I have '76 C3 with 350 with mild rebuild running a Holley 650 single pumper. A while back I began smelling gas in the garage after i parked it. It starts and runs great - all be it a little rich - until you shut it off for a short time. If it sits over night it starts and runs no problem. But if I shut it off for just a few minutes and then start it up, it starts right up but when i begin to accelerate it stumbles big time for a while and then evens out and is fine.

Yesterday I stopped for gas and after I filled up I headed out on the road and it stumbled and fumbled like it was going to quit. I pushed the gas to the floor and it finally cleared up and was fine the rest of the way home.

Any ideas??

Thanks
Barry

 

have you ever looked down the throttle bores after shutting it off and hot to see if gasoline is dripping into the engine? If so you could either have floats set to high or needle and seat assemblies that have dirt or are worn out.

 

It also sounds like you could have a fuel boil over issue too. Is it an aluminum Holley?

 

I haven't taken a look into the bores after shutoff but I will give it a try. As for the carb, I don't think its aluminum.

 

OK Today it did the stumble thing on me twice. After I let it sit for about 5 minutes and then started it up and when I accelerated it began to stumble and buck for about 15 seconds and then smoothed out and was OK. When I got it home I immediately pulled the air cleaner off and checked the primaries. No fuel was seen flowing into it. It was wet but I assumed that was from being run. I could smell raw fuel but not real strong.

I also found that on the 4175 650 cfm spread bore there is no float site window or adjustment. You have to remove the front float assembly to make any adjustment.

So, I am still uncertain what is causing this problem. I don't know if the carb has ever been rebuilt or not. I was on the car when I bought it almost a year ago. However the present problem just started recently - within the last month or so. Any way to tell if its been rebuilt or is that something I will need to possibly look into?

Thanks
Barry

 

have you tried cleaning the small air bleed holes that you see when you look down the bores with carburetor cleaner spray? There s no way to tell if it was rebuilt

 

I had something similar with brand new 750,, gas would seep into the barrel causing a hard start after sitting a few minutes. Also the fuel level was way high on a previously adjusted float.
I removed the float level set screw and assembly fron the top and there was a piece of Teflon tape that found its way in there, I never use teflon tape so who knows in a new carb but all hard starting vanished.

 

I have only seen aluminum Holley carbs.

 

Maybe the new ones are mostly aluminum but not the old ones.

 

When was the last time that the fuel filter(s) were changed?

 

I had a problem with my Holley 650 double pumper several years ago when the carb was not that old. Found the front float that was plastic had developed a leak in the float and was weighted down with fuel.

Replaced the plastic float with a Holley metal one and then bought another metal one to replace the plastic rear float.

 

I cleaned the small air bleed holes with carb cleaner and it didn't help much. In fact today it ran like crap. At a traffic light I could smell raw gas but when I got it home I couldn't find any on the intake anywhere. I can't reset the floats without removing the ends since in this model there isn't a float site hole so I guess the next step is to remove it and start looking internally.

 

Your carb might have some loose screws on the outside of the float bowls housing.

 

Today I removed the carb and took off both float bowl housings; Everything I could see looked fine. I ran wire down the air holes and blew them out with compressed air. Checked the rubber diaphragms on the secondary vacuum and the pump and all looked OK. I couldn't find anything that looked like it wasn't quite right. I put it all back together and put it back on the car. Haven't had time to start it up and readjust it yet but will do it tomorrow or Thursday. We'll see what happens.

 

Good luck

 

Rather than begin a new thread I thought it best to resurrect this one somewhat. I have continued fighting the fuel problem so I bought a rebuild kit from Holley and Tuesday I tore the carb apart and rebuilt it. When I removed it from the intake there was raw gas laying inside the intake and on the gasket between the carb an intake.

I tore it all apart and couldn't see anything the might look out of place or bad. Everything looked clean and relatively new. I replaced all the O rings and gaskets possible and put it back on. Upon starting the car I couldn't get the idle to come down under 9 no matter what I did until I adjusted the screw on the passenger side behind the auto choke. Even then it still idles at about 800.

However, today I took it out and drove it to a tranny shop to talk with a guy and it ran fine. After I came out from the shop and started it up and pulled out toward the street to take off, upon giving it gas it jumped, bucked, and eventually stalled. I pulled off to the side and restarted it and it coughed some more and then eventually evened out and ran OK the rest of the way home.

So, whatever was causing the fuel to drain into the intake while sitting must still be doing it but I don't know where to go next. Any ideas???

Thanks

 

Some have good luck running a Holley on the street and some don't. I never did. There was always something going on that required fiddling and adjusting. I finally took it off and literally threw it as far as I could. After a good rebuild, the original carb ran fine. It was a 1970 AMX 390. Great car, wish I still had it.

Just my experience...your mileage may vary.

 

Can you be specific about how you set the float levels? I still suspect it's the floats being too high.

 

unbolt carb. send to Lars, for professional rebuild, problem solved.

 

The float levels were set according to the instruction sheet that came with the rebuild kit. Since it is a 4175 spreadbore the only way to set the floats is to remove both bowel covers. I then turned them upside down and measured 3/8" gap at the bottom and set accordingly. I also checked to make sure neither of the floats were filled with fuel and leaking. Everything looked good .