cliff
Junior Member
Posts: 42
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Post by cliff on Jul 23, 2008 20:01:52 GMT -5
I am bringing my '81 SR500 back on-line after an engine rebuild, stator rebuild by rm-stator and now a carb. The cost of the three diaphrams on the stock carb and float bowl gasket are more than a new VM-36. Go figure.
Do I want a pumper flatside or do I want one of these non-pumper VM carbs? Assuming cost is not an issue which would you choose.
My engine is uncorked with a K&N and a Supertrapp. I am at 700' elevation what jet and needle ranges would you choose for each?
Are the flat-slides that difficult to sort out? I think a pumper would be great but if it is a PITA then maybe not.
Thanks for your help.
Cliff
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Post by solo2racr on Jul 23, 2008 20:45:03 GMT -5
Without saying the VM is better or not, I can say that jets are cheap and easy to come by and, they are rather easy to tune. I'm sure quite a few people here can get you in the ballpark.
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cliff
Junior Member
Posts: 42
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Post by cliff on Jul 23, 2008 21:22:43 GMT -5
Thanks solo2. One vote for VM non-pumper.
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cliff
Junior Member
Posts: 42
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Post by cliff on Jul 23, 2008 21:52:05 GMT -5
see below for consolidated listings of tunings and sizes.
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Post by StewRoss on Jul 24, 2008 2:38:55 GMT -5
The VM series cabs are easily available, cheap, improve the performance with a few minor mods and are simple and trouble free...36mm or 38mm, your choice...all you need to do is sort out the throttle cable and away you go. Personally I prefer the 38. A high comp piston and a free flowing exhaust system and the SR really picks itself up!  SR  |
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cliff
Junior Member
Posts: 42
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Post by cliff on Jul 24, 2008 8:25:58 GMT -5
two votes for the non-pumper VM to zero for the pumper. Thanks for your tunings on the VM38. Seems the non-pumper gets pretty good gas mileage also. Before the rebuild with stock equipment I was averaging 55mpg, which is not shabby and better than a Prius, of course no conditioned air and talk radio on board.
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pcnsd
Full Member
Posts: 113
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Post by pcnsd on Jul 24, 2008 21:02:42 GMT -5
Another vote for the VM's. I have used both the VM36 and VM38. I prefer the VM36 as providing the best all round performace. The VM38 in better suited (in my opinion, others may disagree) for full race applications where topend power is the primary goal and the head is modified to improve flow beyond the ordinary. They are vintage class legal too, pumpers are not.
PC
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Post by strick on Jul 25, 2008 0:56:13 GMT -5
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Post by strick on Jul 25, 2008 1:25:29 GMT -5
Also since we are speaking of 2-stroke carbs, what about Keihin PWK?
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Post by StewRoss on Jul 25, 2008 2:41:31 GMT -5
The VMS can be setup for 2 or 4 stroke use...not sure about the PWKs sorry. That carb pic is a VM series carby...if it's setup is for a Harley already it might be close to right for the SR as well...  VMS in-situ...  VMS...  As an alternative that Mic flatslide with the pump may be interesting as well...although it would definitely be more expensive than the old style round slides though...  The 'ultimates' for performance are the Kei Hin CRS or the FCRs...I prefer the CRS as it looks more 'period'...neither carb however are cheap devices! The CRS carby is a smooth bore type carby and probably won't operate as well as a VMS down low...they're really a top-end power device for a modified engine. Here's a CRS 38 on one of my engines...  SR |
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Post by solo2racr on Jul 25, 2008 9:49:04 GMT -5
Going JUST by the photos in the listing I would have to say yes. If there was a photo of the ID stampings on the enrichener housing, then we would know for sure. Being off a Harley, they probably set the reserve to high. Like that makes a Mikuni carb worth more  |
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Post by jdbrees on Jul 25, 2008 11:11:05 GMT -5
I've got the 36mm flat slide and it works great for me.
Pulls very clean and strong from low rpms and I really appreciate the oversized idle speed screw - for hot starts I screw it in 3 turns, no throttle and she fires up first kick every time. Three turns back out and I'm down to idle speed again.
