over heating on long runs

[reggie]

this is proberlay my owen fault i was going olong the dual carage way on my rx 50 polini 80cc bore kit, 21mm carb, full arrow i was going between 70 and 75 then my bike cut out lost compression. got a lift home took the head of id burnt a hole in the piston and all the rings were stuck in the piston. from the burnt piston i take it i need a larger jet. is it possible to get a replacement 50mm pollini piston becuse the barrel is in very good condition not scored or worn and would save alot of money, could you suggest a good size jet one that wont eat pistons.

[Azzroid]

Do a plug chop to find ur jet size. Or just buy a few bigger in like increments of 5, then go through them until u get to a good size then buy some more.

For example: go through 80,85,90,95,100 etc then wen u get a decent one say 95 get a 94 and 96, then if 94 is good work from there. Pretty simple really just gotta get the right mix

[williamr]

Plug chop at WOT to get the main jet correct, then chop at part throttle to set the needle properly.

What state is your plug in? Too soft a plug burns holes in pistons even with correct mixture.

While 50s are usually at WOT, no engine likes sitting there for a long time on a dual carriageway. Next time, ease back occasionally.

Rob

[reggie]

what is a plug chop?

[Vikter]

what is a plug chop?

Checking the sparkplug to make sure it is not white (lean) or black (rich). It should be a golder brown color.

[williamr]

Ride up a slight hill in top gear, accelerating at full throttle. Dip the clutch and hit the kill switch to stop the motor. Hold the clutch in while you stop the bike and remove the spark plug. If it's white, the mixtures too weak. If it's black, it's too rich.

This tells you weather you've got the correct main jet. It can also indicate an air leak (lean) or a dirty air filter (rich). Whjen you have the spark plug showing a golden brown colour, repeat the chop at 1/2 throttle. This time the condition of the plug will tell you if the needle setting is correct. As this is deprendant on main jet size there's no point in correcting the needle until you have the correct main jet.

For really accurate setting, use a colourtune kit in conjunction with a dyno. That's expensive.

Rob

[PallOlavsson]

Willamr, many guys on this forum are kinda harsh against you, cause you dont like underagers driving..
But i gotta tell you

You know your shit!

Cheers.
-Páll Ólavsson

[nopainnogain]

you need to get your ctlinder measured accurately,i doubt if it is 50mm as you say,aprilia bbks generally have 49.7mm piston size.

[46robbie46]

I was having the same problem with plugs burning out. Try checking that your exhaust isn't coked up and shitty inside. Once i'd cleaned it out with caustic soda and brute force it ran sweet as a nut.

[slasherslade]

This happened to me but :

I never burned the piston
The rings weren't stuck, but they had completely gone on one side (and not the other)
My barrel was fine
It was over a much shorter distance.

Plug chop at WOT reveals lovely coloured plug. Do you think that the previous owners have thrashed this bike to bits and i just sent it over the edge or could it be 100% my fault?

I was doing indicated 55 at 11,000ish rpm, backing off occasionally, it was actually when i was backing off that it cut out and lost compression.

(It did still have some compression when i got it home..in the back of a taxi)

[bourney2007]

This happened to me but :

I never burned the piston
The rings weren't stuck, but they had completely gone on one side (and not the other)
My barrel was fine
It was over a much shorter distance.

Plug chop at WOT reveals lovely coloured plug. Do you think that the previous owners have thrashed this bike to bits and i just sent it over the edge or could it be 100% my fault?

I was doing indicated 55 at 11,000ish rpm, backing off occasionally, it was actually when i was backing off that it cut out and lost compression.

(It did still have some compression when i got it home..in the back of a taxi)

How the hell did you fit a rs50 in the back of a taxi, and how did you get the taxi driver to agree to doing it?

[slasherslade]

I own the taxi. Thanks for answering my question.

[bourney2007]

I own the taxi. Thanks for answering my question.

oh right lol