CB400SF refusing to start

[AndyCB]

Hi

I bought a CB400SF NC31 1994 recently and have been having starting problems. Rode the bike home without any problems but bike completely refused to start several days later. After fitting a new battery and messing around checking a few electrical connections there was a backfire and bike started up fine after that. Put it down to operator error and a flooded engine. Wondered if carbs float valves leaking and turned off petrol tap when not in use after that.

Since then I changed the oil, coolant, filters and spark plugs. The bike has had little maintenance and has done few miles in the last few years. Took the bike out for a short ride and all was well running smoothly through to 8K (I am old and not been on a bike for a while).

Tried to start it last Tuesday and again completely refusing to start doesnt not even offer to go. Starter spinning motor fine.

Had a look at it tonight in more depth.

Apparently no spark (as viewed one of my old plugs)

Coils measure 2.8 ohm - seems correct in Russian book.

12V getting to ECU (can be interupted by RUN switch)
All earths on ECU seem to be in order. One switched via neutral. One switched via side stand.

Problem might be the Pulser. This seems to measure a high resistance 28Mohm and book suggests 400-500 ohm.

Does anyone have an experience of the pulser unit failing?

Should it read 400 ohms all the time - not really sure how it works thought it was magnetic but there seems to be some sort of cog shown on drawing.

Do I need to drain the oil to take the cover off to get at it?

Will I need a new gasket?

Have spotted one on the usual action site although the web suggests it might be possible to fit a pulser off another model if I can't find a used one from a CB400SF.

Any thoughts?

Andy

[SevenThreeSeven]

If the ohm reading truly is high (if your multimeter testing was done properly) I'd be inclined to bet on compromised wiring rather than a faulty pulse generator. The pulse generator is just a small magnet wrapped from one end to the other in copper wire to create a magnetic monopole. Usually the whole thing is encased/sealed in plastic resin at the factory. There's simply nothing in there that can come loose or get broken.

The delicate part of the pulse generator is the pair of wires connected to it. On the Bandit 400s and GSXR 400s these two wires come up out of the rear end of the engine's left side cover and they are very easy to accidentally hit or bend or yank and the wires themselves are tiny, just a few strands of copper really.

I'd take off the engine's left side cover and carefully inspect the pulse generator wiring all the way from the connector plug back down to the pulse generator itself. On my Bandit 400 I've learned that I can do this without having to drain the engine oil. All I do it lean the bike as far to the right as I can, against the garage wall, then I take off the cover. If you take off the left side cover with the bike leaning left (on its side-stand) oil will come pouring out of the engine.

[AndyCB]

Thanks for the info SevenThreeSeven, great to know there is help out there to keep these bikes on the road. Must admit I was considering a Bandit then then Honda appeared on Gum. Bike is currently outside under cover so not ideal for working on it. Tested pulser resistance at the plug\socket covered by a shroud behind the left side cover. Continuity back to ECU box looks fine. Might drain the oil out of engine before I take off the left hand engine cover, as you say there would seem to be little to go wrong with the pulser and I might barking up the wrong tree. Raining this morning so it will have to wait...

Andy