Enduro bike problems

[farmer boy]

I have a little 1973 100cc bike that I bought at auction last year and it ran good for a year. This spring I pulled it out and started it up and it ran great. Soon enough I heard a bit of a clicking noise and a hugh loss in power. I rebuilt the engine(2 stroke) with a used but in good condition cylinder and piston. It runs good now that I somewhat got the oil mix figured out. The problem is that it after it gets well warmed up it really starts running rough. It will idle fine and handles the lower RPM'S fine but when you get ito the higher rpm's it runs rough and with a power loss. Any help with this problem would be appericated because I would like to sell this bike soon.

 

[old]

What brand of bike is it?? Helps a lot to know which one/who made it because they do not do the same things with all of them.
Hobby farm

 

[Anonymous-0]

Have you cleaned/gapped the points? If you haven't done it in a few months, get a new sparkplug (the correct one) and put in also. I'd lean more towards the points though. I had a Yamaha 100 enduro the same year when I was a kid that took 8 ounces to a gallon mix. Had another one (Yamaha) without points that would act like it was governored at about 30% power when it got hot, turned out to be the magnito.

Good Luck,


Dave

 

[steamnjn23]

my son races nationally. never, never re-use piston rings. they seem to fit each particular clyinder. 2 strokes are wonderful machines. rebuild them right and you'll get a lot of service from them. I'd look into a complete top end kit. a new set of rings for my sons bike is just 17$. but the whole top end kit including gaskets and new piston, is less than 120$, and takes about 30 minutes to complete.

we had a power problem when he moved up to the big bikes. manufacturer said use 32:1 oil ratio, result> no power and fouled plugs. we moved up to 50:1, result> power and no fouling of spark plugs.

 

[farmer boy]

It a kawasaki 1973 100 enduro. Oil injected but currently ran at about 40:1 with mixed gas/oil. I rebuilt it with a piston and cylinder that came from the same bike and were installed the same way so the rings shouldn"t be a problem.

 

[glennster]

the old yammies ran 20-1 oil mix, use a good two stroke dirt bike oil in em. like the other guys said, check out the ignition good, could be the condenser is failing when hot, or could be in carburator. should have a mikuni on it. you may want to try and open the main jet up a notch or two and see if it helps. on the top of the carb where the throttle cable goes in is a big cover, unscrew it and pull the slide out. you will see a long needle and a horseshoe clip. there are notches on the needle, you pull the clip and set it so it raises the needle up to richen, lower the needle to lean out. if it cooked a piston, prolly running too lean. also check the carb to see if its plugged up, and if you pull the carb off, check the reed plate too. if you need parts, try bikebandit.com, they have a lot of parts for older bikes.

 

[steamnjn23]

if it ran fine when you parked it, then this year its running bad, could be bad gas in the carb.
still i'd do a complete top end, and break it in proper. change the oil too. email me if you need good suppliers.

i had an old yamaha rd100 street bike that was oil injected. after the injectors went bad and i ruined a pair of jugs, i started just using mixed gas in the tank. never had any problem with it after that. better to be safe than sorry...and yes the injectors will go bad without warning.

what is your asking price for it as it sits?

 

[james rumph]

Take a can of starting fluid and spray it around the base gasket and head gasket. Spray the intake and the carb boot as well it might be dry cracked. [ while running]
If the rpm goes up your sucking air and it will run poor.[ bad gasket !]

Retorque the head , it may not be flat [ loss of compression].

Something is changing shape on you when it gets warm.

Do a cold compression check then one when it is warm.

There will be a differance but not real large unless the rings aren't sealing.

I do snowmobile motors all winter long here in Michigan and have seen this with heads that are warped on old motors.

If the head is warped it can be fixed at any auto machine shop. Just cut enough to get it flat , you don't want the squish band under .060 or race fuel will be required.

To check the squish use a piece of plumbers solder and bend it like the letter"L" .

Now put it in the spark plug hole[ hold on to it] accross the piston pin, not intake to exhaust!
It must touch the cylinder wall. Turn the motor over by hand a couple of time while holding the solder.

Remove it and mic. the end that was smached between the squish band and the head. This is the important # on something like this i wouldn't go under .070 so you can just run 87 octain fuel.

Hope this helps, start with the basics.

Jim

[email protected]

 

[farmer boy]

A guy is offering me 600-800 depending on the shape of the bike. That"s with a parts bike that has a few identical parts. I figure I should take it because it"s a decent price and if it breaks I might not be able to fix it.

 

[steamnjn23]

if you can show a profit on it, i'd move it. parts are tough to come by with a bike that old, but they are available.

 

[farmer boy]

So I should replace the spark plug to start with? It ran great before and when in neutral you can rev it and it runs good. I think all the gaskets are good. I sprayed a bit of either on it and nothing happened.