1973 Commando...one lunger

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HELP!!! My 850 Commando is making me feel stupid! After new exhaust system, new wiring harness, seat from GPZ, satin black paint job on the now rust free fuel tank, new plugs, points gapped correctly and engine correctly timed, amals cleaned (especially the pilot circuit) and valve clearances set, SHE STILL is running on the left side only. Just did a compression check and she shows 100 psi on the right cylinder that refuses to fire.
I even went as far as to hook up a "dummy" spark plug (with another spark plug in the hole) to the spark plug wire while it was running. BRIGHT spark on every tick over but still no combustion in the right cylinder bank.
It is blowing raw fuel out the right side.....carb???? Ignition is there.....fuel is there.....compression is there.....WHAT THE HECK??? Adjusting the mixture screw seems to have no effect at all on the right cylinder bank...
Timing is almost spot on as she will fire up (albiet only on the left side) on the first kick from cold and it does not smoke at ALL. :?: :? :!:

Any ideas here guys? I would like to get her running good before she goes up for sale.....of course I will post it for sale here before I Ebay it. If I can get it running good I will ask $1800. If you are interested, shoot me a PM.
 
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I had the same issue with a boyer equiped 850, there was only enough of an earth connection for one spark in a cylinder but outside you could get 2 sparks, fixed it by running an extra earth lead from head to frame where the coils are fitted and from there back to the battery.
 
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Might have to replace points condsenor or switch em to know otherwise.
 
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Hmmm....she did fire on the right side and actually sounded good for a moment when I was messing with everything....but that is what is so odd. The dummy spark plug I had hooked to the coil wire sparked on every stroke when it was running (and not a weak spark but a bright spark!). Unless something changes when I actually put it in the hole but that doesnt make sense to me...maybe different spark under compression??? ARRRGGGHHH!!! :x
 
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Can you see spark firing as you kick it slowly through just holding the right hand plug grounded against the head while you kick? Ground left plug against left side of head.

How about trying it switching the plug leads, the right one may have an intermittent fracture somewhere in the length to fool you.

If so, can you switch the carbs right to left to verify it is still the right side that will not burn and fire?
 
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I did switch the coils and they both have a hot spark when the plugs are grounded against the head. That is what is making me think it is more of a fuel delivery problem instead of ignition. Next step is to review the carb rebuild....they are just so simple though, I dont see how I could have assembled them wrong but stranger things have happened I suppose.
Do you think 100 psi compression is enough to run?? I sure seem to think so but I have only been messing with brit bikes for the last 10 years or so....

Still pondering what the problem is.... :oops:
 
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I had a spark plug in my commando years ago that looked fine, but the insulator was cracked all around the electrode & when you held it up the way it is in the engine, it slid down & shielded the spark. When removed for inspection, held up the other way, the insulator fell back to its correct position & looked good. It took a while to find that out!

Bob.
 
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$1800 for a Commando!? I'm definitely living on the wrong side of the world :shock: :(
 

gjr

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If you are getting raw fuel out of the right side I would say that cylinder is flooded. Amals are primitive, but the fuel has to be vaporized to burn. Raw fuel sounds like it is a liquid. Do you have a spare carb that you could try ?

Greg
 

grandpaul

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Sounds carb related...

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...or electrical!

hee hee

Re-check your carb build, and start with a fresh set of plugs.
 
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Guess I will have to dig out the spare 932 Amal I have. I initially put new Champion Spark plugs in it. Thinking I had a bum spark plug, I took it back to the parts store and got an AC plug. No change. The chase goes on....
 
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