twist

I've been watching this thread too. I think I can fabricate a D shaped head but am interested in your progress, flash. If I remember right, the old way was to set carbs with the screw 2 to 2 1/2 turns out on one carb. Adjust for best idle after the engine is warmed then set the other cylinder to the first one to get best idle. If you are really **** you can mess with it a long time and even attach the balance tool so to get both just right. Unfortunately, weather, temp, and all those factors will affect the tune from day to day so it never stays the way it was set up but the changes aren't really all that noticeable unless it's a track bike. I'll be reading with interest.

nath981

yeah that's cool. do we have FCRs?

found this guide to carb tuning:

http://keihincarbs.com/tips/gate.html

Jack Flash

I am probably getting ahead of myself, but, I don't think playing around with the air screw mixture on a daily basis will provide any satisfactory gain. I will set mine as per 8541Hawks suggestion, fine tune from there, and forget about it.

My experience is with Kart racing, two stroke engines. 125cc shifter karts, and 125cc clutch driven karts. Once at the track, temp, humid, and barometric pressure is what I read, and jet accordingly. Carb veturi's are between 28mm to 34mm according to race category, and I can tell you
air screw mixture is pretty stable, and barely need to play with this.

Once again, I am not sure the V-Twin is going to feel it if you play with it on a daily basis, but then again, I may be wrong. Four stroke is different then two stroke engines. Silencer volume and design affects enormously a two strock engine. Even the type of driver, will determine a portion of the jetting I will provide in order to have the engine run right....but now, I'm out of line with this.

twist

+1 there really is no reason to mess with the air mixture but the initial setting or if something is changed in the intake or exhaust. Best to set it and leave it, maybe that's why it has a "D" shaped screw to begin with?

BTW, got a cool boost joint today. Cheers!!

nath981

If you haven't changed a lot, then you can usually get away with following a suggested starting point like stated in the manual. But to do it right you need to get that special tool.........or make one, that will allow you to adjust each carb while the bike is idling.

In my case, with altered pipes, jets, air box, filter,etc., you're on your own. The way I use to get in the ball park is to take it to an extreme point one direction, see how it runs, then take it to the other extreme and see what happens. One extreme will usually be obviously worse. Tweak accordingly. Then, to get it right on, get or make the tool and adjust while idling.

Jack Flash

[QUOTE=twist;345875
BTW, got a cool boost joint today. Cheers!![/QUOTE]

Happy it got to you in timely fasion. It is a cool piece. I now have to get one for mikstr, he wants one also.

Nath, I ended up using a flat head precision screw driver, and applying
pressure on the flat portion of the D shaped screw, slowly got it to budge.
Once it began moving, the rest was easy. Once off, dremeled the head
and tested with my tool, it works perfectly. I do have the 90 deg. screw driver for this job, so, I set at 2 1/4 front, and 2 1/2 rear as per suggested many times. Once the white sh**....eh....snow clears next spring, I'll be able to fine tune as you mentioned.

twist

question: joint has a small hole in it and not wide open like the OEM piece. How will that affect tuning? If the rear has a larger opening than the front will that be enough to make a difference? Drill it out to same ID as OEM?

Jack Flash

If you mean the front, as the part that screws into the cylinder, and the rear as the part with the rubber cap, well, no, it will not make any diffence. This is a vacum fitting, so, as long as there is a pulse, your good.
As for the OEM, part, I've never seen it, so I do not have a reference for you. And, I've always used that with the TecMate calibration tool.