750 commando misfire

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NoiseyNorton

NoiseyNorton

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Jun 4, 2014
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Rebuilt the top end over winter due to oil ring failure. Got it started for about 5 minutes and noticed an oil leak from the cylinder out of a stud/but that bolts the cylinder to the case. Got that taken care of. Got the bike out and took it up and down the road to warm up and see how it was. I have a misfire on the right side pops, bangs, sometimes fire from intake on shut off. I get spark when I tested it last night. Helpful suggestions would be great as I'm trying too actually get it out this year. Could my carbs be the issue? When I unplug the left bank it shuts off right away. But not vice versa. I have the left bank at a good tick over and tried to do the other side and found it won't even run. Thanks
 
Hi,
About oil leak from the barrells/head, be sure the oil returns to the thank oil.
I had the same problem wth a oil leak.
About misfire, the spark plug is too much wet and dont fire well; check a control of the float bowls and change the sparks plug with new one.
Ciao
Piero
 
plugs are dry and looks lean? greyish white on that bank. - oil leak was cured by retorqing the bolts, the one had backed off after 5 minutes of running; i assume from the shaking of the miss? - even if there is spark could it not be strong enough? do coils lose power over time or do they just die? - I will check my float level when im off work, and thinking now that side does take A LOT longer when using the tickler to see any petrol. any other suggestions?
 
the carb that is taking a long time to see gas come out when tickled has the float too low

take that carb's lower body off and gently tap down the brass seat that the needle goes into, this will lower it so that more gas is let in
when tickling, this could explain why the popping relates to fuel starvation on that side
 
Dry plug with spark on a non-firing cylinder indicates lack of fuel flow.
 
Amonst other things, make sure the slides/cable are sync'ed up.

However, that side taking long to tickle seems a solid place to start.
 
What is the best way to move the sleeve down? I don't want to damage anything. And is there a certain amount I should go? Should both sides be equal? Where do I measure at in the hole or at the float?
 
Best way is to buy new stay up floats so you can adjust the tang, not the seat. You may want to check the float height while you're at it. There are various ways, tube off the drain and up the side will tell. Be sure to read all about carbys here http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

And yes, one coil can be weak. But everyone is betting on the carb.
 
Stopped home on my lunch break to check out the floats. My right side ( problem child) was at 1.044" should be at .080" so I have pounded the seat down and got it at .083" close enough I guess. So after work I will see what this had done. My left carb was at .090" should I pound that side up? To get them close together? Or should this be sufficient? Thanks for all the help guys.
 
This is what the Amal fuel level of 0.170-0.240" below top of bowl looks like.
The black marker thickness shows the recommended high and low level.
Just below the screw hole ear.
750 commando misfire
 
interesting, i will have to check to see where the level is at before i put it back together. If i am lucky everything will be smooth and bike will run without issues... doubtful but i guess that is why i still have it, never finished
 
I had the same issue and I found that if I took the plug wire off and just set on the plug (not press it on) my misfire went away. I then doubled the gap in the spark plug and put the wire back on correctly and it seemed to help a lot. I got the odd pop every now and then so I would take the plug out an spay it with carb cleaner to get the black soot off and I was good to go.
 
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