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Unread 05-20-2012, 05:25 PM   #1
lsukevinc
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mc 2100 fast idel afer rebuild

i bought a 1979 cj5 with a 304 about a year ago. the previous owner had hacked the choke system and made it 100% manual. I decided to rebuild the carb last weekend. I replaced the power valve, needle, and all gaskets.

Now the jeep starts fine, but idles much faster than before the rebuild. the idle screw on the throttle body is backed out all the way. i played with the adjustment screws on the front of the carb but still cant get it to idle down. I do not have a tach to know how high it is idling.

This fast idle is after the engine has warmed up. I took it for a ride today and it still will not kick down when i slow down to stop/turn. The engine sort of sounds like grandpa's gasoline international 404 tractor.

Could the float level be off?

any suggestions much appreciated.

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Unread 05-20-2012, 05:32 PM   #2
scottymac62
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Sounds like a possible vacuum leak?
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'77 CJ-5 Renegade 304 / T-150, Dana 20, 30/20 axles, Aussie Locker in the Dana 30, American Racing 15x10 Outlaw II's, 33" Dynapro M/T's" ,Optima Battery, TeamRushed + Summit Racing CDI ignition, FlowKooler water pump, Edelbrock Performer Intake Manifold, Holley 4160 390cfm, Herculiner, Silver Ceramic Coated Hedman Hedders, Flowmaster 40's.
Warn PowerPlant HD 12K Winch, Dirtworx front and rear bumpers.
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Unread 05-20-2012, 06:07 PM   #3
lsukevinc
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I can check and or replace the lines. But the lines seemed to be fine last week before the rebuild.
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Unread 05-20-2012, 08:30 PM   #4
scottymac62
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A vacuum leak could be on your carb itself. Not your lines. Are you sure you plugged and capped all unused vacuum sources on your carb and/or manifold?
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'77 CJ-5 Renegade 304 / T-150, Dana 20, 30/20 axles, Aussie Locker in the Dana 30, American Racing 15x10 Outlaw II's, 33" Dynapro M/T's" ,Optima Battery, TeamRushed + Summit Racing CDI ignition, FlowKooler water pump, Edelbrock Performer Intake Manifold, Holley 4160 390cfm, Herculiner, Silver Ceramic Coated Hedman Hedders, Flowmaster 40's.
Warn PowerPlant HD 12K Winch, Dirtworx front and rear bumpers.
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Unread 05-21-2012, 06:51 AM   #5
lsukevinc
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all of the lines are connected. the line on the front right is plugged because that one was for pollution control. One thing i did not check was the seal to the manifold. i need to spray some carb cleaner while it is running to see if the rpm's change.
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Unread 05-21-2012, 02:50 PM   #6
Ken4444
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Make sure the throttle plates are closing 100% when they should be. Check to make sure that nothing is hanging up on the throttle linkage/cable or the carburetor around the automatic choke area.
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Unread 06-11-2012, 12:09 PM   #7
lsukevinc
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Still cannot get it to idle down. this weekened i look it apart again and flushed with compressed air and carb cleaner. had one old school guy look at it and he adjusted the timing and mixture screws and nothing. he said to replace the set up with an aftermarket craburator and intake. it is the origional carb so the odds that something is worn out is pretty good if i had to guess.

here is my last chane to save the MC2100. i contacted another old school gearhead and town and he wants $85 an hour to dial it in. His fee is not the problem. it is should i have him do it and still fix a unfixable problem or start looking for an aftermarket replacement?
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Unread 06-12-2012, 12:07 PM   #8
lsukevinc
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would the holley 500 cfm be a good replacement with the stock intake manifold? i will install it on a 304 with edelbrock cam, headders, and soon to upgrade iginition (either team rush or Hei)
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Unread 06-12-2012, 12:26 PM   #9
Skerr
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Not sure of the correct term, so maybe you can figure this out, but if the "throttle plate shaft" (butterflys) is not worn out and wobbling I doubt your carb is worn out. It's a good carb. Most likely you still have a vacuum leak. It is common on a MC2100 to leak at the base, and that is sometimes hard to find. Usually it's the gasket. I got very frustrated looking for mine, and I had to get help. Now I know. Use propane in a handheld bottle to find the leak. It could also be around your intake. I can't imagine replacing the carb and intake for a fast idle.
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Unread 06-12-2012, 12:33 PM   #10
lsukevinc
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i have changed the gaskets and installed the red anerobic sealant to try to seal up a possible leak and it still does the same. I have tried spraying carb cleaner around the base and it still does not idle up. i do have a propane torch maybe i can try that but i feel like i have tried everything possible.
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Unread 06-12-2012, 01:02 PM   #11
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Quote:
Originally Posted by lsukevinc View Post
i have changed the gaskets and installed the red anerobic sealant to try to seal up a possible leak and it still does the same. I have tried spraying carb cleaner around the base and it still does not idle up. i do have a propane torch maybe i can try that but i feel like i have tried everything possible.
I understand completely where you are coming from! In my case, the gasket did not fit my adapter plate correctly, and the front of the carb was basically hanging off the plate with a big hole underneath. I spent all my time checking hoses and where the manifolds attach to the head (258). A knowledgeable friend figured it out for me. He also introduced the propane. It worked very well and quickly. The propane readily burns so it "converts" the air to fuel. If it is a vacuum leak you will find it fast with the propane. Just saying because it is worth your time and small cost before you pull the trigger on the expense of manifold and carb. Good luck.
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Unread 06-12-2012, 01:32 PM   #12
brian613
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I would check around the choke. That's where mine was leaking the chokebhas a fine crack in it And was sucking air took me 3 days to find it.
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Unread 07-10-2012, 08:58 AM   #13
lsukevinc
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i tried everything possible inorder to try to get the MC2100 to idle down and could not win. After reading the forum i decided to go with a holley truck avenger 470 CFM and edelbrock intake. in an effort to save some money, i was able to find a holley locally off of a wrecked nissan 280Z for $100. ordered a $35 rebuild kit and installed it. I was also able to find a edelbrock 2131 intake used for $150. i cleaned up the bolt on items and sprayed some left over spray paint i had from my warn M8000 winch. total investment so far about $300. The jeep runs better than it ever has, and yes it now idles down.
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