Pulling my Hair Out !! Help ?

OK chaps , Seasonal Greetings to one and all . Bah Humbug !
I need some thoughts on my 850 MK2 Commandos , two motors rebuilt by a "professional" that are just giving me endless trouble .......
(1) a new stock FullAuto head , PW3 cam , Boyer MK3 ignition , twin Mikuni 34 VM carbs , peashooter exhausts , I had this bike recently running on the dyno after the lengthy rebuild of the motor and complete machine , sorted the ignition and the carbs on the dyno , nice giving 58BHP . Got home , went back to work , week or so later ventured into the shed , the beast wouldn't start , eventually after some 3 hours kicking it fired up and ran nice and warmed thru it settled to a nice tick-over . Job done ( so I thought ! ) a week later , again the beast refused to fire up , after mucho macho kicking it came to life , but only on one cylinder ! After a bit of coaxing it fired intermittently on that pesky cylinder , then settled down and behaved . Another week passes , this time it refused to fire on the other cylinder ! Eventually after a massive flame from both exhaust and carb it ran , but was harsh . Started the beast eventually a bit later that morning , fired on both but one was giving very hot gas and a harsh thump from the exhaust , the other cylinder was much cooler gas and a much much softer puff from the exhaust .
Now , this is just the tip of the iceberg trouble these motors have given me over the last year or so and I'm almost at the point of throwing in the towel , needless to say the timing has been endless agony but was sorted on the dyno , the Mikunis I'm about to melt down and cast into a big finger but they did behave on the dyno and seemed sweet at last ( just toying with me I fear ! ). I've tried 3 different Boyer boxes and coils .......all the same result . I know what all the indications point too ( and the bleedin' obvious ), and they have been checked , checked again , changed and checked again add infinitum ...
And I haven't even started on about the other motor yet !
I need some help here please , before I really lose my rag ( can a motor really have some Ai ? I think these have and it's old Nick not St Nick ! ).

Hi Danno, either your gas is crappy or had been destroyed by any sealant in your tank.......just my two cents!!!
Who is that "ol' nick" ?

You said changed Boyer boxes and ignition coils. Have you checked the low tension leads at the reluctor (electronic points)? Boyer units are famous for the wire to break inside the insulation causing intermittent continuity. When this happened to me I connected an ohmmeter to the wires and pulled on them...lost continuity. Easy to replace the wire, but these will drive you crazy if you aren't looking here.

What did the guy who built the motors have to say on the subject?

J

auldblue said:

What did the guy who built the motors have to say on the subject?

J

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Yes, and is it cold where you are? Are you following normal start procedure? Using choke? Opening throttle? Flooding them? Maybe the plugs are fouling? Have you checked the plugs...replaced them?

Sticking valve?

zotz said:

Sticking valve?

Click to expand...

Maybe the engine builder used STP for assembly...

All of your symptoms are likely the result of partially fouled plugs.

Most likely the jetting is not right in the low speed ranges. Go to a leaner slide.

Low speed jetting on the dyno using an exhaust sniffer stuck in the end of a Norton muffler is worthless. At low throttle settings at least half of the length of a Norton exhaust is going to be contaminated with ambient air and give bad mixture readings. Modern 4 valve motors do not have this problem. Jim

Thanks chaps , I shall look into all of that .....again ! Plugs changed ( lots) , cold starting .....sometimes wants to go with choke , sometimes not.....mostly not at all ! . Will check out the low speed slides and jetting and definitely look into the pick-up wiring tho ...........my overiding feeling is it's somat stupidly simple that I've overlooked but can't see the wood for the trees at the moment .

"Now , this is just the tip of the iceberg trouble these motors have given me over the last year or so"
Dan,
what else is/was wrong with them? maybe that info could help the gurus here diagnose your starting issues.

Generally speaking if you've got fuel, spark and compression, the motor must start. If it doesn't, fit a pair of new plugs one heat range hotter than normal and start again. On rare occasions the carbon left on the plugs can become affected by the fuel when the bike is standing idle and start conducting. If it still doesn't start, then check out your ignition system for intermittent failure. If you have a No 3 slide in the carbs, you should be able to set the low running with the idle screws. If you have trouble starting, it might help to turn them both one turn richer. I usually get the motor running and warm and adjust them leaner until the motor hiccups, then back off slightly. I've never dyno tuned a motor so what would I know ? 'Rough as guts' ? You should remember you are in control and your bike hasn't got much of a brain - never tear your hair out, it is not worth it.

