Tuning woes

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don

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Mar 19, 2005
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after a full resto job. (Atlas) some low down running/starting probs.
Modifications are, New Mk1,s with pilot jets fitted. Standard Airfilter. Boyer ignition using 12volt coils of unknown ohms resistance.
Once running, it runs well in the mid to high rev range. but starting is difficult and runs very poor in the lower revs. It certainly doesnt appear to be running rich down low. I,m wondering whether I should be using 6v coils. or whether I should ditch the pilot jets as was suggested to me once before. It seems like its a carb problem, but everything is new and I assembled the carbs myself ,making everything was clean.
 
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May 22, 2005
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Hi Don
You need six volt coils not twelve volt - that could well be your problem.
Also check the voltage being supplied to the Boyer unit with the engine running – it should be at least twelve volts for the boyer unit to operate properly.
Obviously I don’t know how old your boyer unit is but I threw away the one fitted to my Commando Mk 3 and fitted a Pazon sure fire unit
http://www.pazon.com/
Although the boyer unit was set up correctly I found I had much easier starting with the pazon unit both with the electric and the kick starter and the bike pulls much more strongly from lower revs with a much more consistent idle than the boyer ever gave.
I also know that others have fitted the pazon unit with equally dramatic results.
I hope this helps.
I must also add that I have no connections to pazon other than being a very satisfied customer.
 
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Mar 21, 2006
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Hi Don
On my 850 Commando I observed a lot of dynamic ignition timing scatter with the old Boyer. The advance ramped in almost immediately from very low revs (ie. 1100) and it appeared to be almost on full advance by 1500 and not much less at a rather uncomfortable 1000 idle.
I found the engine hard to fire up, although it never kicked back at me, luckily. The Boyer also seemed loathe to work if the battery was anything but fully charged.
Encouraged by Mike's experiences I also replaced the Boyer with a Pazon Surefire kit. The fitting instructions are good and the installation is neat. I timed the engine statically and fired it up. The exhaust note sounded different immediately and the engine responded well to throttle. However, I could not get it to idle until I opened the slides and weakened the mixture.
I then checked the ignition timing though the rev range. Whereas the Boyer had been dancing around 25/30 degrees even at idle, the Pazon ran at about 10. Thus it was considerably more retarded at low revs, which is why I had to open the throttle slides to compensate.
All this merely confirmed what I had suspected with the old Boyer - it advanced too soon and did not have a progressively increasing advance curve as the revs increased. The Pazon controls the advance curve properly and advances smoothly as revs increase, getting to full advance at around 3500.
On the road the engine is smoother and more tractable at low to medium revs, making it a much more pleasant ride. It is slightly easier to start (an 850 is unlikely to be easy) and I consider it to be a thoroughly worthwhile upgrade.
 

don

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Mar 19, 2005
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Well, the 6 volt coils didnt make any difference. Its a Brand new Boyer Ignition. Its charging at 13 volts but the battery only has about 10 or 11 volts ,so its on the charger now.
 
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Boyers need good voltage, so that could be the problem.
As for coils, I use a Kawasaki GPZ 550 coil. It's a dual output 12 volt coil which seems to work well with the Boyer. The HT leads are removable so you can make your own to the right length. ( unlike many japanese coils).
 

don

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Mar 19, 2005
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Even with a fully charged battery, still no difference, wont run under about 2,000 revs. Kicking it over it has a fat blue spark, I,m inclined to think that its a carby problem.
 
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Don, Presumably you have screwed the idle mixture screws out about 1 1/4 turns to give you a start position for your idle circuit. I forgot to do this once after a rebuild and had similar symptoms to the ones you describe.
 

don

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Mar 19, 2005
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Yes I checked that. I,ve just checked the pilot jets and they are fine. I,m at a loss. well give the leg a rest and carry on tommorrow. It seems like (maybe) its not getting enough juice at or off idle. Coz I really have to give it a good squirt of juice or easy start spray to get it to fire. Spark is excellent.
 
