it does seem like a carb issue based on your description. Check the linkage and butterfly shafts on the outside with a strong light as you change the throttle angle while running and the same thing looking down the 'barrels' as has been mentioned. You may need a carb cleaning/rebuild if any jets and passageways are gunked up.
Squirrel, Could you explain that one more time for me please ,,,,,I got lost when you brought in the Magic ! LoL,,,,Jim,,,,you always know how to get to the heart of the matter . Sometimes they truly are magic,,,,,except back in the day,,,when word got out about carbs that could get 100 plus MPG,,,I think then it was just slight of hand ,,,LoL. Tommy
How can you open the butterflies and not get any change???? If the engine is running, opening the butterflies is going to result in either an increase in rpm or it’s going to stumble and die. What am I missing??
Is it a big truck? Is it vacuum governed? If so the throttle valve is opened by vacuum and only closed by the throttle arm.
Exactly what I was thinking. The only other thing I could think of is an almost completely blocked exhaust system. Check for mouse nests there too!
Accelerator pump not functioning. Not getting a pump shot. You might even get a bit of a bog when pushing the throttle down to quickly.
That's what I thought too. Yes, it's a big truck. 361 with manual choke. Holley Carb Unfortunately my camera lens is so scratched it look like watching a video with really bad cataracts. I'm going to either pull it and rebuild it or buy a rebuilt. I was leaning that way anyway but the lack of response when the butterfly opened is what made me want to double check before I pulled it in case it was something else. It looks crapped up enough that I'm sure it wouldn't hurt. If that still doesn't solve the problem at least I'll know it's not the carb. Probably won't get to it until this weekend or next.
Not it wont. If you accelerate very slowly it will start pulling fuel from the main circuit and the rpm will increase normally. If you jab the throttle from idle, yes, it will die, or backfire.
Soak the components once apart, in carb cleaner, or similar, then wearing goggles, blow out every durn passage. May need a wire to clear certain passages. While you are at it, check the wear, at the throttle shaft/ housing fit. If loose, find another carb
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