Yamaha xl 800 won't hit top speed and won't rev out to max rpm

Clean your plugs and check injection and linkage.

Mike

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get rid of it cadilac are junk

Hi, they have two spline connected drive shafts between the motor and impellor, these splines will be worn and stripped. Both shafts will need to be replaced. Regards Phil.

Impeller is most probably bent. It looks fine but there is a blade bent. Or there is a piece of wood or rock blocking the pump. Doesn't take much.

It sounds like it is working backwards. Around the time your truck was made the industry had different emissions standards for trucks and cars. There were less controls on trucks.

There were vacuum controls that would increase idle speed when the engine was cold. The way this was done is through a water temperature sensor that is commonly called a vacuum tree. It is called a tree because it is shaped like a tree trunk with a few branches and each branch has a vacuum hose. As water temperature increases the vacuum routing changes. The cold setting makes an idle step-up dash-pot raise RPM and close the choke plate. As the water warms, the internal parts of the vacuum tree move and change the vacuum ports.

When the ports change, RPM drops and the choke plate opens and low idle speeds are restored. With the choke plate open high speed operation of the motor is assured without bogging down.

I would say most of what can be wrong is cheap to fix. A new thermostat, perhaps a new vacuum tree. Your problem can also be the vacuum lines are not connected to the correct ports. One thing many people do is to adjust the idle speed at the wrong time. The step-up cams are not in the proper position and when stuff starts working everything is out of adjustment because the changes were made at the wrong time.

This is a job for an old school mechanic.

I have a 1999 yamaha xl 1200 that has just had a new motor put in y the dealer. It revs but will not go foward or rev.