Mc 2100

I have an 81 CJ7 with a 258, MSD box, and MC 2100 carb, The problem is that I have to pour gas into the carb to get it to run, after its "primed" it runs great and will start again with no problem. I have a mechanical fuel pump now but prior to that I had an electric pump that I mounted first at the carb and then at the tank, neither location changed anything. I have a new 3 ported fuel filter and the return outlet is facing up as it should and there are no leaks from the fuel lines. I also have gas in the tank so we can rule that out. So do you think it is a carb problem or fuel problem? Any suggestions on what I should look for?

Ted

 

The MC21xx carbs seem to suffer from dry bowl syndrome quite often. You should take the top off the carb and see if the bowl is dry. Your electric fuel pump should have taken care of a dry bowl, so the electric pump having no effect on the problem is a little surprising.

Have you rebuilt the carburetor? Fuel can ether evaporate or drain from the bowl through a leaky power valve or a leaky power valve gasket. A burst power valve is another common occurrence for these carburetors. You can look under the power valve cover for gasoline, but you'll need to remove the carburetor to do that. If you have an open element air cleaner, fuel will evaporate from the bowl much faster than it would if you had the factory air cleaner.

 

Tim, I rebuilt the carb about 5 years ago, I have no experience with carbs but I followed the directions and it seemed easy from what I remember. I still have the electric fuel pump on the Jeep near the tank it's just not hooked up right now. Would it hurt to hook up the electric pump through a switch to help feed the mechanical pump and once the Jeep is running cut off power to the electric pump? In doing that, if it even makes sense, I could turn the key on to power the pump for a few seconds and hopefully prime the carb prior to cranking the motor.

Ted

 

not too sure the mechanical one will suck fuel through the electric one or if the electric one will push it through the mechanical one .

 

I'm not sure it would work either but it seems like it should. Since the electric pump is still there it wouldn't be hard to hook back up but I just didn't know if it would work or if there are any safety concerns in doing this.

 

If you have a problem with a dry bowl, and have an electric fuel pump, you need to turn the key on and let the pump run until it stops clicking (or whirring... or whatever noise it makes) before you start the car. If you just turn the key, the pump will have no chance to catch up with the empty float bowl. I assume that's what you did...

I'm not a big fan of electric fuel pumps with carburetors. I expect you'll have to follow the electric fuel pump manufacturer's instructions about whether you can run the pump with the mechanical pump or not (a 'booster' pump). When I got my CJ-6 it had a Mr. Gasket electric pump connected as a booster and it seemed ok. But I removed it.

SUmmit Racing typically has the instructions for the parts they sell online at their website. The parts manufacturers typically do too. If you wanted to run say, the Holley Red Top pump, you could go to Summit or the Holley site and see if they allowed usage as a booster.

 

The AC Delco EP12S is designed to work as a boost pump and will allow the mechanical pump to draw through it once the engine is running.