2 stroke Puzzle

[Dmitriy]

I seem to recal 2 stroke CDI’s changing the ignition curves based on RPM, something something pulse pickup timing changes with higher RPM. Idk. If you had another stator to test with it would be ideal, as this point I would be trying to McGuyver a know good 2T stator and CDI system in there just to check if I can get it to rev.
Unfortunately the usual place of REGULATORrectifier.com doesn’t seem to have a stator for your bike

 

[elemetal]

Aside from the stator issues it sounds like it's lean bogging. Since you've checked all the regular stuff I don't have any idea except to check the petcock. Pull it and confirm it isn't clogged and that the oring inside is still intact.
Not sure why the extra resistance at the stator would make a difference unless it if measured from the pick up coil; if the resistance was too high for that coil it's possible at a faster speed it won't generate a strong enough signal for the CDI to pick up (sounds a little hocus but all I could think of).
Trials bikes rev low but that thing is definitely not running right. Trialscentral is another forum to look at, much better advise from trials groups on that side of the pond.

 

[Seizer]

I think it’s an air leak causing a lean condition. Buy build or borrow a leak down tester and confirm all of your parts are sealed correctly. You’re basically pressurizing the motor and testing gaskets, sealing surfaces and your crank seals. Even a small air leak can be really bad in a 2T and will definitely affect your jetting. 90% of 2T electrical problems are jetting related haha

 

[OaklandF4i]

Just tested my Stator. Vendor in UK says if I test the red/ black wire the OHMs should be 5, mine tests at 8. the other test is a green and white wire and vendor says that should be 7, mine says 10. I am no electrician so I don't know if the my higher numbers are a good thing or bad

Open, or the opposite higher ohm (ie resistance), usually mean a defective stator from my limited and crude understanding of moto electrics. I have to read my multimeter instructions everytime I crack it out of the box..... no expert by any means. However, it is my understanding the the ohm reading should not exceed, but instead fall within a range. Suspect it is one of if not the problem.

I hate diagnosing electrical problems and sometimes think my time would be better spent dancing around the bike in a speedo while wearing clogs and drinking SoCo on the rocks. My electrical voodoo dance. :laughing

 

[Rob]

A brand new carb doesnt mean the float level is set correctly

qft

it's been mentioned a few times and a free fix if it's the issue.

 

[ST Guy]

I think it’s an air leak causing a lean condition. Buy build or borrow a leak down tester and confirm all of your parts are sealed correctly. You’re basically pressurizing the motor and testing gaskets, sealing surfaces and your crank seals. Even a small air leak can be really bad in a 2T and will definitely affect your jetting. 90% of 2T electrical problems are jetting related haha

This!

 

[FastCletus552]

Well here is an update.
I was dead certain it was the stator and I was just about to send it back to the UK, when a buddy came over and listened to it run. He said "Rings are shot dude" I said they are new or (at least look new) but he said maybe previous owner didn't hone cylinder and just slapped new rings in. I checked compression and its 100 PSI. I'm guessing that's considerably low. From what I have read it should be in an around 175 PSI. No shop manual to confim?

So I look into buying rings and I think I might as well get new piston to match new rings. I read that this bike has 3 different piston sizes A, B, and C. I have a sneaky suspicion that PO maybe bought an A (which is smallest size) when he maybe should of bought a B. Vendor in UK agrees, and suggest either a B or C Size. Its a $200 crap shoot as to which size to buy. I am thinking if it runs with the smallest size (A) then going to the next size up is best idea (B).
So thats where I am in this puzzle

 

[Frame Maker]

... Its a $200 crap shoot as to which size to buy. I am thinking if it runs with the smallest size (A) then going to the next size up is best idea (B).
So thats where I am in this puzzle

Why not just pull the head off and measure the bore size? No more guessing as the the correct size. You'll need to pull the head and cylinder anyway to install the new rings. Personally, I'd pull the cylinder. Measure it and buy the correct rings AND piston. Then give it a light hone. Re-assemble and have nice fresh top-end.

 

[FastCletus552]

Hoping vendor will give me Diameters so I can do just that

 

[ST Guy]

Why not just pull the head off and measure the bore size? No more guessing as the the correct size. You'll need to pull the head and cylinder anyway to install the new rings. Personally, I'd pull the cylinder. Measure it and buy the correct rings AND piston. Then give it a light hone. Re-assemble and have nice fresh top-end.

Yep. You don't want to be guessing. And watch that end gap on the rings. If it's too large, you could still have problems. Make sure it's correct by putting the rings in the cylinder one by one, squaring it up with the piston, and then measuring the gap with a feeler gauge. Adjust as necessary.

 

[bobl]

Get some long feeler gauges and use them to check the bore to cylinder clearance when you've removed them. Find out what the clearance should be, and measure. I would buy a .001, .0015, .002, and maybe a .0025. Easiest way to determine clearance. With practice you can even feel some taper. They don't cost much, and if you mess with pistons they are a good investment. I don't know about plated bores, but on the old iron liners a thou and a half was about average.

 

[Seizer]

So the compression read 100psi. I’m assuming that’s cold/engine not at operating temperature. That’s not so low in my experiences. It’ll rise significantly when the motor is warm due to piston expansion. Which brings another factor, which is bore to piston clearance. Depending on piston composition (forged will expand less than cast), your bore will require different specs. I’m unfamiliar with piston tolerances for plated bores. This is important stuff if you want a reliable bike that’s going to work as designed. Your best bet is take it to an experienced 2 stroke machine shop and explain what your trying to do. You ant slap these things together half assedly and expect them to work well if at all.

 

[Maddevill]

And make sure when installing the rings you get the end gaps set at the locating pins. If you don't, you'll break the brand new rings.

Mad