Fl350 tuning

[nutz4sand]

And the crank case pressure test went how??????

You "MAY" have compensated for an air leak down low. It will cause the leak to only leak more IF you have one. possibly ruining the piston and cylinder. Not to mention a big weekend of planned riding?

You are dealing with a machine thats quite old. You likely do not know when it was rebuilt or that it was done right.

I pressure test an engine before I tear it down to see what it tells me and after I rebuild it before I start it to make sure I got it right.

Anything less is a gamble and parts for these are not as common as they once were so it only makes sense to be careful with the ones you have.

Crankcase pressure testing should be a common regular part of any two stroke engines life.

If you do not KNOW the bottom end is sealed you could be chasing snipe.

[Buggy guy]

Hehe, don't matter now, blew it up, rotax on its way

[Buggy guy]

Plug fouled solid, exhaust side of piston had ring fused to it. Connecting rod looks good, maybe just a top end rebuild.

[LIDUNO]

Exhaust side of piston failure usually means a lean condition.

You may have jetted it up enough for it to run rich while in low rpm but it looks like it leaned out in the high rpm. You probably have either a fuel dlivery issue or a vacuum leak.

[Buggy guy]

I'm thinking I had a compression issue all along

[nutz4sand]

I'm thinking I had a compression issue all along

Or...... wait for it................................................ . A lower end vacuum leak!

If you rebuild the top end and its still got a lower end leak the new top ends life will be measured in minutes.

Its YOUR money and you can do what you want but if you would like to save some of it the tests are cheap cheap cheap and easy easy easy to do to tell you what you NEED to know with a two stroke.

Did you ever even do a compression check? what was the PSI?
How do you think it was a compression issue all along???

Running cheap local gas with ethanol in it? If so you need to jet a two stroke rich to avoid a lean out as ethanol will make an angine run leaner than a pure gasoline fuel engine.

[DMoneyAllstar]

Or...... wait for it................................................ . A lower end vacuum leak!

If you rebuild the top end and its still got a lower end leak the new top ends life will be measured in minutes.

Its YOUR money and you can do what you want but if you would like to save some of it the tests are cheap cheap cheap and easy easy easy to do to tell you what you NEED to know with a two stroke.

Did you ever even do a compression check? what was the PSI?
How do you think it was a compression issue all along???

Running cheap local gas with ethanol in it? If so you need to jet a two stroke rich to avoid a lean out as ethanol will make an engine run leaner than a pure gasoline fuel engine.

YEP -- agreed! 2-strokes are sooooooo darn simple, but you have to be diligent with setup.

And if switching to a 2-up 2-stroke 470 Rotax, that's TWICE the potential to spring a crank case leak. YOU MUST DO A LEAKDOWN TEST ON A 2-STROKE ENGINE.


2-stroke 101 here...

In order to confirm there are no crank case leaks, you NEED to do a leakdown test with 7-10psi air. Some praise positive pressure tests, some vacuum, some both. Cheap cheap cheap cheap cheap tool that will save your wallet and weekends.

In order to determine fuel octane needed to avoid detonation, you need to check compression. If running north of 150psi, I'd consider 100-110 octane and preferably something non-ethanol. Not like you're running 1,000mi a week in these things, so buy the best fuel and best oil anyways. Plus the "good stuff" has a great scent.

In order to confirm jetting, YOU MUST DO A SEPARATE PLUG CHOP (or at least a PLUG-LOOK) at idle, then at mid-throttle, and then at WOT. Once you are seeing good results, then you'll have a good baseline for condition/jetting changes, detecting snowballing issues, and comparing tweaks/upgrades. And once you have a baseline, you can monitor exhaust temps with an EGT gage.


My weed-trimmer, chainsaws, FL350R's, LT500R's, and all the random SkiDoo's I've owned have always lived nice long healthy lives by following those simple guidelines. I've never blown-up a top-end -- EVER.