carb venturi leaking #2

[escobar]

Hey guys. '76 CJ5 AMC 258 i6 / 4.2l with an MC2100.

I've soaked the carb overnight, blew out everything, it was clean to begin with. Then rebuilt everything in it except the throttle shaft which is tight. Some of you may remember this problem-

After shut down my venturis still drip. Before, it was just one that dripped A LOT, after the rebuild they both drip- but about the same volume of gas combined. This results in flooding, resulting in a long start time and start up fouling of the brand new plugs. As soon as she fires up she cleans up fast. (new plugs with TeamRush short mod)

The float needle shuts down nicely, power valve and accelerator pumps are new with the rebuild.

I'm thinking it has to be fuel line pressure. I'm thinking of buying a new fuel pump.

I've kept the gas cap off, and no difference as well. If I disconnect the line from the carb it releases quite a bit a pressure.

What is causing this? I'm sure my tank is venting. The line isn't close enough to the block or exhaust to be boiling gas. Any ideas?

I'm friggin' stumped.

 

[jeffgtoman]

Make a tee fitting to go between the carb and filter. Hook up a fuel pressure gauge and see what you come up with.

 

[escobar]

I'd have to find a guage rated for it. But assuming I do, what's a normal range? On the vehicles I've worked on, I've never pulled a line and gotten much pressure at all.

I'm going to pull the line INTO the pump and see what I get- see if its the same as above the pump. Maybe I can narrow it down. I'm kind of wondering if a blockage on the tank source pipe might be acting like a check valve, although I haven't seen anything like that before. Its usually a blockage preventing fuel from escaping.

 

[Rescue Diver]

I have a simple idea! You're in luck that you have a 2100 carb. You can run those with the top removed. Take the top of the carb off, start it and let it idle for a few minutes, then shut it off and just look at what it's doing. If the fuel level in the float bowl rises higher than the venturis due to gas being pushed through the needle and seat, you'll be able to watch it in action and you'll know it's either your fuel pressure is too high or your needle and seat are still leaking. If the float level stays where it's supposed to, you have something else weird going on.

What height did you set your float level?

 

[escobar]

Hey good idea. I'm gonna try that. I've bent the float down a little to lower the level but haven't ran it with the top off. My kit (like most) came with a little ruler so I'm gonna measure the level.

 

[Rescue Diver]

Hey good idea. I'm gonna try that. I've bent the float down a little to lower the level but haven't ran it with the top off. My kit (like most) came with a little ruler so I'm gonna measure the level.

My float level is set at 9/16 from the top of the end of the float to the top of the carb body.

The kit listed 7/16" 1/2" and 9/16" for float levels on the various carbs. Try and identify your carb in the kit instructions and set it to whatever it calls for.

 

[escobar]

K cool. I didn't measure the level, though I should have. It was so clean in there and had already been rebuilt I ASSuME'd it was ok.

Man, this baby is SO CLOSE to being 100% mechanically. I can't go to paint until this issue is fixed. FRUSTRATING.

 

[jeffgtoman]

I'm pretty sure you should have between 4 to 7 psi fuel pressure. The original carb and the Webers were a little different but 4 to 7 should be right for the 2100.

 

[Rescue Diver]

K cool. I didn't measure the level, though I should have. It was so clean in there and had already been rebuilt I ASSuME'd it was ok.

Man, this baby is SO CLOSE to being 100% mechanically. I can't go to paint until this issue is fixed. FRUSTRATING.

Never assume the previous owner did anything right!

The carb kit instructions may be a pain to follow, but they are your friend.

I just went through the 2100 I bought from one of our awsome fellow members. I installed a kit in it per instructions and it fired right up and purred like a kitten. The only adjustment that was required after the fact was to set the idle bleed screws using a vaccum gauge, and at 1-1/2 turns out, they were pretty darn close. I did make one small error. I had the accelerator pump rod in the wrong setting so I had a slight flat spot when I pressed down on the pedal. Once I corrected that it went away.

That's one more thing to check. Make sure your pump rod is in the second to highest hole on the throttle shaft end, and in the inner hole on the pump end. It wouldn't have anything to do with your venturis leaking, but if it's not set right, correcting it might help make your throttle response better.

 

[Rescue Diver]

I'm pretty sure you should have between 4 to 7 psi fuel pressure. The original carb and the Webers were a little different but 4 to 7 should be right for the 2100.

Yep, and the needle and seat in the 2100 should be pretty forgiving of fuel pressure unless it's ridiculously high, and I don't see that happening with a stock mechanical pump.

 

[MN CJ7]

I agree, looking at carb needle leak or the fuel pressure too high or the fuel line is getting warm and pressure is building up after a hot shut off.


If the fuel return line is not hooked up the engine heat can warm up the fuel when shut down. This builds up press in the fuel line and pushes the fuel one way or the other. One reason for having the return fuel line, (I & many) decide not to run the return line.

Could also clamp off the fuel line when hot and you shut if off. Ihave done this with small vise grip and rag cushion or other clamp. It the fuel does not drip... the float/needle cannot hold back the fuel pressure. So the fuel press will need to be lessened at shut off or needle work needed.

I have not heard of the 2100 needing less fuel pressure than the Jeep Mech Fuel Pump like we do on the 3-3.5 psi weber needs

The amc mech fuel pump is 6-15 psi..... if I remember right. will take a look in second to conf.

Fred


FYI
I run a weber, no return line, clear fuel filter, and when hot and shut off I can see some of the fuel being pushed out of filter.

A smart guy about jeeps.... told me after my resto work was done..... that the mechanical fuel pumps have std and premium versions. The premium version will have better ck valves and less likely to allow rev flow. I will be using a electric fuel pump made to work with webers next upgrade session... remove mech fan & fuel pump... both will be electric

 

[Rescue Diver]

I will be using a electric fuel pump made to work with webers next upgrade session... remove mech fan & fuel pump... both will be electric

Off topic but I thought about both of those upgrades and decided against them because they go against my keep it simple philosophy. At the low RPMs that my AMC 258 i6 / 4.2l is built to run, I doubt I would gain more than a couple HP switching to an electric fan, and I wouldn't even be able to notice that small of a gain. I don't want a single unneccessary wire on my CJ. I'll bite the bullet though when it comes time to install some off road lights and the wires and relays that go with them.