bike issues, suspect piston?

[Hario]

Hi All,

ive got a mk3 CRM that has always been a bit tricky to start, if you dont get it first kick you are usually in for a bit of a mission getting it to go, although it always has started up eventually

it also strikes me that the kick feels pretty light, ive never used a different CRM so its hard to judge but it feels low on compression to me, its not much challenge to move the kicker through the whole stroke by hand for example (not at starting speed or anything though)

the other symptom is the bottom end feels pretty anemic, the power doesnt kick in until your up a bit in the revs (stock gearing), and at times it feels almost like its bogging coming out of a slow tight corner around town for e.g. from what ive read about the CRM i expected it to be pretty torquey so this seems a bit off too

i guess reading this it sounds like a forgone conclusion that i need a new piston the the trouble is im in Japan, don't speak Japanese and dont have my tools to hand, im going to try and get a compression test negotiated today which should clear things up, but i cant clearly discuss my issues with the mechanic, or get advice etc. so was hoping you guys could clear up a few questions for me:

is there anything simpler worth checking and ruling out? the carb is clean, stock jets and i put a new pilot in previously just to be sure, the bike doesnt smoke excessively, rattle or knock. i thought reeds possibly? air filter is new and clean, good fuel and oil.

if my compression reads low, am i going to be looking at a rebore and piston or might i get away with just rings? the bike shows 15,000k and aside from this issue is in great shape, i would guess its on its first piston, does that sound like a reasonable lifespan?

im guessing CRM's dont have a plated cylinder?

what do people advise for a new piston, wiseco, honda etc?

also, are CRM pistons marked for size or am i likley to have to get measuring?

my last question is, if i tolerate the difficult starts temporarily and keep riding her am i taking a stupid chance of a cataclysmic breakdown? im only in japan for a month, if a rebore and piston order are going to take all that time i would be tempted to use it for the month and bring the cylinder home to get done.

Huge appreciation for any advice on this, this is really putting a damper on my plans!

[davecee92]

Your best bet would be to remove the exhaust and look up the exhaust port for signs of blow by etc but id say its the piston my bike was doing the exact same thing and it was a partial seizure. You are more than likely looking at a rebore and a new piston but you need to find the cause ie poor 2 stroke , oil pump not working etc id say the best piston to use would be a oem if available but wossner and wiseco are both good quality aswell. If your barrel has been overbored in the past the piston will have .50 etc on top if its a standard size i dont think its marked but i could be wrong. The barrels are not plated which means rebores are a hell of a lot cheaper than plated barrels. I wouldnt keep running it untill i had solved the problem and i would never replace a piston without measuring and working out clearances , good luck let us know what you find

[knackeredMk1]

viewtopic.php?f=20&t=5267

[jompy]

If I remember correctly the first piston is meant to be good for up to 14000km

[Hario]

Thanks for the tips, i actually remembered the mileage incorrectly, its more like 19k so probably the first piston wearing out.

I have gotten a bit better at starting her so my feelings are if im looking at a rebore etc. I will ride her for the 3 weeks i have left in japan, then bring the topend home to repair. After reading that link you posted knackered (thanks!) I want to clearly comunicate about shaping the port and powervalve etc. to avoid any problems

Thanks for the advice guys

[Hario]

So, funny story and good result....

After much frustration sorting my CRM out i think ive got it sussed, hopefully this experience will help someone else.

Long story, short. It seems it was my air screw on the carb being set far too rich, and not the piston at all. Makes perfect sense now that it would be hard to start and crappy throttle response but good elsewhere in the rev range.

As for the compression, i put that down to my other two strokes being powervalve free, high compression trials bikes with short kickstarts, the CRM feels feather light by comparison

I had looked at the air screw previously, cleaned the carb and changed the pilot jet. But guess at the time i was using a bad kicking technique and having other 2t bikes with no troubles couldnt accept it was me.

I guess the trials machines i use have such heavy flywheels that once you overcome the compression and get it turning the inertia takes care of the rest every time.

[fallenmikethebike]

A compression test test would give difinative results and peace of mind or at least what your next project should be .
Also, make sure that pilot jet is pristine clean.
Mike

[Hario]

I would have done the comp test but im away in japan, my father in laws garage were funny about doing it and i don't want to buy a guage here when i have one back home in the UK

Just a week left before i go home now, so will just bring my guage along when im back in japan this winter

With 19k on the clock and probably the original piston in there i doubt it can have long left, but as long as it starts well and doesnt smoke excessively there's no rush