heeelllpppp!!!

[Reinald]

Started SWM after last week ends trial - she starts but is 4 stroking??? you know dom dom dom odm dom dom dom dom domm etc seemed to start clean but very quickly went to shit. Didn't wash her, no water at trial, good spark, checked carb bowl and squirted carb cleaner thru orifices - one drop of water swmimming around in there. Still "4 stroking". Taking clutch off to look at inlet as this is sort of how it runs when it had the leaking manifold but worse but not as much smoke. No change. Plug is blackish but big powerful consistent spark. Got airbox apart as it was like there was a rag in there but its fine????
Tried isolating kill switch - could points or condenser just go like that - they were both new !!

Any theories???

[TriCub]

A bit hard without hearing it but is the choke sticking on or is it flooded. Try runing it with the fuel turned off. See if it comes clean just before the fuel runs out then turn the fuel back on. When you say it 4 stroking, is it doing it all the time or only when the throttle is in a certain position?

[Reinald]

Thanks Tri club.
Transplanted carby from no. 2 bike - no change. Fresh spark plug no change.
It is running OK at idle [not perfect] try and open the throttle - runs crap - its not an occasional miss tho'??.

[sherpa]

Exhaust is not blocked, silastic in joins maybe?

[Geoff Lewis]

Hi There, Sounds like you should check that the flywheel key has not sheared throwing the timing out.Or perhaps some one slipped in a CZ motor while you weren't watching! Has all the symptoms.
Regards Geoff.

[TriCub]

As Geoff said check the flywheel key. Had a Aprillia in my shop once that the owners had put the disc valve back in the wrong place after some repair work and it would not rev at all much beyond 3000 to 4000 rpm. I don't think that the disc could go out of time without it coming of it's spline but you may want to have a look at through the inlet to check that the disc is still in one piece, I've seen them with big cracks in them.
The exhaust shouldn't block overnight unless someone stuck a spud up the pipe or you dropped it on a rock, could be worth giving it a run without the rear muffler to test the theory.

[FM350]

If you have replaced points/condenser recently, then the problem is almost certainly related to one of these parts. Pattern condensers are not that great quality, and often cause problems. If running good before you changed these parts, then clean the old points, and refit them as well as original condenser. If it runs ok then, get hold of genuine Bosch parts, and fit them, taking care to set timing carefully at same time.

[Reinald]

Thanks Guys,
@Sherpa - took end box off no change - checked mid box no blockage.
@Geoff - just checked flywheel key its fine. No CZ motor but I thought they were pretty reliable??? Least I know my flywheel puller works.
Induction thing may be probable. The disk was actually refitted one tooth different and it ran beautifully until this event. I believe for a very small time it started sweet and then went pear shape so the whole "it must have happened in transit" may be a furphy.
Seems unlikely now to be fuel or ignition [it will actually idles quite well and it doesn't stall under throttle] but it sounds like there is a rag in the airbox so maybe the induction disk is the next step as Tricub suggested. And fortunately I have another motor for bits.
The following is a quick video of it running - the throttle was opened at on the ninth second of the clip and it then ran out of fuel as the tank wasn't connected. Big throtlle openings are simply met with more induction noise and no big increase in revs.
https://www.facebook.com/video/video.php?v=10150996090729243&oid=251035327372
On Feet up funs [ thanks again for help Dave] suggestion I ran it for at least 7 minutes to see if it was fuel in the cases and I also undid bolt to expel any excess fuel. No change. Checked tank for water - no problems there.
Thanks everyone - at least I'm learning more about how these things may or may not run - will investigate rotary valve next.

[FM350]

If problem wasnt there before you changed points/condenser, its well worth looking carefully at both these things before messing around with the disc valve (which is almost always 100% reliable).

[TriCub]

Tried isolating kill switch - could points or condenser just go like that - they were both new !!

Condensers can fail just like that. Quite some time ago I had a condenser fail on my Maico MX bike and borrowed the condenser out of my Toyota ute to get through the day's racing.
Just had a listen to your video, sounds just like a Bultaco I worked on recently that the owner had neglected to re-connect the condenser which is mounted under the tank on his machine after an engine rebuild. It would start and sort of idle but that was about it.