Compression

[Lethalleigh29]

can some one please tell me what the compression should be for a loncin 250cc motor cheers

Leigh

 

[FMX_22]

around 150psi ??

 

[Lethalleigh29]

damn when i tested mine i only got 60 psi on a new motor with about 5 hours on the clock..

 

[sean01]

are you testing it correctly..

you need the throttle held flat.
you need to be turning the engine over really fast..im guessing this is an e-start engine so use some jumper leads from a car to your bike to keep the volts up..

you need at least 3 good compression strokes to get an accurate reading.
i would consider 120-150psi to be about right.

also adjust your valve clearance because any lack of compression could be related to bad clearances

 

[Lethalleigh29]

damn i didnt test it like that i did the same as a car let it crank over about 4 times using the start button with no wide open throttle.. cool.. thanks for that to bad i have pulled it all down for a rebuild..

 

[sean01]

lol well you even tested the car wrong..

if the throttle isnt wide open how is the cylinder going to fill then compress..

lol 5hrs old and youve pulled it down... dont ya think going to see the company you bought it from would of been the first step!!

 

[Lethalleigh29]

lol well you even tested the car wrong..

if the throttle isnt wide open how is the cylinder going to fill then compress..

lol 5hrs old and youve pulled it down... dont ya think going to see the company you bought it from would of been the first step!!

Yeah maybe but i never think that far ahead lol..
plus it will give me some practice in the mechanics of the engine..
silly me.. so i will put it back together and try again,,

Prob wrong thread to ask this.. as u can tell im a noob's Noob..
meanwhile can i ask why the motor would only idle for a few seconds before dying.. and would only start with a little bit of throttle.. i made no changes to the bike.. but since then have put a NGK sparkplug in.. got me puzzled..

 

[sean01]

could be a few things.

carb tune or sht in the carb, blocked fuel cap, bad valve clearance can add to it. sometimes it can be a mixture of a few things..

 

[Lethalleigh29]

sean, thanks a bunch you have been very helpful i have check the carb and its clean as a whistle i have noticed that the motor is running really hot which to me seems to be valve clearance.. i will check all you have suggested keep up the good work helping us noobs..