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Discussion Starter · #1 ·
I have a 1990 yj . 4.2 engine. Yesterday the guy who does the work on the jeep put in a new HEI dizzy and a new 2100 carb . The cat was taken off and hi-flow muffler put on before the carb and dizzy. The problem I was having before was that going down the road in 5th gear it would start to slow down. When I come to a small hill I would have to down shift into 4th or on a good hill 3rd. . The jeep will not go over 55 mph . The jeep is set up with a 6 inch lift and 33 tires. I bought this setup this way it looks cool it doesn't ride to bad but has no power. The engine doesn't smoke or use oil, ( leaks some) . But putting this new dizzy and carb on wouldn't you think it would wake it up a lot. He said that he took it for a test drive and said you still have to down shift on hills. What do you guys think the problem is and what can be done to fix it. The guy working on it thinks the dizzy is bad and I'm sending it back for a new one. Do you think the big tire and the gear is the problem or something else.
 

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Yeah, IMHO someone running 33" tires should either re-gear or toss those tires/rims...nothing else is going to work.

Also, why a 6" lift? That mall must have hellish speedbumps! :D
 

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I agree with Havasu, I bet the gears are way off..

Jack up and properly support the rear axle.. Put a chalk or tape mark on the tire and one on the drive shaft. With the jeep in Neutral rotate the tire 1 full revolution watching the driveshaft and counting it's revolutions..

If the driveshaft rotates 3 3/4 revolutions per 1 tire rotation you have 3.73 gears, if it rotates a little over 4 revolutions per 1 tire revolution you have 4.10 gears... See the pattern?


Once you know what you have check this link and your tire size to see if they need changed..

http://www.quadratec.com/jeep_knowledgebase/article-26.htm

Now remember if your jeep is 4wd you WILL need to regear both axles!!!
 

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Discussion Starter · #4 ·
I think its all in the gears . They are the stock don't really know what that was but I think something like 307 or something. I think I need 4:11 's or 4:88's in this thing. But I thought it would have made some difference in the way it sounded and the way it runs. It runs the same way it did before he changed the carb and the dizzy.With the carter and stock dizzy.

Do you guys think I should drop down to 31 tires or 30's. The 33 are almost new with the new rims. Is the drop in tire size going to make that much difference. And is there a chart the would tell you how much of a difference it would make . Thanks for your help guys
 

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I think its all in the gears . They are the stock don't really know what that was but I think something like 307 or something. I think I need 4:11 's or 4:88's in this thing. But I thought it would have made some difference in the way it sounded and the way it runs. It runs the same way it did before he changed the carb and the dizzy.With the carter and stock dizzy. Do you guys think I should drop down to 31 tires or 30's. The 33 are almost new with the new rims. Is the drop in tire size going to make that much difference. And is there a chart the would tell you how much of a difference it would make . Thanks for your help guys
It makes a large difference... But watch out, with the lift and smaller tires might really look stupid.. That link I shared in my above post will show that with 3.07 (as reference) you should be on a 23" or 24" tire.. That's a large difference from 33s...
 

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My buddy is running 31s on his TJ and couldn't believe the difference when he regeared to 3.73.. If you have 3.07s you still might not be happy with it.
 
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