11th July 2022
Balancing Act
Following short vid and exchange of messages with HC/FA (The go-to Moto Ears in the SW) have obtained Carb-tune manometer to aid balancing. Had to get threaded ports cut into manifolds at the local engine shop. Now all ready set about adjustments (carb tuning may be a bit of an exaggeration).
Restored jets, barrels and needles to as supplied by Mikuni agent (Allens). (this was simply a needle swap). Aim was to return to an as-supplied baseline.
Checked timing, spot on 2 degrees advance at tick over.
Checked throttle cables and adjusted until there was about 3mm slack both sides, the LH seemed to be a bit tight.
Released carbs from m/folds to allow for eyeball inspection of slide synchro, adjusted until appear to move together.
Fitted carb-tune, started engine, minor tweak to cable adjusters to get both columns moving together. Adjusted tick over until columns level. Checked synchro again
Disconnected one cylinder and adjusted fuel screw for optimum rpm. (first needed to set throttle screw in about half a turn to get a tick-over). Note that unlike VHB Del Orto, the Mikuni VM slow running screw adjusts fuel supply, not air supply. Hard to find best setting, finished at 2.5 turns out. Probably close to max fuel from pilot jet. Repeated operation on other side. Same result. Reset tick-over.
However found that motor fluffed when snapped open and picked up poorly on slowly opening throttle. Sounded strangled and revs just died away as throttle slowly opened. No amount of fuel screw adjustment made any difference.
On the last outing the motor pulled well with the alternative needles in. These are less aggressively tapered and look more like the profile of the original Del Orto VHB needles. So I let the motor cool, then put the alt-needles in (easy swap with these carbs, round screw top, rubber gasket seal).
Repeated process above, results much better, quick pick up on a throttle snap, an even pick up on slow opening. Fuel screw now 1.75 turns out (RH) and 2.0 turns out (LH).
No test ride, too warm and a bit tired after three days away.
UPDATE - TEST RIDE
About 12 miles, mostly country lanes, a bit of open road, and a blast down the dead straight Roman Road back, up to 5500 rpm in top, pulling well, sounding clean. Good engine braking indicating decent shut-off. Link below to short video of current state of motor.
The carb synch was a bit out on return, I tweaked it back, not quite perfect nearly there though.
There was a definite pick up when I turned the pilot screws out by a quarter turn.
No comments:
Post a Comment