Hey Guys~
I'm working on my buddy's 97' 400 Scrambler and I am stumped! At first it would not idle properly, so I removed the pilot jet, blew that out with compressed air, and now the machine will idle just fine. Once you give it some gas, it will bog for a few seconds and then build RPM's. I know it is getting fuel because once it gets up to speed and the main jet takes over, it runs great. I tried adjusting the air screw, but that made very little difference. I checked the needle and the clip is in the middle notch...where it should be. I don't have a clue what to do next! Any suggestions are welcome and greatly appreciated! Thanks everybody!

 

Sounds like it is either starving for fuel or getting too much. Try going down a few sizes on the main jet or back up. That will really make a difference. Once you get it to run right make sure you check the plug to see if it's running lean. Also check the clip on the needle. Put it on the third notch down from the top. It should be the one in the middle. Good luck.

 

I don't have a clue what

Tell us about the modifications

Did you change the pipe? gears? carb? reeds? Tire size?

 

I would try lowering the clip first to make it more richer. If that doesn't work get a bigger pilot jet. But, before you adjust the clip richen the air/fuel mixture screw some.

 

Before you make any adjustments, remove the carb and clean it all properly. If everything ran good at one time then there is something wrong. Do not re-calibrate it to compensate!

 

Hey guys~
Here's some more details: The machine has no modifications except for a DG exhaust silencer. I put in a new spark plug, but that didn't help. The needle clip is in the third notch, or the middle notch. I tried adjusting the air screw, but that made very, and I mean VERY little difference. Thanks for the replies so far guys. Anybody else care to shed some light on the problem?

Robculp~
I did take the carb off and took out both jets, needle, and whatever else would come off. I sprayed everything down with carb cleaner and sprayed all passageways with compressed air. It did run good when he got it, so I'm just at a dead end road as to why it won't run good now!

 

Try removing the Bowl Nut and see if there is any crap in there, some stuff could have flaked off after you cleaned it or you could be getting dirt out of the tank. Did you check that?

 

Hey Rob~
I didn't try romoving the bowl nut yet. I am pretty sure the carb is getting good, clean fuel because once the RPM's get up and the Main jet takes over, the machine runs great.

 

Something is plugged in the low speed circuit. That is why when you adjusted the air screw it made no difference. Remember it takes very little to plug up those small orifices in your carb.

 

[img]i/expressions/face-icon-small-wink.gif[/img] How about this theory?

The spring in the primary clutch is fatigued or broken and the machine is not starting out in the lowest gear range.

or


The spring in the secondary clutch is not preloaded properly causing the same problem.