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Another problem I had which will give similar symptoms is if the Boyer static timing doesn't match the strobe timing. Mine was about 12 degrees out and was a beast to start and run until I got a chum to hold the throttle while I strobed the ignition, it then ran like a dream throughout the rev range. Perhaps if you don't have a strobe light to hand you could advance the ignition by 5 or 10 degrees and see if this is on the right track.
Dave
 
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<Coz I really have to give it a good squirt of juice or easy start spray to get it to fire.>

after seing this I would look for a vacume leak.


bill
 
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Dec 26, 2006
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1. Boyer needs 2 6V coils connected in series, or a 12V dual output coil. I like to use the Harley type dual output coil as they are fairly inexpensive and readily available.

2. Although you have new carbs, did you ensure that all the tiny orifices within the carb body were clear? Don't assume that just because they are new, that they are clean. Machine shops often leave behind "swarf" (residue left over from machining). I spray aerosol carb cleaner into one orifice and verify that it exits all the other proper orifices. Also verify that the float levels are correct. I have a regular routine that I go through every time I open up a carb, that includes checking all the jet sizes, check for proper needle type, and clip position, checking the float level, ensuring the float does not fowl on the float bowl gasket, making absolutely certain all the orifices are clear, ensure that the slide is correct and moves easily within the carb body. With dual carbs, ensure throttle pull is the same on both carbs.

Bought a 69 fastback several years ago with a single mikuni and Boyer on it. Just recently converted to dual amals and started it up with one kick. Had NEVER started it before then. Spent A LOT of time preparing carbs.
 

don

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Mar 19, 2005
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well, getting closer. the timing was out a bit. with it correctly adjusted it is running much better. I,ve checked everything iin the carbs. the only 2nd hand parts I,m using in the new bodies and float bowls is the old floats and nylon float needles which I dont see a problem with, as its not flooding. I think I,m nearly ready to fit tank and do some serious fine tuning , also maybe fitting the air filter may help a bit.
 

don

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Mar 19, 2005
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well, getting closer. the timing was out a bit. with it correctly adjusted it is running much better. I,ve checked everything iin the carbs. the only 2nd hand parts I,m using in the new bodies and float bowls is the old floats and nylon float needles which I dont see a problem with, as its not flooding. I think I,m nearly ready to fit tank and do some serious fine tuning , also maybe fitting the air filter may help a bit.
 

don

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Mar 19, 2005
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I havent tried new plugs ,. I dont think the new ones I,m using are faulty. Spark is excellent.
 
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Jun 3, 2005
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May or may not apply to you: Check the float bowl gasket and make sure the float pin has not worn a groove in the gasket.

My 72 Commando was giving my fits (mostly on idle or low revs) last year, I thought it was the ignition and went so far as to put in the dynacoil and the problem didn't go away. I finally went back through the carbs for the umpteenth time looking for some/any anamoly, as amal and this board has shown how critical the float level is. I finally noticed that the float bowl gasket had indentations from the float pin. I didn't think that was it, but after applying a temporary fix, that turned out to be the entire problem. I was not flooding, but the mixture had become rich enough to spoil the idle/low rpm's. My emergency kit now contains a pair of sealed float bowl gaskets.....
 
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Hi Don

I had aproblem with my 1972 750 commando. The owner before me had clamped up the coils to tight crushing the body, although they seemed to work well, there was a problem. I put in new boyer electronic ingniton unit with a single dual coil, checked all the wiring and strob timmed it.

It now start first time - full choke, flood both carbs and starts every time.

I also put in 2 new amal mark 1 carbs with a proper air filter (not open bell mouths) and tuned them to suit. I found one side was too weak and put in a small washer to lift the needle slightly making it a richer mixture.

I found that the new amal throttle stop screw keeps moving loosing the tick over so a sligth tap with a hammer on the outside of the stop screw housing tightens up the thread to hold the screw tight.

I hope this may help!
 
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Hi Don,
Are you sure the carb bodies haven't got the pilot jet brass bushes fitted? If you've fitted screw in pilot jets you'll be double jetting the pilot system.

I did have a similar problem, it turned out to be a Acel coil going down and cold fouling from an octane booster I was using.
 

don

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Mar 19, 2005
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surely if the(NEW) bodies had the brass bushes fited. then you wouldnt be able to screw in the jets?
 
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Jan 8, 2006
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Those "old Boyer" systems you talk of, would they be the same as a BY12 now available from Brit Spares as I am thinking of buying one and wonder if this is a mistake???
 
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