Bolt on 3+HP

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barncat

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just installed and tested the 1-1/2" long aluminum carb intakes i made the other week for VM's. 3HP is probably conservative, according to seat of the pants dyno and newly slipping clutch. clutch used to occasionally let go in 4th under hard accel, but now 2nd through 5th and it's almost impossible to get to WOT.

so that's the good news. bad news is i have to swap out the old 6/5 plates for 7/6, preferably kevlar with heavier springs. granted it was just 50* today which carbs love (cold dense air), but the extra zip was unmistakable, and smoother delivery too.

the intakes are not tapered but are port matched, and are installed with 3Bond no gaskets. no jetting changes required.

i was pretty surprised, having only used rubber intakes before. if you're running performance carbs pick up a set of real intakes somewhere, you won't be sorry.
 

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yeah, the levers are high dollar items :)

i discovered they're even easier to make with round stock. you just bend them and file a couple notches to engage the brass plunger. they hook over the carb tops and stay "on" with spring pressure. only need 'em a few seconds on cold startup. or you could pay 25 bucks each for aftermarket levers... they're repurposed snowmobile carbs with proper jetting.
 
i do not understand- IIRC...?

i'm not sensing a shift in the powerband, just more torque and more HP from the bottom up. i've tuned a number of 70's project bikes from GS1000's to CB450's, i think it's generally accepted that any time you get new clutch slippage with no other mods you just upped the output.
 
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these are VM34's. they are much harder to find on ebay since so many of us are building bikes these days, especially in matched pairs. 36's are still easy to get last i looked, so many sleds use them.

all the heavy lifting on ballpark jetting was done by Grizld1 etc...

i hand modded the slides from 2.0 to 2.5, 25 pilots with air screws out i believe 1-7/8 (that got changed a lot while tuning as these motors seem very sensitive to idle mix), 6F9's at 4th clip, 159 P-6, 180 mains, floats at 24mm

custom 1-1/2" 2-2 headers into Thrush cans. there's a pic or two in the classifieds under Green Hornet bobber.
 
barncat said:
these are VM34's. they are much harder to find on ebay since so many of us are building bikes these days, especially in matched pairs. 36's are still easy to get last i looked, so many sleds use them.

all the heavy lifting on ballpark jetting was done by Grizld1 etc...

i hand modded the slides from 2.0 to 2.5, 25 pilots with air screws out i believe 1-7/8 (that got changed a lot while tuning as these motors seem very sensitive to idle mix), 6F9's at 4th clip, 159 P-6, 180 mains, floats at 24mm

custom 1-1/2" 2-2 headers into Thrush cans. there's a pic or two in the classifieds under Green Hornet bobber.
Click to expand...
Bull chit vs 34's on sleds.
 
not sure what your point is there racerdave.

over several years of searching ebay, 36mm VM carbs (or larger) were a lot more commonly available from snowmobiles than VM34's.
 
i did leave out one detail above in that the inside diameter of the intakes were significantly roughened perpendicular to flow, with a Dremel and coarse sanding drum. this creates micro turbulence which keeps the boundary layer of gases from sticking to the walls, increasing flow. not a new concept, just included for anyone who may not have heard of that... easy to do to any commercially available parts if needed.
 
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bull chit may have been the wrong term. Not bragging, I've been around sleds since the mid 70's, and I meant vm 34's were much more commonly used on sleds vs sleds with vm36 or 38. Thats one reason 34's may be harder to find. For some sledders restoring etc, replacing a crudded up 34 with another of the same was easy because they were so plentifull. Didn't me to come across like a dick. Sorry.

Agree with your "roughening" of your intakes. Another way to say it is it helps break up the fuel droplets. Also common with some sled 2 stroke engine porters.
 
no real offense taken, and appreciate the clarification. we're all friends here.

i'll be more than happy to defer to your sled expertise. i've only briefly owned one, though i should probably get another one because i own property here that is part of a major league regional groomed trail system.

i think whats going on with the scarcity of used ebay VM carbs of 34MM or less is supply and demand (bikers), and probably aging out. correct me if i'm wrong, but they were used on older smaller machines, and as motors got bigger, so did the carbs and there's more of them in circulation. because i am frugal, i've spent many hours searching for suitable used stuff (you're just gonna swap out brass anyway). that was my only point... i suppose if you lived near a major sled dealer/graveyard it would be easier to shop for vintage carbs. there's one up in Barneveld, NY on the edge of the Adirondacks that i stop into if i'm ever up there.
 
I have 36mm dellortos on mine, I have tapered inlets made, makes a good flow from 36 to the 34mm on the head without a step,
 
sounds like you spared no expense on that setup jay, bet it really moves. what sort of exhaust are you running?

i don't know whether i'll get around to trying out 36mm carbs on an XS or not, the next build gets a nice pair of 34mm TM flatslides that are already cleaned up and on deck. i hear a handful of guys run those but they can be finicky to dial in. plus i plan to do a fairly extensive Jack-style port job. he very generously gave me some parts and pointers on porting the motor in this thread.

i do like to TIG aluminum, and saved $$ by making the intakes above. the commercially available ones are billet of course- they look great but it means a LOT of chips on the floor to cut them out of solid stock.
 
I have mine made in a CNC machine so no chips on the floor,

Exhausts I run 1 3/4 pipes from Hoos with open megaphones with a 3' opening at the end,
 
well, right, nobody makes commercial billet parts with manual Bridgeport style machines these days. just meant there's a lot of waste material, as you know...

i've not made any 1-3/4" headers yet. from what i've read here they are best suited to top end. i'm pretty happy with the loads of torque out of the 1-1/2 mandrel bend stock i get from Speedway Motors.

i also intend to experiment with megaphones on the next build, have a pair of open ones on hand. according to Cone Engineering you give away a wee bit of HP with open "phones" as opposed to light baffling. i'll be putting some glass in them, but will certainly keep your setup in mind.
 
just checking back in...

not that it's earth shattering news, but 7/6 clutch plates are a big improvement over the the old 6/5 setup on these early motors. surface area. got around to swapping them out today. went with good old cork (37 bucks on eBay) and a set of used steel eBay plates that i hit with a random orbit palm sander with 100 grit paper.

also modded the horrible easy-to-strip Phillips clutch screws by flattening the heads a bit on the lathe then drilling through with a 6mm bit to accept 40MM stainless socket screws. highly recommended mod. or you can just buy the kit.

to anyone new to these clutches- make sure you have an impact driver on hand for disassembly. i just use a manual one with a BFH.

all that tractor-like torque is going to the ground now:thumbsup:
 

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