850 Rebuild Question

Okay, So I am a little stumped and hoping to tap into the knowledge base here.

So I just recently rebuilt a '73 850 and for some reason it isn't starting. I understand this can be a multitude of things, however let me do a little explaining. So when I first did the initial rebuild, the bike would start after a few kicks (warm summer months). Although the bike would start, it was only running on one cylinder. The other cylinder problem was not a timing or spark issue and the exhaust would have a slight suction if you placed your hand on the muffler, and after some investigating I couldn't figure it out but had to leave home. After re-torquing the head due to an oil leak, I ensured the valve lash was still spot on. After doing this and now working on the bike after a couple months at sea in the winter time the thing wont start. The bike is getting a solid spark on both cylinders and the timing is 31deg on one cylinder and 28deg on the other. The timing was set when the bike was running - not dead on, but well within the ballpark for the bike to start. When kicking the bike over there is a fuel residue on both sparkplug - slightly more on the right spark plug but noticeable on both however the goshdarn thing just wont start. Any ideas?

Thank you in advance and have a Happy Thanksgiving,
-John Phillips

Also anyone in the Charlotte, NC area?

Nortons don't have 'injectors', are we talking spark plugs here ?

So what spark ignition system has this thing got in it ?
Points and coil was stock..
Only running on one cylinder, incurably, is never a good sign.

In cold weather, the carbs need a very good tickle, or you need to pull some choke on.
Or you may never get anything out of it.
If only one cylinder is actually running, you may have to only try starting it on that cylinder.
Glugged up idle jets and pilot jets is often involved here...

Have you verified/seen you are getting a good solid spark to each spark plug ?

And if the spark plugs are wet/fouled, it will likely need a pair of new ones installed.

Have fun !

Yes, spark plugs :? stupid stupid me.

Points and coil ignition installed. Yes, pulled the spark plugs, placed them on the cylinder head and jacked the bike over until I verified a spark. Thinking of pulling, disassembling and cleaning the carbs, most likely problem?

jcphilli said:

Thinking of pulling, disassembling and cleaning the carbs, most likely problem?

Click to expand...

Very likely - and a somewhat common problem with carbs left standing.
The gas evaporates away, and gums up the works.
Be good to know that both cylinders have good compression and good spark though.

A quick-n-dirty test if the carbs are the problem is to tip a spoonful of gas down each plughole,
replace plugs and plug leads, switch on and give it a good kick.
If it suddenly comes to life, if only for a few beats, you know its all in the carbs...

jcphilli said:

Yes, spark plugs :? stupid stupid me.

Points and coil ignition installed. Yes, pulled the spark plugs, placed them on the cylinder head and jacked the bike over until I verified a spark. Thinking of pulling, disassembling and cleaning the carbs, most likely problem?

Click to expand...

Yes, disassemble and inspect/clean/rebuild the carbs. Once I had a 850 for sale, it was really nice, A person came to look at it, he was a medium sized nerd. I had it on the center stand and he straddled the bike to start it. he stood on the kick starter and fell on the seat basically, but the bike was tuned so well that it started with him falling on the seat sitting on it. Moral of the story ,there is something wrong.

carbs might be likely culprit .... all our bikes have their own starting ritual too .... for me , to simplify my ritual I replaced points with an electronic ignition , did wonders for ease of starting and steady idle .... if it is carb trouble good luck with that , it can become a long list of possibilities dealing with the old Amals ... at this point I am no road burner and enjoy the simplicity / reliability of a single Mikuni carb ... good luck with your Commando ...better days ahead
Craig Phillips

If the plugs are wet they may well spark outside the motor but not when fitted and under compression. Try a new pair of plugs or heat the old ones up to burn off the crap then wire brush them clean. Before attempting to start the bike try; ignition and fuel off and kick it over three or four times on full throttle to blow out any excessive fuel.

Set the ignition to 28btc, 850s don't like a lot of advance.

Best of luck,
Dave