More MC2100 Fun

[Nalanthi]

Good morning, all.
It's time for a carburetor catharisis - mostly to hear myself rack my brain via text (and maybe someone has some input as well).

Well I have my JY MC2100 dialed in and the CJ7 idles, runs, drives, and climbs flawlessly save for the fact that 33s on 3.31s suck badly - but that's beside the point.
One thing that I just can't figure out for the life of me is why it will sometimes run the whole day without issue and other times act up after warm-up by sometimes bucking and sometimes stalling when slowing down, etc. It smells rich despite the use of .46 jets @ 5000ft. Sometimes it fires right back up, sometimes not.
All in all, it's a giant bag of randomness.

What I know:

I've checked for vac leaks ad-nauseum and find nothing.
I'm getting good spark via HEI to Autolite 985s with a .45 gap
The fuel filter is positioned properly above the carb bowl with the return line @ 12:00.
Stock fuel pump isn't starving the carb. I've read that the pressure isn't too much for an mc2100 (correct me if I'm wrong).
Throttle shaft linkage is a bit loose but not leaking.
Timing @ 12BTDC
Vac holds steady @ 17Hg
Float has been adjusted a bit lower.
The only thing that may be questionable is the PV - but it seems to be doing what a PV should be doing. I might go to a 6.5Hg and try that instead of the one that came in the rebuild kit.

I was half tempted to toss the Holley 7883 that came with the Jeep back on and test some more, but I've heard bad things about them and never even gave this one a chance.

 

[Nalanthi]

I said hell with it, tossed the 7883 back on, and tuned it up. Did some street driving, did a few dirt hill climbs, and no problems.
For some odd reason I'm getting more power than what the 2100 was putting out.

Betting it was a bad unit despite having been rebuilt.

 

[Torxhead]

Glad to hear you got things fixed, I have heard a lot of good things about the MC1200 on the AMC 258 i6 / 4.2l though. You might want to take it in the dirt and go up and down some steep hills to see how it will work in those conditions.

 

[Nalanthi]

Thanks.
I ran a few minor hills and much to my surprise the Holley wasn't giving me problems.
It's running a bit rich, but I'll play with leaning it out when I get home today.


Really wish I would have had the mc2100 running due to all the greatness I hear about them. I might just need to suck it up eventually and eat the price of another one (and sell this one).

 

[Torxhead]

Sometimes these carbs can lean or flood out on a steep hill due to how the gasoline flows in the float bowl. I did have an issue like that with the oem Rochester bbd carb flooding and stalling on steep hills in the So. Cal. desert.

 

[Nalanthi]

We have a lot of "steep" out here in NM.

Also... Might bump back to the mc2100 and test some more. The damn Holley started giving me odd rich symptoms now. I probably​ need a fuel pressure regulator since I just swapped to an electric pump this afternoon (despite the fact that fuel isn't pouring out of the float sight hole.

 

[Lumpy Grits]

Did you change your fuel filter when you swap'd the carbs around?
Have you tested your fuel pump for psi?
LG

 

[Torxhead]

We have a lot of "steep" out here in NM.

Also... Might bump back to the mc2100 and test some more. The damn Holley started giving me odd rich symptoms now. I probably​ need a fuel pressure regulator since I just swapped to an electric pump this afternoon (despite the fact that fuel isn't pouring out of the float sight hole.

I would suggest just using the mechanical fuel pump.

 

[Lumpy Grits]

OEM mechanical type is more than enough for this.
LG

 

[Nalanthi]

Thanks for all of the replies. I figure that I'll add closure in this post since running into a lack of such is always a pet peeve when I'm attempting to study up on issues and getting nowhere. Maybe it'll help someone some day.

First off, a correction: I said "7883" in a prior post when I meant to say "7448". I've determined that the MC2100 I'm holding is junk and that I'll pick another one up sometime down the road.

While the Holley 7448 isn't necessarily a recommended carb for this application, I found that mine isn't being too finicky now that it's dialed in.

I decided to stick with the electric fuel pump due to the fact that with summer rapidly approaching in a region where 90+ degree days are not uncommon that I would eventually thank myself when I'm not vapor locking. I did add a FPR and put a gauge to it - reading a steady 4.5psi. After firing the Jeep up, determined that fuel pressure was probably my issue, I was greeted once again by an engine that was loading up. I'd drive about fifty feet, the exhaust would start to make a fluttering sound, and I was putting out copious amounts of smoke.

The culprit? The float.

I thought to myself "well, I have it adjusted to Holley specs where fuel is visible at the threads of the sight hole, so there's no way". I adjusted it down a bit more and conditions seemed to improve a bit, so I adjusted it down just a hair more (quite below recommended specs) and I'll be damned if that didn't clear everything up. I drove around for a good thirty minutes and then decided to go up the road where there's a dirt basin that was intended for water runoff (but serves as a good 4x4 testing ground). I bounced around in the basin for a bit - no flooding/loading. I then decided to simply drive halfway up the basin wall and just sit there on a fairly decent incline - no flooding/stalling.

I wonder if anyone else had to adjust their float below the the recommended spec due to the same issues I've experienced? Either way - I'm ready for the desert now.


Thanks for listening to me bitch about it.

 

[Lumpy Grits]

I run my OEM Carter float just a bit below spec. Helps on steep 'up-hill' when stopped.
Many years ago I had my Carter float 'sink' due to a pin-hole leak.
LG

 

[Belizean]

That's probably what I need to do with my Webber. Works great everywhere except stopping on a steep incline. Problem is if I adjust it I still won't know if it's working better because we don't have any steep inclines within a couple few hundred miles

 

[Lumpy Grits]

If your Weber is a 'front-hung' float as the OEM Carter is. Then it may help.
IIRC: I lowered my setting just under 1/4" from the factory lower side spec.
LG

 

[Torxhead]

Nalanthi, you do know you can go to smaller jets to lean out the mixture right? I did find an off-road kit for that carb also:HOLLEY 4412 7448 2 BARREL OFF ROAD KIT BG DEMON QFT | eBay, not sure if it would help. You could even install an extension tube on the bowl breather to stop fuel running into the venture on a steep hill.

 

[Nalanthi]

Smaller jets was the first thing I did to this carb. It came stock with 61s, so I installed 58s for altitude compensation. Prior to tweaking the float, I was running rich/flooding out even when there was no incline.

Offhand question: is anyone here running a dashpot with their automatic to curb hard braking stalls?