750 occasional problem - Boyer to blame?

Hi all

I have a 750 with Mikuni single carb and Boyer electronic ignition. Compression is good and I don't have any bad oil leaks. Until recently the bike has been going well.

The past couple of times I have been out there has been an intermittent problem - sometimes as I approach a junction and throttle down the engine will start to falter, as if it is going to die. If I rev it sometimes it backfires and sometimes it chugs, but then recovers and idles well. Oddly it doesn't happen everytime and there doesnt seem to be any particular thing I'm doing for this problem to happen.

The bike pulls well all through the rev range with no problems or hesitation.

I thought that I might have some crap in the carb so I stripped it and blew it through, there didn't seem to be any blockages, and I still have the problem intermittently as before so I don't think its a carb problem. The manifold and fixings are all tight and good.

I haven't done any work to the bike which I can think would make this happen, I'm wondering if it might be something to do with the Boyer equipment...anybody got any thoughts on what I might do next? (One option which I was considering anyway is fitting a tri-spark unit since the Boyer unit is so voltage sensitive! I keep the battery on the optimate all the time to make starting a bit more guaranteed)

Thanks

Alex

At the risk of stating the obvious it does sound like an electrical fault, backfiring etc. May not be the Boyer though, could be any connection from the batt + or -, kill switch, ign sw, coils etc. Boyer timing cover connections are the favourite start point. Mine did a similar thing years ago and because the wires were tight the fractured joint only gave trouble under certain vibration/rpms. The Boyer could be going down as could a coil itself. Tell us what you find!

Also check the battery, if its getting old it may not be giving out 12V as you brake to the lights with the brake light on.

Pay good attention to the wires were they go through the timing cover,actually pull the connections apart the wires go hard and brittle and fall apart

Alex,

A common problem with the Boyer is the wires from the pickup coils break from vibration. When this happens the indication is very similar to the problem you described. These wires break inside the insulation, so a visual inspection will not show the break. Once either wire parts, the vibration at a certain RPM range will cause a misfire, usually in the low end up to about 3000 RPM. Check for continuity with an ohm meter. Wiggle the wires with the meter connected.

Thanks to all for the help so far.

The battery is good...bought new last year, kept happy on Optimate, checked with electronic battery condition metre last night and no problem there.

Going to go through all of the wiring connections next and will post the result. Managed to get a blast around Oxford yesterday evening as the sun was setting, hardly any traffic on the roads - sublime - makes up for the problems.

Alex

Alex; JimC might have the answer for you. I had exactly the same thing happen on my roadster. After fixing the wire which had broken inside the insulation, I glued a piece of soft foam to the inside of the cap so it lightly presses on the leads and keeps them from shaking. Good luck.

old grey biker said:

Thanks to all for the help so far.

The battery is good...bought new last year, kept happy on Optimate, checked with electronic battery condition metre last night and no problem there.

Going to go through all of the wiring connections next and will post the result. Managed to get a blast around Oxford yesterday evening as the sun was setting, hardly any traffic on the roads - sublime - makes up for the problems.

Alex

Click to expand...

Had a similar problem years ago ended up replacing the coils and that cured it.