Topic: 2 carbs instead of 4 on a 750?

[cafe2be]

I have seen a kit that does this. It using a 2 into 1 manifold. Is there any benefit to running 2 carbs instead of 4. I image its easy to tune 2 instead of 4. Performance?

[Johnny5]

Easier? Probably not since you're still tuning carbs, just two less. So the only benefit is less chance of carbs getting out of sync, and a little quicker to tune because of two fewer carbs.

[kayaker43]

Ceratinly a little less performance. More restriction and the intake runner length is too long. It might give you a tiny low end boost, but long runners will hurt high RPM power by some small amount.

The only good reason for two carbs would be for looks on a chopper.

[Jerry Rxman Griffin aka MuthaF'er]

I've seen the setup once and the guy was having problems with the throttle cable attaching correctly and pulling both carbs correctly. It was not a stock frame so I don't know how this would work on a stock frame. I understand there are fitment issues on a stock frame however.

[Geeto67]

I assume we are talking about Ken's Kit for the 750. Cycle Exchange's right?

Fitment issue is the carbs don't clear a stock frame with filters. He used to sell a manifold to fix this but now if you ask him nicely he will just tell you where to get it.

Ken has dyno numbers to back up his claims about the carbs. The intake runner is not too long, it works the same as tunnel rams used to work on old hot rods. If the carbs are sized right (and they are) it shifts the power curve down to favor low end grunt, but you do not come out with less hp overall. In fact the system does make hp, it just makes it in different places than say a set of FCRs would.

I have seen drag bikes run similar setups (and I have an ancient setup for a cb750 from the 70's that uses two giant mukunis) and it works for them because there is less to fiddle with between rounds.

I personally don't like the setup because it works on the principle of averages. Don't follow? let me explain. In a carb'ed v-8 car every hole runs a little different. Usually the rear cylinders run leaner than the center cylinders. Basically every cylinder has a different volumetric efficiency. Want to adjust just the rear? tough luck kid, one change in the carb affects all cylinders so the best running combo is the setup that is ideal for all the cylinders on the average. In the 60's and 70's you saw a lot of multi carb setups to try and work around this. They worked but tuining 8 carbs is a pain in the azz and if you used IDA's there is a good chance you were putting out carb fires as much as you were tuining.

With a cb750 if the number 2 cylinder is lean, you can adjust it because it has its own carb. Feeding 1 and 2 off the same carb means that that carb has to be jetted so both work, which means you will either have a carb jetted to the cylinder with the worst VE, or one that is just good enough to keep both running at diminished capacity without hurting anything.

If your motor is stock, then really it won't do any damage and you will see an improvement. On a hot rod motor, CR carbs are the much better choice for the money.

If you want something that a lot of non-racer people are going to look at and go...ooohhhh, then it is a cool piece of kit. If you are going to hang out at Bar Matchless with Dave Roper and crew, I don't think those guys will give it a second look because they know it is all for show.

[cafe2be]

mskes perfect sense. I was just wonderinig about this.

[gerhed]

I run the Cycle-x setup.
Carbs are tight--almost no clearance to the frame.
I fitted some thin screens.
Plenty of power--tuning not an issue, really.
bike is a '75 F