Mikuni carb kit from Performance 670

[turbof250]

About to order the single Mikuni kit from Performance 670, I have some jetting questions. They set the carb up for a base line, they are at 1200' of elevation. I am at sea level in Florida, anyone have any good tips on the changes I will need?

[slonomo]

Originally Posted by turbof250

About to order the single Mikuni kit from Performance 670, I have some jetting questions. They set the carb up for a base line, they are at 1200' of elevation. I am at sea level in Florida, anyone have any good tips on the changes I will need?

It should start and run out of the box. Fine tuning a Mikuni seems a little tricky but once you tune one you'll get it. I recommend watching a good YouTube video that explains the process.

Most likely you'll just be playing with the idle air/fuel jet screw and idle speed screw. Both are super easy. The main jet should be good, that's the wot. The needle setting will fine tune the midrange.

This is a good one
https://www.youtube.com/watch?v=67Nb3DI-B3s

VM vs CV vs Flat Slide is chocolate vs vanilla, but the tuning process is nearly identical.

What questions do you have?

[turbof250]

Well, you answered them without m having to ask. Was wondering if wold have to change jets but sounds like I just need to fine tune it and I should be good. Thanks for the help!

[slonomo]

Originally Posted by turbof250

Well, you answered them without m having to ask. Was wondering if wold have to change jets but sounds like I just need to fine tune it and I should be good. Thanks for the help!

You're welcome. You won't find it diffucult to tune if you watch a few videos.

[Greg001]

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.

[slonomo]

Originally Posted by Greg001

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.

[kellett5261]

Originally Posted by slonomo

It should start and run out of the box. Fine tuning a Mikuni seems a little tricky but once you tune one you'll get it. I recommend watching a good YouTube video that explains the process.

Most likely you'll just be playing with the idle air/fuel jet screw and idle speed screw. Both are super easy. The main jet should be good, that's the wot. The needle setting will fine tune the midrange.

This is a good one
https://www.youtube.com/watch?v=67Nb3DI-B3s

VM vs CV vs Flat Slide is chocolate vs vanilla, but the tuning process is nearly identical.

What questions do you have?

where would you order a carb from? I found a 30mm for $93 shipped but I'll still need the adapter to, where would you get yours from?

[slonomo]

Originally Posted by kellett5261

where would you order a carb from? I found a 30mm for $93 shipped but I'll still need the adapter to, where would you get yours from?

If it's for a Predator 670 just order the kit from Performance 670 and be done. Their carb is prejetted for that engine, and all the adapters come with it etc.

If it's for a Vanguard, I got mine at Backwater Performance. FYI the Performane 670 kit will fit a 2bbl Vanguard intake, although it's a single plenum vs. a dual plenum from Backwater.

You can use any Mikuni you want. The adapters are available online on all the big websites as well as the afore mentioned retailers.

[kellett5261]

Originally Posted by slonomo

If it's for a Predator 670 just order the kit from Performance 670 and be done. Their carb is prejetted for that engine, and all the adapters come with it etc.

If it's for a Vanguard, I got mine at Backwater Performance. FYI the Performane 670 kit will fit a 2bbl Vanguard intake, although it's a single plenum vs. a dual plenum from Backwater.

You can use any Mikuni you want. The adapters are available online on all the big websites as well as the afore mentioned retailers.

so your referring to this one? I do have a 670, I love it other than the constant battle with the idle on the carb and plugs . I'd like to go with a Mikuni and be done with it . I'm sure it would be Night & Day difference with the stock Junker.

[slonomo]

Originally Posted by kellett5261

so your referring to this one? I do have a 670, I love it other than the constant battle with the idle on the carb and plugs . I'd like to go with a Mikuni and be done with it . I'm sure it would be Night & Day difference with the stock Junker.

That's the one. It will be night and day difference. You'll still have to tune it to get it to idle and run perfectly. They should be able to help you with tech support also. (note: I have NOT used this kit on this engine)

One thing, that carb is going to make you want to drive faster Be carefull not to over rev the engine or you can damage the valvetrain components. Most stock engines will safely rev up to 4000 rpm. You could install their rev kit to help prevent that and safely rev to 5000 rpm.

On the stock carb, I found this carb to be easy to tune once you remove the caps on the idle circuit screws. It takes a little patience. Mine is dialed in pretty good and surprisingly it feels like there are no dead spots or sputters.