Hole in TS1 225 Piston - Bit of a mystery so far

[paulnobodyimportant]

On the way back from Euro lambretta, I was overtaking a set of wagons, when I heard a high pitched whistle and then no power. Photo shows being loaded onto wagon 100 miles from Europort. At the time I suspected a leaking inlet manifold due to lots of oily matter around that region.

However, today, did a leak down test and no air leaks what so ever, but hole in piston. FYI carb rubber is OK and no sign of leaks at cylinder base or head.

Now at the rally, I bought a new TMX35 as my current one was worn and running too rich despite a 58 needle. Anyway, new TMX jetted with 56 needle, 2nd clip from top, 22.5 pilot and 330 main jet and 17 degrees static timing. Ran great, with good plug colour, till it went too hot and put a hole in the piston.

At the moment I'm scratching my head as i was convinced that the cause was an air leak.

Any ideas?

Plus, I note that there are now many piston for the TS1, but are there any benefits in paying more than the one that AF Rayspeed sell for around £100.00

[Stampede]

Had the scoot a refill at a petrol station before the breakdown?

[storkfoot]

Only a theory but your old TMX had been too rich at certain throttle positions and, maybe, just right at other throttle positions. The new TMX may have been generally nearer the mark overall, but too lean at the one part of the throttle progression that you were riding at just before it popped?

I have just had same quandry re piston. On the basis that I had good service from the old original one over 5 years, I just got another. But then I am not a boy racer anymore

[holty]

when you have ruled out all the obvious things, like air leak, i would suggest its down to the carb, i did the same thing coming home from whitby at easter, id done a plug chop a couple of weeks earlier and had a nice dark brown, but i hadnt held it at full throttle long enough to see it was weak, i found out on the way home as it was a massive headwind and i was able to hold the throttle open for longer and holed a piston, ive fitted an egt gauge now so i will know if its too weak before anything melts, although ive upjetted now, a run on a dyno might be a good idea once youve rebuilt it, good luck,
holty

[vespanic]

You swapped the needle jet from 2nd clip 58 to ? 56. That looks to be the main answer. I don't understand these things but looks to be that it was too big a jump. Could have tried just moving circlip up first just to lean your mixture slightly. Then as I understand it if that doesn't weaken carb enough then go to next slide but on richest setting first ie clip on bottom. As holty says above moving needle has an effect across the range. I couldn't explain different sizes across needle but years ago on a dellorto the dealer/tuner used some wet n dry to remove a bad running spot because of the needle. It worked too. Hope you get it sorted, I have too many pistons like that.

[drunkmunkey6969]

56 is richer than a 58...


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[vespanic]

56 is richer than a 58...

That's probably where I'm going wrong then lol
Cheers for that, blows my theory out the water

[shocky]

Float height ?

[roadrunnerian]

I have a ts1 225 set up with a tmx35 using 320 main jet 56 needle did plug chops got it near enough right so I thought took on the dyno and it was slightly weak on the the mid range ended up at 340 main jet and 57 needle still 2nd notch down funny how you have to go bigger jet and leaner needle to get it right

[paulnobodyimportant]

Just to answer some of the questions, before coming to my conclusion.

Journey there was using Exol fully synthetic, which I've used for a good few years and came back with Rock oil from team Francis, as I had run out of Exol and all at 3%. Plug was a 9. 10 miles before the holed piston, we had all filled up. Can't remember if it was 95 octane or super, but I put 8.5 litres into a 12 litre tank, but i don't think petrol was the real culprit.

Timing was 17 degrees static, but will check timing over rev range on re-build this Friday to make sure that its not roaming at higher revs. I will also be re-sealing inlet, exhaust and barrel. Then I'll do an air test which does have one of those blood pressure monitors as seen on SULK.

As for cause, the good thing about forum feed back is that all your comments make you think. I was set on a leaking inlet gasket, but that proved not to be the case. So as Warkton says (LCGB Forum) and he is correct, look at what you have changed, in my case a new carb, which I took for granted I had jetted safely.

And then Adam (LCGB Forum) did get me thinking about speed and revs. So the first full day was spent on Autobahns and A roads, probably cruising at 60-65mph and overtaking at 70 plus. Now I've got to admit that on that first day, I did hear the high pitched whistle when overtaking. Of course, checked plug color at two fuel stops, I know that its not a plug chop, but colour looked OK and inlet manifold seemed tight.

Second day, the fateful day, whistling sound again on overtaking, which when the power went I put down to an air leak. However, I'm almost convinced that my jetting has caused the problem. When I was overtaking, I was not on full throttle, but probably still on the last part of the needle, with the whistling occurring. So my thought is that I was running extremely lean at that rev range and the whistling was my piston being torched.

Lesson learn't, do plug chops. So when i re-build, I will go to a richer needle and start from there.

Apologies for the ramble, but thanks for the suggestions.