Runs well, plugs foul....

A bit lengthy but please bear with me, just making info as complete and accurate as I can.

1974 850 Cmndo. The engine starts and runs well through full RPM range...until the plugs start to foul...within 30 miles.

I am running twin Amal 932's that I have overhauled. New slides, 3 position needles, main jets (standard 220's), floats and float needles. Synchronization between the two is good.

Tri spark ignition with ign. pack, fresh plugs and leads with proper resistance...set dead nuts on at 28º BTDC.

While overhauling the head this fall, I went back into the carbs as the combustion chambers and plugs displayed rich mixture in color/deposits.
Upon reassembly I set the needles at their upper most setting, looking for a leaner offering.

The carb work was meticulous. Idle jets clear with smooth operation throughout. Reassembled everything and fired on 3rd kick. No air leaks around the fitting faces.

As I rode and started and tweaking the air adjustment screws to find an acceptable mixture I noted how far in the air adjustment screws needed to be turned from recommended 1.5 turns out, 1.10+ back in apprx., thus enriching the mix.
I attributed this, partially to the K&N air filter allowing more air intake.
Popping gone, decelerates smoothly, good throttle response.

Dirty/a bit sooty plugs found when starting became difficult.

My next step is to adjust the needles one setting, to the #2 position, richer, and reset the air adjustment screws to 1.5 out from seated and see where that takes things.
I have other ideas but would like to hear from those the have been there - done that.

I have a clue as to how carbs work, Holley's, Webers, SU's.
I really like the simplicity of the Amals and know there is a sweet spot in there somewhere. I would like to find said sweet spot rather than getting pissed off and end up sitting on the curb beating my dick with a brick because the beast won't run or start.

Thanks for reading.

Dare I ask about the float level?

Rich plugs could be a weak spark or wrong plug heat range, weak coil, poor engine ground, weak battery, weak alternator, or anything that weakens the spark as you ride. If your battery is old, change it. Put a voltmeter on your bike as it runs and see if the alternator is charging when you use the throttle...

We haven't even gotten to the carb stuff yet and there's a lot to check...

I have a similar set up('74 850), but no resistor plugs & use original Amal needle setting. Carbs recently rebuilt & wassell ignition, NGK BP7ES, K&N filter. Generally I'm at close to 1 1/4 turns out on both depending on temperature, also at sea level.

What exhaust do you have installed?

o0norton0o said:

Rich plugs could be a weak spark or wrong plug heat range, weak coil, poor engine ground, weak battery, weak alternator, or anything that weakens the spark as you ride. If your battery is old, change it. Put a voltmeter on your bike as it runs and see if the alternator is charging when you use the throttle...

We haven't even gotten to the carb stuff yet and there's a lot to check...

Click to expand...

Been through it all. Just finished a ground up restoration.
CNW ignition pack. New battery, 12,2 V out at 3500, always on maint. charger, ground solid, new plugs supplied with new ignition set up. No more coils or points.
Thanks for reading.

I'm sure you have coils of some sort.

1up3down said:

Tri spark ignition with ign. pack, fresh plugs and leads with proper resistance...set dead nuts on at 28º BTDC.
========================

Assume you mean you used a strobe light and raised the rpm's to fully advanced at 28?

- the Trispark ignition requires a "resister" between the coil and combustion chamber
so for example are you using resister spark plugs like NGKBPR7es?
or resister plug leads? But NOT two methods of resister, not both plugs/leads

what coil set up? a single 12 volt dual lead like CNW recommends with Trispark?

Click to expand...

Resistor plug leads. The ignition system supplied by Matt. Understood about redundancy on resistance.
28 degrees strobed. Initial setting with degree wheel.
Thanks for reply.

batrider said:

I'm sure you have coils of some sort.

Click to expand...

Guess I should have made it clear when I said CNW ignition pack earlier.....no traditional coils

Thanks for the read.

Onder said:

What exhaust do you have installed?

Click to expand...

Thank you for looking.

Did you replace your needle jets?

jbruney said:

I have a similar set up('74 850), but no resistor plugs & use original Amal needle setting. Carbs recently rebuilt & wassell ignition, NGK BP7ES, K&N filter. Generally I'm at close to 1 1/4 turns out on both depending on temperature, also at sea level.

Click to expand...

Original needle setting.
So you set the clip, from top down, to the # 2 position on the needle?

CanukNortonNut said:

Did you replace your needle jets?

Click to expand...

Yes.
See original post, 3rd sentence.

Thanks for the interest.

The logical me says that because it's both plugs on a dual carb bike, you either have both carbs set up with the same erroneous setting, OR it's electrical because it's effecting both sides... I'd run an extra ground from the engine to the battery and also from the positive terminal of the coil to the battery. (assuming pos ground)

the 12.2 volts at 3500rpms is lower voltage than I would expect...

The 12.2 V out is with all LED lighting turned on. 13.3 V out with lights off.

Jets are all original spec., with The Madass sync. plate in place and adjustment settings as specified by Amal.
I will try redundant ground even though the meter tells me ground is good.

Thanks for the insight.

Are you using the new style floats? (stay up floats)? Brass or Aluminum float needle valves?
If you have a drain plug at the bottom of the bowls then make up a small level check device to see where the level actually sits while running. https://andover-norton.co.uk/en/shop-details/20569/fuel-level-checking-kit-amal-mk1
Like this.

Onder said:

Dare I ask about the float level?

Click to expand...

Have yet to check for accurate float level.
Do you have an accurate technique to measure this on Amals. I did a search but not clear on method described.
Assuming a rich condition would mandate lowering float deeper into the bowl closing off needle valve sooner?

CanukNortonNut said:

Are you using the new style floats? (stay up floats)? Brass or Aluminum float needle valves?
If you have a drain plug at the bottom of the bowls then make up a small level check device to see where the level actually sits while running. https://andover-norton.co.uk/en/shop-details/20569/fuel-level-checking-kit-amal-mk1
Like this.

Click to expand...

New style floats with black tipped aluminum (I assume) float needle valves. Bowls can be drained.
Thank you for the link.

According to Roy Bacon's Norton Twin Restoration: 850 mk2a option for 74 would be 220 mains. The carbs should be stamped R 932/33 and L 932/34 My 74 850 Interstate had 260 mains but when I changed the cam(Megacycle) required 270 mains. My guess and Onder's is that the floats are influencing the needles during riding.