M88 or Mikuni

[panzer45]

Just finished my 45” flathead rebuild for a 1946 Servi-car.
I don’t have a carb, and was wondering if a stock M88 type carb or a 42 Mikuni is a better choice.
Thanks!

[RUBONE]

It all depends on what you are trying to do with it. The stock carb on a '46 Servi was an M16, so anything other than that comes down to your personal use. The Mikuni has more performance potential, but without other mods it is wasted effort. The M88 was military use so needs a few mods to be a good all around carb on a stock engine. So????

[Pascal]

A Servicar is meant for lowspeed town-plodding.
It needs lowend torque over highspeed performance.
If you restored it as OEM, install an M16 carb and small manifold.
If you're doing a roadburner...a Mikuni is perhaps a better choice

[Frankenstein]

Just a suggestion, a 34 or 36 would be a better choice than the42.

[RooDog]

The 42 MM is better suited for an 80 inch OHV motor....

[kitabel]

I've used a VM36 on a 45" engine (Sport Scout) but it was entirely convenience - I had it on hand. I don't think there was any performance increase over a smaller Mikuni.
Even a 30mm flows more air than an M88.

[RUBONE]

A stock M88 only has a 15/16" Venturi. It is fine for a stock "G" engine with low compression and a small intake manifold however a larger WL manifold will allow a gain of a bit of top end with the 1-1/16" venturi from a 1-1/4 model carb (like an M51) which can be notched like the M88 one or an external vent hole can be drilled to allow it to work without a notch. The high speed needle can be changed to the adjustable type for more fine tuning. All other internal features are in common. Add a pair of #6 heads and the engine will then be the same as a standard post war WL.
Anything larger than a 34MM Mikuni on a stock 45 will be very difficult to try and tune. A 28MM Amal actually works quite well.

[JUGPAM11]

On my servi the 34mm is difficult to tune for wide open throttle!!

[kitabel]

What jetting are you using?

[JUGPAM11]

numbers are hard to read. looks like pilot-20 ,needle jet-159p6,jet needle -6dh3, throttle valve-2.5, air jet-1.0, main jet-240 , tried lots of different mains with no help. runs great till a mile down the road then seem to run out and back fire through the carb. thanks for asking and being interested to help. help is greatly needed here because no one here knows anything about mikunis.

[Frankenstein]

It's possible the float needle orifice is too small. They come in different sizes, something to look into. Several of the aftermarket catalogues have them. western power sports, tucker rocky, maybe even Drag.
As I recall, they're numbered like 1, 1.5, 2, 2.5 etc.
DD

[JUGPAM11]

yes needle and seat have been changed from 3.3 to 3.5. thanks

[kitabel]

The pilot is a bit smaller than what I would use, everything else looks normal.
Are you sure your gas tank is vented?
Factory petcock?
When running WOT: if you back off the 7/8 throttle is it better or worse?

[JUGPAM11]

Kitabel, pilot should not effect full throttle. Is that right? Tank and gas caps are ok. Ran with it off also. Derusted the tank and cleaned good and a new screen. Just checked the flow in to a marked off jug and got 1 pint at 1:10 and 1 gal at 2:30 seconds and about the same on reserve. If I back off when I first notice it is ok but if going farther it is worse. Stop and wait a bit and its ok for another run. Does that make sense?

[kitabel]

Can't think of anything else.
What plugs? Gap?