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Old 04-05-2021, 05:11 AM   #6
slonomo
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Join Date: Oct 2009
Location: Medina, Ohio (NEOHIO)
Posts: 11,421
Default Re: Mikuni carb kit from Performance 670

Quote:
Originally Posted by Greg001 View Post
What size carb are you getting? I bought the VM30 from them and it is tuning adventure to say the least. I put it on a stock Predator 13hp. As it is, it comes setup way too rich. I am at 180' above sea level. I am still ironing out the adjustment.

Comes with:
Main jet 260- I am at 210
Pilot jet 35- I am at 17.5
Needle jet Q2- I am at Q0
Jet needle 6DH4- I am at 6DH3

I have not gotten to throttle valve or air jet. The throttle valve only effects a narrow range. If you can get it lean enough with smaller pilot jet the air jet is OK.

If I had it to do over I would have gone with smaller carb, 30mm is a whole lot of carb.
30mm on a 420cc engine is probably a bit large with a stock cam, head, and valvetrain. But on a 670 a 30mm would be just right. I used a 42mm CV Mikuni on my 23hp Vanguard (627cc) and it was close, but too much, big power up top but not ideal at low rpm. Switched to the VM34 and it was much better, big power over stock. With a cam and headwork it would have been perfect. I really thing a 30mm would have been perfect for normal use in the yard/campground etc.

I don't recommend big carbs, smaller is better for drivability. Any well tuned and properly sized Mikuni will perform much better than the stock carbs. The Mikuni will idle at 800 rpm and have super clean idle quality. Revs will be smooth all the way to max rpm. Just a fine carb. It does take some patience and a little skill to get them just right though.
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