no power in 4th gear

no power in 4th gear


texas panhandle
1980 Cj5 Renegade
inline 6, 4speed transmission, dana 300 transfer case
I just bought a 1980 cj Renegade and it has inline 6 with a 4 speed transmission. Jeep runs and sounds good in gears 1-3 but when i get on the highway in 4th i cant get over 45mph or so. the jeep is lifted with 33 inch tires. my question is does it sound like it could be a carb problem or just geared lower? it doesnt really bog down in fourth just no get up and go. engine doesnt even rev up like it wants to go when i floor it.
Thanks for the help
Do'es it run fine in 1st thru 3rd
what transmission and what gears do you have? These will be big helpers in figuring out what is going on.
Also, please tell us whether your rig has a catalytic converter. A clogged cat is another potential cause of what you are describing...
yes it runs fine in first through third and not sure what gears. i just bought it and havent checked into that. As far as the tranny goes im pretty sure its still the factory one. sorry i cant be a whole lot more descriptive about it. just kinda boggles my mind unless it is geared lower
most likely it is a gearing problem
at what RPM do you have the most torque, and at what RPM does it like to cruise in 3rd
where is that RPM range when you are in 4th

when you put on larger tires, you effectively change the gearing of a vehicle, it is optimum for street use to get the gearing back to factory settings, so you regear, there are many charts about gears, rpms, tire size to cross reference, you need a base though, and that base is what size tires came on it stock and what gears were in it, from there you go to present tire size and look at what gears will put it back to stock RPMs. Regearing cost about 5 to 6 hundred an axle and you need to do both.

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