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VM36 jet sizes (Read 29 times)
r-tru-d2
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VM36 jet sizes
04/30/07 at 14:29:58
 
Those of you using the VM36 - what jets are you using?  I'm using a large K&N filter (modded the airbox and battery box to get it to fit), a straight pipe, and all the goodies that lancer provided in the kit (dial-a-jet, UFO, iridium plug, etc.).

I'm finding that the bike is too rich to ride with the 210 main and 12.5 pilot jets (smallest sizes that came in the kit), even when I back out the fuel mix screw 5 turns (just for testing).  Float height is in spec, compression is good, valves are in spec, new gas, fresh oil change, etc. etc.  I'm thinking I need to start by dropping the main jet down a few sizes, getting that right first, then adjusting the idle circuit as needed.

This is a 1987 model 650 with only 4,000 miles on it.  I'll post some "after" pics here soon, as I've done quite a bit of work on it recently for my wife (deuce risers, drag bars, sissybar & brake light removal with welded holes, new rear signals, sportster seat, new paint, plus all the carb mods, etc.).  Right now, my wife's just interested in getting it back on the road as quickly as possible.

So, speak out about what you're using.  I'm curious to see where I'm off.
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vroom1776
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Re: VM36 jet sizes
Reply #1 - 04/30/07 at 14:42:03
 
Hey,

I'm running (well was, and hope to be soon again) VM 38, big KN pod, & a cherry bomb for a pipe.  My main is a 240 or a 250, and I'm at 4000 feet.

why do you say you are rich?

Witht he Dial a jet, you are supposed to run it a little rich, right (or is it lean)?
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r-tru-d2
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Re: VM36 jet sizes
Reply #2 - 04/30/07 at 18:28:22
 
vroom1776 wrote on 12/31/69 at 16:00:04:
Hey,

I'm running (well was, and hope to be soon again) VM 38, big KN pod, & a cherry bomb for a pipe.  My main is a 240 or a 250, and I'm at 4000 feet.

why do you say you are rich?

Witht he Dial a jet, you are supposed to run it a little rich, right (or is it lean)?

With the dial-a-jet, you're supposed to use a baseline setting w/o the dial-a-jet, and back off the main jet 2 sizes to allow the dial-a-jet to make the adjustments.

I say it's rich because it's blowing black smoke, and the plug is black and sooty.  It doesn't idle very well, either.
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barry68v10
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Re: VM36 jet sizes
Reply #3 - 05/01/07 at 02:50:02
 
Quote:
even when I back out the fuel mix screw 5 turns (just for testing).


Sounds like you may be going the wrong way on the pilot jet.  Were you trying to make it more rich?  or lean?
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r-tru-d2
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Re: VM36 jet sizes
Reply #4 - 05/01/07 at 05:42:30
 
barry68v10 wrote on 12/31/69 at 16:00:05:
Sounds like you may be going the wrong way on the pilot jet.  Were you trying to make it more rich?  or lean?

It came with a 15 jet, and I leaned it out with the 12.5 jet that came in the carb kit.  That's the leanest I can go on the jet with the jets provided.  I don't think I should go any leaner on the jet - something else is wrong.
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vroom1776
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Re: VM36 jet sizes
Reply #5 - 05/01/07 at 10:23:22
 
are these mikuni jets or dyno jets?

the main should not be affecting the idle at all.
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Re: VM36 jet sizes
Reply #6 - 05/01/07 at 10:27:01
 
vroom1776 wrote on 12/31/69 at 16:00:05:
are these mikuni jets or dyno jets?

the main should not be affecting the idle at all.

Mikunis.  You're right about the main jet.  I just couldn't think of anything else to check, so I thought it was worth a shot.
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Re: VM36 jet sizes
Reply #7 - 05/01/07 at 11:03:54
 
I've always ahd trouble getting my VM to idle correctly.  Still haven't figured it out.  try upping the idle and running on PRI.

as for the main, take the dial a jet out, for now (at least, that's how I'd do it).  Go down 1 or 1/2 size on the main.  run the F out of the bike at high speed, wide open throttle.   if it stutters and stumbles, you are too rich.  go down another 1/2 size. repeat until it runs like a raped ape, as they say.  now install the dial a jet and back off the main as the dial a jet folks say.

getting the idle right?  let me know when you figure it out...
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Re: VM36 jet sizes
Reply #8 - 05/01/07 at 12:05:46
 
vroom1776 wrote on 12/31/69 at 16:00:05:
I've always ahd trouble getting my VM to idle correctly.  Still haven't figured it out.  try upping the idle and running on PRI.

