Have a 1998 454 4X4 with 5200 miles on it. It seems to only rev up half throttle. Has had rough life on farm and ranch. Have checked intake and exhaust for retrictions, nothing found. Seems to pull ok as in no loss of power but will not get up to speed and doesn't seem snappy. Any help appreciated, TORK.

 

Are you the original owner, the reason i ask this question is to determine how long it's been like this ; there are several thing's that could cause this ! Dirty airfilter/carburator, carbon buildup in combustion chamber or your spark aresster in the muffler could need cleaning ; first thing i would do is give it a good serving ! Change engine oil,oil filter,clean airfilter,install new spark plug and put some seafoam in the gas tank ; then ride untill you need to refill the tank ! I put seafoam in every tank full of gas in my 06 ac 400 , seafoam is a fuel cleaner/stabilizer it will clean out the entire fuel system ; and also your combustion chamber ! You can get the seafoam at O'Reillys,Auto Zone and Advance auto parts stores; i get mine from O"Reillys for $4.99 plus tax price may vary according to your location, it could take running a couple tanks full to get full result's ; if this doesn't fix it you will have to pull the carb and do a complete carb cleaning ! Throddle slide in the carb may not be opening up all the way so a complete carb cleaning should do the fix if this is the problem , it could also be a streached throddle cable or rev limiter ; but i would try all the above first ! And also check with a dealer for proper carb adjustment if you have to remove the carb for cleaning , keep us posted on how everything turn's out ! ...............williebee

 

when mine did this it was a bad diaphram in the carb, the one that actually opens the slide

 

I don't own the unit. Have been the mechanic for it all it's life so I know it's use and history. Just serviced unit 50 miles ago, about 1 month. At that time had the carb off and cleaned. Already tried the seafoam. Removed exhaust because that is what it sounds like (restriction), no change in performance, just louder. Unit is all stock, I opened up the intake on the air box cover to give it more air, stil no improvement. Unit seems to hook up good but top speed is only 30 MPH. This unit has ran 55 on the speedometer before. Starts right up and sounds good but just no top end even in neutral. Going back in to the carb next, thought I would see if anyone had other ideas. Thanks, TORK.

 

Try a valve adjustment. Valves get out a little from wear and tear and it can get hard to start and loose some power.

SJ