Commando rebuild help with possible ignition issue

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Hey everyone I’m hoping for some input. I just recently rebuilt this project 850 Commando .
It’s all back together and runs and starts great except at 3-4K rpm it’s like it hits a rev limiter and just stays pinned at that rpm and won’t go any faster, doesn’t matter what gear it’s in. It has old Boyer electronic ignition that came with the bike…. Im thinking it’s the Boyer ignition but would like opinions of the more experienced before I buy a new one. I also think it has an old Tympanium regulator if that was With it if that matters. Here is how the bike turned out

Any inputs is appreciated. Thanks!
 

baz

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It could be Boyer related
The connections on a Boyer have to be tip top
As does the earth on the top of the motor
And the battery/ charging system
Most electrical problems are fuel and vise versa
So check the carbs aswel, maybe a needle dropped down etc
A lot of people turn the choke lever the wrong way , should be cable tight for off just incase you don't know
There are lots of things it could be
You are going to have to work your way methodically through it
Cheers
 

ashman

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Nice work you done as for the ignition could be a lot of things, old Boyers can be reliable and I ran one for 34 years and was still going when I replaced it, your timing could be out, could be carbs, could be faulty coils, could be the pick up wires shorting out, could just be something simple like a loose wire or bad earth who knows, I be going though everything before replacing things, anyway good luck with fining the fault.
 
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Good eye on the choke, I did not realize It has been full on but makes sense as I felt it was running rich. Coils are new. Has all brand new wiring harness,I did wire negative earth because of the LED lights so I’m pretty confident about wiring I’m less confident about the old electronic ignition and carbs. I will correct choke and see what that changes since it it obviously incorrect.
 
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Also I’m confident timing is correct. That’s what I thought the issue was at first
 

Derek Wilson

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I have had this exact problem with a few Boyers in the past. It is definitely the Boyer.

Which version of Boyer do you have? If it is not a Mk4, it is well worth the upgrade to a Mk4, or if you have the budget, a Trispark.

FWIW
 
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How do I tell what version of Boyer I have? If it’s not choke or carb related I was going to swap the old Boyer for Trispark… do they play well with Tympanium Regulator or would I need to swap that as well?
 

L.A.B.

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It’s a micro mklll

Assuming you checked the ignition timing with a strobe then did it advance to 31 degrees BTDC?

However, you need to check if you could have been riding with the choke on if you are not sure.
 

johnm

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I have found that the choke levers sold these days seem to slowly move and close the choke unless they are screwed down so tight that they basically cannot be moved with fingers.

So either you have a choke you can adjust to start the bike but it keeps moving closed over an hour or so running.

Or it's so tight it can't be used.

I have yet to solve ths issue.
 
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Assuming you checked the ignition timing with a strobe then did it advance to 31 degrees BTDC?

However, you need to check if you could have been riding with the choke on if you are not sure.
Yes I set timing with degree wheel and strobed to 31 degrees.

I was 100% running with choke on so that’s the first thing to correct and so how it runs.

Thanks for all the suggestions I’ll report back after I correct the choke
 

baz

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Yes I set timing with degree wheel and strobed to 31 degrees.

I was 100% running with choke on so that’s the first thing to correct and so how it runs.

Thanks for all the suggestions I’ll report back after I correct the choke
It's just the choke then
By the sounds of it, not unusual
Cheers
 

cliffa

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Nice job z3ro. A well documented problem with the Boyer on Commandos is the the wire strands in the fly leads to the pick up plate breaking due to the engine jumping around on the ISO's. This causes bad running at the sort of revs you are experiencing. They are definitely worth checking anyway. See here for one thread on the subject:


Cheers,

cliffa.
 
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I have found that the choke levers sold these days seem to slowly move and close the choke unless they are screwed down so tight that they basically cannot be moved with fingers.

So either you have a choke you can adjust to start the bike but it keeps moving closed over an hour or so running.

Or it's so tight it can't be used.

I have yet to solve ths issue.
I have not purchased a "modern " choke lever. The old ones work fine with disassembly and synthetic grease to all moving parts and a large screwdriver top screw tightening up to quite tight. The drop downs for me too happened until I did this. Now never.
 

johnm

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I have not purchased a "modern " choke lever. The old ones work fine with disassembly and synthetic grease to all moving parts and a large screwdriver top screw tightening up to quite tight. The drop downs for me too happened until I did this. Now never.
Hi. Yes I have tried what you have recomended but unfortunately no success.

I made this suggestion because I have several times set the chokes fully open but then after 10 mins riding found ithem partially closed.

This may be the OPs problem
 
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Hi. Yes I have tried what you have recomended but unfortunately no success.

I made this suggestion because I have several times set the chokes fully open but then after 10 mins riding found ithem partially closed.

This may be the OPs problem
Yes, I can see this being the possible issue. Remove the chokes to find out.
 

johnm

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Yes, I can see this being the possible issue. Remove the chokes to find out.
Hi. Your suggestion promped me to go out into the shed and clean regrease and try again. I also bent the stainless washer a little more to increase the friction.

Tightened the centre screw so I could barely move the choke lever and worked the choke about 5 times. The centre screw is undoing as I work the choke. After 5 cycles the screw is so lose the chokes drop under their spring tension.

However I also went through my box of bits and found an old choke lever. So shall substitute it.

There will be some (many) who will say remove the chokes completely but I have been down that road and my bike likes the choke on a cool day.

Thinking this through there is clearly an issue with this lever. The screw should sit down on the upper section and clamp it to the lower piece. Leaving a gap for the lever to move between the upper and lower parts damped by the friction of the spring washer. The lever action is undoing the screw therefore it must be contacting the upper section.

I'm going to have to pull it apart again and inspect it more closely.

Sorry to somewhat sideline this thread but the choke may actually still be the OPs problem.
 
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