I purchased a mk3 commando last year it has been off the road since the early 90's. I had a hole in the side of the gearbox iI could fit my fist through. I found a mk3 case and gears to rebuild and finally installed it in the frame last week. the wire harness was pretty butchered do to the PO deleting the the e start and all of the mk3 handle bar switches and other e start electronics for earlier simplified systems. So I purchased a new lucas mk3 wire harness and handlebar switches rebuilt the carbs cleaned out the oil and fuel tank and put new spark plugs in it. Today I tried to start it for the first time with no luck. The bike came with what I assume to be a very old boyer(PO said he had it on there since the late 70's). I made sure via boyers instructions that I had it wired properly. I am getting battery voltage from the w/y wire I connected to the cdi white wire. I am not getting any power to the coils. I checked the coils resistance with an ohm meter and I'm getting 2.1 ohms on both from the tabs and about 9k ohms from the primary where the plug wire attaches. What that mean the cdi is bad? or am I missing something? I am kinda on a budget so I really don't want to buy a new unit but I do have the original points plate with the points attached. How hard is it to revert to a points system? What would the steps be? I am new to British bikes but I have points on all my honda bikes. Thanks guys!
Mk3 project
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I suppose the ignition timing should be checked to verify that it is to specification.
Then check for spark at the plug, and check that fuel is getting to the plug.
Kick it over a few times with the plugs removed and the overhead valve rocker oil feed bolt loosened to verify oil is getting pumped up there.
Place your thumb (or compression gauge) over a spark plug hole while kicking and feel for that compression pressure.
Good luck.
Then check for spark at the plug, and check that fuel is getting to the plug.
Kick it over a few times with the plugs removed and the overhead valve rocker oil feed bolt loosened to verify oil is getting pumped up there.
Place your thumb (or compression gauge) over a spark plug hole while kicking and feel for that compression pressure.
Good luck.
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KevinS said:
That suggests the Boyer box is functioning but the pickup could be faulty? This can be caused by a wire breaking unseen inside the insulation often in the area where the wires enter the crankcase or failure of a soldered connection to the pickup plate.
http://www.tioc.org/boyer/boyertestnewweb.htm
KevinS said:
You'd also need the auto advance unit (AAU), two ignition condensers and a ballast resistor.
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Spark plug wet?
Remove the sparkplugs and put a couple ml of fuel (gas, ether, acetone, etc) in each cylinder. If the engine is mechanically sound and it has spark it will at least start, run and respond to throttle for a few seconds under this scenario. If it starts and runs only momentarily you can return to the carbs to sort out the lack of fuel supply issue. Or maybe you'll be fortunate and it may simply start and continue to run!
Yes I tickled the carbs a few times and fuel comes out within a second of doing so. I kept the needle position what they were when I pulled them out. I will try putting some fuel in the cylinders today. The bike is kind of hard to kick its pretty tight Im not really sure if thats the way it should feel I haven't had a norton before. I do have a 78' tiger 750 and it kicks a lot easier.
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Have you drained sump? hard to kick over could be it has wet sumped.should only be a small amount in sump,don't top up oil tank until you have done this otherwise bike will blow out excessive oil from breather
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should have also mentioned when you rebuilt gearbox did you put in upgraded layshaft bearing?
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KevinS said:
I just helped a friend get his `76 Bonneville running (rebuilt his carbs) and was amazed how easily it kicks over and started. Like kick-starting a 450 Honda.
Commando's are different animals for sure. I once tried starting my 850 (with an audience) after it had wet sumped a bit and the temp had gotten into the mid 30's that night and I my normally easy starting bike would not fire. Just couldn't spin it fast enough. My 140 lb friend couldn't even kick it through once. Later that day after it warmed to the 60's it started on the 1st kick (no audience).
Yes, remove the sump plug and drain out any oil (if you haven't done so already).
Makes it a real bitch to kick over especially if it's cold.
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KevinS said:
The only wires that should be connected to the coils are the Boyer box black and red, plus the connector wire (Boyer diagram).
Any existing white/blue or white/purple wires should be completely disconnected, however, due to the fact that you said you get sparks when BY and BW are touched together suggests there may be nothing amiss with the coil wiring, but as yet, you haven't reported back if there is a problem with the pickup as I suggested or if you are also getting sparks when the engine is kicked over with the plugs resting on the cylinder head?
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