Single Carb for Royal Star

[AmnChode]

I have been pondering doing a 28mm-32mm carb swap on my '96 RS, and for whatever reason, the thought of doing a single carb setup popped into my head. So, of course, I did a search here and came upon the following thread:

http://www.venturerider.org/forum/showthread.php?124413-A-new-twist-on-the-single-carb-swap&highlight=holley

 

Now while this was based on Gen 1 Ventures, shouldn't it be just a possible to use on our RS's, albeit, maybe with a cleaner install . More importantly, would we get the same'ish performance increase considering, for us, it would be an increase compared to our 28mm carbs. Seems like it would be an easier and cheaper way to get a performance increase and make bike maintenance a little easier...

 

Thoughts?

[Patch]

Well I can toss some thoughts up for kindling..

 

If you over think constant velocity we tend to loose faith in them.

 

What we do to a short haul or track bike usually won't suit a touring machine needs.

 

That said some years back I struggled with 32mm on something I thought just needed more potential. I pondered for a long time on switching to a central injection system Mighty Squirt was still in early stages and was an open platform so... Then I picked up a parts bike with 36mm that I really had no use for and started a conversion on an extra v4 I had on the bench.

I haven't finished it yet but likely soon as I am breaking down the shop planning on just keeping 2 bikes.

 

What I would be hesitant on first is, the length of the intake tubing, especially for the higher rpm range.

Next is that any gains will be had by taking advantage of matching close to... displacement,(an easier fill is also a quicker fill) then jetting for stochoi!

 

In short I would stay with CV and jump to 32mm from the 28s or 32s to 34/6, likely it would be an easy 1st start and tuning would be minimum.

 

I would and likely suggest a little porting (head on) nothing major but ensuring nothing in the way of grinding gets past the valves!

 

You might assume that this will require free flowing yapy exhaust? Well I'd rather discuss oil then exhaust or even better ride while others chase that tail;)

 

Patch

Edited August 19, 2018 by Patch

[AmnChode]

From my understanding, the longer runners will increase the low end torque. Considering we can't wind these Royal Star engines up as much as the Gen 1&2 Venture builds (due to the spings, lack of a counter balancer, etc), I dunno how much of an effect it would actually have on the top end. What I mean is, right now the Royal Star builds are severely 'choked' because of the 28mm carbs, so performance wise, they are at a severe disadvantage.

 

As pegscraper has pointed out, by swapping out the cams and springs from a Vmax, thus giving it a more agressive cam profile and a set a springs that can keep up without floating a valve, and then swaping the carbs to a 32mm set, he found a ~50% increase in power....and he notedly stated that is the carbs that was the major thing holding these engines back. So, while not particularly thrilled with yanking the enginge to swap in the cams and springs, swap out the carbs are a different story. However, if I am already goingto have a machinist build me a set of adapters and shave the runners, might has well build an intake and simplify the entire intake/fueling system. At least that is my train of thought....

[Patch]

I was wondering if you were going to bring up the torque puzzle;)

 

In this case my experience says not going to happen.

 

But I do like the question and you do have a hint at length and torque but you are missing no less than 2 parts to the puzzle. If I just blurt it out then you will only have another piece, a better understanding of "what" flows will really bump understanding.

 

Pick your favorite example of improved torque and visualize all the components and where in the system they are located.

 

For the last sentence simplify, you won't be doing that either. Filling the jugs is a very big part of increasing output, this can also be very complicated with only one constant! It is that constant that you, we usually look to make the most of!

 

very nice

Patch

Edited August 19, 2018 by Patch

[AmnChode]

Well...all I have is a very basic knowledge of the 'mechanics' and little piece of here and there; hence, why I posed the option the the greater masses. While gaining the most efficiency and/or performance would always be a great goal, sometimes there has to be a compromise of ease of use/convenience over max performance. If it was pure performance thing, you would see a helluva lot more flat slides being installed.

 

So, if the performance is relatively close to what a Venture (Gen 1 or 2) puts out, which is considerably more than a standard Royal Star, that's good enough for me....especially if I don't have to do as much carb work. AND...it would make rejetting so much easier

 

Really wish that PKR Customs would have followed through with that dyno run. Then we could have seen the difference and be able to compare with some firmer numbers vs butt dyno.

[Patch]

I completely get what you are saying. If I have provided reason enough to pause then its up to you.

I can tell you that swapping cams even when you don't fully understand duration and lift, is less difficult by far, then any magic bullet you will find when it comes to fuel ratios, charge, velocity and, keeping the fuel mixed in gaseous state by the time it travels that length. One of the issues is, velocity can separate the fuel mix? This happens in part because of friction and gravity. That post you referred to was experiencing such but- below operating temperatures (he mentioned). It was both an experiment and experience for him and likely he will or has grown because he took the chance. Or maybe he did achieve some success?

 

My experience would suggest that these torque band efficiencies were developed around injection systems. (true we had high rise way back but we couldn't claim efficiency) Injection easily allows for moving the heavy sticky fuel ratio as close as possible to the valve chamber where mixing accrues quickly, at predictable temperatures and where the stochie charge is then split and vortex'ed through the twin valve chambers; then into the combustion chamber, distance traveled is minimum! Go figure;)

 

Bore & stroke x rpm range are important factors to consider, you would likely want a variable intake system to handle moving towards WOT.. (even if you don't plan going to WOT we are always pulling in that direction)

 

In short its not that you/we can't, its more what is the gain and or reliability and outcome for a touring bike...

 

Having said all this I saw a while back a setup for sale on a link here through ebay or parts for sale??? 5 or 600.00

 

I've been wrong before

Patch

[RSTDdog]

Can't help with the single carb set up. From a reality standpoint, all the mods and effort still doesn't get you to the stock HP of an RSV or 05 up RSTD. If more power is the goal, the easiest solution would be to swap in an engine from a 99 up RSV or 05 up RSTD. You get more horsepower and the balance shafts right out of the box. You could massage the heads and intake on that that motor to get a bit more out of it before the install. One reason you can't Vmax HP out of the RSV/05RSTD engine is the air flow limitation on the inlet side of carbs. There is a thread somewhere with a link to where a guy made a custom fuel tank and essentially had the part of the fuel tank that covers the carbs hollowed out and had velocity stacks up through the center of the tank. That may be a work around also for your single carb idea. Pinwall Cycle parts has used engine assemblies, carbs, just about everything.

 

Here is the link to the Royal star with Vmax motor and velocity stacks https://www.motorcyclecruiser.com/batman-one-maxed-out-yamaha-royal-star-motorcycle#page-3