Author Topic: The Mikuni VM26 Thread. (Read 5367 times)

KrautKoffin · « **on:** January 12, 2014, 02:40:06 PM »

If you've got any info please post it here. I've done a lot of research on running these carbs on a 74 550, and it all seems to be scattered. I hope this thread will pull all of that info together in one thread. I picked up a set of vm26's off of a member here with adapter plates to achieve a true 'straight flow' intake system. It'll be a few weeks before I can get them broken down and cleaned, I was hoping to get some jetting guidance from the mikuni gurus of sohc4.

The build:
600cc cruzin image kit
MotoGPWerks pipe
Ported and polished head
+1 mm over valves
Knife edged crank

Anyone have aome ideas on jetting?

seanbarney41 · « **Reply #1 on:** January 12, 2014, 04:53:03 PM »

I think I will be adding to the confusion.

I just bought a set with adapters for a cb750. Plus, I need to get used to tuning these things, so I have a clue with the Suzi's and Kawi's. I am hoping to gain a tuneability advantage with the Mikuni vm26's, as there is no size advantage over stocker cb750 Keihins. Seems like I read somewhere that Mikuni's venturi design tends to flow more air than a comparably sized Keihin...I post my questions and findings here.

KrautKoffin · « **Reply #2 on:** January 12, 2014, 07:41:46 PM »

Quote from: seanbarney41 on January 12, 2014, 04:53:03 PM

I think I will be adding to the confusion. I just bought a set with adapters for a cb750. Plus, I need to get used to tuning these things, so I have a clue with the Suzi's and Kawi's. I am hoping to gain a tuneability advantage with the Mikuni vm26's, as there is no size advantage over stocker cb750 Keihins. Seems like I read somewhere that Mikuni's venturi design tends to flow more air than a comparably sized Keihin...I post my questions and findings here.

Much appreciated! If all goes well I'll pick up a set for my k7

PeWe · « **Reply #3 on:** January 13, 2014, 03:27:56 AM »

Interesting details to read about Mikuni Carbs tuning
http://www.generalfiles.biz/go/154097798300

KrautKoffin · « **Reply #4 on:** January 19, 2014, 11:32:38 AM »

Here's some pictures of the carbs I picked up off a member here and his adapter plates for the 550 platform:

The carbs weigh a metric ton and I'm surprised that there's no choke!
I need to read a lot more before trying to tune these.

bwaller · « **Reply #5 on:** January 19, 2014, 12:34:39 PM »

Yeah those carbs do weigh a lot. There is no choke persay but an enrichening circuit!

PeWe · « **Reply #6 on:** January 19, 2014, 12:47:40 PM »

They look like my VM29. I call it for choke. Give much richer and higher idle. Very effective!

turboguzzi · « **Reply #7 on:** January 19, 2014, 02:16:37 PM »

indeed, chokes dont have to really choke...

BTW, the guy selling the RC cyl block on feebay has a VM26 set for 150$

bwaller · « **Reply #8 on:** January 23, 2014, 10:06:05 AM »

I found a note from Kayaker43 when I was considering these carbs early on. He was using them on a 592 race engine.

mainjet 127.5-132.5
needle #5J9 raised 1-2 notches (stock needle 5DL31)
needle jet #08 (stock 04)
slide 2.5
pilot?

TG told me he ran a 140-145 mainjet in his 500cc, with the needle clip in the middle.

It surely doesn't pinpoint a baseline for you but before I tossed the note....

I can check what jets are in the set I have to compare. They were off a latter stock Z1.

KrautKoffin · « **Reply #9 on:** January 23, 2014, 01:02:24 PM »

Quote from: bwaller on January 23, 2014, 10:06:05 AM

I found a note from Kayaker43 when I was considering these carbs early on. He was using them on a 592 race engine.

mainjet 127.5-132.5
needle #5J9 raised 1-2 notches (stock needle 5DL31)
needle jet #08 (stock 04)
slide 2.5
pilot?

TG told me he ran a 140-145 mainjet in his 500cc, with the needle clip in the middle.

