Carb ?s

[ryanroo]

so i am working on the other guys truck again. got it going, runs good being timed by ear, but i am seeing a fuel drip at the throttle shaft. is there a seal in there that i missed when doing the rebuild? any other reasons why this is happening?

still having the some overpressure problems even with a return style filter and a FPR set at ~2psi.

sorry for my ignorance, carbs are not my forte. i am better at fuel injection
ryan

[Jester]

exploded diagram

http://www.oldcarmanualproject.com/m...ages/1920.html

[randyscycle]

There aren't any seals in the throttle shaft. The only way you'd get liquid fuel out of there is if the float level is too high and/or the floatis compromised, and its either overflowing into the venturi, or dripping out of it onto the throttle plate, then coming out around the shaft.

I'd go back and check that float level really closely and be sure that the float isn't coming up so high that its hitting the top cover and keeping it from closing off the needle valve completely.

Also check the needle valve: Is it the Viton tip needle (looks like a rubber tip) or metal? I find that the Viton tips sometimes if the kit is a bit older tend to get stiff. I also find that if you sort of "pre-seat" the needle into the seat with a light pressure before installing it, that helps it to seal a little better.

Is the float brass or phenolic plastic? If its brass and has a very tiny leak, it could also be losing its ability to float. Give it a shake next to your ear and see if you hear fuel in it. Same goes for the plastic ones although they can be harder to spot, because they act like a sponge and soak up gas reducing their ability to float. You have to weigh them to determine if they are soaked with gas.....or just toss them and replace if you suspect a problem.

There isn't any reason that at 2 PSI if everything is functioning properly the needle should be unseated.

[brute4c]

If the throttle shaft is worn enough, it will leak...some carbs have kits to rebush the hole to make it fit better with a new throttle shaft...ours do not have this...so then the cure is a new carb without the wear.

[kwai]

Fuel pressure for the stock carb should be 4-5.5 psi. If the throttle shaft is leaking you probably need another carb to rebuild. As far as I know that is not repairable.

[kwai]

Also, check the float level. the float is solid so it should be good (it won't fill with fuel and sink). Download the tune-up manual if you haven't already done so. Lot's of good info in there.

[hiker]

A carb/electric shop can rebush the throttle shaft bore if its worn, but that can run into some money. Another used carb might be cheaper. Your carb problem sounds like it's in the float circuit like everyone is saying. Excess fuel is pouring out of all small openings. Check the Wet float level with the carb and its top installed. Do this by removing the "Economizer valve" Ref #37 and 37 in above exploded diagram. You would measure from the top of the cover to the top of the fuel with a 6 inch scale. I don't have the spec with me, but one is available. If fuel is just flowing out the top of the carb, then find out why the float needle and seat are not sealing.
Robert-CA

[hiker]

From TM9-2320-34 page 98:

(5) Checking wet fuel level.
(a) With engine running and vehicle on a level floor, fuel level can be checked or measured through the economizer diaphragm opening.
(b) Using a 6-inch scale with a depth gage, measure the distance from the machined surface. (Fig 4-12) The measurement should be 3/4-inch. If not correct,
readjust float setting by removing fuel bowl and adjusting float tab using needle nose pliers.

[ryanroo]

i had already checked the float, it still floats. and the needle does stop fuel. i checked that earlier as well. sounds like its just worn out
Thanks
Ryan

[moosejr]

As was mentioned, the throttle shaft can be re-bushed, on these carbs it shouldn't be too expensive, but if you know somebody with a machine shop with a small boring lathe, it is relatively easy to do. Basically what you have to do is line-bore the carb housing and install brass bushings to compensate for the wear in the housing. The shaft is much harder than the aluminum body, so it is usually fine. This was a very common problem on the rochester thermo-quad because of its plastic housing. Those were expensive to do because you had to fit a bushing in the middle of the carburetor. Personally I would check with your local machine shop and see if they can do it, or refer you to someone, as when you start looking for used carburetors, you may run into the same problem. . .