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cliff
Junior Member
Posts: 42
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Post by cliff on Jul 25, 2008 12:32:50 GMT -5
VM-34, VM-36, VM-38 TM-36, TM-40 (HS-40) Sizes and tuningsGreat tuning manual for Mikunis TM-36, TM-40 and HS-40www.mikuni.com/pdf/hs40_manual.pdfVM34-168Engine side:40mm, Aircleaner side:58mm This from Spindlehead in regards to a VM34-168.: [ If you have:
aftermarket intake (e.g. K&N, Uni, or other free-flowing device) AND
a freer flowing aftermarket exhaust (e.g. supertrapp),
then a 240 main,
25 pilot,
P8 needle jet, and the 6DH4 needle that comes with the carb is a good start.
If you have:
aftermarket intake (e.g. K&N, Uni, or other free-flowing device) AND stock exahust
then a 240 main,
25 pilot,
P7 needle jet, and the 6DH4 needle that comes with the carb is a good start
I suggest buying main jets 220-260; pilot jets 25, 27.5, 30; and the P7 and/or P8 needle jet.
VM-36Most stock VM36's come: Mikuni VM36 round slide carburetor: Jet sizes : Main : 310; Pilot : 35; Needle : Q-5; Throttle Valve : 2.5; Jet Needle : 6FJ6; Air Jet : 2.0. Engine side:43mm, Aircleaner side:62 Curley's setup VM36"
Here's my VM36 specs
Pilot 35
Main 230
Slide 2.5
Jet (needle) P2(188) custom drilling 1or2 thou larger
Needle 6FJ4/7 Top clip with a shim
VM-38Engine side:43mm, Aircleaner side:62 StewRoss VM-38 tuning recommendation: 280 main
30 pilot...possibly too small?
Needle 6F8/2
3.0 slide cutaway
Perhaps a P4 needle jet...
Powerjet is blocked off...
I have several lots of 38 settings, so to totally confuse you here are some more:
240-270 main
30 pilot
Needle 6F8/2
P4 NJ
#2 air jet
1.5 slide cutaway
or
270 main
35 pilot
Needle 6F8/3
P6 NJ
#2 air jet
7.0MM slide cutaway (MEASURED)ColinJAys race engine with a VM38:230 Main
6F9 needle on the 2nd clip
P-6 needle jet
#2.0 Slide
20 pilot jetTM -36-68Most stock TM36-68 flatslides come stock like this: 42mm air spigot (engine side of carb) 54mm-air cleaner side Jetting: 130 MJ, 12.5 PJ, P8 needle jet, 2.0 Slide, 1.0 airjet. Engine side:42mm, Aircleaner side:54mm Cliff's TM36-68 settings: all stock except: 17.5 PJ (pilot jet) adj approx 1.5 turns out 140 MJ (main jet) Needle clip 3 from top including supplied shim. I tried leaner needle jets but none worked. The P8 is good. K&N pod filter and Supertrapp with 8 discs. Greymin's tunings for the TM36: pilot 17.5 screw 1.25 turns out
main 150
needle clip second from leanest
factory default needle jet (p-8) and needle.
"I get 50 mpg. and I ride 45 miles a day round trip to work.
I also backed the pumper adjustment way off for better economy.
It won't really buck until I lug it under 2750 rpm. My old bike with stock carb would buck at anything below 3 krpm.
11 discs in the Trapp."TM-40 or HS-40Engine side:43mm, Aircleaner side:55mm Steve's suggestion for a HS-40 (same as TM40) pumper flatslide:
I don't know if this will be any help but the HS40 that I just put on had a #150 main (actual size=1.50mm) and 17.5 pilot jet but was slightly too rich at full throttle so I just went down to a #140.What about all of these snowmobile VM36 and VM38 (mostly VM38s) carbs sold on Ebay? What is the electrical cord for? Heat? I would guess you might have to change evey jet in them. Cliff
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Post by aero on Jul 25, 2008 14:56:21 GMT -5
Some good info. My current project has a brand new and very expensive TM36 adorning the inlet. I have yet to see where the extra money went, when the bike is finished I hope to find out. In the past I have had standard SRs fitted with VM 34 and the difference in running has been marked, for the better (then stock carb) Two and four stroke carb differ only in the design of the emulsion tube (part the needle slides into) and jetting sizes Steve your taste in coffee sucks  |
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Post by StewRoss on Jul 25, 2008 17:39:14 GMT -5
Heh, heh...only wanted it for the jar so I could put fuel or brake fluid in it... ;D I'm a tea drinker...  SR |
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