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Need help with 4.2

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carb no power
2K views 17 replies 10 participants last post by  catcalls 
#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.
 
#3 ·
I think something minor is wrong. I have a 4.2 and I have to downshift from 5th to 4th to go up a hill. I have 31" tires and a 3:07 ratio. I can do 75 MPH on the interstate. I could probably go even faster but I want to live.

One of the biggest improvements in power was when I installed a new timing chain and retimed the distributor.

Your problem may be something as simple as where the distributor advance comes off the carb or the manifold. Another issue could be the advance weights in the dist. I think the first place to look is in the timing and then take a look at how the carb is set up.
After you run it for a while (15 to 30 min.) pull your plugs and take a look at the tips.

Did your mechanic check your vacuum with a gauge?

How did it run before the new carb & distributor?

Keep us posted & Good Luck, L.M.
 
#5 ·
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.
 
#6 ·
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
 
#7 ·
I have the 4.0 f.I. and had 3.07's with 33's and seldom used 5th gear. Im at 4.10's now and can use 5th again. I'm thinking it might be gears. What made get a new 'dizzy' and carb? Not sure what a dizzy is but if you have a friend with 30's or stock wheels try them out before dumping the $
 
#11 ·
The 4.10's you need came stock in a YJ with a 2.5 and 5 Speed Transmission, [I didn't want to say Tranny, we all have to be Gender cops now].
 
#12 ·
I know. I googled Jeep tranny.

HOLEY COW!! I needed eye bleach.

Good Luck L.M.
 
#16 ·
Chief, I'm sure you meant, "no need to re-gear" the D-35. IHO don't spend any money on a D-35 if your going to run 33" tires. Re-gear the front, or find a used one from a 4cyl 5speed YJ and then install a Ford 8.8 in the rear, 4.10 gears to get you to stock, with bigger heaver tires you may want 4.56 gears for more power.
 
#18 ·
Street driving was too much for my d35. Looking into upgrading. I've got a 4.0 with a HEI and Holley 2300. I can use fifth cruising down the highway at 75 or so and can use 4th going uphill at 75 no problem at all. I'd say a good tune up with timing and vac advance will help at higher rpms.
 
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