Sluggish and slow to gain speed

[Rustybux]

took both sleds out today (84 Formula Plus rotax 521 and 87 Formula MX rotax 462 and the MX takes off quick but the Plus is very sluggish on take off but will eventually gain speed. Neither will go past 6000 RPM (55 MPH) wide open throttle and they should redline at 8500 to 9000. after turning off the 521 for a while, very very hard to start, plugs dry, prime a little and still wont start unless I open the throttle full and pull the rope about 10 times then it starts. Think it could be Carb problems?

I know this was a long question but trying to explain the problem. NO RPMs on both and one is very hard to start after shutting it down for 5 minutes.

 

[winter brew]

Would be a good idea to go through the carbs and make sure everything is clean and replace the needle/seat.
Have the clutch spring been replaced? Clutches clean and belts in good shape?

 

[Rustybux]

won't rev up and sluggish

I will clean the carbs this weekend. How can a clutch affect RPM's? Engine speed? Once the sled get's up to speed, it's fine but won't rev past 6000 rpms. It has a new belt. If the clutches were not moving all the way, I would still get high rpms like it is supposed to but not top end. like a car in 3rd gear...no top end but engine will still rev up. Just my idea...probably wrong.
thanks

 

[winter brew]

The clutches have a huge impact on RPM....if the springs are shot then it will place too much load on the engine as it will upshift too fast.
As you say, like a car stuck in 3rd gear.....try to accelerate a car from a stop in 3rd gear and the RPM's will stay low.

 

[Rustybux]

The clutches have a huge impact on RPM....if the springs are shot then it will place too much load on the engine as it will upshift too fast.
As you say, like a car stuck in 3rd gear.....try to accelerate a car from a stop in 3rd gear and the RPM's will stay low.

I'll check the clutches. seems that the belt on the engine clutch is at the bottom and the big clutch has the belt at the top so that is Low gear... takes about 20 seconds of holding the throttle wide open to finally start pulling and hitting 6000 rpms. My mx is much faster with smaller engine.
thanks and I will check the clutches...not sure what to look for but i'll give it a shot.

 

[winter brew]

I'll check the clutches. seems that the belt on the engine clutch is at the bottom and the big clutch has the belt at the top so that is Low gear... takes about 20 seconds of holding the throttle wide open to finally start pulling and hitting 6000 rpms. My mx is much faster with smaller engine.
thanks and I will check the clutches...not sure what to look for but i'll give it a shot.

Have the springs ever been replaced? If not, I can almost guarantee they are shot. I would start with new springs.