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VM Carb tuning guide/help

  • Thread starter Thread starter giganticflying
  • Start date Start date
G

giganticflying

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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.
 
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.
 
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.
 
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.
 
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The other questions are

What do you have for exhaust and airbox?

What jets do you have in your carbs now?
 
Stock exhaust and airbox. I haven't measured, but the jets all look stock when I last cleaned the carbs (a few weeks ago).
 
Stock exhaust and airbox. I haven't measured, but the jets all look stock when I last cleaned the carbs (a few weeks ago).
 
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.
 
:) well at least I don't have to feel bad about taking this term of college off anymore.
 
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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?
 
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