Diagnosing a failed or failing pulse generator or CDI 1983 XL600r help?

Thanks in advance for any help. 


Back story: Complete motor rebuild, carb clean rebuild, clean tank, new fuel line, and will only pop but not start. 


Post rebuilt double check:  timing chain, crank, cam and timing alignment, and valve rocker gaps, all dead on. abusive compression as usual


electrical: coil 300 Kohms and sends a decent spark, impulse generator 0.300 kohms regardless of position (seams very low as spec is 500 ohms), cdi ohms readings flash a reading within factory spec but then go to infinity.


Syptoms: pops on kick over, but never starts. Some times back fires threw carb. It may pop twice but never starts. 



My guess: either or both, bad impulse generato and or CDI.


Any ideas from those who know?


Thanks, Andy




You are getting good BLUE spark from a plug when turning it over,,constant spark,,not just one spark then nothing...????


If it has good fire,,constantly........look at a fuel delivery issue...pour a little fuel in the cylinder or spritz it in THE carb inlet with a spray bottle while attemting to start it...



Edited by brianhare

Recheck those rocker gaps..Don't set them ridiculously tight..ie,,You want the feeler gauge to slide in and out between the two points reasonably easily..too tight will make for hard starting. Also try upping the idle screw knob one or more turns..sometimes helps with the initial start of the older twin carb 600s..Still no start then as Brian says I'd be looking at some sort of carb/fuel issue..What sort of rebuild/cleaning did you do on them..??. Seems to be a huge variation between what I associate with cleaning carbs and other peoples idea of it..eg..standard answer here is throw them in pinesol and soak them for a few days..That to me is not cleaning carbs,,half pie effort. :naughty: .All jets and associated pipes need to come out all passages need blowing out with compressed air and all small holes on all sides of all jets and tubes jets screw into need poking out with the strand from a wire brush..


Also be aware that front right rocker is always notoriously difficult to set due to the hand operated decompressor that works by actuating on it..Disconnect the cable so you know it's not somehow interfering with the gap and set it then,,once done reconnect the cable also making sure it's not crazy tight..It only has to be set so when you pull the hand lever it releases the compression..set it so it does that and it should be good..forget manuals on it and there recomendations..hook it up..test compression by attempting to kick the bike over..if solid pull the lever..if compressions relieved it's set right..


Bit of a ps..I have no faith in readings from ohm meters on parts, My repair method is to replace the maybe offending bit..Never had a pg fail on any XL/XR600 I've owned,,not to say it isn't possible..CDI's are cheap from Ebay..just get the correct one for whatever year the bike is though most are interchangable between years with a small amount of wiring messing about..What year is your bike???,,,whoops 83,, :banghead:  ,the oddball year with the round plug on the CDI and which also has that other valve in the head for a decompressor..

Edited by Horri

Make sure the little pin that goes in the head directly under the auto decomp on the cam isn't jammed down in the hole, dunno what the bloody thing does but I rebuilt a 600 a few years back and had all sorts off grief trying to start it (Similar sounding problem to yours) and it turned out to be that damn pin causing all the problems. 

Sounds just like mine but it was caused by the ACV.

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