whip 400 carb swap

[75whip]

Hey guys. I'm tired of my walbro carb on my 75 400 whip. Got a couple mikunis laying around. A VM 34mm and I got a 40mm also. What carb would work best and does anyone know what jets to use. I'm looking for advice from anyone who has done this with this motor. Thanks

[scorp11]

40 is too big. 34 will work fine if jetted right. I have used a 38 on a 440 with a Sting Pipe and that works good. 38 is probably too much for a normal pipe. . somewhere someone posted their jetting for a 34 mm. have to do some searching to see if I can find it.

Make sure you get Main Jet, pilot jet, needle, needle Jet and slide cutaway. Many people just look at jetting as main jet an that isn't enough on the Mic's

[weverat]

I have to do the same thing to a 340 whip. I agree a 40 is to big, I am thinking 34 or 36, and am hoping someone has already done this, and they can get us close. I imagine the 4 and 6 bolt motors will be differant?

[admin]

Might be some related info in these threads,

scorpionsleds.proboards.com/search/results?what_at_least_one=jets&who_only_made_by=0&display_as=1

[75whip]

admin thanks for the link to those older post. I know i have seen this before just could not remember where. If my memory is right the 34mm was on a Polaris single carb 440 Fuji. I believe the jets are 330 main 30 pilot and 159 Q0 needle. I think that was standard on the vm34. 6DH3 jet needle is what I should use for a single carb application if all my info is right from on here and my other notes I should be set to go with this. I'm going to go with what i posted here.
weverat I remember having a old jlo 4 bolt head all apart a few years ago, and if i remember right the cyuna 6 bolt head had more ports in the cylinder, and the lower end was different i though the center seal was way different, and basically it looked like scorpion made it more beefy when they brought out jlo/rockwell. I melted down a cyuna in my range whip the seal behind the carb rotted out and it was sucking in air, and I pulled them both apart outta curiosity. so maybe a 340 jlo may require a smaller carb yet 30mm??? 32mm??? or maybe a tilly HD. I will keep everyone posted on how this comes out. Anyone please correct me if im wrong.

[scorp11]

I think everything you said is "yes"

6 - bolt
- Two center bearings and lip type center seal instead of labyrinth type. Stronger double row PTO bearing (pretty sure) (All)
- All had boost ports in they cylinders next to transfers.
- Much bigger intake ports (440 - 400)
- bolt on exhaust on bigger motors (440 - 400)

The smaller later cuyuna (some rockwell) motors (340 and 290) were 4 bolt, but also had boost ports and same bottom end as 440 / 400

ALL 76 and up Cuyuna motors (I think 75 Rockwell too but not 100%) interchange almost all parts. Cylinders, pistons and heads are the only differences.

if you run a smaller motor, smaller Mic. I think the 340 JLO we did we used a 30-32MM but not 100% certain of size

As for starting jetting it sounds good, Use the Mic test procedure to determine if pilot is ok. Sounds ballpark though. I start rich always and go leaner.

[weverat]

Thank you admin,there are lots of good posts, we certaintly have hashed this over before.

Scorp11, what is the Mic test procedure to determine pilot ?

[75whip]

Here is a good web page for help in tuning mikuni carbs. I got mine running good crab swap great success. The Needle jet, needle I listed above are correct. Main jet 320

www.smellofdeath.com/lloydy/jetting.htm

[75whip]

needle set second slot to the top.

[jjakiela3four]

On my 400ccw port motor with a modified Polaris expansion chamber pipe I run a 34mm round slide mikuni. 40 pilot 380 main with the needle clipped up 1 spot from the bottom or bottom position if it pings mid range. Seems to happen if i hammer on it a lot climbing hills. if it's wide open on the lake or street for a long time it pings a little with a 380 but it stays plenty cool for trail riding and it's snappy. 390 seems to be good for lots of wide open running. 400 is safer but probably too much for that weird stock muffler . Seems like ccw motors run super hot in general compared to similar engines. Lot's of Compression for what it is.