Difference in 1 or 2 carbs?

[harold]

I have read all the posts I could find on putting a single carb on a Baghira, although most are about doing it on a Scorpion, which I assume is the same motor in a different frame. I have a 42 HSR Mikuni which I could make an adaptor plate to fit with a Grizzly manifold from what I have read. That would be some work, but then jetting would be a snap compared to the stock carbs, as the main jet can be changed without removing the float bowl or carb on a Mikuni. Needles, jets, and everything else are readily availble both new and used.

Bear in mind, I have a Baghira, not a race bike, and want low end snap and mid-range, not top speed or high RPM.

What is the difference in performance in single or dual carbs, all other things being equal? The Raptor has 2 carbs, but Yamaha puts a single carb on their racing 450 YZF? My Raptor had more torque and acceleration compared to a brand new 450, but of course it had 210 more cc's- basically 50% more displacement. Harleys have a single carb for 2 cylinders, and have great low end torque. All other muticylinder bikes were one carb per cylinder at most. Why did Yamaha go to the expense of putting 2 carbs on this motor. Their 4 cylinder bikes had 5 valve heads until just a few years ago and did just fine with one carb per cylinder, as did all the others with 4 valve heads. The Grizzly (I think) had a 5 valve head, but only one carb.

What is the difference? Why 2 carbs when everyone else gets by cheaper to build with just one?

[Bill Jurgenson]

the Grizzly has 4 valve head.
so
Low end torque is a no-go by definition from a short stroke engine with little flywheel weight. Demanding performance below 3500 from an XTZ motor is unrealistic and will break it in short order.

you haven't read thoroughly. Recent threads (last week) covered exactly this topic. The archives contain much more.

The single carb delivers more midrange performance as long as it is not too big. Galen Miller decided after much testing that 42mm is the limit for everyday usage. The single carb delivers, not because it is single but due to the much longer intake manifold necessary to mount it. Of course it is also easier to setup - to a point, but the 42 can be very critical with quiet exhausts with high backpressure. The 40mm is far easier both to set up and to ride, in particular from mid range. Top end is naturally down.
Dual flatslides on long headers also increase midrange and the Teikei would also benefit from increased length for which reason various sources sell a spacer plate ( about 20mm) for the Raptor which of course fits any 5 valve head. I think these originated with Barker about 10 years ago for singles racing, Skorpion and SZR.
In your case, I would fit one of these first to the stock Teikei.
Whether the Teikei dual carb or the Mikuni CVs used on the Raptor an Grizzly and nearly all inline 4s before injection, the choice was for ridability for those who cannot ride. CVs (the Teikei is half CV) meter according to vacuum, regardless of what the uncontrolled right hand does. modern injections are the same. Flatslides must be learned.

[basser23]

Bill,
I have also wondered about using those Raptor spacers on my Skorp...may have to try them,and use K&N type pod filters...
Know anyone who has tried them? Id love to have an FCR set,but cant spend the money....thats the wife's job at which she excells

[harold]

Bill,
Thanks for your reply. I did read about what you mention about the right wrist. On my Buell, the CV carb to Mikuni was done for increased snap, mostly from what I believe is from the accelerator pump on the Mikuni. I did not notice any negatives, and there is a small Hp increase.

Maybe you or someone else then can help with the jetting. Stock pilot is a 48 from what I have read, and the only larger one that I could find is a 50, which I have ordered. With the D&D muffler, the thing was running lean and popping badly on deceleration. Turning the pilot screw out to around 6 made a large difference, but in other carbs this would indicate the pilot jet was too small. To go larger than the 50 apparently involves drilling, something I don't have the bits for.

What about the main jets. I have read they were too rich to start with, and elsewhere that people increased them, and still elsewhere people increased the CV jet and decreased the other. I have ordered a 135 and 170, but don't want to put them in if it won't help. Taking these carbs on and off is not fun.

I don't see how I would fit a spacer plate on the Baghira, as the CV carb is almost hitting the frame as it is. Making the spacer that goes (on top?) of the diaphram seems like a good option.

What about grinding the welds in the header? On the Honda XR650L forum, some said doing that didn't improve anything. Their reasoning was the slight increase of back pressure helped.