Loss of power

[AirborneMedic]

So. I'm cruising down the road, done 50 miles already on my vs800. Suddenly it loses power. I can only get up to 40mph, so had to cut short my journey and limp.home. spark is good on both cylinders. Not sure wtf has gone on. Any thoughts?!!?

[navigator]

Check your carb sync.
Check your fuel flow.

[AirborneMedic]

But why would it suddenly go after 50 miles? Tbh, I have now stripped the chopper top off, taken carbs off and cleaned them out completely, there was a wire from the top carb to the rear carb. Short cable. Is this what you mean?

[rocksandhammers]

The wire you're referring to is the idle sync. There are two syncs that need to be adjusted on these carbs. The idle makes sure they are giving off the same fuel/air mix at idle. Doesn't sound like the problem since it was a loss in power. The other sync is the throttle cable that comes from the grip and then splits to each carb. You have to get the cable lengths adjusted so that both carbs open the same amount when you twist the throttle, otherwise you'll only be going as fast as your slowest carb. It's a tedious job that takes a lot of practice to get in the sweet spot, but it's nice riding when you get it.

The other thing I would check is your air filters. Make sure one of them didn't get clogged up with something.

[navigator]

Check your fuel flow, you may only be running on one cylinder.
Could be a bad fuel pump or a clogged inlet screen.
Pull the hose off the front carb and stick it in a jar...crank the engine and see if you get correct flow.
There is a downloadable service manual pinned at the top of the tech page.