4xflyer
06-08-2007, 09:10 AM
Our Jetmoto 200GY-A began running rough and wouldn't pull without "missing"above 40 mph. Condition became worse after full warm-up.Plug showed very lean. Rather than ruin the engine I decided to check the valve lash. I found that intake and exhaust valves had zero clearance
First of all when we originally put the bike together we removed all the tank shrouds and louvers as they added eye appeal but no functionality and looked like the louvers would block air flow to the cylinder.
Remove the side panels,seat and tank.
Loosen the rear muffler mount.
Remove the center muffler mount and loosen the front to rear clamp. ( you might have to remove the front pipe from the cylinder due to a weld on the front down tube).
The carb top might have to be loosened or even removed to not contact the frame.
To get the valve cover off you must remove all engine bolts except the lower rear (which should be loosened). The front two bolts that attach the front down tube to the bracket should be removed leaving the two bolts mounting the bracket to the engine can be left attached. The reason for leaving the lower rear engine bolt attached is that it makes aligning the engine during reassembly much easier.
The idea is to rotate the engine down far enough to remove cover out the right side.
Sure enough both valves were slam tight..no clearance. While my manual says to adjust to .05 mm (slightly under .002") Jetmoto says to adjust to .004" intake and .006" exhaust which I did.
Use Red's excellent sticky valve adjust article. While the OHC is different the principle and details are the same.
Upon reassembly I intentionally left the sloppy fitting engine bolts snug at first but not real tight. The vibration really increased. By letting the engine sort of hang loose on the bolts (all the way down in the mounts) before tightening them up tight! helps the vibration level . It's my opinion that with the longer stroke of the OHV engine the manufacturer probably used a smaller/lighter piston which would throw the engine balance off. Boring the engine and installing the OHC piston might correct to some extent our balance/vibration problems. Hmmmm.
I bumped the main jet up to a 110 from the original 105 which solved the real lean condition. You can barely hear the tappets now and next time I might try .003"/.005".
All in all a success!
First of all when we originally put the bike together we removed all the tank shrouds and louvers as they added eye appeal but no functionality and looked like the louvers would block air flow to the cylinder.
Remove the side panels,seat and tank.
Loosen the rear muffler mount.
Remove the center muffler mount and loosen the front to rear clamp. ( you might have to remove the front pipe from the cylinder due to a weld on the front down tube).
The carb top might have to be loosened or even removed to not contact the frame.
To get the valve cover off you must remove all engine bolts except the lower rear (which should be loosened). The front two bolts that attach the front down tube to the bracket should be removed leaving the two bolts mounting the bracket to the engine can be left attached. The reason for leaving the lower rear engine bolt attached is that it makes aligning the engine during reassembly much easier.
The idea is to rotate the engine down far enough to remove cover out the right side.
Sure enough both valves were slam tight..no clearance. While my manual says to adjust to .05 mm (slightly under .002") Jetmoto says to adjust to .004" intake and .006" exhaust which I did.
Use Red's excellent sticky valve adjust article. While the OHC is different the principle and details are the same.
Upon reassembly I intentionally left the sloppy fitting engine bolts snug at first but not real tight. The vibration really increased. By letting the engine sort of hang loose on the bolts (all the way down in the mounts) before tightening them up tight! helps the vibration level . It's my opinion that with the longer stroke of the OHV engine the manufacturer probably used a smaller/lighter piston which would throw the engine balance off. Boring the engine and installing the OHC piston might correct to some extent our balance/vibration problems. Hmmmm.
I bumped the main jet up to a 110 from the original 105 which solved the real lean condition. You can barely hear the tappets now and next time I might try .003"/.005".
All in all a success!