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98 rm250 push starts only plz help

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  #1  
Old 09-22-2013, 06:55 PM
pete sake's Avatar
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Smile 98 rm250 push starts only plz help

Hi new here was hoping for some help
Just got my rm250 out shop re bored
new piston reeds and rings cleaned carb
New plug fuel filter etc. Anyway it won't
kick start its not broken in yet shop mechanic
Says go through 3 tanks of fuel without high speeding
It only starts by pulling with another bike and put it on 3rd
Gear my compression is at 85psi I know its real low but
Maybe after breaking in it will increase also bike revs up on
It's own in gear and neutral like its sucking up air or something
Is making it rev up every couple seconds.
Any help will be greatly appreciated thx
 
  #2  
Old 11-21-2013, 10:24 AM
morghul's Avatar
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Smile Here is your answer

Hey fellow Suzuki rider!
Sorry for my wrong english, its not my first language.
The problem is your compression.
Most likely, the guy that rebuild it didnt put the right piston in it. (if its really a fresh rebuilt)
A good running 250 2 stroke is gonna be close to 200 psi.
Yours is 85, and even if the piston is wet of oil, its never gonna come close to a firing compression with the kickstart.
When you push it, the piston is lubricated by the fuel/oil mixture and it seals a little better and it probably reachs about 100 psi, because a 250 2 stroke needs about 100 psi to run.
And when it runs, its gonna run almost fine, but its gonna eat spark plugs like a big fat kid with a bunch of candys.
If its the right piston, your rings may be broken or damaged and so may be the piston and cylinder.
Or, the cylinder is out of shape. (dont know if it make sense to you(not perfectly round)
Also, it could be a cracked head or a very wrong cylinder head seal.

So what your gonna do:
Remove the exhaust expension chamber.
Take a look of what you can see of the piston and a part of the rings.
You may see something.
If not, remove the gas tank, remove the carb, remove the ignition wires, drain the coolant.
Take the cylinder head cover off and look how the top of the piston look like.
At this point, unhook the exhaust valve pushrod thing and pull the head off.
Take it to some one who know these kind of things to mesure it right and mesure your piston also. Hes gonna also look for damage in the cylinder with may cause low compression.
As i said, im pretty sure its the wrong piston. But if its the right one and the piston and cylinder is on good shape, which is unlickly, just rebuild if back using a new gasket and seal kit and seal every single gasket with silicone gasket maker.
Make sure also that every part on your engine is original.
I already had a 2 stroke that hat the wrong head cover and had bad compression because of that.

You got to understand that the compression is made in the very top part of the cylinder.
The exhaust, intake and everything doesnt have nothing to do with compression.
The only things directly related to compression are: Piston, rings, cylinder shape, cylinder head cover gasket and o rings and the size of the combustion chamber, also wet vs dry tests.

Hope this help.
In fact i have a 1985 Rm 250 2 stroke and a 1992 Rm 250 2 stroke engine on my kitchen table right now completly torn appart.
So if youve got any questions, i guess im the guy to ask.
 
  #3  
Old 11-21-2013, 10:35 AM
morghul's Avatar
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Plus, the piston may be a forged piston.
These have a tendency to expend in diameter with heat.
So when it does start, it heats up and runs a little better.
But quite often, the diameter is like 1mm or 1/2mm wrong.
But it does make a big difference in compression.
 
  #4  
Old 11-21-2013, 10:35 AM
morghul's Avatar
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and no, the compression is not gonna increase with time...
 
  #5  
Old 11-21-2013, 10:59 PM
LeonardoDiCaprio's Avatar
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Last edited by LeonardoDiCaprio; 11-17-2014 at 06:51 AM.
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