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Louie
Louie, Technician
Category: Motorcycle
Satisfied Customers: 11454
Experience:  25+ yrs. experience
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I have a 2000 Yamaha VSTAR 650 that I purchased about 2

Customer Question

I have a 2000 Yamaha VSTAR 650 that I purchased about 2 months ago. When I bought it, it ran and sounded excellent. All of a sudden, while riding, it started bogging down and now sounds different. It starts right up and runs but has no power. What could this be?? Carburetor issue?? Or something else??
Submitted: 2 months ago.
Category: Motorcycle
Expert:  Louie replied 2 months ago.

Hi, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially, are both cylinders firing evenly? ...exhaust equally hot?

Customer: replied 2 months ago.
Not sure. How would I go about checking this?? I'm a rookie!! Lol.
Expert:  Louie replied 2 months ago.

I understand.

Can you try....

After a fresh start before fully warmed up, feel but not touch if the cylinder heads heated up and then compare. A cylinder that is not firing would still be cold compared to a cylinder that is firing.

Customer: replied 2 months ago.
OK, where do I look for this?
Expert:  Louie replied 2 months ago.

The cylinder head would be the top most part immediately above the finned part. The 2 cylinders would be forming a Vee thus 1 of the cylinder heads would be underneath the front of the fuel tank while the other would be below the rear part of the fuel tank.

Customer: replied 2 months ago.
OK let me try this. Get back with you asap.
Expert:  Louie replied 2 months ago.

Yes please.

Customer: replied 2 months ago.
OK, after firing up the front cylinder is cool to the touch where as the rear one hot.
Customer: replied 2 months ago.
The front one is getting warm gradually.
Expert:  Louie replied 2 months ago.

We have now identified the front cylinder as not firing.

That only 1 cylinder is firing would cause the "...bogging down...sounds different...no power...".

Now let's see why the front cylinder is not firing and determine if it is electrical/ignition related or fuel delivery/starvation issue. Proposed preliminary checks (if have not been done):

  • • start/run the engine and play with the throttle but do not allow it to warm up;
  • • shut down and carefully remove the spark plug of the suspect cylinder;
  • • determine if the the spark plug tip did get wet with fuel;
  • • cautiously perform a spark test.
Customer: replied 2 months ago.
I pulled the front spark plug wire and checked it. It has goo fire. I put it back in and took it for a spin at first it was bogging but all of a sudden took off like it should. Also sounded normal. Sounds like a bad connection maybe?
Customer: replied 2 months ago.
Fired it up again and ran like a scalded ape.
Customer: replied 2 months ago.
What do you think??
Expert:  Louie replied 2 months ago.

Sorry; Internet was down.

That there is "...good fire..." would eliminate ignition/electrical as a possibility; not even a bad connection.

This would then make a likely fuel delivery/starvation issue; a carb concern.