Tune up help...misses...Still backfiring...

Just got '73 850 back together after top end rebuild (and just about every thing else but tranny and bottom end and carbs) and thanks for help from many along the way. Good to take it out for first rides in 5 years.

However: Does any one have a summary or detailed article of sequential precision tuning instructions. I have installed new points, plugs and wires. Have not yet timed and did not get chance to fully clean amals but will likely this week.

This is what I have found on first rides - about 70 miles so far. Ride though lovely has been somewhat rough and no decent idle yet. On two of my first runs (have done 3), motor ran reasonably well and then one side seemed to quit and unbelievable backfiring ocurred. 5 minutes later as I am limping to get home ... it smooths out again? It occurs to me there is likely someone who can tell me best sequence of doing a good tune up job including best or initial turns on pilot air screw.

Valve job was done at rebuild and valves, points and plugs accurately set. Only thing not done yet only because I wanted to ride .... was cleaning carbs and timing.

Long story....

Any help appreciated.

Re: Tune up help...misses...backfiring...

Clean the carbs, and adjust them correctly. http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

Dave
69S

Re: Tune up help...misses...backfiring...

Definitely do the bushman link on Amals but read it carefully. I did it and think I may have mis read the section on setting slides:

This is my thread when I did mine over the weekend: http://www.accessnorton.com/hesitation-when-throttling-neutral-with-video-t10584.html

Be sure to make sure the pilot jet is clear. My bike still seems to like to react better to the left side than the right, sure I have some more adjusting to do!!

Stiil in need ...
right cylinder still has wicked backfire and misses more than not

So far: new plugs, wires, points, gas taps (were leaking), fuel line, carbs dismantled and cleaned.

Did not replace float chamber gasket but that is next.

What I see through new fuel line are "air bubbles" I am guessing the possible problem.

Question is where is air coming from and how do I stop?

2nd question. When I carefully cleaned the carbs, I did all except did not play around with "captive" pilot jet.

Any help appreciated.

This is what I have found on first rides - about 70 miles so far. Ride though lovely has been somewhat rough and no decent idle yet. On two of my first runs (have done 3), motor ran reasonably well and then one side seemed to quit and unbelievable backfiring ocurred. 5 minutes later as I am limping to get home ... it smooths out again? It occurs to me there is likely someone who can tell me best sequence of doing a good tune up job including best or initial turns on pilot air screw.

Click to expand...

Duh this is so classic of so many of my fueling symptoms that electric fault fixed.
Start it after dark and look around while probing wiring and connections and blipping. Its possible to have a loose carb gasket getting floppy then sucked up tighter seal. Its possible a carb needle is bouncing around too. Its possible a point condenser is gone sour, even if new out the box, ugh.

Des,

The timing was OK before you did the head, pretty sure it is still close enough to right that you need not worry about it at this point.

When the bike is back firing, press down on the primer and see if you get a wet finger, a dry finger will indicate a fuel starvation issue.

I very recently put in new fuel taps, after about a 100 miles, my bike started back firing and carrying on, the fuel taps had partially blocked with little pieces of its own gasket, I drilled the bastards out with a 5/32 drill bit and have been smooth sailing since.

Having air bubbles in the fuel line sort of confirms the possibility of what I am suggesting. When you turn on the fuel tap, the air in the lines should find itself in the fuel tank, the only way the air can stay there is if there is a restriction above, i.e. in the taps.

If the above doesn't work, run the engine and spray CRC or WD40 around the manifold gaskets to see if one is sucking air ?.

Thanks to all.

New taps were installed today.

Tomorrow I will buy an inline spark plug circuit tester to go between plug and wires so I can view spark to see if spark is consistent from coil.
Anyone have experience identifying a faulty , weak coil?
What happens with coils start to fail? I do note the backfiring seems to get worse as engine gets hotter.

Thanks again
R

Warm coil shorting out tends to misfire/lack of fire rather than back fire out muffler or carb.

Start the bike cold, warm up / heat the offending coil with the wifes hair dryer, that will accelerate the symptoms if that is the case...............P.S. Do not get caught using the wifes hair dryer in the shed, women generally do not see the funny side of these things, if you do get caught, RUN !!!!!!!.

I've been though enough wives to tell ya if you use her stuff w/o permission, and you get caught, then its yours and only way to nullify the sense of injustice is buy her another even better one she picks out.

Once after an especially exhilarating spanking sneer whipping off sports bikers, feelling brave I used something in kitchen and got caught, so I thought I'd take another risk and responded...
Well its easier to ask your forgiveness than permission.

That took some fancy handling to settle down the oscillations. Beware how stupid some us boys can be after a cycle ride.

My stupidity knows no bounds, got busted for both of these gems.......

Backfire is out of muffler alone. As well whole side will quit then may start firing again - with backfires.!

Oh cool someone gets a used parts washer with smirking wife as you realize the hard harsh way what strong alkaline detergents do to Al in short order.

For muffler back fire unburnt fuel must get there then an ignition source. Sticking exhaust valve? Air leaks famous for this too. Maybe just maybe gasket leak from compression stroke side into the exhaust stroke side? Maybe that explains the heat soak onset? Didn't a famous fictional character say when all the possibles are ruled out what left but the impossibles.

A waste spark ignition and a fouled plug can do the same . Failing to spark under compression and sparking on the exhaust stroke.

Cash

oh yeah cash good point I'll keep in mind. But something would have to degrade the spark on that side so back to start on where to start.

Well~ I had a lot of issues with both my Nortons backfiring ~

Both bikes (ES2 and 850 Roadster) had leaking exhausts ...

I originally found for some strange reason the LH header pipe repeatedly worked loose. But turned out on the original build , the seal ring had been left out!! ??

That resolved that issue ~

But I found that after some miles the seal/s would break and the bike will/ would start backfiring . So I would reseal the pipes with Selastic and it is fine.

Now ~ the worst offender has been the LH pipe and muffler ~ I find that the header pipe struggles to get purchase into the Muffler ~ thus the issue of working loose ~

I am currently ready to reassemble the pipes and muffler after accumulating a few SS parts including muffler / foot peg SS mount plates.. and I will endeavor to bring the muffler forward < 25-35 mm > .

But something would have to degrade the spark on that side so back to start on where to start.

Click to expand...

Yeah Steve, I've fitted hotter plugs to a few Commandos near me to stop plug fowling. The 750 burns a little oil so fair enough. The 850s are pretty economical on oil, I can only put it down to light use, or over use of the choke and this modern fuel . :?:

Anyhow, they all run really well now.

Cash