engine died and won't crank back up

[uBER_SLO]

Last week I went out to a bike night with my little 1980 GS 250. Admittedly, I rode it pretty hard. Heading home, I merged onto the interstate and when I almost got up to about 70 mph it backfired super loud and died. It hasn't started since. Today I pulled the spark plugs and they seem fine and both are firing. I then check compression, which if you turn it over until the gauge stops climbing it gets to about 105 psi. If you do the 3 ticks of the compression gauge rule it gets to about 75 psi. I then sprayed starting fluid into the airbox and it still would not start.

Could the motor (which only has 4400 miles on it) possibly jumped time? What else can I check? Or is this motor ready for replacement?

Thank you in advance

[BassCliff]

Greetings and Salutations!!

Hi Mr. uBER_SLO,

Wow, that doesn't sound so good. Start with the basics, fuel, spark, compression. I'd take the valve cover off and check the timing chain and valve clearances. You'll find some troubleshooting tips on my little website. In the meantime, here is your "mega-welcome". I'm glad your here.

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Thank you for your indulgence,

BassCliff

[uBER_SLO]

well I checked timing and it is spot on. I checked compression again, this time without the carbs on and right side cylinder has 120psi and left side has 90psi. Im goin to guess its time for some engine work.

What other motors fit in the 250 frame? I've searched quite a bit with no progress.

[tkent02]

well I checked timing and it is spot on. I checked compression again, this time without the carbs on and right side cylinder has 120psi and left side has 90psi. Im goin to guess its time for some engine work.

What other motors fit in the 250 frame? I've searched quite a bit with no progress.

Those compression numbers are NOT the reason it's not running.
Do the engine work and you will still have a problem, unless you find it first.
You can't break in an engine that isn't running well. Find it first.

You have spark, you have enough compression, how about fuel?
Carbs cleaned correctly? Petcock working correctly? Got enough gas in the tank?

[tom203]

[QUOTE=uBER_SLO;1279067]well I checked timing and it is spot on.
You checked valve timing right?? cam cover off, etc.?
What tkent02 says makes sense, so find out what's wrong before you tear into it.

[uBER_SLO]

Yes i had the cover off to check cam timing. It has spark and timing is correct. I've sprayed starter fluid in the carbs and no difference, there's my fuel. Let me say again that when it stopped running I had been running it quite hard to a bike meet. On the way home, as I was merging onto the interstate, it backfired really loud like and died. Hasn't run since. This is why I feel I may need to do some more digging and start pulling parts so I can check out the cylinders. That's really all I can think to do now. Then there's always the option of having some fun with it and upgrading the motor. That's why I ask what will fit on this little frame.

[tom203]

Yes, I remember the backfiring really loud and dying stuff- I'm lost there.
But you have adequate compression ( yeah, your cylinders may be scored, your valves may be burnt, etc. ), so if you add fuel and your spark is about right, it has to fire, though it might run pitifully. I have to ask- any chance you switched plug wires in your haste.

[nevillebrown]

Sounds to me like your timing has jumped off.Check carefully