MOPED ARMY

If the air filter is a paper element... use a very light oil.. and not too much.

If it's foam any regular motor oil is fine... again not too much... or your four stroking will get a lot worse.. (squeeze out the excess oil)

Bikes sometimes get brought into dealers and the only thing wrong is the owner put too much oil on it.

On the four stroking.. just put a smaller jet in and try it again (after you put the oiled filter in).

Compression on a ped is pretty low (don't have a figure though).. usually I look for it to blow my finger off the spark plug hole when I kick it.

I wouldn't go crazy on mods.. I wouldn't do the carb.. too much hassle.. not enough gain.. you are limited most by not being able to change the gearing.

See if you can find a cheap "tuned pipe" off something else and adapt it.. (a guy named Tim here found that a stock Tomos pipe perked up a Puch pretty good.. and was cheap)

Reed valves on Jap bikes last forever as far as I'm concerned.. they are made out of spring stainless steel.. Want to check it?.. Take it off and try to suck air (with your mouth) through it the wrong way... No air?.. It's good

Wouldn't do the bore kit either.. If it goes 30 to 35 mph.. leave it.. don't kill it.

If you want to go faster..buy a small motorcycle.

I'm thinking of K&N filters which come with special oil.

I guess he should follow the instructions that came with his filter.

Mopeds aren't exposed to to much dust (usually) so I probably wouldn't use any oil on a paper filter.

Dave,

Sounds like you are winning.

You do have a problem when looking for more low speed torqe. I don't know if your ped has more than one gear, but if it only has one, you are going to have a hard time making it faster off the line.

Most modifications are related to improving mixture flow through the engine at higher rpm and this is obviously not what you want.

If you are still too rich, this will affect your power at all rpm. 2 cycles run better and better as you lean them out, then they seize up! So be carefull and check your plug color.

The only mod that would really give you more low end would be a 700cc kit. Increasing compression will give you a little improvement but may force you into higher octane gas.

Have you thought about the advantages of l.p.a. (light pedal assistance) when getting off the line:-).

Ron

Dave,

On spark plugs, you should be using whatever the manufacturer recomends, or an exact replacement from another manufacturer. Under some circumstances, going up or down one heat range is ok but the reach, or thread length, should be the same as the original. Using a differnt reach can cause the plug to hit the piston, if longer, or allow the threads to gum up and lower compression if shorter.

The single speed problem is more or less insurmountable. When you take off from a stop, the clutch wastes power generating heat until the ped is going fast enough to match engine rpm. You might want to play with the throttle when engine rpm is low. Most engines do better with a smaller throttle opening at low rpm.

Yuo are right about the bigger carb/exhaust when increasing displacement. If you decide to try this, look for another Yamaha with larger displacement and compatible parts. If this does not exist, I would stick to a slight increase in compression and learn to smile at the irate motorists.

Ron

Dave,

According to www.ngksparkplugs.com, a 1974 QT50 takes a BP4HS gapped at .028"

If this is the plug you got from the dealer, the crud you found on the lower threads may have been from the threads left exposed by the short plug.

You should be able to look in the hole with a flash light and see how many threads you have in the head.

Beware the Tasmanian Devils!

Ron