Update on my ped (technical)

david f martin /

As per your suggestions:

I changed the gear oil. I drained almost 1 qt. of very dirty oil out, and put in 300cc of new 90w. The clutch is now engaging sooner, which is good.

I got new jets and installed them today, and re-installed my aircleaner. The bike still 4-cycles, but not as badly as before, and I'm getting a higher top rpm. Very good! What kind of oil should the aircleaner element get? Also, I noticed that the throttle slide has some kind of weird wear (maybe primative machining by the previous owner?). I may replace that next, if I don't solve the 4-cycling problem...

I installed new front brake shoes. That got rid of most of the annoying squealing, and now the bike stops effortlessly.

Next project (once I get the bike running like new) will be speedometer repair. I had to disconnect the speedo so it wouldn't self-destruct, because it was buzzing pretty loudly and the needle was bouncing around. The cable is good.

A couple more questions for the gurus. What is normal compression for a ped? Does the reed valve ever go bad, and what would normal symptoms be from a bad valve? Has anyone ever installed (possibly modified) performance parts of a different make on thier bikes? I'm thinking carb and exhaust first, possibly bigger top end, and as far as I know, no one makes performance parts for my brand of bike.

BTW, this is a Yamaha QT50 (Yamahopper), not that it should matter. Ped Gurus would know that all peds are pretty similar and operate on the same principles (same as auto gurus, music gurus, etc)...

Finally, I bid on a manual for my bike on ebay. This manual is very hard to find. Hopefully it will answer some of my questions...

david

Re: Update on my ped (technical)

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.

Re: Update on my ped (technical)

Ron Brown /

David,

I agree with everything Fred said except for oiling a paper air filter. Every paper filter I ever had instructions for said blow with compressed air and re-install.

I would think that any kind of oil on a paper filter woud plug it up. Fred?

Ron Brown

Re: Update on my ped (technical)

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.

Re: Update on my ped (technical)

david f martin /

Thanks for the great info.

Right now my bike is my main transportation, so I can't really tear it down and study it. Rather, I'm trying to go after any problems bit by bit, during my lunch breaks and in the evenings after work...

My airfilter element was already presoaked with oil when I bought it new, and I cleaned it with carb cleaner trying to get rid of the 4-stroking problem. We sell K&N airfilters for cars at the VW shop I work at, and they come with a can of oil to treat them with, but I have no idea what kind of oil it is.

Since installing new jets and reinstalling the aircleaner element yesterday, I've put about 40+ miles on the bike. It is running much better now.

As far as mods go... With the small wheels and short wheelbase, it goes as fast as I'm willing to ride it, going downhill. Any faster and I'd be afraid of it. There are a lot of hills between work and home, and if there's any kind of headwind, my speed can drop to as low as 10-15 mph going uphill. Taking off from a traffic light on a hill can be kind of embarrassing, too. Holding the hills is all I'm really after. I guess what I'm interested in is more torque, rather than more top end.

I built a larger than stock engine for my '67 VW bus last year, not so I could spin tires or show off, just so I could keep up with traffic. My '84 QT is the newest vehicle I own, and I baby all of my machines.

Anyway, thanks for the help. I'm sure I'll have more questions for you later...

david

Re: Update on my ped (technical)

Ron Brown /

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

Re: Update on my ped (technical)

david f martin /

Thanks Ron,

Don't have pedals, so l.p.a. won't help. Only one gear, which has the obvious disadvantage of gearing ratio, but on the other hand keeps the machine simple to fix.

The spark plug that came with the bike is a short plug, possibly for a chainsaw or something like that. I got a couple of NGK plugs from the Yamaha dealer to keep in my toolbag, tried one of them and could tell no difference, so I put the short plug back in. It is a nice grayish brown, just like it's supposed to be.

I'm still new to these little machines and I've been reading everything I can find on them. I'm curious about the 70cc upgrade, but 1)no one makes performance parts for my bike, as far as I know, and 2)I've heard that the upgrades are cheaply made and are a good way to kill your bike.

I'm working on getting a shop manual for it. I'm hoping that it will have technical specs for the piston/cylinder/head (I.D., O.D., stroke, etc), with the idea that I could find a stock 70cc top end kit (for another bike) that would work (possibly with machining on the case to accept it).

Still speculating, if I were to upgrade to 70cc, wouldn't I have to feed it with a bigger carb/intake/exhaust?

Maybe these long climbs up those hills are giving me too much time to think...

david

Re: Update on my ped (technical)

Ron Brown /

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

Re: Update on my ped (technical)

david f martin /

Well, I thought it was kind of weird that the NGK plug stuck out of the head so far, and when I pulled it out, the first 3 or 4 threads were black from being in the combustion chamber. I wondered if this plug is what was originally recommended by Yamaha, or if it is the closest equivalent that NGK sells... If I can get the manual, I'll find out for sure.

That's the other problem I'm having right now. I won an auction on Ebay for a manual, but the seller is in Tasmania, Australia and my emails to him keep bouncing back. I'm hesitant to send him money for the book if I can't contact him reliably...

david

Re: Update on my ped (technical)

Ron Brown /

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

« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account