VM Carb tuning guide/help

[Guest]

So, I see a lot of help for CV carb tuning, but not much definitive information for VM carb tuning. Can anyone point me in the right direction? I have a Morgan Carbtune, but it would be nice to read up on how the circuits work and how I can perform a plug chop as well.

[78550GS]

Plug chops will work the same no matter what carbs you are using, and I think the locations of the circuits are the only differences in fuel metering between the CV and VM carbs.

If I am wrong, however, someone will point that out.

[tkent02]

The main difference is in how they compensate for changes in elevation, and the
VM carbs are tuned from the bottom up, not from the top down like CV carbs.
There is information on this forum someplace.

[chuck hahn]

Section 3 of this write up describes then circuits. Google different things and youll find lots of tutorials

http://www.mikuni.com/pdf/vmmanual.pdf

[giganticflying]

Thanks Chuck, that's super helpful.

If plug chops are the same, I could use the same speed/rpm described for the CV carbs?

Also, any advice on the Carbtune? I've never used a carb sync before.

[Big T]

The other questions are

What do you have for exhaust and airbox?

What jets do you have in your carbs now?

[giganticflying]

Stock exhaust and airbox. I haven't measured, but the jets all look stock when I last cleaned the carbs (a few weeks ago).

[giganticflying]

Stock exhaust and airbox. I haven't measured, but the jets all look stock when I last cleaned the carbs (a few weeks ago).

[chuck hahn]

And some other helpful tidbits you should save somewhere..

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html#A01

http://www.iwt.com.au/mikunicarb.htm

http://members.dslextreme.com/users/bikecliff/images/carb_sync_notes.html

[chuck hahn]

In fact, just got here and look around undwer the manuals menu and youll see many tutorials on each side. Click around on the site and remember its existance. Youll be there many times as long as you have a bike...I promise you that.

http://members.dslextreme.com/users/bikecliff/

[giganticflying]

Managed to get a low end plug chop, jets what they look like:2015-02-26 17.11.49.jpg

Now I'm going to read up like crazy tonight to figure out what that means. The good thing is she runs better than ever since I adjusted the floats.

[chuck hahn]

Well I wonder "WHO" might have yet another batch of info to heap on you.

http://jetsrus.com/FAQs/FAQ_spark_plugs.htm

http://www.strappe.com/plugs.html

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

http://www.ngksparkplugs.com/pdf/DYK_HeatRanges.pdf

[giganticflying]

well at least I don't have to feel bad about taking this term of college off anymore.

[chuck hahn]

Get reading and dont miss any details....test on Wednesday!! LOL

[Scooter]

Did you ever sort out your carb tuning issue? My plugs look similar. My #4 is rich, #3 is lean and the other 2 seem lean as well. When I adjust the fuel screw I seem to go between lean to rich pretty quickly, like within a 1/4 to a 1/2 turn. Had them at 1 1/4 turns out and then had a problem starting, too much fuel and it would stall out. I've got them set at 3/4 of a turn out and my air screws are 1.5 turns out. Still getting s stumble when I push it above 3000 rpm.

Thoughts?