LANCER
Serious Thumper Alliance Member
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Savage Beast Performance Parts
Posts: 10700
Oklahoma
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Lancer, Clearly you know the Savage like few others on this site. I am curious why you selected the carb that you did for your kit. The quick answer is that the VM carb provides the biggest bang for the buck.
More detail: A roundslide carb is the traditional performance carb of choice for professional racers of big singles. They are simple, inexpensive, easy to tune, and make very good power. They have been used for over 40 years with great success. The Mikuni VM roundslide series carburetors have been used more than any other carburetor in the history of motorcycles. The 36mm & 38mm VM carbs retail for only $150 +/-which makes them very cost effective.
I have seen other members are using the 40mm Mikuni flat slide pumper. In your opinion, how do these units compare? The flatslides, with or without an accelerator pump, are very good carburetors, produce good power and in some cases (w/o acc. pump) are pretty cost effective.
Carb size: I think a 40mm flatslide is too large for the LS650 engine. As mentioned by another member, its larger bore will slow intake air velocity which will reduce power in the lower throttle range. A 36mm carb is a better fit for a stock engine or one with the Stage 1 Performance Camshaft . A 38mm carburetor is more appropriate for a more highly modified engine with ported head, higher compression, Stage 1 or especially Stage 2 Performance Camshaft , bored cylinder, and custom header of at least 1.5" ID or 1.65" ID and a performance muffler like a Supertrapp or Hard Krome, etc.
Back to VM roundslide vs TM flatslide ... As I already stated, cost is a prime factor. From a performance standpoint, a VM carb with a UFO installed under the slide will outperform a flatslide carb of equal size in the low-mid throttle range, and equal or near-equal performance in the high throttle range.
Thunder Products (mfg. of the UFO) dyno tests of VM (w/ UFO) vs TM carbs clearly show the performance advantage of the VM carb. A UFO is only $30 and when installed on a well tuned VM carb will boost power by 1 hp per 100cc of engine size. That works out to a 6 hp boost on the LS650 engine. The increased power and near instant throttle response is so pronounced that it takes some getting used to; having to retrain your right hand on throttle control touch. It is amazing. The bike virtually jumps when you crank it on !  Really !
The accelerator pump on a flatslide carb will provide a short boost when you crack the throttle open quickly but then its affect deminishes. The UFO strongly boosts power & responsiveness up to about 5/8ths throttle.
I am considering putting a new carb on my bike (I already have a K&N, a dyna muffler, and a rejet-thanks to Serowbot.) I will probably order your kit, so that I don't have to worry about all of the bits and pieces, but I am curious. Also, after putting on a new carb, would there be an additional benifit of going from a dyna to a SuperTrapp? YES. Even more so if you replace the stock header with a 1.5-1.65" header as mentioned above.
the high flow and tunability of the S/T make it a very good choice for a modified LS650 engine.
Thanks for any advice. Always appreciated.
PS: I forgot to mention an important point. Why choose a 36mm or 38mm VM carb when replacing a 40mm CV carb ?
One of our forum members, KLX650, who is a professional builder of perfomance exhausts for a variety of machine types, posted some info in the past about CV vs roundslide or flatslide performance carbs.
It is important to take notice that in the way a CV carb is designed and built, there is a butterfly valve which is operated by the throttle cable. There is also the vacuum controlled slide. A 40mm CV carb has an effective throat size of only about 37mm when the size of the butterfly valve is subtracted from the total volume of the carb bore.
When this is taken into account you can see that a 36 or 38mm round or flatslide carb is equivalent in bore size to the 40mm CV carb.
The roundslide and flatslide still have a better air flow velocity though, because there is nothing in the bore to interfer with that flow, like in the CV carb where the butterfly valve is like a barn door in the way of the flow.
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