Gas Gas comprssion question.

I picked up a 96 Gas Gas Pampra 250 with low compression. Can anyone tell what the cylinder compression should be? This one only reads btwn 25 and 30 PSI with one stroke of the start lever.

I would say at least 145 - but you need several kicks to read peak compression.

Is there a certain amount of kicks that is optimal to reach the 145lbs? The bike OldGrunt is refering to also seems to be "Not" getting fuel into the cylider or at least the plug isn't getting wet. We are wondering if maybe there needs to be a certain amount of compression to draw enough gas into the cylider bringing the gas in? Any ideas would greatly help.

Shawn

We just basically kicked the starter about 3 to 5 times until the pressure gauge seemed to peak out.

If you have a dry cylinder, you can squirt a shot or two of oil into the spark plug hole and see if you get a momentary spike in compression to normal or almost normal for a few kicks. If you do and it then goes back down, you probably have a ring problem.

If it doesn't spike more than a few PSI, then you have something more serious going on.

Is there a certain amount of kicks that is optimal to reach the 145lbs? The bike OldGrunt is refering to also seems to be "Not" getting fuel into the cylider or at least the plug isn't getting wet. We are wondering if maybe there needs to be a certain amount of compression to draw enough gas into the cylider bringing the gas in? Any ideas would greatly help.

Shawn

You guys are thinking too much. If it doesn't pump over 90psi at the spark plug, you need to take it apart and find out why. It will probably be obvious.

A Pampera may not make as much pressure as a Trials bike due to the different porting.

For the record compression doesn't draw anything into the cylinder, vacuum does, and it doesn't necessarily draw gas, it draws air which hopefully brings some gas with it.

You guys are thinking too much. If it doesn't pump over 90psi at the spark plug, you need to take it apart and find out why. It will probably be obvious.

A Pampera may not make as much pressure as a Trials bike due to the different porting.

For the record compression doesn't draw anything into the cylinder, vacuum does, and it doesn't necessarily draw gas, it draws air which hopefully brings some gas with it.

That's kinda what I was getting at. I did pull the the cylider and looked at the piston. There wasn't anything that jumped out at me though. But again I have never seen the piston of one of these before either. And we couldn' t explain why there wasn't any gas getting to the plug. Here's a stupid question. Would the reeds just quit working or stop alowing fuel into the cylider? I was under the impression that they loose there functionality but don't nessesarily stop letting gas in.

It sounds like you should go through a very basic troubleshooting procedure staring with the basics and working your way up. The odds of a cylinder issue or reed failure being the reason for a bike not to start are pretty slim. You did not give any background but odds are you have a clogged carb from a bike that has been sitting with fuel in it. What part of WA are you in?

That's kinda what I was getting at. I did pull the the cylider and looked at the piston. There wasn't anything that jumped out at me though. But again I have never seen the piston of one of these before either. And we couldn' t explain why there wasn't any gas getting to the plug. Here's a stupid question. Would the reeds just quit working or stop alowing fuel into the cylider? I was under the impression that they loose there functionality but don't nessesarily stop letting gas in.

There is nothing unique about your engine. You can follow the troubleshooting procedures for any case reed 2 stroke engine. Reeds and reed cages can break and stop the engine from running. A visual inspection should tell you.

Thanks for the feedback. I'll have some time tomorrow to dig into it a bit. I'll check the carb and the reeds. I live in Bremerton Wa and ride Tahuya forest a lot. I'll report back tomorrow. Thanks

When you pull the reed cage look for broken pedals and daylight between the rubber block and the reeds. The first can prevent starting and the latter poor low speed performance. Reeds are cheap, Boyesons for some some bikes are as cheap as $30.

As laser17 said you need several kicks to reach full compression pressure and the throttle should be held full open.

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