MC2100 fuel pressure issue

[thistle3585]

I had put a Holley carb on but struggled with it so I decided to go back to the MC2100. I hadn't had the MC2100 carb installed for about 6 months while I did an engine swap. I have installed a clear fuel filter between the tank and the pump and between the pump and the carb. In addition, I have a small fuel pressure gauge between the pump the carb. When I had the Holley carb on, I noticed that the filter leading to the carb was 1/2 to 3/4 full with fuel but with the MC2100 it is always dribbling in to the filter but never full despite the fuel pressure gauge reading 6 psi. The filter between the tank and pump is always full. The engine idles well and "cruises" well but stumbles at acceleration. Obviously, it isn't getting enough fuel for acceleration and I'm not sure if that is a float issue, a power valve issue or what. What would cause back pressure causing the fuel filter not to fill?

 

[rocmoc]

Rust plugging the sock on the fuel line leaving the fuel tank INSIDE the tank. When I installed my 2100 I also replaced my tank and fuel lines. When I pulled the fuel gauge (also the fuel line leaving the tank) the sock on the end was filled with rust. I removed my sock since I was installing a poly tank and two filters inline. Cause of rust, Ethanol added to our fuel! Ethanol attracts water in the tank.

rocmoc n AZ/Mexico

 

[gert]

I never have figured out why that filter always looks empty but it does, I have thought it to be trapped air. stumbling will be caused by your power valve adjustment if you have 6 psi you have good pressure

 

[IOPort51]

The "sock" filter may be dirty and more than likely is but that would cause low pressure on the down side of the pump, I would think. I would be looking at the accelerator pump and the float level, in that order.

I still run a bypass filter on my 2100 and have no noticeable hesitation problems.

 

[Fastatv]

With a mechanical fuel pump, I'm not so sure that filtering on both sides of the fuel pump is a good idea......again, I'm not sure. The stumble could be several possibilities. Accel pump would be my first choice, then power valve, then float. And, is your vacuum advance hooked up correctly and working? If the carb sat for a while....the pump diaphragm and/or power valve could be dried out....hard, and/or function correctly. Rick

 

[thistle3585]

Thanks guys. Guess I'll just go through the whole thing. When the Holley carb was hooked up, in the same system, the fuel filter was completely full so it has to be related to the MC2100. The tank replacement is about a month out. I wondered if I filled the filter up then hooked it up then it would stay full, but I don't know that I would be accomplishing anything.

 

[Fastatv]

Thanks guys. Guess I'll just go through the whole thing. When the Holley carb was hooked up, in the same system, the fuel filter was completely full so it has to be related to the MC2100. The tank replacement is about a month out. I wondered if I filled the filter up then hooked it up then it would stay full, but I don't know that I would be accomplishing anything.

No, it wont accomplish anything for you. Didnt you have a similar "running" problem with the Holley...a stumble or hesitation? Thistle, I build carbs for a living. I might get with one of the moderators on here and find out if its ok for me to offer a rebuild for those that have problems. I just don't want to get in trouble.

 

[thistle3585]

No, it wont accomplish anything for you. Didnt you have a similar "running" problem with the Holley...a stumble or hesitation? Thistle, I build carbs for a living. I might get with one of the moderators on here and find out if its ok for me to offer a rebuild for those that have problems. I just don't want to get in trouble.

I think the issue with the Holley was a combination of timing and vacuum leak. There was a cap on one of the ports but it wasn't sealing very well. The timing was well advanced. I rebuilt the Holley but haven't tried it out yet. Thought I might put it back on while I go through the MC2100. I also realized that the new engine doesn't have the two tubes for the choke assembly coming form the manifold. As I understand it, they circulate hot air. I'm not exactly sure how the manual choke system works. What would be my options there since I don't have the tubes?

 

[harleydragon]

manual choke utilizes a cable so you can manually close and open the choke butterfly on the top of the carb..you can buy the kit at oreilly or similar auto parts stores for about 10 bucks..they are simple

 

[thistle3585]

Do I remove the choke assembly? The black housing etc?

 

[Fastatv]

Do I remove the choke assembly? The black housing etc?

I haven't bought a manual choke in a while. The actual housing should be aluminum in color ( and material ), the "black" thing is the thermostat which I believe may come in the choke kit and tho it looks like a t-stat, it isn't. That's what you will be attaching to the housing and connecting the functioning end of the manual cable to. You may also need to make a mount to support and hold the cable.

 

[harleydragon]

Do I remove the choke assembly? The black housing etc?

the kit normally comes with a new black cover to replace yours with as well as mounting brackets to secure everything

 

[thistle3585]

Got it cleaned and back on and its running much better. I have a power valve on order. I'm just going to replace it since I understand backfires to be bad on them. Right now, a burst of smoke with a little backfire comes out of the carb if I really stomp on the accelerator. I have a small checklist of things to go through, but hopefully am making headway.

 

[IrishCJ6]

Backfire from carb sounds like ignition timing to me, worth a look there.

 

[thistle3585]

Just wanted to update. I set the timing last week, first time timer, and didn't realize that I was supposed to disconnect and plug the distributor. No wonder it was backfiring and running rough. It was off by a lot in the wrong direction. I set the timing at 10 degrees at 650 rpm. I was told to use a little higher rpm due to the age and mileage. It is running much, much better. I might need to adjust the idle screws some more but will do that tomorrow. I haven't replaced the power valve and will probably hold off for now. So far, so good. The Holley will probably be going on the auction block.

I did wonder if anyone still uses the NLVR in their system? As I understand, it uses both ported and manifold vacuum and senses changes between the two. Can I just pull it and use ported vacuum to the distributor?

 

[harleydragon]

hook it to manifold vacuum..this explains vacuum advance....

http://www.corvetteactioncenter.com...ported-vs-manifold-source-vacuum-advance.html