Author Topic: Mikuni Smoothbores Vs. CR's For 750F (Read 5481 times)

Porscheguy912 · « **on:** March 30, 2009, 08:28:30 PM »

Hello all,
I Have The Opportunity to get my hands on a set of Mikuni 29mm Smoothies for a reasonable price.
I have been doing some research on here and I dont know if I'm missing something but i'm not finding a lot of info on performance difference from stock. I'm finding more on issues of Fitment.

I have 1978 CB750F with Aftermarket 4-1 with a cherry bomb, Solid 145psi compression. I Rebuilt The stock carbs, sonic cleaned them and all the Accel pump squirters function great. I'm running 120 mains with pods.
The Stock carbs are working Great but i figure if i can get these mikunis for a good price i should.

What Kind of Performance Difference's could i expect from switching to these smoothies?
Or... Should I Look for a set of CR 29s?

I know that the Sock carbs have the Accelerator pump to aid power off idle.
What kind of difference should i expect in that area without the pump on mikuni or CR carbs?
What Kind of Hp Differences are there?

Thanks!

Porscheguy912 · « **Reply #1 on:** March 31, 2009, 08:45:24 AM »

Shameless Mid-day bump

tinyrobot · « **Reply #2 on:** March 31, 2009, 08:55:56 AM »

VM29's and stopping asking so many questions...

Porscheguy912 · « **Reply #3 on:** March 31, 2009, 09:02:18 AM »

Pipe down Tiny!

Sweep · « **Reply #4 on:** March 31, 2009, 09:51:17 AM »

If your bike is stock and your carbs are dialed in I wouldn't touch the setup with a 10 foot pole. If and when you do make the motor different than stock go for the CR29s. Not that you won't get any benefit by switching now but that benefit comes with quite a bit of pain and dialing in. If not done right you'll lose performance.

I have no experience with Mikunis for Hondas but for Harleys they are the cats jammies.

MCRider · « **Reply #5 on:** March 31, 2009, 10:00:47 AM »

Quote from: Porscheguy912 on March 30, 2009, 08:28:30 PM

Hello all,
I Have The Opportunity to get my hands on a set of Mikuni 29mm Smoothies for a reasonable price.
I have been doing some research on here and I dont know if I'm missing something but i'm not finding a lot of info on performance difference from stock. I'm finding more on issues of Fitment.

I have 1978 CB750F with Aftermarket 4-1 with a cherry bomb, Solid 145psi compression. I Rebuilt The stock carbs, sonic cleaned them and all the Accel pump squirters function great. I'm running 120 mains with pods.
The Stock carbs are working Great but i figure if i can get these mikunis for a good price i should.

What Kind of Performance Difference's could i expect from switching to these smoothies?
Or... Should I Look for a set of CR 29s?

I know that the Sock carbs have the Accelerator pump to aid power off idle.
What kind of difference should i expect in that area without the pump on mikuni or CR carbs?
What Kind of Hp Differences are there?

Thanks!

What's a good price? $200-? I jump on them just to have them. $300+? Save it for something else. My personal experience with the 29s was wonderful. Benefits included faster warmup, less choke to startup, crisp linear throttle response, and certainly more performance.

But... I had a Yosh head, cam, big bore, pipe, etc. Without at least head work, I don't know that you'll get anything from just the carbs. Probably something, but not optimized. As far as set up, it was a few hours fiddling or less, a set of jets, piece of cake. YMMV

I'm comparing to K2 style carbs. I have no experience with pumpers.

cafebob · « **Reply #6 on:** March 31, 2009, 10:09:10 AM »

just thought I chime in. I have used the mikuni smoothbores and liked them. Mush nicer than the stock carbs. I have also started using kiehn CV carbs off of cb650's on these bikes. the carbs from 83 and 84 bikes are 29mm, the 85 carbs are 32mm. any of the three are diaphragm type carbs, not the aluminum piston type. The are very much like modern CV carbs used on a variety of non FI bikes, in fact many of the parts are interchangeable. I have found them to be a very nice modification, they have the same (or very close) spacing as the stock 750's, and bolt right on. You will need to modify the return carb cable. Best thing is they can be had for a song. 50-100$.

Tuning them is very easy, and I have found them to be superior to the smoothbores.

crazypj · « **Reply #7 on:** March 31, 2009, 10:23:11 AM »

In my experience, either smooth bore works fine.
Compared to any stock CV carb they are a breeze to dial in.
If you have 3 jet carbs, they are probably best for stock set up and a nightmare for anything modified
PJ

Jim F · « **Reply #8 on:** March 31, 2009, 02:37:10 PM »

Smoothbores seem to be a little easier to dial in compared to CRs
I have a set of 29s and a set of 32 CRs and the CRs are tough to get right
and very little input to the air screws makes a big difference

good luck

Jim

eurban · « **Reply #9 on:** March 31, 2009, 02:45:27 PM »

Quote from: big-jim on March 31, 2009, 02:37:10 PM

Smoothbores seem to be a little easier to dial in compared to CRs
I have a set of 29s and a set of 32 CRs and the CRs are tough to get right
and very little input to the air screws makes a big difference

good luck

Jim

Maybe its the bore size??

cafebob · « **Reply #10 on:** March 31, 2009, 02:56:16 PM »

"Compared to any stock CV carb they are a breeze to dial in.
If you have 3 jet carbs, they are probably best for stock set up and a nightmare for anything modified"

The CV's I'm talking about are 2 jet. Slow and main. for my 836 40/122 seems nice at 5200 feet. stock they are 35/115 which would probably be fine for a stock 750.

eurban · « **Reply #11 on:** March 31, 2009, 03:19:37 PM »

Quote from: cafebob on March 31, 2009, 02:56:16 PM

"Compared to any stock CV carb they are a breeze to dial in.
If you have 3 jet carbs, they are probably best for stock set up and a nightmare for anything modified"

The CV's I'm talking about are 2 jet. Slow and main. for my 836 40/122 seems nice at 5200 feet. stock they are 35/115 which would probably be fine for a stock 750.