It surely doesn't pinpoint a baseline for you but before I tossed the note.... I can check what jets are in the set I have to compare. They were off a latter stock Z1.

Very much appreciated! I'm in PA till Sunday then I'm going to dig into my set. I noticed the carbs don't have any part numbers on them, how do I know that I have 26's and not 28's?

Turbo, I saw! There was also a set that went for $81 a few days ago.

bwaller · « **Reply #10 on:** January 23, 2014, 01:56:30 PM »

Measure the throat. The 26's are actually a little larger than 26mm.

seanbarney41 · « **Reply #11 on:** January 28, 2014, 05:57:56 PM »

I got around to mocking up my vm26's on a cb750k4 parts bike. Everything fits pretty good. Managed to get the stock pull throttle cable to work with some fairly radical re-routing. The stock push cable won't work at all.

Bwaller pmed me the Motion Pro part numbers of the cables he used successfully on a 550 racebike with low bars. He was also using a non stock throttle assembly but he thinks a stocker would work with the same cables. Actually, I think I will just cut and paste his whole pm, 'cuz it has some good info...

Good morning,

Looks like you're in the "cold zone" again...been an old time cold winter.

I read on Rons thread your question about cables. My original plan was to use the VM26's on my racebike so I went through the cable deal. I ended up with a set of VM29's but cables are likely similar. I found that MotionPro cables (pull-#01-0233 & push #01-234) are made for Mikunis. At least they work perfectly with the smoothbores. I use a Motionpro throttle housing and re-work an R1 throttle sleeve for 1/4 turn but I bet these will work for the stock Honda throttle as well. These cables are very good quality.

I'm not sure what you'll find with the VM26's (closer to 27mm) on a 750. If it's disappointing consider WiredGeorge.com. He has given up paying crazy money for 29 smoothbores in favour of oval boring the 26's. He claims he has worked out any issues & they flow very well.

Cheers,

Brent

KrautKoffin · « **Reply #12 on:** January 28, 2014, 06:13:57 PM »

Awesome, thanks! I'll end up with those cable and low bars for sure

Drummer · « **Reply #13 on:** December 05, 2014, 06:57:25 PM »

What boots did you use to mount those VM 26's on the 750 ? I got a set and am trying to figure out whether there is a way to get it done without a lot of money.

seanbarney41 · « **Reply #14 on:** December 05, 2014, 07:20:33 PM »

Quote from: Drummer on December 05, 2014, 06:57:25 PM

What boots did you use to mount those VM 26's on the 750 ? I got a set and am trying to figure out whether there is a way to get it done without a lot of money.

I think they are aftermarket adapter boots. That is all I know as I bought the carbs with the boots used. You could try pming member 23tbucket, as that is who I bought these from. I have not seen him around here in quite some time though. Also, there are a few other members running vm29's on 750's, PeWe comes to mind, and they may know a source for boots.

bwaller · « **Reply #15 on:** December 05, 2014, 08:37:19 PM »

Sudco has boots, check with Z1 Enterprises too. Jeff is a member here. Also maybe Dynoman.

Lostboy Steve · « **Reply #16 on:** December 13, 2014, 10:58:27 AM »

Quote from: KrautKoffin on January 19, 2014, 11:32:38 AM

Here's some pictures of the carbs I picked up off a member here and his adapter plates for the 550 platform:

The carbs weigh a metric ton and I'm surprised that there's no choke!
I need to read a lot more before trying to tune these.

Are those adapters mass produced?

FunJimmy · « **Reply #17 on:** December 13, 2014, 11:58:51 AM »

Quote from: lostboy on December 13, 2014, 10:58:27 AM

Are those adapters mass produced?

I doubt they are. They look suspiciously simular to the adapters I made for CR26 carbs.

750cafe · « **Reply #18 on:** December 15, 2014, 09:55:31 AM »

15 or possibly 17.5 pilot jets, needle jet set on the center clip, 105 to 110 main jets depending on altitude and exhaust system back pressure.

Eric

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Author Topic: The Mikuni VM26 Thread. (Read 5367 times)