Well, back to the build
Have spent quite some time lately testing on the backroads. The bike is surprisingly well behaved, starts first kick almost every time. Idles fine, and feels "right". My main issue has been a large power drop when shifting into fourth. I get a significant drop in RPM, and unfortunately run out of road long before I´m able to pick up the revvs again. No doubt of it leaning out at WOT.
My first thought was (what I understand almost all are struggling with) to little flow to the fuel bowl.
First measurements showed a measly 0,2 liters of flow per minute. Realised that with my setup there may be a need to keep the tank full to get enough flow, and I had only filled in a couple of liters (or half a gallon). A full tank got me to 0,5 l/m, a huge difference.
Next couple of runs showed a (very) slight improvement, but still far from good enough. Went crazy on the mainjet going from 160 to a gigantic (and silly) 210 in a couple of steps, but still had a leanout
Drastic steps where called for:
I really, really hated doing this! knowing all to well I was going to mess up an otherwise fine carb I drilled the inlet from 4 to 5 mm`s. Just had to be sure, and have a couple of carbs in spare. The idea was simply to test, and if finally getting it rich enough, mess with making/finding a suitable float/needle setup later.
Took off with fuel spraying out the overflow, but still, a leanout in high gear
bummer!
It suddenly dawned on me, that maybe my carb was too large (38 mm Keihin butterfly). It makes sense (to me at least). Up to third I may be running on the pilot jet at a moderate throttle opening giving me a good vacuum signal in the venturi to draw the fuel. Shifted into fourth, hammering the throttle, my high gearing (got a very widespread "trials" gearing) drops RPM on both engine and of course blower enough to loose a lot of vacuum in the venturi combined with a fully open throttlevalve.
Next logic step:
A Keihin CV borrowed from my shovelhead. Larger at 40 mm, but being a CV should help keeping my airflow, and thus vacuum at WOT.
First tests have shown a huge improvement. I´m able to go full bore, and still have the bike accelerate albeit a bit slowly.
Still think I need a smaller carb, so got these yesterday:
A row of 36 mm Mikuni CV`s taken from a FJ 1200 Yamaha. It should be possible to get at least one good carb out of this, and leave me with enough spares to experiment. This will be my project for this weekend.
Where I`m at now
Still way to lean. Would one of you in the know please have a look at the "firing ring" (what`s the right expression?) marked with the red arrow. Got a feeling I may run a bit too advanced. It should be in the middle of the bend on the side electrode, not?. Comments on this, the look of the plug in general, and everything else will be greatly appreciated