Hi , did you check if the pilot/idle jets are clear, and not clogged by any deposit (previous sealant or 'oldnick's hair beard)?

comnoz said:

Low speed jetting on the dyno using an exhaust sniffer stuck in the end of a Norton muffler is worthless. At low throttle settings at least half of the length of a Norton exhaust is going to be contaminated with ambient air and give bad mixture readings. Modern 4 valve motors do not have this problem. Jim

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Jim,

I take it this is related to the long stroke and time between firing strokes...is that correct? I've been thinking about putting an O2 sensor and gauge on mine...so would like to know before I get there. Would like to understand this better. The wideband sensor on your FI isn't effected by this, but a regular sniffer is? Does it help to get further up the pipe? Is it because the sniffer is only reading one exhaust stream?

Dennis

A while ago I got off my backside and took the Seeley to Winton for a practice. I blew a tyre on the trailer on the way which I fixed at the side of the road. When I got to the circuit, I unloaded all my garbage and the electric starter, fuelled up the bike and tried to start it - it was as dead as a maggot. Not even a cough, even with a fully charged battery, full tank of methanol, and plenty of compression. There is a pleasant young guy who runs a tuning business who decided he should help the silly old fart with his bike. He decided my problem was with the low running circuit in the carbs, so I watched him fiddle around with a screw driver on the idle screws, said nothing. Eventually I sent him home (around the corner) for a couple of new spark plugs and a plug spanner. Put 'em in and fired it up. Then told me other mate how to readjust the screws. I don't believe I've ever had both plugs simply drop totally dead prior to that. The bike had been standing for several months.

The O2 sensor sounds like it is an asset. I'll have to try that some time when I'm feeling very patient. ( I can afford to be sarcastic, With methanol you have twice the room for adjustment errors - with petrol it is much more critical that you get it right. It's the reason I never use it for racing. It's like women - 'once you go black, you never go back'.)

dennisgb said:

comnoz said:

Low speed jetting on the dyno using an exhaust sniffer stuck in the end of a Norton muffler is worthless. At low throttle settings at least half of the length of a Norton exhaust is going to be contaminated with ambient air and give bad mixture readings. Modern 4 valve motors do not have this problem. Jim

Click to expand...

Jim,

I take it this is related to the long stroke and time between firing strokes...is that correct? I've been thinking about putting an O2 sensor and gauge on mine...so would like to know before I get there. Would like to understand this better. The wideband sensor on your FI isn't effected by this, but a regular sniffer is? Does it help to get further up the pipe? Is it because the sniffer is only reading one exhaust stream?

Dennis

Click to expand...

Dyno exhaust sniffers are notoriously incorrect on a Norton because they only go 6 to 12 inches into the end of the muffler.

With the wild [stock] cam timing and unrestricted exhaust there is heavy pulsing in the exhaust which causes air to enter the end of the muffler and travel halfway to the exhaust valve. The air will cause false lean indications from the O2 sensor at lower throttle openings.

Dyno operators who are familiar with tuning a modern bike often do not take this into account. Cam timing like used on a Norton would be top fuel territory on a 4 valve engine.

To use an O2 sensor on a Norton you would need to have the sensor at least 6 inches in front of the muffler to pipe junction but behind the second bend to keep it from overheating from exhaust gas temp.

To use an exhaust sniffer at low speed you would need a tube at least a couple foot long and a pump to draw the exhaust up the tube. Note the length of the sniffer tube in my exhaust extractor. Jim

comnoz said:

With the wild [stock] cam timing and unrestricted exhaust there is heavy pulsing in the exhaust which causes air to enter the end of the muffler and travel halfway to the exhaust valve. The air will cause false lean indications from the O2 sensor at lower throttle openings.

Click to expand...

Wow! This is important information...I never would have thought this could happen. It makes sense though.

I was hoping to get closer to the exhaust valves. Originally thought about the crossover pipe (the stock one up by the head), but from what I can tell from the engine running the discharge is not consistent...don't know this for sure, but there seems to be something weird about how the exhaust moves with the crossover pipe. It's supposed to let the discharge go out both pipes, but observation says that is really not happening particularly at low engine speeds.

I'm starting to understand why your pipes are set up the way they are...good thing I haven't settled on pipes yet

Hi Dan, you said you had a PW3 , how far could it protrude outwards ? your Boyers magnets could be too close from the pick up stators.........at the end of that post, you will have a million of different advises, and no hair on your head !!!

Marina ....I'm almost bald ....just hanging on to the comb-over !

Where yer based Dan ?