Rebuilt two stroke refuses to start - I am stumped!

[Triple Jim]

The manual calls for setting the Point of ignition to between 3 and 2.5 mm Before TDC depending on that gas you are using.

I don't know what the stroke is on your engine, but with a Kawasaki 350 triple, 2.6mm before TDC corresponds to 23 degrees before TDC. 

Irutt, are you possibly confusing mm before TDC with degrees before TDC?

[nunzio]

I don't know what the stroke is on your engine, but with a Kawasaki 350 triple, 2.6mm before TDC corresponds to 23 degrees before TDC. 

Irutt, are you possibly confusing mm before TDC with degrees before TDC?

Thanks Triple Jim.!!!

I am going to pick-up a '74 Suzuki GT750 tomorrow and I've never had a two stroke before ,so, I've been looking at how they work and trying to figure out what you guys were talking about.
The TDC confusion in now cleared up in my pea brain Thanks to you.   ....Alan

[Triple Jim]

Slow combustion requires allot of advance.

23 degrees doesn't seem like a lot, compared to 4-strokes that typically have 30-40 degrees at running speed.

[Triple Jim]

Thanks Triple Jim.!!!

I am going to pick-up a '74 Suzuki GT750 tomorrow and I've never had a two stroke before ,so, I've been looking at how they work and trying to figure out what you guys were talking about.
The TDC confusion in now cleared up in my pea brain Thanks to you.   ....Alan

Hey, congratulations!  That's a cool old 2-stroke that has a lot of potential if you want to play with it, and is a great touring bike in stock form.

[265coupe]

I don't think that it's been covered yet but it might be worth checking the exhausts. I've had a couple of small capacity 2 strokes that have had fully or partially blocked exhausts that will not run. A wasp built a nest in the muffler outlet of one and that engine would not fire. Broke up the mud blockage and fired straight up. On another the spark arrester screen was blocked with carbon and that engine would only just idle and die when asked to rev. It's a long shot on a twin but maybe worth looking at if you haven't already. Good luck.

[erik_w]

Mystery has been resolved!

Just as we suspected - it was low compression that was the culprit! After taking the cylinders apart again and having them rebored properly together with oversize pistons the compression is finally up to spec.

130 psi read cold and now the bike starts up on the first kick!

With 80 psi it simply refused to start at all and with 130 it starts every time.

I hope this can serve as a cautionary tale - have your cylinders done properly and not sloppily and save time!

[Groover]

Great! Thanks for the follow-up. I have been wondering about this. Glad you worked it out, and this is good to know. I've started 2-stoke engines with hardly any compression, so this is a learning experience for me too.

[Kentktk]

no, there �s nothing to stop it from working, no sidestand kill function or anything like that.

No, i didn't curse the bike at all in fact - bad manners!   

I guess the question is really this:

If compression is only 80 psi - will this make the bike impossible to start during anything condition or only given that the crankcase preassure is ALSO too low?

It didn't start even with a drop of gas down the spark plug hole.

I told you that on July 31st post #16. Happy you got it fixed though.

[Sasquatch Jim]

  Just an odd thought but, could the cylinders be out of round?  If that were so, oil in the cylinders would give compression but as soon as it burned away the engine would die.