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Old 04-03-2021, 11:18 AM   #1
turbof250
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Default Mikuni carb kit from Performance 670

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?
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Old 04-03-2021, 04:19 PM   #2
slonomo
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Default Re: Mikuni carb kit from Performance 670

Quote:
Originally Posted by turbof250 View Post
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?
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Old 04-03-2021, 04:58 PM   #3
turbof250
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Default Re: Mikuni carb kit from Performance 670

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!
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Old 04-04-2021, 09:12 AM   #4
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Default Re: Mikuni carb kit from Performance 670

Quote:
Originally Posted by turbof250 View Post
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.
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Old 04-04-2021, 12:34 PM   #5
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Default Re: Mikuni carb kit from Performance 670

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.
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Old 04-05-2021, 05:11 AM   #6
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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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Old 04-06-2021, 05:34 PM   #7
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Default Re: Mikuni carb kit from Performance 670

I ran a 32mm CV pumper on my 420, it has vegas cam and rod, head is cut and ported, header, 1.3 rockers, etc. I could not get much top end but it ran great, started great. Finally tied up the spring in there and it was better. Got a 30mm slide carb and more top end for sure, it starts and runs good also. It will bog a tiny bit at low speed if I floor it but not always, my clutch is not set up perfect but most of the time its fine. I also have an intake I built that puts the carb above the cylinder with a pipe around to the head. I really like it but don't know how it affects performance. Its 32mm also. They run 32mm on clones but I think those are built kart engines. Seems like a 30-32 would be fine for a 670. Its big for a 420-460 unless it has a big cam IMO. I would guess I hit 5500 with mine now but I slow back down. It is still pulling there, much better than the CV carb that did not want to open all the way I guess. It hit 5200 with the CV, it blows right past that speed. I had it to 41 it will go faster but its getting dicey so i let off.
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Old 04-12-2021, 10:20 AM   #8
kellett5261
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Default Re: Mikuni carb kit from Performance 670

Quote:
Originally Posted by slonomo View Post
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?
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Old 04-14-2021, 05:32 AM   #9
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Default Re: Mikuni carb kit from Performance 670

Quote:
Originally Posted by kellett5261 View Post
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.
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Old 04-15-2021, 08:15 AM   #10
kellett5261
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Default Re: Mikuni carb kit from Performance 670

Quote:
Originally Posted by slonomo View Post
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.
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