quick carb question

[Mercury Mike]

What should I look at in my carb if it runs, but then all of the sudden starts to stumble, when I hit the gas pedal, it hisses and stumbles, and then it dies, with a quick hiss, and a spurt of gas out of the carburetor? Oh, if I hit the gas right away, and keep my foot verrrry steady, it will just hum. =) The sound of it humming is beautiful, but I can't for the life of me get it to stay idling. I know that nothing's stripped in the carburetor or anything, so it might just be time for a rebuild. I got it from a buddy who said it ran good, but...... you all know how that is. Is it just time to clean it out and re-ring it, so to speak?

 

[matt1967]

sounds like it's running rich, just tune it

 

[johnnyzoom]

I'd rebuild it or at least check that the float valve needle isn't sticking, and that the float is set for your car. Is the hiss a possible vacuum leak?

 

[Mercury Mike]

I thought it might be a vacuum leak as well... but I checked it and there's no leak. It's also not a constant hiss. I was thinking maybe the needle was sticking as well... I will pull it and see if it is. It's a pretty old needle, so... we'll see. Last time I pulled the needle it had some paper in it, so I pulled it out and cleaned it up. We'll see how it goes. It's the right float, and I have used it before. I tore down 2 holley 1940s and built 1 super carb with the parts from the two, and it ran okay.... but... there's this problem. =\ We'll see. I ordered the repair kit today, so I will have it on saturday. I will tear down the carb tomorrow or saturday morning. I am thinking about doing it at my grandparent's, because my grandpa has an air compressor, and I don't. It'll make things nice.

 

[addo]

Most of those older carbs make a hissing/sucking noise at low idle. Don't just charge in; try to do a little more diagnosis. Have you checked with a vacuum gauge to rule out vacuum leak, or do you just think there isn't one?

What about compression testing? A bad valve can cause poor low idle, and give the impression of carb problems as the vacuum power valve overfuels the motor.

If a carb hasn't been messed around with, it should be able to run like new. Disturbing air and fuel passages with inappropriate cleaning tools may cause faulty flow at various transitions in carb operation. If you're certain everything is how it's supposed to be, then time to look elsewhere. Ignition dwell would be one to check IMO.

Also, although the motors were marketed as "economy" engines they were probably set up to run slightly on the rich side even when new. Shorter service intervals and more prevalent highway driving possibly tended to strike out issues we have now with plugs fouling, for example.

I am starting to place more blame on the modern fuels for common gripes; it would be interesting to run a motor on AvGas and see whether I'm correct.

 

[Mercury Mike]

Well..... when I first got the carburetor, I pulled it apart. I had another 1940, which I had rebuilt but ran like hell, because some of the screws were stripped on the airhorn and it wouldn't seal, so I changed the SCV and used the new gaskets, and everything sealed good. I did a compression test, all very good. I'll see if I can find the paper and give you direct results, it's still a relatively new motor. It ran good with the autolite 1100 at idle, real good, but it wouldn't accelerate because of the poor pump, and it sputtered and such, and the idle screws would turn themselves in and out because they were poorly seated. I haven't vacuum tested it, because I don't have a gauge. I will try to find one. I will also mess with the idle screws a little more. I didn't clean out the carburetor or anything, and I have no idea how long it'd been sitting. I am planning on rebuilding the carburetor, anyways, since I don't know much about it, and it will be nice to just have it clean. I'm good at it and it's a quick job with these 1940s. The accelerator pump isn't smooth, either, like there's some gnarly grime in it. When I move the throttle lever, the pump moves slooooooooowly, whereas on my other holley it is very fast and right where I like it. =) I will get the carburetor squared away, and it will be nice. I am pretty sure that it's a stuck needle or something... combined with a poor pump, and probably clogged jets and a poor idle setting. I was trying to get some opinions on if it COULD be those things, and since they're possible, I can try to find them. I will definitely update on vacuum findings, and try to find that paper with my compression readings on it. I have done CTs every few months since I got the motor, so I could monitor it. Thanks for your input!

 

[mach1 mark]

can anyone suggest a book or manual on the Holly carb, how it works, whats the best thing to do to it w/the Ford 200

 

[Mercury Mike]

http://www.themotorbookstore.com/holcarman.html

 

[jahearne]

Since it happened all of a sudden, i was going to suggest a jumped timing chain, but then you said it is a fairly new motor. Maybe something got past you fuel filter or somehow plugged up the carb. I had a rusty fuel line between the pump and carb that kept plugging up the filter. Good thing the Autolite had a filter at the carb as well as the one I placed before the pump.

Good luck,

 

[Mercury Mike]

I checked for a jumped chain already. The timing is great, right on. I am almost 100% sure that it's a carb problem. I don't know how long it sat, where it sat... I am gonna give it a good cleaning and a good overhaul and go from there, since I planned to do it anyways. I'll at least get it squared away to the point that I would like it to be at.