1949 WL - Spark Plugs, Carb. & Faltering

[1962300]

Hello -

Have a '49 Solo; with the engine & trans that came out of a Servi-Car.
The motor is a fresh rebuild, with less than 2K miles on it.
It has started to incur an issue where it falters (misses) in the upper rpm's of each gear.

So yesterday....Replaced & Adjusted the following:
- Battery - New & Fully Charged 12v Yuassa Battery
- Points & Condenser - New & properly gapped / timing set as per shop manual
- Spark Plugs - New Champion D16's; gapped at .025"
- Valves - Adjusted as per shop manual
- Carburetor - Have a Linkert M16 (which is correct for the Servi-Car). Pulled float bowl & adjusted float to 1/4"; as it was at 3/8"

The bike idles better than ever.
Still falters going through the gears at the higher rpm's of each gear.

Questions:
- Spark Plugs - Are the NGK AB6's better? Should I try a different gap?
- Carburetor - Should I save up to switch to a M51, M52 or M88? I know that also requires a larger diameter Intake Manifold
- Any other thoughts to check?

Thanks!

[panheadrider1961]

Drag pipes ? Fuel flow carb being drained till this point and no gas ? Gas caps non vented or one side vented ? High speed jet not blocked and adjusted? Everything on manifold to heads tight?

[Pascal]

The M16 is 7/8", which is fine for a torquey low-pulling Servi...not so for a high(er) speed solo.
So it probably needs a bigger carb and manifold I guess...

[Excalibur]

Could it simply be set too rich or lean on the high speed jet? How have you determined that setting?

[1962300]

Thank you all for responses, to date...!


RESPONSE #1:
Drag pipes ? Fuel flow carb being drained till this point and no gas ? Gas caps non vented or one side vented ? High speed jet not blocked and adjusted? Everything on manifold to heads tight?
No drag pipes; stock muffler. Fuel flow is fine; just readjusted float to the correct 1/4" drop. Same single gas cap that has been on the bike for many moons (the other tank is solely for oil). High Speed Jet - Maybe needs to be blown out with compressed air and/or adjusted. Manifold & Heads are good & tight. It idles so perfect there cannot be a vacuum leak

RESPONSE #2:
The M16 is 7/8", which is fine for a torquey low-pulling Servi...not so for a high(er) speed solo.
So it probably needs a bigger carb and manifold I guess...
You are correct in the thought that the M16 is designed for torque rather than higher speeds. This M16 was working fine for a good while. Maybe it needs to be gone through, but the ultimate plan would be to go to a M51, 52 or 88. Would just need to save up about a grand for the carb + larger manifold

RESPONSE #3:
Could it simply be set too rich or lean on the high speed jet? How have you determined that setting?
This could be the answer. I need to check this setting & follow the shop manual on the adjustments.

Thanks All!