MC2100 Poor Idle/Needle and Seat

[84_CJ7]

I have had this mc2100 on my 258 for about 3 years. No problems.

The carb required rebuilding because I let it sit too long with fuel in it. I have successfully rebuilt several of these with no problems (my old Ford trucks).

After the initial rebuild it ran OK but it just wasn't right. It would crank right up and run great as long as you gave it throttle. It then began to idle down, struggle then die. Give it gas it fires right back up.

I was thinking vacuum leak. Not finding anything obvious I replaced the manifold gasket. Still no magic bullet. Using propane I found a slight leak around the throttle shaft.

I had looked at the fuel bowl earlier just to check my float level running and it was fine (7/16). Later I noticed it trying to flood (choke completely off) - I looked in the fuel bowl and I found another problem - the needle and seat were continuing to geyser fuel even after the float seated the needle (float set to 7/16). I could only stop it with my finger pressing it down.

What in the world could cause this?

[buckshot500]

This happened to me, last time I rebuilt mine.
Check the needle & seat for ant minute particles of crud or rust from the tank.

Also check the spring clip for proper installation.

Next, check the float pivot to be sure it's all the way down in it's grooves.

Finally recheck the float level. I did all of these things & it ended up solving the problem. Hope it works for you as well!

[84_CJ7]

Originally Posted by buckshot500

Check the needle & seat for ant minute particles of crud or rust from the tank.

My original post could have been much longer with all of the details. The carb was pulled, cleaned, rebuilt, pulled and cleaned again after a couple of backfires - along with another set of gaskets, power valve, etc. Overkill - but I was trying to eliminate any questions.

Originally Posted by buckshot500

Also check the spring clip for proper installation.

Did this several times

Originally Posted by buckshot500

Next, check the float pivot to be sure it's all the way down in it's grooves.

Did this, too. Made the most sense. Even replaced the needle and seat to see if it made any difference

Originally Posted by buckshot500

Finally recheck the float level. I did all of these things & it ended up solving the problem. Hope it works for you as well!

Did this, too. Probably did it the most. I even pulled up on just the float and it would not completely stop the gas - only mashing the needle down with my finger stopped it.

What bothers me is it was running fine. I had recently swapped in a true HEI Dist and decided I liked my Duraspark Dist with the stealth HEI better. We were working on getting it tuned in when the carb started presenting problems. We already had the "old" ignition system reinstalled, timed to 9 BTC and driving around when the low idle got erratic.

During all of this I removed the factory return fuel filter and put in a glass filter I had to watch the fuel progress, and to look for any trash that might be trying to come through. Nothing.

It's almost like the fuel pump overpowers the needle and seat.

Thanks for your suggestions - don't mean to come across like I'm shooting you down - been on this all weekend with no luck and I'm pretty frustrated.

[Caver Dave]

Originally Posted by 84_CJ7

Even replaced the needle and seat to see if it made any difference

Did this, too. Probably did it the most. I even pulled up on just the float and it would not completely stop the gas - only mashing the needle down with my finger stopped it.

In that case, check the return line (if still equipped) running off the outlet side of the OEM style fuel filter. If this line (bleeds excess fuel flow & pressure back to the tank) got crimped/plugged, it cause the needle to get "blown out" of the seat... causing the issue you stated.

[84_CJ7]

I removed the filter with the return line and replaced it with a glass filter to monitor fuel flow -

BUT -

You have brought up a good point. Is the filter with the return line necessary to run the 2100 properly? I always thought it was more of a safety thing. When I ran a Weber for a while fuel pressure was a constant battle.

I can hook the other filter back up easily enough - it's all right there - the glass filter was temporary. It will be interesting to see if it makes a difference.

[jeepnut_nh]

just a thought here.....

when the fuel is still coming in though the needle should be sealing it....can you tell if it is coming through the valve? or from the AREA of the seat?

what im getting at is im wondering if there is a crack either in the seat itself, or right around it (been a loooooong time but i think the seat threads into place ) its possible if the seat or mount has a crack, that it would seal up with extra pressure on it (pushing with finger)....never seen it in my limited carb rebuilt experience, but have seen similar stuff countless times in my workplaces (industrial maintenance)

just my $.02, good luck with the carb

[84_CJ7]

Coming straight out of the valve - about an 8 in geyser.

The more I think about it the more I like the idea of the fuel filter being the culprit here. I swapped out the bypass filter with a straight filter to view the gas flow - it was after this that the flow became an issue. I was trying to solve an idle problem and possible created another.

I think I'll swap the other filter back and see if that solves the overflow problem and then get back to my original poor low idle issue.

I'll also consider checking the fuel pressure and installing a regulator. My understanding is that these 2100s only require 4-5lbs of pressure - my guess is I'm pushing closer to 7.

This could have been avoided by continuing to drive my CJ instead of letting it sit for about a year. Let this be a lesson to everyone. When you build your own house DON'T let your Jeep sit idle. Shame, shame on me!

[84_CJ7]

Put the original filter back on and it fixed the geyser problem. Now I'm back to my other problem no idle. I'll start another thread for that.