Fuel Problem?

Roadster Rich

Roadster Rich

Senior Member
I am full of questions these days. I just installed a rebuilt zenith carb this weekend. It was rebuilt by a recommended person on this list and I got the carb last summer, but just changed to install it this weekend. The car starts up and will run (at about 1/4 throttle or less) for about 20 to 25 seconds really sounding great. Then it just starves out of fuel. I wait about 1 or 2 minutes and repeat and does just the same. I have the GAV open about 3/4 turn (actually tried to open even more but that was no good), and the throttle air jet open 1.5 turns. Any help where I go next?

The other carb I took off because I saw a pin hole leak in the bowl, only to find out from you guys that it is a weep hole by design. Problem is that I dropped it on the floor and broke off the threaded end of choke shaft, so I have no alternative until I get the new parts to fix that.
 
The car starts up and will run (at about 1/4 throttle or less) for about 20 to 25 seconds really sounding great. Then it just starves out of fuel. I wait about 1 or 2 minutes and repeat and does just the same.
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Not getting proper fuel flow to the carb. Need to investigate to see where the restriction is and remedy.
 
Check to see that your gas cap vent isnt plugged - loosten the cap start the car. If it runs normally for longer then previous it needs cleaned out.

Ive also heard the fuel line can stick too far into the carb and cause poor flow

could be rust/dirt clogging the fuel outlet in the tank.

NOW

did your car run perfectly fine on the old carb? If it did then id be looking internally of your new carb. Could be sticky float valve sticking closed.
 
Could be ignition also. Do a diagnosis to determine where to head

Try running on spray to see if it's fuel related...

Any kind of driveability issue needs to be diag'ed first... Yes anyone can make guesses , it sounds like this or that.. Would you want your modern guessed at spending 100 plus / shop rate hour and parts>>>
 
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It sounds like a problem with the new carb, but just to be sure...turn off the fuel valve, disconnect the fuel line at the carb, put a container under the open line, turn on the fuel valve. If you get a flow of fuel out of the open line, the problem is going to be with the new carb. If not, you'll have look closer at the fuel delivery system to find the blockage.
 
Sounds like the carb float valve is sticking in the closed (or almost closed) position.

If the carb is using a rubber tipped float valve its more likely to stick than the two steel ball type valve (faux Grose Jet Valve).

Sometimes a few light taps on the carb near the valve will unseat the valve, but if this is the problem, then replace the valve with a two steel ball type valve.
 
Got home tonight and pulled the carb. I had verified good fuel flow and had taken the valve off the tank to make sure the pencil filter was clean. The carb is one I had rebuilt by someone I had talked to on this site over a year ago. It was in a box waiting for my second car to be ready for it. Now I really look at the rebuilt carb and am a bit dismayed. The throttle shaft has horrible play and moves a full 3/32 flopping around. The choke shaft is almost as bad. I did take the two halves apart and made sure I could move the float valve freely, and it is not the ball style. But given the condition of the two shafts I am very skeptical about the quality of the carb rebuild. I put all back together and still get the same situation. I will follow up as soon as I get the replacement choke shaft for my other carb.
 
Sorry to hear you were taken, but they are not that hard to rebuild using the proper tutorial and parts. An oversize throttle shaft is available and a set of flow tested jets from renners corner will get you going good... For the record I use the viton tip valves and never had an issue...the key to any float valve is to not have crap in the tank..
 
Who is the go to guy for carb rebuilds?

A friend got a Zenith from a "trusted" rebuilder here that "runs every carb on his own car to insure it is perfect". The carb worked poorly. The throttle plate was installed upside down (among other problems). There is no way the car the seller installed it on would idle.

I could tell my own horror stories about a spedometer rebuilder here but let's stick with carbs.
 
Roadster Rich said:
...and made sure I could move the float valve freely, and it is not the ball style...
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Just so you are aware, the rubber tipped float valves can stick during operation, but seem fine when you take them apart. Guess how I know! I've used the two-ball type since the 70's, when I can get them that is.

Rebuilders typically don't use them because they are more expensive. You must specifically ask for them.
 
The choke shaft is not nearly as important as the throttle shaft but says a lot about the quality of rebuild.
The throttle shaft must be a very close fit or it will not idle well.
A quick check on fuel flow with everything hooked up is to loosen or remove the drain plug under the high speed jet. That checks everything right away.
Al
 
Al 29Tudor said:
The choke shaft is not nearly as important as the throttle shaft but says a lot about the quality of rebuild.
The throttle shaft must be a very close fit or it will not idle well.
A quick check on fuel flow with everything hooked up is to loosen or remove the drain plug under the high speed jet. That checks everything right away.
Al
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Al is right on the money with the throttle shaft. The drain plug idea is a good one!
 
Well this just gets worse. I followed you advice Al, and as soon as I put a wrench of the drain plug it fell out. There is gas coming through and the plug hole threads are all worn out. you can just catch a thread and hold it but cannot tighten or it falls out and just light finger tight it will stay there. I guess it is a lesson learned and this is a piece of junk. Me bad. Now I will decide if I pay to have the tillotson on the town sedan rebuilt or send this body in to someone good to rebuild the zenith.
Not much more to this thread until I get a decent carb on the car!

Al, I am retiring in December and will be down there at our place for January and February. I will be sure to get in touch.
 
Consider Berts for a carb if your not up to doing the rebuild.. Theirs are road tested and adjusted, reasonably priced.
good reviews are always posted... Send your crappy one in for the core and call it a day
 
If I remember correctly, I read here on the Barn, you can use a threaded plug from the carb inlet filter/screen with the screen removed as a drain plug after re-tapping the bottom of the carb.
Al
 
The rebuilt carb I bought came from a person in Mass. I believe he is no longer in business and I guess it makes no sense to give a name at this point.
 
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