jdmae92 GRM+ Memberand New Reader
9/3/08 6:46 p.m.

So I have a Suzuki GT250 that I am working on. I got it put together and running, one cylinder has good compression and the other one doesn't, both cylinders were running fairly smoothly. I rebuilt the carbs today and the cylinder with good compression doesn't want to run very well, replaced the coils (with other used ones) and the spark plugs and it is still the same, just putting along but not firing like it should. It has no power and is vibrating quite a bit over 5k, more than it was before.

Jensenman SuperDork
9/3/08 7:00 p.m.

1) Ignition timing way off 2) leaky crank seal causing a vacuum leak 3) the jug with low compression will have low vacuum as well due to 2 stroke engine design. No good news here, sorry.

jdmae92 GRM+ Memberand New Reader
9/3/08 7:19 p.m.

I didn't do anything to the timing since I installed new points and timed it so I don't think that is the problem, it could be the crank seal though. I have another engine that needs rebuilt I was just hoping I could put this engine in and use it until I rebuilt the other one. Oh well, I guess its time to start rebuilding.

HappyAndy New Reader
9/4/08 7:15 a.m.

I am not farmiliar with this particular engine, but does it have reed valve induction? If the weak cyl has a bad reed it could explain the problem. I have seen a 2 stroke with a bad reed valve reed decent compression but not run.

9/4/08 5:38 p.m.

I haven't worked any any of these Suzuki engines, but plenty of Yamaha RD's. If you get serious about troubleshooting the engine, I would take it to a motorcycle dealership familiar with working on twin-cylinder two-stroke engines and have them perform a leak-down test. There are probably four seals on your Suzuki's crankshaft and anyone of them can cause problems if damaged. Depending on which seal is damaged, a vacuum or oil leak will result and you'll never get the engine to run right until fixed. You should also check for stuck piston rings on the cylinder with low compression. Very common on these types of engines and especially one this old. Since you put in new plugs, I would pull them and read their color for rich or lean conditions. On an old bike like this, there are so many things to check.

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