With the PD carbs my 836 seems to pull more fuel (bigger slugs or the higher CR perhaps) from the stock 35 pilot than the engine did when stock and is happy the IMSs out around one turn. Don't necessarily assume that a bigger pilot will be required for a 836 10:1 cr engine . . .Or in your case that a smaller pilot would work better on a stock engine.

SOHC4 Cafe Racer Fan · « **Reply #12 on:** March 31, 2009, 04:24:01 PM »

The CR's will definitely give you noticeably more grunt. I think the other posts may be right about CR's being more difficult to dial in -- I had mine done on a dyno to get them right, but what a difference.

Right now, I'm waiting to see what kind of gains I'll be getting from my 836 kit, porting, valve job and Yosh cam!

Jim F · « **Reply #13 on:** April 01, 2009, 06:12:22 AM »

Quote from: eurban on March 31, 2009, 02:45:27 PM

Quote from: big-jim on March 31, 2009, 02:37:10 PM
Smoothbores seem to be a little easier to dial in compared to CRs
I have a set of 29s and a set of 32 CRs and the CRs are tough to get right
and very little input to the air screws makes a big difference

good luck

Jim

Maybe its the bore size??

Well the 29s use to be on a GS750 with an 840 kit
but the CRs are on my 836
I have herd of people having 29s on 836 kitted Honda's with better luck
in getting everything right so it might be the size of the bores

Porscheguy912 · « **Reply #14 on:** April 06, 2009, 05:12:32 PM »

Well as usual I dont listen to direction Very well.
I'm Prob going to go for the Mikuni VM29 Smoothbores.

I have heard that they slip right on to the 750K Head boots, But They dont seem to line up with my 750F Boots. Tinyrobot here, mentioned to me that he heard that i can maybe rotate the boots on the F to make them fit. Any feedback? Do i need to custom make a set of manifolds or get an adapter?

I sent my Fuel tank out to the plating shop so i have a while to mess with this idea before i get a chance to ride.
Thx for all your responses to far!

MCRider · « **Reply #15 on:** April 06, 2009, 05:16:29 PM »

Quote from: Porscheguy912 on April 06, 2009, 05:12:32 PM

Well as usual I dont listen to direction Very well.
I'm Prob going to go for the Mikuni VM29 Smoothbores.

I have heard that they slip right on to the 750K Head boots, But They dont seem to line up with my 750F Boots. Tinyrobot here, mentioned to me that he heard that i can maybe rotate the boots on the F to make them fit. Any feedback? Do i need to custom make a set of manifolds or get an adapter?

I sent my Fuel tank out to the plating shop so i have a while to mess with this idea before i get a chance to ride.
Thx for all your responses to far!

I do not think you can get the 29s to fit with stock boots. You may be able to force them but they are not an easy fit.

DYNOMAN sells the boots for $160 or so. http://www.dynoman.net/carb/inMani.html

Hmmm I see Dynoman boots are for 69-76. Yours is later? maybe you'll have more luck with stockers.

Sweep · « **Reply #16 on:** April 06, 2009, 05:36:49 PM »

Quote from: Porscheguy912 on April 06, 2009, 05:12:32 PM

Well as usual I dont listen to direction Very well.
I'm Prob going to go for the Mikuni VM29 Smoothbores.

I have heard that they slip right on to the 750K Head boots, But They dont seem to line up with my 750F Boots. Tinyrobot here, mentioned to me that he heard that i can maybe rotate the boots on the F to make them fit. Any feedback? Do i need to custom make a set of manifolds or get an adapter?

I sent my Fuel tank out to the plating shop so i have a while to mess with this idea before i get a chance to ride.
Thx for all your responses to far!

I don't think we as a group are people that listen very well.

Porscheguy912 · « **Reply #17 on:** April 06, 2009, 07:15:31 PM »

1978 CB750F
Rats! Sounds like I'm going to have to fab up somthing.
Although I read on here that Z1 makes an adapter but I can't find it on his site.
Maybe this project will have to wait if $160 is the neighborhood of pricing for adapters I dunno if I can swing it.

MCRider · « **Reply #18 on:** April 07, 2009, 05:08:03 AM »

Quote from: Porscheguy912 on April 06, 2009, 07:15:31 PM

1978 CB750F
Rats! Sounds like I'm going to have to fab up somthing.
Although I read on here that Z1 makes an adapter but I can't find it on his site.
Maybe this project will have to wait if $160 is the neighborhood of pricing for adapters I dunno if I can swing it.

Since Dynoman says his adapters are for 69-76, I'd contact him and ask whats necessary for a 78F.

MRieck · « **Reply #19 on:** April 07, 2009, 05:33:30 AM »

The OD of the F2 intake spigots are to large. The Mikuni require those boots sold by Dynoman AND Sudco. Those boots would work on the 77 78 K. Maybe those new boots can stretch to accommodate the F2 (because they are a different material from the originals) but I don't know. Ask Buzz. Once again the F2/3 has bit people in the - - -

tinyrobot · « **Reply #20 on:** April 07, 2009, 07:41:42 AM »

You could follow through on that K head switch and I have boots for you. Next time you come over we can measure the 75K, 78K, and your 77F we should be able to figure something out. Or call Buzz at Dynoman like MRieck said, he'll most likely have the answer for you in seconds.

News:

Poll

Which Carbs Do You Run? Or Which Do you prefer for your 750?

Author Topic: Mikuni Smoothbores Vs. CR's For 750F (Read 5481 times)