Tomos ST (A55) - No power off the stand

Hi Guys,

I have a Tomos ST with the A55 engine and I've been chasing an issue with it for a while.

It currently has a 70cc airsal kit and a Mikuni VM18 carb.

I've checked for air leaks with carb cleaner around all the mating surfaces and also a bunch of different jet combinations but still have the same problem.

On the stand the bike will idle great and the rear wheel spins fine with some throttle, but once it's off the stand it barely pulls at all. It'll go maybe 5 mph.

I've also done a gear oil change and took a quick peek around in the transmission, the clutch lining looks okay, but maybe it needs to be re-corked?

Has anyone seen this before? Is there something that I should be looking for here besides an air leak?

Thanks!

--

Mike

Re: Tomos ST (A55) - No power off the stand

Sounds like you've checked everything , except the timing .

You might also check compression .

Re: Tomos ST (A55) - No power off the stand

Mike George /

I forgot to mention that I tested compression as well, my tester reads 120psi

Looks like I'll have to get into the timing then.

Thanks!

Re: Tomos ST (A55) - No power off the stand

run it w the choke on half way, and see if it takes off

Re: Tomos ST (A55) - No power off the stand

Mike George /

If that works, what will it tell me?

Air leak? Wrong jets?

Re: Tomos ST (A55) - No power off the stand

i refuse to tell u, THINK mofo.

Re: Tomos ST (A55) - No power off the stand

Mike George /

Alright, haha

I'm thinking that would tell me there's an air leak somewhere and I'm not looking hard enough to find it

Re: Tomos ST (A55) - No power off the stand

Probably Fred /

Put the stock phva 14 carb back on with a 64 jet, 13$ metal mesh filter, middle needle clip and see how it works (edited)

Re: Tomos ST (A55) - No power off the stand

Mike George /

I've done some digging on this and I believe the flywheel/magneto is the culprit here. It's pretty chewed up on the inside. I plan on sourcing a new one, and probably upgrade the crank while I'm at it, hopefully it fixes the problem.

Re: Tomos ST (A55) - No power off the stand

That hub could probably be cleaned and brought back to functional .

And , FYI : In this case , the flywheel is part of the magneto . They are not interchangeable .

Re: Tomos ST (A55) - No power off the stand

Mike George /

Thanks for the clarification.

After cleaning, what would you suggest to repair the groove that the crank pin has started to dig?

Re: Tomos ST (A55) - No power off the stand

I'd use jewelers files ( needle files ) .

No tool box is complete without them . ;)

Re: Tomos ST (A55) - No power off the stand

Mike George /

I have some larger files, but ill pick up a set like you pictured since they look quite useful.

Am I correct in thinking that I can clean all the junk out of there, fill any gouges with JB Weld, then file everything down smooth and file back to the original shape of the keyway?

Re: Tomos ST (A55) - No power off the stand

That's pretty much what I'd do . I'm not sure I'd use any filler from a tube .

If you lap the flywheel to the crank taper , you likely won't even need a key .

Just have to re-set the timing .

Re: Tomos ST (A55) - No power off the stand

Mike George /

This is my first time hearing of lapping the flywheel and crank, just making sure I understand here.

Once I smooth out inside the hub of the flywheel I shouldn't even have to worry about the gouges from the broken woodruff key since lapping the flywheel and crank should create enough surface area for everything to stay snug once torqued to spec?

This is what the key on the crank looks like also:

Re: Tomos ST (A55) - No power off the stand

> Mike George Wrote:

> -------------------------------------------------------

> This is my first time hearing of lapping the flywheel and crank, just

> making sure I understand here.

>

> Once I smooth out inside the hub of the flywheel I shouldn't even have

> to worry about the gouges from the broken woodruff key since lapping the

> flywheel and crank should create enough surface area for everything to

> stay snug once torqued to spec?

>

> This is what the key on the crank looks like also:

>

> https://i.imgur.com/rx0KsXV.jpg

Exactly .

By the looks of the crankshaft , unless the flywheel has been off for a long time

, there was a minimum of contact with the flywheel .

Note all the rust and the small amount of shiny area .

By that^ , I'm sure a lapping would be beneficial .

And , you might want to de-rust the rest of the stator surfaces .

Re: Tomos ST (A55) - No power off the stand

Check yer spark plug! LOL!

Re: Tomos ST (A55) - No power off the stand

read up on lapping tapers, pretty well covered. takes less than an hour.

Re: Tomos ST (A55) - No power off the stand

That flywheel looks scary.

Best of luck on that ashtray.

Re: Tomos ST (A55) - No power off the stand

Mike George /

I cleaned up the inside of that flywheel with a combination of hand files and one of those cone shaped griding stones on my dremel, punched the key out of the crank and lapped the crank and flywheel.

After a couple tries of positioning the flywheel and adjusting the stator plate I started her up and took off just like I would have expected!

Looks like it worked! Unfortunately it's raining tonight in NH, so no joy ride yet.

That being said I'll probably look for a replacement flywheel when I do the bottom end on this bike since I'd like to throw in an upgraded crank to go with the 70cc kit. Plus now I'll be sure to lap all my cranks and flywheels.

Thanks pdcomm for enlightening me on taper lapping, and thanks everyone else for the input and helping solve this problem.

Re: Tomos ST (A55) - No power off the stand

Good you got it . ;)

Re: Tomos ST (A55) - No power off the stand

What, no after pics?

Re: Tomos ST (A55) - No power off the stand

Mike George /

I'll pull it apart tomorrow and get some pictures!

Re: Tomos ST (A55) - No power off the stand

Mike George /

Hey guys,

I finally had some time to drop the engine to prep for a new crank and snapped some pictures of what the crank / flywheel look like after lapping:

I'm probably going to lap this flywheel to the new crank unless I can find another.

--

Mike

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