Bonneville America Forums Forums Technical Forums Performance Mods single carb for parallel twins

I made a deal yesterday to work with a carb company to develope an intake manifold and single carb for our bikes. He seems to think we can get a better, and more flow than the two CVKs can. We discussed the limitations of the CVKs and why they can never be a high performance carb.
We shall see how it works out.

Why wouldn't a single CVK work? Like the Tiger s (TR 6,7 s) of old. Only one cylinder fires at a time.

The limits .....well, that woud be a lengthy and indepth conversation. Basically the vacuum operated slides cause a slow response time. The needle and jett combos even with the pilot jets actually do leave a lot of areas for compromise, not to mention that the slider causes turbulent flow. All making for limitations when trying to maximize out put potential.

Not exactly, the flow limitations would leave ya starving the bike when it comes to performance. We are looking to gain as much flow as possible.

A single carb can actually get you better performance on the 360° engines. It'll be interesting to see how it works on a 270°.

So what would you run, a 45mm or bigger single carb?

You would probably run something close to what you use with dual carbs, depending on other mods. The main advantage will be a smoother, more constant air flow; as well as not having to sync them.

We have a lot to work out yet. How big the ports are, how much vacuum the cylinders pull, how long the intake tubes are going to have to be, what the actual cam duration is, along with other factors. I'm going over to his shop Monday to get some measurements and do some tests.

I always like the single carb bikes better on the old stuff.

I'd bet the mileage would improve as well along with a smoother running engine.

We are pretty shure after doing some tests that we can get more power, a fast response time, and a much smother runing engine, with much more torque. We are begining fabrication now for the intake manifold.

i want one yesterday!

Once its developed. we will sell kits that will be an intake manifold, carb, air filter, and mounting brckets. We will also include extra jets for fine tunning with your exhaust and climate conditions.

Would it be possible or even plausable to incorporate a forward facing air filter? Kinda like a ram air intake.

Its possible yes with the carb positioned where its going to have to be. nearly any intake configuration is going to be possible. You will be able to get many different brands and styles of after market intake accessories for the set up. The sky will be the limit, but we have lots of testing to do after the prototype is fabricated and meets our requirements. Lots a work yet to be done but the work has begun.

I'll be interested in a purchase after I see some before and after dyno numbers

Good luck with your endeavour Chad.
Just make sure that replacement carb has plenty of that "bling" factor for our prized mechanical ponies.

JUST GREAT, , ,I finally get the bugs out of my Freak 45/145 1 shim punched 2 baffle removed 3rd, and now I get to START ALL OVER FOR MORE HP!!!!

Thats the fun of it bistro. The never ending search for motorcycle de ultimo.
Thank you John.
I don't have before runs, Dave. I guess I can tear it back off reinstall the original carbs and get a run. I didn't think about a before run because we all know what they do now. I guess it would be good to see the contrasts on paper though.

You can always do a back to back test on the same day.

I gotta find a dyno around here. It seems like in Houston it would be easier than it appearantly is.

Why would you choose an S&S Super E butterfly carb, over, say, a Mikuni HSR or a Keihin FCR?

Partly to get rid of the variable venturi, and needles, they react slower.
To use the the booster jet system better atomization of the fuel and instant reaction time.
The vacuum does not have to move a spring resisting slide up to move a needle up to open up the jett more to allow more fuel.
With the patented booster jet the more air flow the more fuel the only mechanical devices involved is the throttle opening the butterfly.
The carb engineer has had a lot of success with this on the race track with Vtwins. Now we are going to try it on ours and see what happens.

Ok not faster than the HSR as is, but yes after the booster jett is installed. The booster jett is the key. But its a patented secret so I can't tell ya how it works. Can't use the booster jett in the HSR because the way the throttle works. can't pull up a needle that ain't there.
Please understand HSR and FCR are very very simular.

Your on to something here Chad. Can't wait for the product

The variable venturi carb used on motorcycles is superior to a fixed venturi. That being said I do know some variable venturi carbs that didn't work well at all on cars.I am interested in the results as well.

That booster venturi looks like any booster that's in a fixed carb.(except how it attaches/connects to the main jet). They still use an "accelerator" pump to cover up the lag time between when the throttle is opened and and booster starts to flow.

I'm not an engineer, but the fellow I am working with is. He has had a lot of success with his design. I hope it works out as well for our bikes. If it gives us what we think its going to be sweet.
My shop is for all motorcycles and riders. I cater to beginners and women in general because noone else does, but many of my customers are seasoned motorcyclists who know what they are after.
This project is for us though. I see potential in our bikes that is untapped.
I hate the stock carbs because they are the weak link. My carbs are closer than its ever been but its response time is sluggish and the top end is weak. At 110 my bike is not near the rev limiter but just will not pick up more speed. Off the line yes I can take most 900cc cruiser class bikes, and even the stock 1200 sportster sometimes. I think our bikes have more than this in them.
I know all this race talk is not appealing to everyone, but more power and smoother operation will make for a better cruiser for the long haul, and stronger two up riding.

We have a working prototype now. Things are looking very positive.

PICS!!!

Forget pix just send it to me and I'll test it out for a week or 2

No can do yet. The prototype intake is a bit ugly, lol. The finished product will be perty though. There will be options powder coat or chrome.

Please, sir. I want some more.

Ok, you win...you pressured me into posting some pics. lol.

I am trying to iron out an off idle hesitation, but from there up is great. Even better at higher throttle.

Can you back the camera out a bit, I can't tell much from the close ups.

Alright then gee.......I thought you might want to see it in relationship to the bike. I'm no photographer. I guess Keith should come down and takr the pics. His are always great.