Mikuni

[wyatt emp]

Still trying to get my 30 VL running. It tries, but nothing serious. An old timer told me my problem was that the 38 mm Mikuni carberator I have on it will not work on a VL. Is that right?

[wyatt emp]

Here is a reply I got from a carb guy:
"I think the problem is the way this carb is set up and the way the flathead intake and chambers are. The vl's had linkert carbs at that point and the fuel shot inward actually. I think! Other then that thought. I could not see any other problems. Where i work we have a 40s flathead with this mikuni. And runs fine. We also sell at work this kit but with flathead adapters and we have never had a problem. Ask the old timer why he says they wont work."

[Rubone]

38 is pretty big for a VL, a 34 or even 30 would work better. There is no reason it wouldn't work though. The fuel doesn't "shoot" anywhere. On a slide or butterfly carb the fuel is drawn in by the pressure differential created by rotation of the engine timed to the opening of the valves and dependent on the good sealing of the rings. Carb design doesn't matter.

[wyatt emp]

Thanks for the info. It would be way cheaper to try a 30 then a Linkert

[T. Cotten]

Wyatt!

Most "carb problems" start at the manifold.

Have you bubble-tested?: http://virtualindian.org/11techleaktest.html

....Cotten

[shelbyinparadise]

38 is pretty big for a VL, a 34 or even 30 would work better. There is no reason it wouldn't work though. The fuel doesn't "shoot" anywhere. On a slide or butterfly carb the fuel is drawn in by the pressure differential created by rotation of the engine timed to the opening of the valves and dependent on the good sealing of the rings. Carb design doesn't matter.

Very sound statements, speed of air flow is determined by size and the smaller the bore size of the carb, the higher the air speed caused by the intake stroke of a given motor as Robbie describes. As Cotten pointed out, any possibility of air leak between carb and motor must be eliminated. From that point the rule of thumb from the old days is you must have a air to fuel ratio of roughly 15 to 1 for a running motor. Carb circuits, low mid and high all attempt to maintain this ratio or a more rich ratio for starting. The Mikuni has 5 tune able circuits that make it one of the most tunable carbs for dirt bikes to give full power at all RPM's, each circuit allows for the overlap of going from one circuit to the next to be seamless in performance.

My experience with the older bikes, tells me most hard starting ( with all other tuning items correct) comes down to the riders procedure inconsistent, Some motors work better with partial retard than full, number of prime stroke (s) and choke setting. Way to much fuel will make it over rich and tend to wet plugs, While if carb is set too lean or has air leak around disc for linkerts the air fuel ratio changes below the required amount to keep running.

Most all of early bikes came with small bore carbs and cams were designed for same. MHO, Shelby

[Frankenstein]

I've been running 38 VM Mikuni's for years on all my UL's. If it came from Sudco, which virtually all of the Mikuni's for Harley's have, all you need to check is that the Idle circuit jet is anywhere from a 25 to 35, the main jet 310-330, Idle air screw turned 3/4- to 1 1/2 turns out, and it should start and run. With the Mikuni's enrichener system for cold starts, you can dispense with the "priming" kicks. Just turn on the switch, no or VERY slight throttle opening, and she should take off. However, you must check for vacuum leaks first, as Cotten suggests. If you're not using Peek, you should be,
Dick