VHB Adjustments

[halfpast]

Hello all,

Daft question: Been trying to adjust the idle and mix on my bike, and neither screw seems to be making any difference.

Which is the idle screw, 1 or 2? Thanks very much.

[graeme]

2 is idle
1 is mixture

[Jordan]

If you don't get any result from turning the idle (throttle stop) screw, something very basic is wrong - maybe cable slack.
Note that VHB has its mixture screw on the engine side of the throttle bore, rather than upstream nearer the air intake.
That is a clue that the mixture screw when turned clockwise creates a weaker air/fuel ratio, and anti-clockwise richer.
Typical number of turns out from bottom is in the range 1-3/4 to 2-3/4, according to the widecase workshop manual supplement.

[halfpast]

Much appreciated!

[ducwiz]

Sufficient free play in the starter valve cable is essential, otherwise the bike idles too rich, the mixture screw does not work.
Also important: the rubber seal in the bottom of the starter valve has to be airtight and still in a soft state. This here

Starter-Kolben.jpg

is in a bad condition. If it is still soft, you can peel it out of it's seat, turn it over and push it back. Onthe other hand, this little item (Valve or piston) is not really expensive.

Hans

[Jordan]

Good point Hans.

Just to mention, if anyone has a starter valve stuck:
I recently worked on a Mikuni carb that has the same type of valve, with the plunger stuck because of corrosion.
I tried penetrating fluid overnight, heat and a big pull on the cable but it would not move.
I appealed on a forum for help, and vinegar (weak acid) was suggested so I tried a little around the plunger.
After soaking overnight, the valve plunger was removed easily.