rochester monojet leaking fuel

[Jordanbsparks]

i do believe this will be my first post btw, so iv got a 72 c20 with the 250 i6. i have just rebuilt the carb with a bigger jet. was 60 is now 105. i pulled the biger jet out of a chevy stepvan with a 292 in it. so i got it all back togeather with the new jet an all, started the truck and 1 it runs rough and has a mild black smoke and will not idle but also the carb is leaking fuel extreemly bad from underneath the carb through the acc pump arm. i know the float level effects this. iv re adjusted float level many a time with the same result. im starting to think that something else is the problem. would i have to change the needle for the jet as well? i have nfi what is causing this. and this is my dayly driver. if any one out there has had and fixed this problem please chime in. thank you!

[69chevy lwb]

you sure you didnt over jet the motor? i know at my elevation you actually need to jet everything down a ways it runs better and gets better mileage theres not a high enough air concentration at a high elevation to run much jetting i would buy a jet kit and start with what you had and step up untill it becomes negative then drop one size

[BMERDOC]

My Monojet leaks at the accelerator pump too. The linkage was bent and wore the opening out a bit. After several days it leaks down bad enough that I have to prime the carb on cold starts. It would seem that since I've rebuilt my carb and experienced this problem that I have found others on the forum that have posted this kind of thread. I am not a Carb God but I do know how to set a float and I know that mine is set fine.It would seem that the linkage wears the casting.
Going from a 60 to a 105 sounds like a big jump but I am only used to Holley jets and am not sure how it translates to Rochester. Is your black smoke only at idle? Your idle mixture could be a little rich and that would mean that you have two problems and not one big one. Are you setting idle with a tach and vacuum gauge?

[Jordanbsparks]

hey thanks guys for the replys. iv not gotten it to run long enough to set any idle or mixture screws. i called the carb shop around heer and they are saying that its all in the float and that i probly have micros of dirt in there getting stuck between the needle and the seat not allowing it to close all the way. that wounds reasonable to me. also had another guy tell me that i had a dirty gas tank and needed to replace the pump, lines, gas tank, and all filters going to the carb. i defanitly dont the time or money to do that and im thinking hes blowing smoke up my ass an how. like i said it didnt leake like this until after i pulled the carb off. i tryed a control last night and instaled the old jet with the same results.... so ima just take the bad muther to a carb god n have him a go at it.

[Wrenchbender Ret]

Pull the needle out of the seat& remove the filter. Blow air through the seat. Check the float make sure it hasn't soaked up gas. It should bobbel around in some gas. Make sure you have the gasket between the throttle body & fuel bowl on correctly & the right gasket. @ gaskets come with the kit. Select the one that matches the old one & make sure it is in correctly. It is easy to get it in backwards. If you use the large jet you need the rod that came with it. That is not causeing the leak though.

[BB72CHEVKT]

If you have a 40yr old gas tank it would be reasonable that there is some garbage in the tank.

[68gmsee]

^ agree. The guy was not blowing smoke. These tanks also accumulate rust particulates that get passed on to the carb. Best thing is to install an inline fuel filter along with the regular inline filter if you don't want to mess with cleaning out the tank for now.

That being said, that may not be the problem. First go with the recommended procedures about double checking the float and making sure the bowl and needle valve and seat are clean. Also, the fuel that you see leaking is probably caused by the excess fuel in the bowl. Easy enough to check.

Preliminary adjustments that I do for the idle air screw is in until it seats and back off about 1-1/2 to 2 turns. Then use a vacuum gauge to adjust for highest vacuum.

I also agree that you should go back to original jet size. You're not going to gain a whole lot of extra power with the larger jet and it may mess you up in the other adjustments.