I recently purchased a 1999 Scrambler 400. It has an after market DG Pipe, as far as I know this is all that is not stock.

It seems to really take off at around 1/4 throtle but at half throttle is bogs down. When I go full throttle is kicks in again???? Is this normal or should I have acceleration when I want it threw all ranges of the throtle?

It also seems to sometime rev really hard without accelerating to keep up with the revs....

Any help would be appreciated..goood or bad news welcome. Thanks.

 

Putting a pipe on a 2 stroke will change the power band, you need to re-clutch to "get on the pipe" to make use of the new power band the engine is putting out. Either that, or the former owner tried to mod the clutch himself, and didn't put the right springs or helix in the clutches.

 

Best advice is to get a dif pipe.That pipe is hard to get clutched where it will work.
Check out HPD,RcR,Aaen,HSP or Dynoport.Then get the recomended clutch kit and jets

 

You might want to go through the carb and clutches and get them cleaned up first, a pipe shouldn't be the culprit in your situation. Personally, I had 3 of those '99 Scramblers 400 4x4's, doesn't need the pipe, POO jetted those too rich from the crate. Depending on your rising style, I would clutch the quad for low to mid response, drop a jet or two depending on elevation in your area, check your reeds to make sure pedals are good. If my memory serves me right the carb is a 34mm Mikuni, and your description sounds like it is running rich

 

I have had the same problem with 400s that are not properly clutched to the pipe.
Go to a stock pipe and stock clutching or a good aftermarket with proper clutching and they run great.
Never hurts to clean carb.But the DG pipe is junk always has been always will be.

 

I have found out it is a factory pipe with a DG (SQUARE TYPE) silencer. Would this make much difference?

 

Check the clutching.You should have a plain spring with white paint on one end and S55 weights.Take the secondary clutch apart and check the ramp buttons.Clean the carb and check the belt for wear.
It may just have a higher engaging spring in it

 

I just found out that the PIPE and SILENCER are both aftermarket DG.... I was told that the carb. was not messed with... Should I rejet and if so to what size... Thanks for all the time/info.

 

Best thing to do is find a new pipe.DG is hard to dial in to run right.In the mean time rejet to 260 main to be safe.
Find a HPD,Aaen,Dynoport,Hotseat,RcR pipe and get the matching clutch kit for the pipe