Timing check

[Patarusky]

New member here. How do I check my timing on my 85?Bike starts & idles ok on choke. after warming up it runs fine to about 1800 rpm. It will rev way up but sluggish after that. I've only ran it up to 5500 but it doesn't seem to have much power past 2000rpm. I think the spark advance might not be working right or the timing is off. Just bought it at a garage sale. New gas in tank;all carbs drained & fuel pump run till fresh gas came out carb drains. closed carb drains & key on & bike started. Ran fine for 10 minutes and I shut it off. Drained tank again and added 2 gals fresh gas with SEAFOAM in it. Took it out for test run around the block. Real easy. Next day took it out for a 3 mile run. Ran better as the seafoam worked it's way through the fuel system and carbs. But no difference in power. Took the airbox top off and checked carb slides to make sure there is no sticking. All looked good. Took another 3 mile test ride. Same. So I need some input. If there was an obvious miss I would feel it. All pipes hot, no smoke or knock. Once I learn about the timing and spark advance from this forum I will move forward. A carb rebuild kind of thing might be over my head but we will see. Thanks

 

[Radioguylogs]

Seems like fuel starvation.

Fuel filter OK?

Gas tank vent working? (Open gas cap after running it and see if it hisses)

 

[MaxMidnight]

If not already obtained I suggest you acquire a copy of the Service Manual which explains the operation of the ignition/ timing.
There is no adjustment, the timing is fixed and is set by the flywheels position relative to the pick-ups.
The only way it could slip would be if the woodruff key was not in place and the flywheel was not placed in the correct position.
Advance is controlled by a vacuum operated unit; the test procedure is in the Service Manual. They rarely fail.

 

[Fire-medic]

https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf

The first 64 pages are annual supplemental bulletins reflecting model year changes, after that begins the service manual. Look at the Appendix as that has helpful info, like cable and hose routing, fastener sizes and locations, and torque settings.

If you decide to remove the carburetors to send them out, beneath the left Yamaha scoop is a white plastic junction box for the 'push/pull' throttle cables. Be careful with the tiny screws! They like to run & hide from you as you remove them. The throttle cables are actually 4 individual cables. Open that long narrow plastic box, and carefully remove the plastic block that connects each upper cable to its corresponding lower cable. Now you can remove the carb rack after undoing the clamps for the airbox and the carb bottoms to the VBoost manifold rubber donuts.

Take lots of pictures as you begin to remove things, they will guide your efforts to replacing things later.

Many of the VMax parts are interchangeable over the years, but there are differences in the brakes, suspension, ignition boxes, and the frame. Here is a good thread (start at its beginning) that covers many of the changes:
https://www.vmaxforum.net/threads/vmax-parts-compatibility-list-by-year.17148/

It was begun by member Dave, who I don't believe is riding any more, but his contribution lives on.



Bikes sitting for months or years get stale gas, and the carburetor passages become filled with by-products of stale gas. You can try the 'shotgun' or the 'peashooter' methods to clean the carbs, use the upper-right search function for either term, and follow the directions. If they don't work, you may be in for a carburetor tear-down and I suggest using an ultrasonic cleaning to take care of things. There are several members on here who offer carburetor cleaning, it's not cheap, but if you have carburetor issues, they will fix your problems.

dannymax Carb cleaning/rebuilding @ BRC Carb Shop, 16 Taylor Hollow Rd, Ghent, NY 12075 email: [email protected]

Sean Morley is one2dmax on here. His email is [email protected]

Kyle Clegg is CaptainKyle here, his email: [email protected]

Some help to understand the VMax downdraft Mikuni carburetors. Read the entire thread, start at the beginning after seeing where the link first takes you.

https://www.vmaxforum.net/threads/float-set-28-5mm-suggested-so-what-would-30-mm-act-like.53658/

This is a good thread: https://www.vmaxforum.net/threads/to-rebuild-or-not-to-rebuild.53701/#post-538277