Commando starting and running problems

Possible can of worms here! Could be electrical but sounds more like carb settings. Unless the Boyer or its leads are sitting right on top of a coil there should be no conflict. My Atlas had a twin output coil by the headstock and the Boyer just 3" away and it worked fine.

The rough running could be due to Float level issues, Pilot Jet problems, wrong Needles and so on apart from the Main jets, which only chime in at bigger throttle openings. I can not understand why the new Carbs would also run rough unless the settings are way out or there was an electrical problem. Could be duff leads in the Pick-up Plate. Also check every single wire/connection. There might be one loose or broken somewhere.

My suggestion would be to try and borrow another Boyer system and coils to check out if all the chunks are working correctly.

Attachment gives big twin carb settings. Note that generally the Commando 750 used 930 carbs with 220 main jets and 106 needle jets.

I'm no commando expert but If adjusting the carbs makes no difference I'd suggest there's a good chance it's electrical, have you checked the spark, timing and operation of the advance retard?

Dan

Is it possible that the valves are out of adjustment?

Or that a valve seat/head is burnt? Have you checked compression on both sides?

Mike

what Ho,

I had a similar prob Dave Evans cured it with a Mikuni. A future investigation showed a blocked or partially passage behind the air screw. The carbs were Amal Mk !âs

I wouldn't expect the Premier carbs to suffer from blocked airways because they can be accessed via the blanking screw opposite. Strobing the ignition would reveal any problem with the boyer advance and eliminate a potential problem. Strobe with the bike on it's wheels and not on the centre stand. Get a buddy to operate the throttle, while you get down with some earplugs in and pray to the timing god. A compression check would be worthwhile also.

Is there any possibility that the leads from the Boyer box to the pickups have become reversed ? This appears to cause problems with the auto-advance function.

Difficulty starting and rough running at low revs may indicate an over-advanced situation.

If you haven't replaced the wiring from the pickup then that would be my starting point. If the cables are breaking internally then just re-positioning them can be enough to cause the strangest of symptoms.

Previously richard_payne wrote:

Is there any possibility that the leads from the Boyer box to the pickups have become reversed ? This appears to cause problems with the auto-advance function.

Difficulty starting and rough running at low revs may indicate an over-advanced situation.

If you haven't replaced the wiring from the pickup then that would be my starting point. If the cables are breaking internally then just re-positioning them can be enough to cause the strangest of symptoms.

If the pickup wires are reversed the unit will not advance the spark timing as the engine speed raises. A simple check if you have trouble following the wires or doubt the unit is working is to check the timing with a strobe light an you should be able to see the timing move with engine speed plus check it is correct at same time.

Now Richard reminds me of a issue I had with my Boyer a few years ago. Being a smart-arse I soldered a couple of solid copper wires (insulated) from my boyer stator to a domestic chocolate block screw connector diagonally across the stator to eliminate the possibility of the wires coming adrift from the stator. This setup just wouldn't run right. The bike was sick as a seaside parrot with ignition timing all over the place. reverting to standard stator wiring solved the problem. Might save someone a lot of time.

Previously richard_payne wrote:

Is there any possibility that the leads from the Boyer box to the pick-ups have become reversed ? This appears to cause problems with the auto-advance function.

Difficulty starting and rough running at low revs may indicate an over-advanced situation.

If you haven't replaced the wiring from the pick-up then that would be my starting point. If the cables are breaking internally then just re-positioning them can be enough to cause the strangest of symptoms.

If the only fault is a reversed pick-up lead to a Boyer (or RITA) then the advance curve is cancelled and with fixed retarded ignition bike will be hard to start and revving up will be very sluggish, but the two cylinders will show the same sympton ie it will be on both cylinders the same. Certainly swapping the pick-up leads is quick and easy or as it says here, have a good look at the advance (or not) with strobe and engine running.

I have never had any issue with the position of the Boyer amplifier and coils. Again if you can get it running at a steady speed waggle all the wires/connectors especially the pick-up, any dodginess will seen show up in a dead engine.

AO

not got a commando but i have had a battery give similar running problems on my es2 with a thorspark igniton fitted no tick over wouldnt rev ect i eventually traced it to a bad connection of all places within the battery the terminal had come loose where it connects to the cell it would show correct voltage charge up ect but failed under load.

I had a similar problem in 2014, My MK III(with Boyer) ran really roughly, left cylinder ok, the right banging and stumbling.I tried the usual stuff, swapping coils, leads, and removing/cleaning carbs, replacing the leads& the same cylinder consistently & frustratingly played up after a few miles.

I had to remove head to get new guides fitted, soI put everything back together and addednew coils. On restarting it was obvious thebattery was cream-crackered& determined to break my ankle (battery showed charge & had a2 day top up on the optimizer whilst re-assembling). I stopped kicking before self harming& purchaseda new sealed Yuasa battery; started first kick after charging &, touch wood, no problems since then.

I suspect that myproblem was that one of the coils was breaking down (they were nearly 15 years old), exacerbated by a failing battery (again >10 years old),

I'm no expert on electrickery, could it be that the exhausted battery only just holds 'enough'charge and is rapidly drained by starting & test running (like theAA batteries lurking in the kitchen drawer that work inone's torch the first night ofcamping for about 10 minutes, then rapidly dim to leave one in stygian blackness!).

How was the battery left whilst you were re-commissioning? Could it be that it is just too discharged & now cannothold enough smoke to keeprunning. Iircthecommando engine 'borrows' from the battery up to about 2.7k rpm, and only above that does it commence repayment (those who know will correct me!), I used to top the battery up frequently with theoptimizerwhen commuting from Kingston to Lewisham, because there were few places en route to really get therevs up.

Just my 2p's worth, good luck!

Mike

Hi Steve,

I`ve been down this road myself recently & all the bloody side streets as well. In the end mine turned out to be the crap quality fuse holder on the new wiring loom i`d fitted, not having enough contact area therefore not passing enough current to keep the Boyer happy despite the voltage being ok. The arcing caused blackening on the ends of the fuse & overheating which eventually showed the cause up. I chopped out the new fuse holder & stuck the old one back in. Worked for mine so might be worth a look at as it only takes a minute.

Good luck, Al.

Boyers are extremely fussy about the wiring - especially on the low tension side. Personally, I would not own one unless all the connections were soldered - that is, no bullet connectors of any kind. Been there, done that!

Steve, going through the thread from the start again you may have a problem with fuel flow from the tank. Getting it running reasonably then having it start to misfire smacks of running out of fuel on that side. If you have drain plugs in the float bowls you could remove them (one at a time)and see what rate of fuel delivery you have. You could have a blocked tap or a float needle issue. Lets put some figures to this. lets say 60 mpg = 1 gallon in an hour so 1/60th of a gallon in 1 minute on 2 carbs. 1/120th of a gallon in one minute on each carb. 1 Gallon= 4.545 litres =4545 cc divided by 120 = 38cc in one minute.

So check if your fuel system delivers at least 38cc to each carb float bowl in a minute. seemples