Hello, about two or three months ago I bought a 2007 S40. At first I had absolutely no problems, then out of nowhere the engine started to act very sluggish. Its a 650 and before I had no problem getting up to 60 without feeling like I was pushing the bike too hard. Now I feel like getting up to 60 is doable but it also feels like its pushing high rpms. Around the same time the exhaust started to whistle, which turned out to be a loose rivet on the exhaust. The mechanic told me that if I pull the choke out half way that it would run better, I did try this and it did kinda work but there is still the power issue. It still has a hard time getting to 60 without feeling like its at a high rpm. This problem did was not there when I first bought the bike but it seems like it has appeared out of nowhere. Does anyone have any suggestions?

Currently there is 7200 miles on it, I have not had any service yet. I did get a mechanic to inspect the bike and he found nothing wrong, though I am not sure how far he dove into it because we were both kinda confused by the problem. I bought it used three months ago and had no problems up till about 6800 miles.

WE really need more info, stock jetting? white spacer mod? clutch cable adjusted? stock petcock? You need to be able to check over the bike yourself .carb . been cleaned?   these bikes should be able to go 85-90 miles an hour in factory trim, but yours must have sat around a long time to have that low mileage ,could be carb is dirty,seeing you had to choke it to get it to run a little better.

High RPM, low speed.

Slipping clutch?
What oil is in it?
Is there any slack in the clutch lever?
Where is the pointer on the clutch cover?

If the condition improves when you pull the choke half way out, it could be that you are running lean.  Have you pulled the spark plug?

I would pull the plug and check the vacuum line that goes from the tank to the right side of the carb (if you have the stock petcock).  That's a built in air leak waiting to happen on our bikes.

Mine was leaking there for a few days and the bike was running very lean.  A lot like you described. Pulled the spark plug and it indicated a lean condition.  Replaced the vacuum line plug (my bike has a raptor petcock so the line has been removed) and it's running much better now.

The slipping clutch would be another place to look.  Make sure there is a little play in the line.

Unless your clutch is slipping your RPM at any given speed while in the same gear will always be the same and you did say it only "feels" like higher RPM.  But you were definitive about it being sluggish at higher speeds and that could mean a faulty petcock failing to supply adequate fuel.  A petcock is easy and cheap to replace.  Read the thread  named "petcock? fuel issue at full throttle" that is also active at this time.

What oil did you use? This bike has a wet clutch system and car oil will make the clutch slip...

Yoshi wrote on 08/31/16 at 10:31:42:



Good point.  Wrong oil=clutch slippage as JOG is suspecting.