258 sputters revved. - JeepForum.com
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post #1 of 2 Old 09-14-2009, 09:51 PM Thread Starter
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258 sputters revved.

ok, this one is a little long and complicated.

a couple months ago, the old engine in my cj7 started sputtering all of a sudden while playing in the mud. but it cleared up and ran fine until it got swapped out for another 258. (it had cracked rings).

now about a month ago, the new 258 in my cj7 started sputtering all of a sudden, just like the old one. there is a loss in power, but not much. it still holds 5th gear just fine on the road(4.56 gears with 32" tires). it will sputter between about 1000-1800 rpm. anything higher and it runs smooth. also, if i run the rpm's up very slowly, it's fine too. it doesnt need to be under load either, it will do it just sitting in neutral.

now it does have a 4wd HEI in it, and yes, i know the issues with it. it ran great in the old engine. i swapped in an engine out of an '81 AMC Eagle. a week after the new engine was in, it started doing it and hasnt stopped completly since.

the jeep has an MC2100 carb on it. when it started sputtering, i took the top off the carb, and sprayed out the inside with gumout. it cleared up for a couple minutes. the next day, i added some stp gas treatment to it and ran fine all day.

this one has me stumped. i think its the carb, but it was just rebuilt a month before the new engine went in.

i know the issues with the HEI, but it will run just fine sometimes, and others, it doesnt.

any input would be appreciatted.
sorry for the long, complicated post

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post #2 of 2 Old 09-14-2009, 10:01 PM
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1979 CJ7 
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Check to make sure your engine block is grounded well.

'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.
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