After being distracted on another bike restoration, I am back to finally tuning this 55 6T to ride. When it came to me as a basket case it had a “pre Monobloc
” 276. I decided to treat it to a 55 6T spec Monobloc
from Burlen. A 376/42 is a 1 1/16, 270 main jet, 106 needle at position 4. It is my understanding that a Monobloc
wants 2.5 turns out at the idle screw vs. 1.5 turns out of a Concentric
. Correct me there, if incorrect. Ramp cam engine, valve adjustment at .010. Complete fuel system is new, though anything is suspect.
Here is the issue. Bike starts first kick no matter what with partial choke. Idles easily. Runs down the road apparently well. Once warmed up, bump the choke off at a stop, idles. Go to leave the stop and it will not take the throttle, flick the choke lever a small bit, bike picks up and runs through the gears and gets me home. Doesn’t seem to smoke, the new head pipes aren’t blue yet.
I started at 2.5 turns out on the idle mixture, along the way made several stops to turn it in by increments to 1 turn out, with no improvement.
Changed the main jet from 270 to 290. No improvement.
Raised the needle 1 notch. No improvement.
I have checked for vacuum leaks, can’t find any, and I don’t twist everything to 100 ft lbs.
The engine is not modified.
L82C plugs gapped at .025, sooty by the time I get home on choke.
Below is an paragraph from an August 55 TSB.
This is the time when I typically go wildly back and forth between ignition and fuel, make wild, multiple changes per tuning session. Before I do that, I am wondering if a more experienced, wiser person would have a suggestion or point me in a direction before I start changing slides for a different cut-a-way, going bigger on the main jet, or hiking the needle up higher.