carb. geniuses needed

dwiles71

Active Member
Joined
May 16, 2007
Location
north wilkesboro, nc
just completed the mc2100 1.14 swap on a 1980 cj7 w/ 258 that has all the emissions removed. I also done the tfi igntion upgrade. Heres the problem the engine idles fine but as soon as you throttle up it spits and sputters then clears up and runs fine. The other problem is that it is running rich, as it idles it puffs black smoke, and is fouling the plugs. How do i fix this. Here is what ive tried, rejetted to 45's, changed gasket, checked and set timming to 8 btdc, sprayed crab cleaner at base of carb to ensure there is no leak. I have noticed that this carb does not respond to change, i have screwed the mixture screws all the way in then backed them out 2 1/2 turns then back in 1/8 turn and hardly no response. Ive checked the float depth and set it at 0.85 in. The only thing i have not changed is the power valve, but i dont think this will help lean out the carb. Ive played with the acc. pump linkage but doesnt help the hesitation. Does anyone think that the 1.14 instead of the 1.08 is to big? Can anyone help with this problem?
 
Sure sign of a vacuum leak somewhere. I'm not a Quadrajet guru or anything, I've never actually touched one to my knowledge, but it is still a carb. Not responding to the tuning changes and the spitting and stalling usually indicate a leak somewhere. Either that or the power valve or accellerator pump is not functioning properly. It's leaning out somewhere. Was this a new or used carb? Is the throttle shaft tight or does it have some slop in it? It or the bushings may be worn out. Carb cleaner is not the be-all, end-all for finding leaks. Is the baseplate warped? What kind of condition was the motor in before you changed the carb? It may be on it's way out and the factory feedback carb was compensating for a loose motor. Do a compression check.
 
dwiles71 said:
just completed the mc2100 1.14 swap on a 1980 cj7 w/ 258 that has all the emissions removed. I also done the tfi igntion upgrade. Heres the problem the engine idles fine but as soon as you throttle up it spits and sputters then clears up and runs fine. The other problem is that it is running rich, as it idles it puffs black smoke, and is fouling the plugs. How do i fix this. Here is what ive tried, rejetted to 45's, changed gasket, checked and set timming to 8 btdc, sprayed crab cleaner at base of carb to ensure there is no leak. I have noticed that this carb does not respond to change, i have screwed the mixture screws all the way in then backed them out 2 1/2 turns then back in 1/8 turn and hardly no response. Ive checked the float depth and set it at 0.85 in. The only thing i have not changed is the power valve, but i dont think this will help lean out the carb. Ive played with the acc. pump linkage but doesnt help the hesitation. Does anyone think that the 1.14 instead of the 1.08 is to big? Can anyone help with this problem?
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dwiles71, I do think your problem lies with the 1.14 venturi size. I did this swap with the recommended 1.08 carb, & it has been working very well. There is A goldmine of information on the subject, at jeepsunlimited.com the search function will give you more than you can process. Very specific on the 1.08 size, & also on rebuilding the carb. My power valve was 7.5HG, & I needed an 8.5HG. Mr.P's speed shop in Rockhill had one made for Holley carbs. It is the same as the one for the MC2100. But I think you would do better to get A 1.08 Mc2100 to start with. You could re-jet the 1.14 to lean it up A bit, but it still has too many cfm's, from what I've read. I'll try to check back with you, & see how your doing.
 
buckshot500 said:
dwiles71, I do think your problem lies with the 1.14 venturi size. I did this swap with the recommended 1.08 carb, & it has been working very well. There is A goldmine of information on the subject, at jeepsunlimited.com the search function will give you more than you can process. Very specific on the 1.08 size, & also on rebuilding the carb. My power valve was 7.5HG, & I needed an 8.5HG. Mr.P's speed shop in Rockhill had one made for Holley carbs. It is the same as the one for the MC2100. But I think you would do better to get A 1.08 Mc2100 to start with. You could re-jet the 1.14 to lean it up A bit, but it still has too many cfm's, from what I've read. I'll try to check back with you, & see how your doing.
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^^Truth^^
 
Hmm

Did you post this on Pirate?

Here are some CFM ratings. The 1.14 isn't drastically larger than the 1.08. It would not cause the problems you describe.

1bbl YF Carter = 187-220 CFM
2bbl BBD Carter = 275 to 280 CFM.
2bbl Progressive 32/36 DGEV Weber = 300 CFM
2bbl Synchronous 38 DEGS Weber = 400 CFM
MC2100 1.08 = 287
1.14 = 300
1.21 = 351

Are you certain you have the right spark plugs? Which ones are you running? It really sounds like you have fouled plugs and that's what's causing your problems (not the other way around).

Set the float height by idling the jeep with the top cover off of the carb. For off road use you actually want to set it lower than normal.
 
Look for Holley P/V link

dwiles71 said:
yeah, i did post pirate, running stock plugs. Will changing to 10.5 power valve lean it out?
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Hey dwiles, here is the link to J/U's MC2100 database.http://www.jeepsunlimited.com/forums/showthread.php?t=735139&highlight=mc2100 there is A whole bunch more info, on this site. Just don't go to Off-Topic, unless you are thick skinned! Oh the link I gave you, has my post, with a link to Holley power valve video. Going by their methods, is how, I found out I needed an 8.5HG power valve. As far as plugs go, I was using auto lite, now using E-3 plugs, barely noticeable difference. But they are a little better. Only thing I could think of other than 1.14v size is, did you rebuild this carb? Rebuild is easy, 1st one I ever did, & by all accounts A necessity with this carb. On Mc2100 database, you will see A port that needs to be epoxied shut, did you do this? Also there may be an air leak, under the throttle linkage side of carb. Some MC2100's will leave a small gap between the carb base, & the adapter plate. What I did about this, was to J B weld to the adapter plate along that side. A few small, shallow drill holes, will lock the epoxy in place better. I clamped the plate to A piece of cardboard, & formed a bevel along that edge of the plate, with J B weld, & let it set over night. This only needs to be done on certain MC2100's. Laying the gasket on the carb, before install will show, if it's needed.
 
Spark plugs

I am not talking about what brand or even type. Either get Champion copper plugs, or plain NGKs. Anything "performance" is a total waste of money.

What I am interested in is what heat range plugs you're running. Should be a 14 in Champion numbers. I keep bringing up the spark plug thing because I had the exact same symptoms you describe, and it ended up being that my plugs were fouled.

If you over tighten the carb base plate bolts, that can warp the carb and cause it to not seal. Usually if you loosen the bolts and then retighten in the correct sequence, not too tight, it is fine.

I'll reiterate, the 1.14 will not cause the problems you describe. The only difference would be a loss in bottom end, and maybe a reduction in fuel economy. There is ~20 cfm difference between the 1.08 and 1.14.

A 1.08, with 46 jets, and a 9.5 pv is about perfect for a stock 258. That combo on 33x12.50s yielded 21 mpg Hwy for me.
 
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