Short answer: yes, but don't. Griz is on the money on this one.
You will gain NOTHING with the VM 36 (slide) carb over the stock 38mm (constant velocity) carb on a stock motor. It will cost you a bunch of money, time, and aggrivation to get back to performance square one with this swap.
Spend the money on porting the head if you really want some performance improvement for your money.
We know ya meant VM36's, Blaine. Re. starting, the VM's are a little cold-blooded. Your fuel consumption is a tuning issue--I'm running a modified mill with 700cc displacement, ported head, Shell #1 cam, Mac 2-2's with straight-through glasspack baffles, Uni pod filters and VM36 carbs. It runs to redline in 5th on stock gearing and uses 48-50 mpg even on high-speed runs.
You might want to do a high-speed throttle chop and see what your mains are doing. You're going for a thin dark line ("smoke ring") around the base of the insulator (and no flecks of aluminum on the insulator that used to be part of a piston). Second suggestion--for years I thought I could do a fine job of setting idle and lift sync. manually, till I mounted a pair of VM's in vacuum barb mounts and checked my results with a manometer. You may use that tool already, but if not I'd recommend it.
You might look closely at timing; I like to check the marks with a good TDC indicator and degree wheel, as the factory marks are frequently off a degree or two. Also, be sure to dial in the marks, both retard and advance, with a strobe, and make sure valve adjustment's on the money.
Mburns, from a performance standpoint you're absolutely right--porting is the biggest bang for the buck, and no two ways about it. As to the viability of the VM36 on a stocker, I dialed a pair in on a stock engine to baseline 'em before doing engine mods with very good results--three figures of speed on demand, good low end response and no operating issues. Still, if I were choosing a carb for a stock engine at standard displacement, I'd take my old VM34's off the shelf and hang 'em.
One man's aggravation is another man's recreation, I guess. Many of the problems are caused by one particular vendor who sells carbs that just aren't decently baselined. Others occur when guys assume they can do a mount-and-go installation and don't inform themselves on the tuning process first--sort of like trying to build a house from a kit without looking at the plans.
Griz............your right on the money about the VMs or Tms being cold blooded in regards to being jetted lean in the pilot circuit. My 38 flat slides need at least a minute or two to fully warm before twisting the throttle wide open................Jack
Post by blainethemono on Jun 3, 2007 21:30:48 GMT -5
"We know ya meant VM36's, Blaine. Re. starting, the VM's are a little cold-blooded. Your fuel consumption is a tuning issue--I'm running a modified mill with 700cc displacement, ported head, Shell #1 cam, Mac 2-2's with straight-through glasspack baffles, Uni pod filters and VM36 carbs. It runs to redline in 5th on stock gearing and uses 48-50 mpg even on high-speed runs"\
Yeah Griz, thats where Im @ now.... plugs are a dark brown electrode with a light black dusting around the rim, that rubs off... as it warms up, (spring, summer), they are getting a bit sluggish off of idle, so Im going to lower the needle, add a shim or two, and go from there. Im in the ball park, and getting close to home plate. & Yeah...I meant 36mm
I was wondering, & hope you realize, that Im running the ORIGINAL pipes, so Im thinking, that they may be a bit more restrictive then the aftermarket ones. I might even try a 175 main....other then that she is running fine. Im around 38mpg, so yep......just have to dial her in now.. Been using a nanometer for decades, and it has helped alot with my past tuning..
Far out....I was looking at the very same carbs on eBay today, thinking what a bargain they were. Found this thread on a random reading/learning session and have now decided against swapping my old BS38's off my (mostly) stock '79 special. So the BS38's are good 'eh? Might order in a kit and give the old girls a clean-up! This site really is the best thing on telly! Lee.
Hey man, sure they'll work, but...I've had VM's, BS34's, and BS38's on my 81...and in my opinion you already have they best of them; the BS38's from the 78/79 were that carb perfected and was only dropped to meet EPA regs. ...perfect what you now have...save some money and have the best carbs...
I bought a set of vm34's off SFL got them cheap,paid another £50 for jets & got them more or less spot on.Apart from pulling slightly harder i saw no real gain.I think it was £350 wasted,the throttle was very heavy,they where a pain in the arse to set up & the induction noise is awfull. I put my 38's back on & i can't fault them,as soon as it fires up i can turn the choke off & it idles perfect & from cold it runs like it's been running all day.The throttle is as light as a feather & i'm getting about 50mpg.I've also noticed on most of the pictures on this forum that most of you seem to run standard carbs anyway.
Post by blainethemono on Jul 9, 2009 23:34:00 GMT -5
All I can say is that once dialed in, my install has been nothing if not a joy.... She can pull the ton+ now, pulls even harder out of corners and has been completely tractable in a variety on riding situations.
7/12/2008 Recent 1300 mile trip to Eastern Canada last year got me and average of 44-45mpg and that included some WOT canyon carving.
7/19/09 Now with the new 2 into 1 Header system installed, she really cranks.....
7/25/09 My best mpg has been 56....
7/31/09 Oh yeah, please take a CLOSE look at my header pipes. Notice the nice GOLDEN sheen instead of the WAY TO LEAN blue crapola..... Those are correctly jetted carbs, thanx to excellent feedback from Griz, and a lil bit of elbow grease on my part.......
Rule of THUMB.... To RICH and you only have fouled plugs. To LEAN and you have blue header pipes, or WORSE, a hole in your piston....
Running 36mms isnt that difficult and you no longer have to deal with that crusty/stiff/cracked diaphram stuff...
8/2/09 Ive also dropped my teeth count on the rear to 32 and with the new clutch plates, Ive tapped 110..... ;D
did I mention Im running POINTS on this install?
FYI: I only recently noticed that my site email address was null and void. For those who may have tried to email me with questions or rants, , I apologize.. I wasnt intentionly snubbing you. This has been corrected.
I will happily offer my humble learning experience thru this entire process, for those who may be interested.
r80rt: :)This is a splendid write up, THANK YOU!!!!
Dec 26, 2015 16:54:05 GMT -5
mashermoto: What the what is this shoutbox for? Or should I shout, WHAT THE WHAT IS THIS SHOUTBOX FOR!
May 12, 2016 22:22:21 GMT -5
motormike: Good Day ...just a FYI.. Wild Cat is this Labor Day weekend. Still go'n on. A few 650's still make the scene. Various rides at different skill levels each day.. awards dinner sunday eve. BS in the park'n lot after dinner.
Aug 23, 2016 7:57:01 GMT -5
lsettle: First post in over 6 years!
Aug 28, 2016 19:45:17 GMT -5
kardon: Wow quiet here, where did they all go.
Oct 7, 2016 2:18:13 GMT -5
gggGary: XS650.com LOL
Feb 16, 2017 20:49:02 GMT -5
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
Aug 16, 2018 8:55:08 GMT -5
bob99: how do I post a question. I am new to the forum
Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5