Hi,

Question for the experts! I've got a 99 roadstar, with a nemesis manifold, MaxAir intake, size 172.5 main, 35 pilot, Cobra pipes. What, if anything, would I gain by switching to a 42mm carb? Does it make any sense to do so if I'm not planning on changing to HC pistons?

Thanks,

Pete

There is a performance advantage that goes to the design of the carb more so than the bore. Our stock 40mm carbs are constant velocity carbs, and tend to respond to throttle input more slowely than a flatslide will. When you turn your throttle, you are are actually turning a butterfly valve that sits in the throat of the carb between the slide and the manifold. The slide responds to air flow and vacuum, and will rise up in an amount that allows it to maintain a fairly constant velocity through the throat. Form the time you turn the throttle, it can take a few fractions of a second to respond.

On the HSR42, turning the throttle directly lifts the slide. You turn, and it lifts immediately. If you want to be faster getting off the line, this is how to do it.

Net result is more immediate throttle response and a bike that is faster getting off the line. It won't add much power, and Dyno's have shown that. You might get 2 to 5 horsepower depending on the other accessories on your bike. Most folks fall to the low side of that scale.

GRAM

Thanks! Now I've read enough of the old "Voes/TPS" article to be completely confused. As I don't have an aftermarket ignition, can I still take advantage of the 42mm carb? What do I do about the TPS?
Pete

What the tps/voes do is provide switching inputs to the ignition. The stock ignition (or 3000, 2000 etc..) have two curves in them. On is for normal operation, the other is for WOT. The WOT curve is slightly retarded to prevent pinging. Without a TPS or VOES, you will constantly be in the WOT curve, and your bike will not accellerate like you want it to.

There are a couple of companies who can hook you up with an adaptor for the stock TPS. The adaptors will allow you to hook the TPS up to the Mikuni 42mm carb. Its highly recommended, and will be the easiest way to address this.

There is no standard established for the VOES, and if you go that route you are going to need to futz with it to get it right.

GRAM

Thanks GRAM,

I'll go the TPS route. Can you tell me who the companies are that make an adaptor?

Pete

I think you found them Pete. I was thinking of A1

GRAM

Do you know if I can do the work myself, or is it absolutely necessary to send the carb to them?

Pete

I am also looking for a TPS adaper for a 42mm carb, could you please tell me where I could find one, thanks

Call Joe at A-1 Sports to get the 42mm TPS adapter.

Do you mind posting the web address or phone number, I am not having much luck finding A1 sports, I get everthing from baseball cards to car racing, thanks