Why can’t I start my bike?

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Larry S

Larry S

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On my last ride out my bike would not idle at stops - I had to blip the throttle to keep it running. It would run ok the wider I opened the throttle but it was time to turn around and head to the shop. Total run was six miles. Now trying to start it doesn’t even try to fire.

Info about the bike: 1975 850 MK3 electric start, new AGM battery, Power Arc electronic ignition with resister plugs, leads and dual coil, single 34mm Mikuni carb. Compression is 155 psi on both cylinders.

My first thought was that this is a carb issue so I drained all fuel and checked fuel flow. Flow was good. Removed the carb, disassembled and cleaned with carb cleaner. Reassembled carb and refit. Fresh fuel, turned fuel taps on, enricher on, key on and push starter button. No go. Pulled plugs and they didn’t appear wet. For shits and giggles I checked spark at both plugs. Good spark. Put them back in and sprayed starting fluid in carb intake. Bike fired up on the starting fluid and quickly died. Pulled carb an cleaned again. Still no go. What am I missing?

Please help, the weather is supposed to be nice in a few days!
 
Larry S said:
On my last ride out my bike would not idle at stops - I had to blip the throttle to keep it running. It would run ok the wider I opened the throttle but it was time to turn around and head to the shop. Total run was six miles. Now trying to start it doesn’t even try to fire.

Info about the bike: 1975 850 MK3 electric start, new AGM battery, Power Arc electronic ignition with resister plugs, leads and dual coil, single 34mm Mikuni carb. Compression is 155 psi on both cylinders.

My first thought was that this is a carb issue so I drained all fuel and checked fuel flow. Flow was good. Removed the carb, disassembled and cleaned with carb cleaner. Reassembled carb and refit. Fresh fuel, turned fuel taps on, enricher on, key on and push starter button. No go. Pulled plugs and they didn’t appear wet. For shits and giggles I checked spark at both plugs. Good spark. Put them back in and sprayed starting fluid in carb intake. Bike fired up on the starting fluid and quickly died. Pulled carb an cleaned again. Still no go. What am I missing?

Please help, the weather is supposed to be nice in a few days!
Click to expand...
Did you remove the pilot jet and poke a wire through it ?
 
Forgot to say that I also tried new correctly gapped plugs with no difference.
 
I'm not sure what the symptoms are if the plunger seal on the enrichment jet are playing up?
But did you check it ?
 
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Why can’t I start my bike?
Why can’t I start my bike?
 
Last edited:
I have had this recently on my Mk III. If the battery is slightly low and the electric starter is used it would not start, but when kicked it started right off. My thoughts are the starter drew so much voltage there wasn't enough to fire the ignition. If the plugs were out to check spark there would be less load/ draw on voltage when electric starter is engaged.
 
baz said:
I'm not sure what the symptoms are if the plunger seal on the enrichment jet are playing up?
But did you check it ?
Click to expand...
I checked everything including the plunger and all appear clean. My knowledge of carburetors is very limited but from the research that I’ve done the problem appears to be in the enrichment circuit. I don’t really know for sure though or what to do if that’s the case.
 
Larry S said:
I could see through the entire jet. Cleaned it just the same.
Click to expand...
The JET isn't the problem. The teeny tiny drillings into the carb throat just downstreem of the slide can & do plug up, they are much smaller. I use a wire plucked from a wire brush held with needle nose vice grips to poke them out, then VERIFY flow with an aerosol solvent. Also, the air passage from the intake horn must be verified.
I've had Mik's that wouldn't idle, always a blockage.
 
Larry S said:
On my last ride out my bike would not idle at stops - I had to blip the throttle to keep it running. It would run ok the wider I opened the throttle but it was time to turn around and head to the shop. Total run was six miles. Now trying to start it doesn’t even try to fire.

Info about the bike: 1975 850 MK3 electric start, new AGM battery, Power Arc electronic ignition with resister plugs, leads and dual coil, single 34mm Mikuni carb. Compression is 155 psi on both cylinders.

My first thought was that this is a carb issue so I drained all fuel and checked fuel flow. Flow was good. Removed the carb, disassembled and cleaned with carb cleaner. Reassembled carb and refit. Fresh fuel, turned fuel taps on, enricher on, key on and push starter button. No go. Pulled plugs and they didn’t appear wet. For shits and giggles I checked spark at both plugs. Good spark. Put them back in and sprayed starting fluid in carb intake. Bike fired up on the starting fluid and quickly died. Pulled carb an cleaned again. Still no go. What am I missing?

Please help, the weather is supposed to be nice in a few days!
Click to expand...
Larry, I see your in IL, first ride after a winter layup?
Or has it been ok this spring, then suddenly not right?
 
concours said:
Larry, I see your in IL, first ride after a winter layup?
Or has it been ok this spring, then suddenly not right?
Click to expand...
I had it out once this spring and it seemed to run ok although it surged a little at low speeds in town.
 
concours said:
The JET isn't the problem. The teeny tiny drillings into the carb throat just downstreem of the slide can & do plug up, they are much smaller. I use a wire plucked from a wire brush held with needle nose vice grips to poke them out, then VERIFY flow with an aerosol solvent. Also, the air passage from the intake horn must be verified.
I've had Mik's that wouldn't idle, always a blockage.
Click to expand...
I wasn’t sure if it was cool to run wire through all the fuel and air circuits so I didn’t do it. I have read conflicting information regarding the wire clearing tip. Thank you for the confirmation that this is acceptable. I will try this tomorrow.
 
Larry S said:
I had it out once this spring and it seemed to run ok although it surged a little at low speeds in town.
Click to expand...
Sounds very much like ethanol fuel deposits in the smallest of passages has ruined the fun.
If you're not carb comfortable, bribe a talented friend with unlimited beer... it always worked when we were younger....:cool:
 
If it fires a few bangs then dies and no more bangs, could you have a blockage in the tank vent in the flip cap? Try with cap open.
 
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