But, The YZ426 only has one carb and it is feeding 5 valves.

 

Okay, You got me!

 

I would have to agree that there may be some troubles with the one to two pipe being that one side may need more than the other.

But, my friend has a one to two intake on his banshee, and with all the mods, it tops 100 mph. But the Banshee has equal intakes, and with the twin, it has alternating pulses, so it balances out.

So, one in two works on a Banshee, and extremely well, but I don't know about the Raptor. I will have to look at my 426.

RM

 

I can't find the link now, but the MuZ 660 had a kit out for it to go to a single carb and if I remember right, it added around 4 - 6 HP.

 

Check my newest post, I think I've found a workable kit.

 

I guess I need to see the design of the head up close to be absolutely sure, but a properly designed single carb intake would allow some "Plenum" space before the carb to equalize & smooth the flow thru the carb, much like your typical intake manifold for an automotive multicylinder engine.

At this point, the carb does not care that the flow thru the valves ahead of it may be uneven (much like the carb on a car or truck doesn't care that flow between individual cylinders may be a little uneven), it only cares that air is being drawn thru it & that there is vacuum. The engine is not going to care which valves are feeding it and if more mixture comes from one or another, because it has already been mixed & the mixture won't change appreciably if less flows thru one valve than does thru another. The engine only cares that the flow potential is there.

Any problems with cylinder filling will be inherent to Yamaha's head design and independant of the carb setup.

However, problems you describe sound like the exact reasons not to run a dual carb setup to a head configured like this. If you are drawing more/less air/vacuum thru each carb, that is where serious nightmares can arise.

The YZ426F & YZ250F seem to work fine on a single carb with a 5v head.

The Banshee is a whole different animal being a twin cylinder 2 stroke. You have to deal with many other factors & interaction between the 2 independent cylinders.