as for the main, take the dial a jet out, for now (at least, that's how I'd do it).  Go down 1 or 1/2 size on the main.  run the F out of the bike at high speed, wide open throttle.   if it stutters and stumbles, you are too rich.  go down another 1/2 size. repeat until it runs like a raped ape, as they say.  now install the dial a jet and back off the main as the dial a jet folks say.

getting the idle right?  let me know when you figure it out...
Ah, finally someone else with a VM.  Tell me about your setup.  Jet sizes, other products installed (UFO, dial-a-jet?), filter & pipe setup, etc.  Just trying to get an idea of what others a running, and what works.
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Re: VM36 jet sizes
Reply #9 - 05/01/07 at 12:15:22
 
I'm running (well was, and hope to be soon again) VM 38, big KN pod filter, & a cherry bomb for a pipe, 1.75 ID straight through, 14" long main body, with a thumbscrew in the exit end to add back pressure.  My main is a 240 or a 250, and I'm at 4000 feet.  I don't recall if I'm running a 30 or 27.5 pilot, prolly the 30.  No dial a jet or UFO (yet).  runs great at high rpm.  as above, I haven't got the pilot sorted out yet.  Also, I have an exhasut elak at the muffler-header connection.  Makes for some nice backfires.
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Re: VM36 jet sizes
Reply #10 - 05/01/07 at 12:24:08
 
vroom1776 wrote on 12/31/69 at 16:00:05:
I'm running (well was, and hope to be soon again) VM 38, big KN pod filter, & a cherry bomb for a pipe, 1.75 ID straight through, 14" long main body, with a thumbscrew in the exit end to add back pressure.  My main is a 240 or a 250, and I'm at 4000 feet.  I don't recall if I'm running a 30 or 27.5 pilot, prolly the 30.  No dial a jet or UFO (yet).  runs great at high rpm.  as above, I haven't got the pilot sorted out yet.  Also, I have an exhasut elak at the muffler-header connection.  Makes for some nice backfires.

Oops.  I should have scrolled up a bit - didn't realize you were the same guy who had responded before with the 38.

Thanks for the info.

I *think* I have it running right now - at least, it idles in the garage just fine now, no more black smoke, and plug looks light brown.  I took the carb all apart, and blew the passages clean with some carb cleaner.  I'm not certain, but I think I dislodged something in the air mix screw intake hole (the small hole next to the air jet that connects with the air mix screw passageway).  That passage exits with 2 very small holes near the engine side of the carb.  I think when I blew the carb cleaner through that passage, I freed something up.  Now, with a 210 main and 12.5 pilot jet, it seems to idle fine without the problems I was previously experiencing.  I do find it odd that absolutely no choke is required, so it still might be slightly rich, but not enough to keep it from running.  Will do a more extensive test once I reassemble everything and finish bleeding brakes tonight.  I had a spare braided stainless line laying around in the garage that I'm going to use.
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vroom1776
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Re: VM36 jet sizes
Reply #11 - 05/01/07 at 12:39:09
 
there is no choke on these carbs (or the stockers for that matter - it's a fule enrichment circuit).  there is a starter plunger instead.
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Re: VM36 jet sizes
Reply #12 - 05/01/07 at 12:41:53
 
vroom1776 wrote on 12/31/69 at 16:00:05:
there is no choke on these carbs (or the stockers for that matter - it's a fule enrichment circuit).  there is a starter plunger instead.

Yes, I know that, but in practice, it's still most commonly referred to as a choke - heck, even the folks who make the lever for Mikuni still stamp it with the word "choke" right on it.  I suppose that's easier to stamp than "fuel enrichment circuit."   Wink
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Re: VM36 jet sizes
Reply #13 - 05/01/07 at 12:59:33
 
I can't get mine to run w/ the 38 mm VM right now.  running the stocker.  Need to clean it again, I guess, try running it... we'll see... too much sh*t to do
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Re: VM36 jet sizes
Reply #14 - 05/02/07 at 19:53:50
 
Well, it's still not great, but I have it running.  Everything off idle is awesome - smooth, clean, available power whenever I want it.  Idle is still a bit rich - I can smell it, and tell when I chop the throttle that it's bogging down when transitioning to the idle circuit.  I've had to turn up the idle speed quite a bit just to keep it running.  Still doesn't require any choke at all (it's about 70 degrees right now).

I guess I'll try even smaller pilot jet sizes to see if that helps any.  We'll see.  I might try running without the UFO installed, too, and see if that makes any difference.
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