Detonation?

[mr dirtbike]

When i rev the throttle and shut off as the engine slows down is makes 'pinking' noises untill it returns to idle!
Its done this for as long as ive had it,
1mm oversize bore
full dep
just had full rebuild but the noise was there before.

[knackeredMk1]

Pinking/detonation occurs when you have some kind of load on the engine, definitely not when you shut off the throttle. You've probably got a little piston slap but without hearing the noise directly it is difficult to tell. What did you do to the engine when you took it apart

[mr dirtbike]

[quote="knackeredMk1"]Pinking/detonation occurs when you have some kind of load on the engine, definitely not when you shut off the throttle. You've probably got a little piston slap but without hearing the noise directly it is difficult to tell. What did you do to the engine when you took it apart :?:[/quote]
Just had top and bottom rebuilt,piston,con-rod brgs etc.
It had the same noise before the rebuild.
It sounds like a misfire and only occurs when the engine is slowing down after ive rev'ed it!
(pinking was not the best description sorry)

[knackeredMk1]

2 questions:

Have you had a 2 stroke before

Have you set it to tickover with no throttle

[mr dirtbike]

[quote="knackeredMk1"]2 questions:

Have you had a 2 stroke before :?:

Have you set it to tickover with no throttle :?:[/quote]

Hi,
yes ive had 2 strokes from the age of 8 im now 29 , mechanic by trade 'cars unfortunatly'
ive had the problem before with a yamaha yz 250 but sold it before i found the cause.
Ive set the tickover its running perfectly on idle-full throttle

[knackeredMk1]

Excuse the first question - there are often those of 'lesser experience' that frequent sites like this.

I can't be sure, obviously, but I think it might be just an idoisynchrasy of the CRM engine and the fact that it is set to idle. My theory is that the engine is basically occasionally 'misfiring' on the way down because there is some mix coming in because it is set to idle on no throttle. A lot of bikes make this sort of noise and if you can meet up with another CRMer you might well find it is nothing to worry about .

Try turning the idle right out and if that reduces the 'missfire' then you can be pretty certain that that is what it is .

But I could be wrong as I've really no idea as to how it sounds

Anybody have any other thoughts

[jackdim]

'pinking' sounds scary, but you mean it kind of 'pops' lightly as if it's misfiring? If this so, then its normal (especially on bigger singles).

As it only happens when closing throttle and its doesn't increase when reved then I'd highly doubt its down to engine wear/damage.

[mr dirtbike]

Thanks guys!
funnyly enough ive only noticed the problem only on my 250's never the 125's
Ill try the idle adjustment if that cures it ill feel totally stupid as it makes perfect sense!

[fallenmikethebike]

Ringgggggggg dingggg dinggg dingg ding, ah, wouldn't want to hear anything else, MMMmmmmm .
Regards Mike

[mr dirtbike]

[quote="fallenmikethebike"]:D :D Ringgggggggg dingggg dinggg dingg ding, ah, wouldn't want to hear anything else, MMMmmmmm .
Regards Mike[/quote]
That is the exact sound i was trying to describe,ha ha guess mines not the only one then!
Tried the tickover adjustement,new plug,did a plug chop increased my main jet slightly + fiddled with the air screw no change ringggggggggg dinggg dinggg dingg ding idle!
Guess theres no fault just a crm'ism.

[fallenmikethebike]

Ringgggggggg dingggg dinggg dingg ding, ah, wouldn't want to hear anything else, MMMmmmmm .
Regards Mike

That is the exact sound i was trying to describe,ha ha guess mines not the only one then!
Tried the tickover adjustement,new plug,did a plug chop increased my main jet slightly + fiddled with the air screw no change ringggggggggg dinggg dinggg dingg ding idle!
Guess theres no fault just a crm'ism.

Your welcome, and if it's a simple answer you want, I'm definitely your man
Regards Mike