VM34 Tuning Help

[kvanderploeg]

OK, so I fought with the BS34's and decided to give the VM34's a chance. Bought a set from Michael Morse of 650Central.com. I put the carbs on last night and it would start but ran like total crap. Went in for the night and read the Mikuni Guide, the Sudco book, and the guide here from Panic (very helpful).

Bike will start, but giving it a fairly quick snap to maybe 1/4 throttle will cut the bike out. If you feather it past that it revs well. Here's what I've done so far:

• Adjusted Cam Chain Tensioner - Was very close, but I adjusted very slightly.

• Adjusted Valves - Left side intake and exhaust were very close to correct. Right side intake was also very close. Right side exhaust was slight out of spec.

• Checked Timing - I have a Pamco with Ultimate Coil and had originally set it to the approximate spot where it is recommended to make it run. With a timing light, I made a very slight adjustment and locked it back down.

• New spark plugs gapped to .036"

• Checked compression again this morning. This was a cold check with the kicker and holding the carb slides open.

Left Side 152​

Right Side 155​

• And these are the carb settings per the sheet Michael sent:

MJ - 180
PJ - 25
Needle-clip - 6F9-3
NJ - P-6
CA - 2.5
AJ - None
FL - 25​

Mounted VM34's, attached throttle cables, set air screw to 1.5 turns out per Michael's document. I also set the slide height with a 5/32" drill bit, then set the adjusters to pull the cables at the same time. With that said, here' the video of what's happening:

I did find that turning the air screws all the way in did seem to help this problem, but when I pulled the plugs after running it that way for ~10 minutes they were already quite brown and wet. Please let me know if I've omitted any important information. Any help and/or thoughts are appreciated. L

 

[scabber]

I would mount the throttle cable properly first thing not all bent around the frame like you have it now.

 

[racerdave]

What happen if you use the enricher {choke's} at that stall point? If it runs better you are lean on the pilot.

 

[kvanderploeg]

Ok, this was my fear, but I had to find some way to test. With my old BS34's I had a problem with the right side not firing when under 1/4 throttle as well. I cleaned the crap out of them and still no luck. With no known good carbs to test with and hoping for a bit of a performance upgrade, I bought these VM34's. Well, the right side is doing the same thing with the new VM34's. I have swapped plug cables and it does not change sides. I also checked the advance unit and it appears to be functioning just like the Youtube video from Pete. What the hell else could be causing this?

As you'll see in this video, my hand is not getting pushed very much from the exhaust pressure until I get above ~1/3 throttle.

Kent

 

[kvanderploeg]

I would mount the throttle cable properly first thing not all bent around the frame like you have it now.

I'll try almost anything once. I moved the cable for now so it is over top of the backbone rather than under it. That didn't help.

Kent

 

[racerdave]

Check the bad side intake manifold for cracks, leaking air. If you put your hand over the carb throat when running does the bad side have less suction on your hand?

 

[Ironsled77]

Sounds way to fat to me. I would check for leaks first (spary with carb cleaner listen for idle to race) then I would drop some jet sizes. Go down on the pilot and main. Are you 6 from the bottom(deepest) or 6 from the top (shallow) That is always a confusing topic..

 

[kvanderploeg]

Alright. It's my bad. Sorry for wasting everyone's time. When I set the timing I must have been asleep or blind. Set the timing properly this time results in a much better experience. Thanks for the help and suggestions, guys!

Kent

 

[Ironsled77]

the true test is under load! take it for a ride and see what you think

 

[kvanderploeg]

Took it around the block and it feels good and strong. I'm sure I'll need some fine tuning but it's running good enough for now. Sorry it's so windy.

Kent

 

[Tim of DO THE TON]

Was going to ask about the timing etc. as your jetting is identical to mine and I've been riding it for 3 seasons with no problems. I've found it a touch rich in spots and have tried lowering the needle etc. but kept coming back to these settings as the best.

 

[kvanderploeg]

Good to know. Since I had eliminated the carbs as the issue, the only other thing I could think of that was subject to RPM was timing. Have you had good mileage with your setup as well?

Kent

 

[Tim of DO THE TON]

Have no idea Don't pay much attention to how much gas it uses - figure there's nothing I can do about it and as long as it's running well that's all that matters. It doesn't get ridden a lot - 3000 miles in 3 years so far. I have a couple other bikes that keep me busy.

I'm building a new motor for this bike - 750 kit, ported, phased etc. So will be going through carb tuning all over again, but likely still with VM34's.

 

[kvanderploeg]

I don't have a odometer or trip meter, so I likely won't have much of an idea either. lol I'm hoping to do the same to my engine next winter. That's part of the reason I bought the VM34's, so there was some room to grow.

Kent