new member, exhaust pipe colours?

teddy boy · Dec 25, 2008

Found a 74 850 in a garage, hadn't been started in 5 years.
15.000 on the clock, unmolested example, exept for Boyer.
Fiddled with it, and finally running pretty well.
Installed 2 new exhaust pipes as orig. crossovers were cracked.
Anyone know why right side pipe went very blue immediately as if its very rich. and left side stayed clean chrome, and is cool to the touch at low revs. warms up on revving but not all that hot. as if its too lean.
Pulled right side plug lead whilst running, bike wants to stall, pulled left side, and almost no difference in idle, as if left side is not firing.
Once revved up and running, bike runs well and idles well at about 1300.
Checked spark to plugs, good.
Right side plug is perfect colour, whilst left side looks whitish, as if too lean.
Checked timing, adjusted valves, cleaned carbs, swapped mags, no difference, all seems fine. Installed new plug leads. and new plugs. right side still perfect colour. left side still whitish.
Getting about 45 mpg around most roads.
Could I have a cam going bad? If its not spark, not fuel, then what?
Any clues would be most appreciated, been reading the forum for a good while and what a wealth of info!!

JimC · Dec 25, 2008

I'd bet you 5:1 you've got a bad wire from a pickup coil on the Boyer board. These little buggers break inside the insulation near where they are soldered to the board. I wouldn't troubleshoot anything else until I was satisfied this is not the problem.

mcns · Dec 25, 2008

Sometimes a spark plug will show spark when it is not under compression, but when you put under compression it won`t.

teddy boy · Dec 25, 2008

JimC said:
I'd bet you 5:1 you've got a bad wire from a pickup coil on the Boyer board. These little buggers break inside the insulation near where they are soldered to the board. I wouldn't troubleshoot anything else until I was satisfied this is not the problem.

Hi JimC: excellent clue! When I first go the bike, it would not start no matter what I did. So out of curiosity, cracked open the Boyer cover and began fiddling with the wires. One instantly broke off in my hand. Re solderd that, and got the bike to fire immediately.
All my mates have points on their Commandos, and are not familiar with the Boyer,
so thanks to you, I'm going back into the Boyer and see if I can find another bad wire connection. cheers. Teddy Boy

teddy boy · Dec 25, 2008

Hi MCN : are you saying then, I could have a bad plug? I have tried at least 4 different new plugs with the same results
thanks. Teddy Boy

BillT · Dec 25, 2008

I agree with the bad spark plug hypothesis. How were you checking for spark? By pulling the plug or pulling the lead? If you pull the lead, you should see an immediate difference in engine idle, and hear the arc of the lead as you reconnect it. If you hear a consistent arc but no improvement in idle, the plug is bad or wrongly gapped. Did you try swapping plugs between cylinders? If the plug is bad, your problem will migrate to the right cylinder.

The richer the mixture, the cooler the engine will run. Pipe turning blue right away generally means correct to slightly lean mixture. Since your left pipe hasn't turned, you're either running really rich, or not firing correctly.

Remember, a Norton will run OK on just one cylinder.

teddy boy · Dec 25, 2008

BillT said:
I agree with the bad spark plug hypothesis. How were you checking for spark? By pulling the plug or pulling the lead? If you pull the lead, you should see an immediate difference in engine idle, and hear the arc of the lead as you reconnect it. If you hear a consistent arc but no improvement in idle, the plug is bad or wrongly gapped. Did you try swapping plugs between cylinders? If the plug is bad, your problem will migrate to the right cylinder.

The richer the mixture, the cooler the engine will run. Pipe turning blue right away generally means correct to slightly lean mixture. Since your left pipe hasn't turned, you're either running really rich, or not firing correctly.

Remember, a Norton will run OK on just one cylinder.

Bill: I pulled the left plug lead off whilst bike was idling, and it made almost no difference in the running of the bike. Then pulled plug out of cylinder with lead intact, and did get a decent spark at the plug.
Pulled lead off right side and bike almost stalled. Tried a second and third plug on left side, made no difference. Did not try swapping plugs.
So I have been running the bike like this for about 500 miles. Every time I check the left plug its whitish in colour, instead of that nice light brown from the right side. Seems like the bike runs ok like this, as I can keep up with other Commandos, as if on higher revs I'm getting power, but how can this be? Thanks for any additional info.

Jeandr · Dec 26, 2008

teddy boy said:
BillT said:

I agree with the bad spark plug hypothesis. How were you checking for spark? By pulling the plug or pulling the lead? If you pull the lead, you should see an immediate difference in engine idle, and hear the arc of the lead as you reconnect it. If you hear a consistent arc but no improvement in idle, the plug is bad or wrongly gapped. Did you try swapping plugs between cylinders? If the plug is bad, your problem will migrate to the right cylinder.

The richer the mixture, the cooler the engine will run. Pipe turning blue right away generally means correct to slightly lean mixture. Since your left pipe hasn't turned, you're either running really rich, or not firing correctly.

Remember, a Norton will run OK on just one cylinder.

Click to expand...

You could have a weak coil, come to think of it, make sure both coils are 6 volts and connected in series. As mentionned, you can just exchange the plug wires from side to side since they both fire on each revolution (can't do that with points). The trigger coils eiter work or they don't, there are only two wires coming out and these give a signal once per revolution of the crankshaft.

Jean

Bill: I pulled the left plug lead off whilst bike was idling, and it made almost no difference in the running of the bike. Then pulled plug out of cylinder with lead intact, and did get a decent spark at the plug.
Pulled lead off right side and bike almost stalled. Tried a second and third plug on left side, made no difference. Did not try swapping plugs.
So I have been running the bike like this for about 500 miles. Every time I check the left plug its whitish in colour, instead of that nice light brown from the right side. Seems like the bike runs ok like this, as I can keep up with other Commandos, as if on higher revs I'm getting power, but how can this be? Thanks for any additional info.

L.A.B. · Dec 26, 2008

But, if it was an ignition/plug problem, I'd expect the L/H plug to be wet, if it's not firing properly?

Any Amals that have been left for long periods could need their pilot systems thoroughly cleaned? http://www.jba.bc.ca/Bushmans%20Carb%20 ... html#PILOT

L.A.B. · Dec 26, 2008

teddy boy said:
Pulled right side plug lead whilst running, bike wants to stall, pulled left side, and almost no difference in idle, as if left side is not firing.

Pulling the plug caps off with the engine running can damage the coils and electronic ignition system, so it's not advisable.

JimC · Dec 26, 2008

Teddy,

Re-soldering the Boyer pickups is a temporary fix, at best. The problem being solder wicks up the wire some distance. This portion of wire then becomes solid. The continual flexing of the wire caused by the vibration causes it to break. A more permanent fix is to crimp small ring lugs to the original points wires (the ones going to the black box). Remove the two short wires from the board. Drill a small hole (3/32") in the board where the pickup coil wires exit and use a #4-40 screw and nut to attach the ring lugs. There are probably more sophisticated connections to use, but just be sure not to use solder on the two wires connecting to the Boyer board.

new member, exhaust pipe colours?

teddy boy

JimC

mcns

teddy boy

teddy boy

BillT

teddy boy

Jeandr

L.A.B.

Moderator

L.A.B.

Moderator

JimC

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