single carb.... can I use a S&S

[AceofSpades]

ok I am seriously considering a long tube (tunnel ram) style merged intake and I was thinking that I could get away with a carb off an 883 Sporty.... any thoughts? maybe an S&S? figured if nothing else, I could find parts at any shop..

 

[TeeCat]

Ace, there are a lot of people on here who can give you a more educated answer than I can, but I'll go out on a limb and say I can't see why not. Is that carb vacuum actuated or direct pull? It seems to me that if a single carb is feeding an 883 that it can feed a 650 adequately, with the contingency being proper jetting across all the circuits. I think the carb you use might matter less than the way you jet and the intake you use.

TC

 

[AceofSpades]

TC.... That was my line of thinking.. and the fact that I have half a dozen family/friends with HDs.. I figure I can pull one of thier stockers out of storage, and give it a shot.. as far as intake, I am thinking a forward facing carb on 14-18 inch runners . probably gonna have to fab my own intake.

 

[TeeCat]

Ace, someone on here - and I can't for he life of me think who it is - used an older Harley carb on a homebrewed intake, albeit with short runners, and said it works beautifully. I would find it very hard to believe that you could not rejet a variety of carbs to meet your specific need.

One thing that I have heard is pretty important is to make sure that the inner and outer diameter of the intake side of the carb is close to the same as the inlet on your intake. This will aid in affixing the carb to the intake, as well as smooth the flow of air/fuel into the runners, I'm told. But if you're fabbing your own intake, then you know more than I do.

TC

 

[grizld1]

Sure, you can make that work. But the bigger the venturi, the weaker the vacuum signal, and you won't to gain a thing (besides a lumpy idle) and you'll lose low-end and midrange power by hanging a 40 mm. carbie on an XS650, even with a 750 conversion and go-fast mods. There's no percentage in it.

 

[Hooligans]

Ace, someone on here - and I can't for he life of me think who it is

TC

you would be talking about "everyday12s". He has a homemade stainless intake with a harley carb

 

[oldbiker]

hi guys abot 5-6 years ago i was very lucky too meet a guy with a xs650 at scorsby swap meet ,in outer melbourne australia its purely motorcycle items.... anyway the guy had a side draught webber carb and tubes and mesh on the end of tubes along with an electronic cut off fuel set up from the tank,, of a vl commerdore ... he ws tickled pink with it ..the petcock was not there instead this electronic shut off set up to the tank and all looking neat ,,he rectoned he was always riding ,, he live in belgrave somewhere hope this help regards oldbiker

 

[AceofSpades]

Sure, you can make that work. But the bigger the venturi, the weaker the vacuum signal, and you won't to gain a thing (besides a lumpy idle) and you'll lose low-end and midrange power by hanging a 40 mm. carbie on an XS650, even with a 750 conversion and go-fast mods. There's no percentage in it.

so what carb would you recommend for a single carb conversion using 12-14 inch runners? I just want to get the best performance possible while getting some serious shock factor and wow the crowds that seem to be drawn to my bike... gotta keep it evolving.

 

[hutch08]

I'm currently building a custom 2-1 intake for my xs, from the research I've done... I'll be going with a mikuni VM carb... Probably the 34mm... These carbs work well, simple design, easy to jet... And there's already some baseline jetting available.

Whatever works on a stock dual carb setup will work with the 2-1... jetting is actually quite similar, each cylinder is out of phase, so only one is on the intake stroke at a time.... So don't think that you need double the size carb because the fuel won't be split between each cylinder....

Hope that helps some... I'm no expert so if anyone else has input, speak freely.

 

[grizld1]

You're thinking right, hutch08. Ace, you want to keep in mind that if you go from a butterfly carb to a carb with an unobstructed throat, you're effectively increasing venturi area. Some full-race 750's mount carbs as large as 38 mm., but no power advantage is seen before around 7K rpm, and that's gained at the expense of low-end and midrange power; 34 mm. is a common choice for tighter, slower tracks and TT, and 36 mm. is a common choice for general use.

The key factor is the strength of the vacuum signal--the larger the venturi, the weaker the vacuum signal to the carburetor. If you want some "serious shock factor" you'll want fast throttle response, and you won't get it out of an oversized carb. Think reasonable venturi size, accelerator pump, and high compression. The TM36/68 Mikuni flat slide pumper is a good choice on a modified engine.

 

[AceofSpades]

just out of curiosity, what if you were running a rephased 750? with stock phasing and 650, would I be ok with a rejetted stock carb? ( 75 xs650 standard )

 

[hutch08]

Blacksmith billy built a 2-1 intake and used the stock carb, had to change the jetting obviously but he said it ran great, there's a video clip on youtube to hear it running...

 

[grizld1]

Whew. With crank and cam rephased at 277* you're going to need to take a close look at intake valve timing with the camshaft you plan to use. If the intakes are open at the same time anywhere in the combustion cycle, things are going to get tricky. With 360* phasing, your stock BS38 should work fine with either stock or 750 cc. displacement.

Remember that there's always a trade-off involved in any performance modification. The main advantage to using the vacuum carb is that it compensates a bit for atmospherics, making it much less touchy about changes in weather and elevation. The advantage to using an aftermarket performance carb is that mechanical actuation of the slide and the unobstructed venturi deliver crisper throttle response and a bit more power--if the carb is selected and tuned right. BTW that's a very long runner length you have planned; when you look at the formulas, bear in mind that the intake length they specify is measured from the valve face.

 

[Beau]

My buddy is running a 883 carb on his Honda CM400. He has a lot of trouble getting enough fuel to it. He had the Harley dealer tune it. Runs great now!

 

[AceofSpades]

the runner length is not a definite. I just rough estimated it as I want the carb to be forward facing and the fuel bowl will be just below the plane of the fuel outlet on the tank ( likely to remain the stock tank- what could be more different than keeping a stock style tank on a bobber? lol) I will be running a 360* 650 for at least the next year or two, and I am planning on making it more of a highway capable cruiser, but with some bar-hopping power. thinking an 18-30 gear set should give me comfortable in town 3rd gear cruising and long legs on nighway runs..