Commando just won’t start

[Dave Harvey]

My 850 mk3 broke down, sounded very rough before it stopped I haven’t been unable to get it to restart. The bike is fitted with Boyer ignition, I have good compression on both cylinders, fuel is getting through and there is a good spark to both plugs but it will not start. I have reset the timing several times using the marks on the flywheel but it still refuses to start. Tried to put a little fuel in the carb and a plug holes also a squirt of brake cleaner when cranking and still nothing not even a pop or back fire. I have also set tdc through the plug holes also and turned the piston back 10 mm but nothing just won’t start.

 

[Schwany]

Try new plugs. I know that sounds like a simple bit of advice, but it works on occasion. I also know you said you have spark with the existing plugs.

 

[kommando]

Today's rubbish fuel will stop spark plugs firing inside, as @Schwany says first port of call is new plugs. If the Boyer is a MK3 black box then longer term you need a box that will over advance at low V's such as when cranking an electric start Mk3.

 

[o0norton0o]

Go back to basics.

Take the plugs out, put your finger on the spark plug hole and kick the bike. Did you feel compression against your finger? Now do the other plug hole... Same question??....

What do the plugs look like? are they chocolate or oily or bone dry? This might just be a hint which way to go

As a rule, substitution of parts is not the best way to troubleshoot, but in the case of spark plugs, it erases the previous visual condition of the prior plug completely and you get a look at the ignition situation inside the cylinder AFTER the bike crapped out on the new plug. Did it not fire and come out looking wet? << that would tell me you are chasing an ignition problem since the new plug shows fuel is present.

Do you have one of those handlebar kill switches ?? They can stick basically shorting out your ignition....

Gotta run.... good luck

 

[Dave Harvey]

Try new plugs. I know that sounds like a simple bit of advice, but it works on occasion. I also know you said you have spark with the existing plugs.

Thanks I have fitted new plugs but nothing joy.

 

[Dave Harvey]

Try new plugs. I know that sounds like a simple bit of advice, but it works on occasion. I also know you said you have spark with the existing plugs.

Yes fitted new plugs they are both sparking

 

[dobba99]

What does this mean? 'I have also set tdc through the plug holes also and turned the piston back 10 mm' In relationship to what? You need to go through it methodically. If you have good compression, fuel, and sparks at the right time it will start. What carb/s is fitted? how old is everything? wiring, fuel pipes, etc. What is your history of the bike? Sounded very rough when it stopped, what was the noise like?

 

[Dave Harvey]

Go back to basics.

Take the plugs out, put your finger on the spark plug hole and kick the bike. Did you feel compression against your finger? Now do the other plug hole... Same question??....

What do the plugs look like? are they chocolate or oily or bone dry? This might just be a hint which way to go

As a rule, substitution of parts is not the best way to troubleshoot, but in the case of spark plugs, it erases the previous visual condition of the prior plug completely and you get a look at the ignition situation inside the cylinder AFTER the bike crapped out on the new plug. Did it not fire and come out looking wet? << that would tell me you are chasing an ignition problem since the new plug shows fuel is present.

Do you have one of those handlebar kill switches ?? They can stick basically shorting out your ignition....

Gotta run.... good luck

Plug were a nice brown. Did a compression test both barrels came out at 125 lb/in the cut out switch works ok and when the ignition is on, switching the switch makes the plugs spark but I will check it out. Thanks for your input put

 

[MichaelB]

Are you getting spark by kicking or cycling the ignition switch?

 

[Tornado]

Coils and ht leads/caps can work ok with plugs sparking outside engine but when under compression, sparks could be compromised. Try doing basic resistence checks on the coils as per book specs...usually 1.8 or 1.9 ohms at primary coil terminals on an OEM lucas type 6v single output coil. Do this without any other wires connected to the coil. Check if caps have 5k ohm resistence if they are suppressor type, near zero if non suppressor. Generally do not run both suppressor caps and suppressor/5kohm plugs together on Boyer EI systems. One or the other...so 5k ohm total per coil.

 

[gpzkat]

Did you fuel up the bike the day it broke down? I topped up 2 of my project bikes from a can I had recently filled at the station, and they both started running terribly, backfiring, etc. All it took was a bottle of 'dry gas' (alcohol) to fix them, so it was water in the fuel.

 

[Dave Harvey]

What does this mean? 'I have also set tdc through the plug holes also and turned the piston back 10 mm' In relationship to what? You need to go through it methodically. If you have good compression, fuel, and sparks at the right time it will start. What carb/s is fitted? how old is everything? wiring, fuel pipes, etc. What is your history of the bike? Sounded very rough when it stopped, what was the noise like?

