YJ MC2100 tuning help

[zilla24]

I am new to the forum here and am having a heck of a time sorting out my MC2100. I recently acquired a jeep on trade and it was barely running with the factory carter carb, I thought this would be a good opportunity for a swap to a MC2100 since everyone raves about their simplicity. I took a stab at the float height, set it with the carb flipped over to about 1/2" from the flange. Installed some #47 jets and adjusted the idle screws to two turns out. It started up, and won't stay running. It will continue to run above 1500 rpm and sounds pretty good there, but it won't come anywhere close to idling. Runs rough then dies out, I've also had a few backfires through the carb. I have a power valve save installed so I'm hoping that worked. The electric choke is hooked up and appears to be working (slowly opening after a minute or so). I will try and put a timing light on it today, with a HEI is should be 8-9 deg at curb idle correct?

Any suggestions?

 

[xt master]

What type of jeep is it and what motor?

 

[zilla24]

It's an 88 YJ with the 4.2 and manual trans. It's stock except for the MC2100 and a HEI ignition.

 

[zilla24]

Ok so I've messed around with it a little and I belive that part of my problem is with the choke not operating properly. When it's cold it wants to backfire and carry on, once it's warmed up it's halfway responsive. Once I finally got it warmed up I was able to set the timing to 9deg btdc at 800 rpm. It runs ok but is doing a pulsating idle. It will idle at 800 for a few seconds then rev up to around 2000. It continually repeats that, any suggestion on where to go from here?

 

[Collin the Hen]

Hmm... sounds like a vacuum leak. Have you noticed anything that sounded like an old TV when it revs up?

Also, you may want to make sure your air horn gasket is good and that the fuel isn't leaking through if your float is off.

My timing is set at 9. I painted the 9 degree mark on the reference and the notch in the pulley white to see it better if you have a dimish timing light. I think it's 9 anyways. :scratch:

 

[zilla24]

I pulled the carb and discovered I have gas in the power valve cover. I replaced the power valve gasket reassembled it and it runs 100% better, it idles smooth and responds well. I let it warm up and after 5 minutes it started the pulsating idle again. I shut off the jeep and the power valve bowl is full with gas again, I'm not 100% sure if the powervalve is bad or not but I'm leaning more so towards a bad gasket seal. How tight should I be tightening the powervalve, I am afraid of ripping out the threads, right now I am using a 1" socket by hand and tightning it as much as I can. Is there a way to check if the power valve is bad?

 

[Collin the Hen]

I used an adjustable wrench and snugged it up pretty tight. You may have to replace your power valve if that doesn't help. If you haven't rebuilt your carb, rebuild kits are around $20, and I would highly recommend rebuilding it.

 

[zilla24]

I rebuilt the carb before I installed it, however I damaged the power valve that came with the rebuild kit (still had some glass beads in the threads left over during carb clean-up). I put the used 2 stage PV that came with the carb and tightened it up, the jeep will now idle but it is impossible to bring the curb idle down below 1000rpm. The curb idle screw is not even touching, good thing is the pulsating is gone. I ordered a new 8.5 hg power valve and it should be here today, I also picked up a new 1/4" thick carb to manifold spacer gasket. I did hear the "old tv" noise so I am suspecting a vacuum leak however I could not find it with a can of carb cleaner. I will post results when my parts arrive today.

On a side note, is it 100% necessary to plug the 3/16" choke passage on the underside of the carb? I have not yet done that since I am still using the electric choke.

 

[Collin the Hen]

Don't plug that if you are using an automatic choke. If you go to manual, then yes, plug it up.