motovita Posted September 17, 2009 Report Share Posted September 17, 2009 (edited) 3 weeks ago I picked up a 199A (1978 or 9 350) to try my hand at vintage Trials. I got a very well used example but it started right up and seemed to run fine. I rode it almost daily as I replaced various rotting rubber parts, missing fasteners and such (including a new air filter). It always started easily and ran well. Last weekend was our premier at a local vintage Trial. We both were doing well,considering our respective age and condition (me and the bike). After the 19th section as I rode slowly between sections the bike died as if running out of fuel or fowling a plug, not a clean cutoff like hitting the kill switch but a brief on/off, trying to stay running before dieing for good. I pulled the plug, it didn't appear fouled but I installed a new on anyway, that didn't help. I pulled the floatbowl off (stock Bing) didn't see any problems so I pulled the pilot jet cleaned and reinstalled it, still wouldn't start. Then pulled the new plug out to check for spark, big fat spark. tried flooding the carb a bit and checked the plug a couple more times still nothing more than an occasional pop or two. Now I've got it in my shop. I've cleaned the carb, it is immaculate and in good condition, other than some visible wear on the jet needle, but it ran fine. The float valve works properly and the float level is good. I removed the exhaust and checked for obstructions, verified both primary and secondary compression and vacuum. The piston and rings look fine through the intake and exhaust ports. I checked the timing, 2.5mm BTDC with strong looking spark at the plug. Just to be thourough I removed and inspected the points and reset the timing. Every thing looked fine. Everything checked out so I replaced the fuel. Still the bike won't even try to start. I'm at a loss. I can find no reason that this machine won't run. Apparently there is something I don't know about making a simple two stroke run. Please help, I feel both impotent and ignorant. Edited September 17, 2009 by motovita Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted September 17, 2009 Report Share Posted September 17, 2009 How exactly did you check the timing? And the spark? Quote Link to comment Share on other sites More sharing options...
motovita Posted September 17, 2009 Author Report Share Posted September 17, 2009 (edited) Spark is at spark plug while grounded against head. Timing set with dial indicator and cellophane to show opening of points. I initially tried to use an ohm meter to verify point opening but the current flows back through the primary coil to ground making this method unuseable unless I first disconnected the wire from the points. Edited September 17, 2009 by motovita Quote Link to comment Share on other sites More sharing options...
feetupfun Posted September 17, 2009 Report Share Posted September 17, 2009 Is the fuel in the float bowl getting mixed with the incoming air? You haven't said if the plug is getting wet or not. If the plug isn't getting wet by you trying to start it, then the fuel is not getting mixed with the incoming air. You also didn't mention checking the pilot air passage for a blockage (old filter foam maybe). Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted September 17, 2009 Report Share Posted September 17, 2009 Spark is at spark plug while grounded against head. Timing set with dial indicator and cellophane to show opening of points. I initially tried to use an ohm meter to verify point opening but the current flows back through the primary coil to ground making this method unuseable unless I first disconnected the wire from the points. Best to do this with a simple bulb set up, you have cleaned the points of course, sandpaper style? Quote Link to comment Share on other sites More sharing options...
wayne_weedon Posted September 17, 2009 Report Share Posted September 17, 2009 I would recommend you change the condensor and put fresh crank seals in it even if just to remove those from the equation. Both are simple parts likely to cause much frustration for no known reason! On Bults laid up for a while I have also seen sticky points pivots cause severe frustration! Wayne.... Quote Link to comment Share on other sites More sharing options...
motovita Posted September 17, 2009 Author Report Share Posted September 17, 2009 Is the fuel in the float bowl getting mixed with the incoming air? You haven't said if the plug is getting wet or not. If the plug isn't getting wet by you trying to start it, then the fuel is not getting mixed with the incoming air.You also didn't mention checking the pilot air passage for a blockage (old filter foam maybe). Pilot passage is clean (immaculate carb) as is the enrichener circuit. It seems the plug is getting slightly wet but as much as I've kicked it it could be wetter, but I've also put raw gas in the venturi through the air filter boot and a small amount down the spark plug hole (seperate attempts) with no effect. I've checked crankcase vacuum by holding my hand against the carb mount. It seems strong but I have neither a gauge nor a specification to measure it against. Float bowl vents are also clear. Can you suggest anything that might cause the crankcase not to draw fuel? Today I will get some ether and see what effect that has (I'm quite desperate at this point). I will also find a condenser and replace it although I don't see how that can be the problem since I'm getting spark at the plug. Any more ideas? Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted September 17, 2009 Report Share Posted September 17, 2009 Are the earths all ok, no wires getting trapped, lighting circuit in or out? Quote Link to comment Share on other sites More sharing options...
motovita Posted September 17, 2009 Author Report Share Posted September 17, 2009 Points have been removed, inspected and tested with an ohm meter. They are clean and work fine. Quote Link to comment Share on other sites More sharing options...
motovita Posted September 17, 2009 Author Report Share Posted September 17, 2009 (edited) Best to do this with a simple bulb set up, you have cleaned the points of course, sandpaper style? Do you disconnect the points then? Or do you watch for a variation in the bulb when the points open? The lighting coil is still there, although there are no lights. There are two wires (green and yellow I believe) that are spliced together and dead ended under the gas tank. Curiously one seems to come from each coil. I've always thought of lighting and ignition coils as being seperate. There is also a second, parallel wire run from the moveable side of the breaker to the condenser, which is mounted up under the tank. This second wire seems superfluous to me.Of course I have spark and the machine ran fine for quite some time before it died. Edited September 25, 2009 by motovita Quote Link to comment Share on other sites More sharing options...
b40rt Posted September 17, 2009 Report Share Posted September 17, 2009 My moneys on the condensor. Quote Link to comment Share on other sites More sharing options...
motovita Posted September 17, 2009 Author Report Share Posted September 17, 2009 I'll find a condenser today. Can anyone tell me if the under tank condenser is stock? There is a mounting space for it under the flywheel as well. Quote Link to comment Share on other sites More sharing options...
wayne_weedon Posted September 17, 2009 Report Share Posted September 17, 2009 I'll find a condenser today. Can anyone tell me if the under tank condenser is stock? There is a mounting space for it under the flywheel as well. It's a common mod. Makes life easier when changing them and also will be in a cooler enviroment. You only need the one wire coming up from the stator to coil and a ground. Wayne... Quote Link to comment Share on other sites More sharing options...
motovita Posted September 17, 2009 Author Report Share Posted September 17, 2009 So I'm guessing that the second wire that is now running from the moveable contact to the condenser terminal was origanally intended to be a ground from the mag to the condenser mount. Would that be typical? Quote Link to comment Share on other sites More sharing options...
wayne_weedon Posted September 17, 2009 Report Share Posted September 17, 2009 (edited) The original Ground would of been a green wire if I recall correctly and would of started at the grounded ends of the stator coils and via the connector block terminated at the coil mounting bracket. LT was Black I think! and was connected to the points and the other end of the LT Stator coil. To make the ignition work you only need a Good Ground and the LT wire connected. Wayne.... Edited September 17, 2009 by wayne_weedon Quote Link to comment Share on other sites More sharing options...
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