Measured tdc then as a rough guide retard the piston back 10 mm as I read this on another post I was trying to save removing the chain case off to fit my timing disc. Bike felt like it was short of fuel cutting out and starting again. Commando is a Norvil rebuild and everything replaced as required. I Have owned the bike for 2 years having bought it from a deceased estate. I contacted Boyer asking if there were any know problems, they sent me a flow chart as if there was no spark. I can’t tell you how many times I have reset the timing checked and re checked.Thank you for advice

 

[Dave Harvey]

Did you fuel up the bike the day it broke down? I topped up 2 of my project bikes from a can I had recently filled at the station, and they both started running terribly, backfiring, etc. All it took was a bottle of 'dry gas' (alcohol) to fix them, so it was water in the fuel.

No all the fuel is fresh

 

[Dave Harvey]

Are you getting spark by kicking or cycling the ignition switch?

Yes cut out switch on then switch off sparks the plugs

 

[Tornado]

Measured tdc then as a rough guide retard the piston back 10 mm as I read this on another post I was trying to save removing the chain case off to fit my timing disc. Bike felt like it was short of fuel cutting out and starting again. Commando is a Norvil rebuild and everything replaced as required. I Have owned the bike for 2 years having bought it from a deceased estate. I contacted Boyer asking if there were any know problems, they sent me a flow chart as if there was no spark. I can’t tell you how many times I have reset the timing checked and re checked.Thank you for advice

Removing primary case outer cover should not be necessary...The MK3 has a crank timing plug hole under the timing case, lower front side of crankcase. Remove the large headed bolt and slowly turn engine watching for the notch in the flywheel to appear. This places crank at 28 BTDC I believe. There is a thread in tool with a plunger to lock into this notch from AN, but not stricly needed. With crank at 28 btdc, you can then confirm your timing scale on the stator rotor through the primary case timing inspection cap hole. Be sure it is left side piston on compression stroke when setting crank to 28 btdc. Check boyer stator is now in correct inital position as per manual. Once started a strobe can be used to fine adjust the boyer but should be close enough to run ok.

 

[MichaelB]

Yes cut out switch on then switch off sparks the plugs

What happens when you kick it?
Not sure but I think the Boyer can cycle a spark with the cut out, bit if there is a bad connection at the stator wires, spark won't go to plugs. Boyers are know for their wires breaking at the solder joint on the back side of the stator.
Suggest kicking it to verify spark at plugs.

A poor stator connection would also cause rough running...

 

[Dave Harvey]

Removing primary case outer cover should not be necessary...The MK3 has a crank timing plug hole under the timing case, lower front side of crankcase. Remove the large headed bolt and slowly turn engine watching for the notch in the flywheel to appear. This places crank at 28 BTDC I believe. There is a thread in tool with a plunger to lock into this notch from AN, but not stricly needed. With crank at 28 btdc, you can then confirm your timing scale on the stator rotor through the primary case timing inspection cap hole. Be sure it is left side piston on compression stroke when setting crank to 28 btdc. Check boyer stator is now in correct inital position as per manual. Once started a strobe can be used to fine adjust the boyer but should be close enough to run ok.

Thanks tornado I have been using the flywheel slot in the flywheel to set the 28 btdc on compression stroke then followed Boyer instructions for the stator set up. But still no start.

 

[MichaelB]

What happens when you kick it?
Not sure but I think the Boyer can cycle a spark with the cut out, bit if there is a bad connection at the stator wires, spark won't go to plugs. Boyers are know for their wires breaking at the solder joint on the back side of the stator.
Suggest kicking it to verify spark at plugs.

A poor stator connection would also cause rough running...

Could also have a bad connection to the stator wires.
Trace the stator wires from the bottom up to under the tank.
Confirm good connection. Old Lucas connectors can have issues.
After that, confirm contunuity of Stator wires to stator.
Mark stator position before removing stator.

I'm referring to the Boyer stator here, not the alternator stator.

 

[Tornado]

Thanks tornado I have been using the flywheel slot in the flywheel to set the 28 btdc on compression stroke then followed Boyer instructions for the stator set up. But still no start.

Ok, confirm if it is left clyinder on compression...you could be out 180 degrees if not.

If you suspect carb not fueling while cranking, look for air leaks carb to inlet ma.ifold or manifold to head, or at the manifold cross over hose connection. Other things to check...fuel flow from the petcocks, tank cap vent needs to be clear to prevent a vacuum effect. If this is amal concentric, are you tickling until overflow? Is the air control valve/choke set to off (tight wire)? Has the cable broken?

 

[hhh]

Ok, confirm if it is left clyinder on compression...you could be out 180 degrees if not.

If you suspect carb not fueling while cranking, look for air leaks carb to inlet ma.ifold or manifold to head, or at the manifold cross over hose connection. Other things to check...fuel flow from the petcocks, tank cap vent needs to be clear to prevent a vacuum effect. If this is amal concentric, are you tickling until overflow? Is the air control valve/choke set to off (tight wire)? Has the cable broken?

It makes no difference which piston is at compression with a Boyer since it's wasted spark.