Good evening. I’m at the end of my troubleshooting carb skills here…stock 59AB in my 29 that was just rebuilt and this carb is giving me hell. Stock 94 carb rebuilt by engine builder looks real nice. It does great around town with no issues but if I’m running on the highway around 55 mph and hit the off-ramp it stumbles and dies gushing gas out the top hole in the carb the small port next to the fuel inlet. It floods, I tap it with a hammer reseating the needle valve and it’s usually fine unless I hit the highway again and get off. I thought it was a pressure issue so I put on a new pump that came from my old motor and never gave me pressure issues. It did it again dumping fuel all over my new hot motor. So today I replaced the top with one I never had needle valve issues with. Now it barely idles and I don’t know how the top would affect that. So I can put on the old carb top and leak or this one and run like crap. If it helps it’s a stock cowl tank and stock motor except for Petronix ignition which is working great. The other strange thing it does is seems to have gas coming out of the center jets for less than a minute after shut down. The base of the carb seems to seep a bit, I’ve noticed the base is moist with fuel after it sits. This only really is an issue when I’m coming home from work on the highway but obviously unsafe. The idle screws are 1 3/4 backed out but the idle stop screw on the arm is almost all the way in. Thanks for any help I’d like to take this on some distance runs with confidence
Either the needle and seat are leaking or the float is set way too high. The float also may be leaking, filling it with gas. Gas in the float is not an unusual problem and can be fixed with a little solder. One thing that few are aware of is percolation. There is an exhaust passage that runs under the carb to prevent icing in cold, humid weather. It is not thermostatically controlled and can get the manifold really hot , especially at highway speeds and get the gas boiling, thus flooding badly. Especially bad after shutting off a hot engine. It sounds to me like the carb needs a proper overhaul, especially float level. An inch and three quarters open on the mixture screws is an awful lot. The float level gauge they give you with a carb kit is useless. To get the absolutely best level, you need to do it using a standpipe tool. This is covered in my other posts. It includes directions for making and using the tool to get the proper fuel level, which is 11/16" below the gasket surface on the bowl. I'm talking fuel level, not float level. Common cures that folks used in the old days was things like putting pennies over the little exhaust ports under the intake manifold, installing longer carb studs and an insulating block under the carb, etc. Your pump pressure should be fine. Make sure the anti percolation port on the carb is clear and that you are using the proper base gasket. All look right but some do not have the little holes that control vacuum. Check the manifold and carb base to see if you need the gasket with the little holes. Severe under hood temperatures can add to the problem, also.
Thank you so much for the help. I’m going to give it a proper overhaul this weekend and really check those levels as you suggested. I’ll keep you posted on the progress, thanks again.
If the idle screw is all the way in the carburetor isn't in idle circuit. Maybe mixtures screws need adjusting. The flooding and tapping with a wrench sure sounds like a float valve problem. Do get a pressure gauge on it so you can monitor it.
Check the needle too under magnification, if there is any sign of a groove it won't close off in the seat. A new needle and seat will fix this. Also there is a 'check valve plunger' for the accelerator pump that looks very similar to the needle make sure one of those wasn't used accidently. I run all the Hollys with a 2.5 psi inlet pressure max Also, since a fuel logged float was mentioned, the way to check a leaking float is to submerge it pot of hot water right below boiling temp. Look for air bubbles from the expanding air in the float...you can pinpoint a leak that way, Good luck
You guys are too good. I pulled it apart today and if anything it was a nicely restored carburetor the builder put on it which made the job somewhat easier. I think there may have been some media left in it from blasting so I soaked it all day and blew it all out. The float was off way more than I could have guessed and when I pulled the needle valve it was much shorter than my spares for some reason so a new valve and seat and then found some crud under one of the idle mixture screws. It runs like a champ now but first big drive tomorrow so I’ll keep you posted. Thanks again for the advice it’s a lifesaver.
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