I have just acquired a 1970 Suzuki GT250, it had been laid for years with the old fuel left in it. The bike is a resto project, the whole fuel system was bunged up with a tar residue which took a while to clean tank, fuel tap, and both carbs. I rigged up a dummy fuel tank, fresh fuel and kickstarted the bike into life, it fired up on both cylinders lovely, posi lube system seems to be working fine. As it got warmer it just petered out dead. The spark plugs were wet through, Points cleaned and re-gapped same again and the warmer it got the the lest time running. With the fuel tank off i note the both coils the outer casings on both are cracked, indicating the internals have expanded and maybe the cause of the problem. Any thoughts lads ?
its been yonks since I tested a points and condenser ignition system. I would check the power and switching on the coils using a test light. but if I had new points and particularly condensers, I would have them on first as you will no doubt be renewing them anyway and new coils later during the rebuild.
Cheers bro, if the condensers were down it would still run, only under load would break down and cause burning up the points contacts Yes ? If the coils were breaking down inside as their external appearance would indicate the warmer they get the more chance of making and breaking the circuit inside ? Hard to test whilst running ?
you would probably need an oscilloscope to check it when it was running. I don't think the condensers are really affected by load In the same way the high tension side is. unless the carbs are doing something the longer it runs I would go with the serviceable items first
Portboy If you have a multi-meter capable of measuring resistance, you could measure the resistance across the secondary coil at room temperature, and then warm the coil with hairdryer/bath of warm water and see if there is a significant difference.
I just popped the the coils off the bike and done a continuity test both coils read within accepted ohms ?
I don't think i'll submerged them in water, the outer casings are cracked ! They both measured around 12k on secondary and 4 on the primary side. I will try and warm them up and re-check, thanks.
You would be lucky to get the bike to run at all if the condensers have gone T. You probably remember, if you get one start to go on a car it would pop and bang to begin with before refusing to work at all if you were lucky . They usually fail completely which is better than going intermittent. Anything that’s been sitting anywhere near damp nearly always ruins the condensers as it sucks all the moisture in between the plates causing corrosion and short-circuiting.
Coils when warm seem to be the obvious culprit but are here any obvious carb issues - float settings, leaks?
The initial start up was good, lots of smoke in the garage, ran for a couple of minutes , plug check wet through , each start after that got shorter, obviously wetted plugs are not helpful, just blew them off with compressor each time. After the carb strip down the right hand carb flooded on its own so a gentle tap on the float bowl stopped that.
Sounds to me like a flooding issue, but have no solutions further than you've done with the carbs short of complete rebuild? Any diaphragms on the carbs that could be split?
The carbs seem ok now no leaks, float height possible not changed it other than de-gunged everything was gummed in the carbs slides stuck in the bodies and every jet and orifice gummed up and cleaned through. Just took Chris's advise and warmed the coils up and a increase of 2k 12.5 cold and 14.5 warm is this acceptable ?
Resistance increases with heat, I'd expect a significant increase to be a problem to stop a spark? I reckon carbs is the issue, flooding somehow - maybe the slides are still sticky and running too rich??
as i stated i rigged up a dummy fuel supply, the tank fuel tap has diaphragm prime system incorporated within it, i blanked off the intake on the manifold to eliminate the air leak, the original tap has been cleaned but the original filter gauzes have split so have ordered a replacement tap minus the prime system as the original type are so rare, the only one i could source was in the states £200 no way.......
A hot water bottle full o boiling water laid over the top of your coils or condensers will warm them very nicely and keep them dry
