Author Topic: Mikuni RS34's & CB 750 (Read 40651 times)

mick7504 · « **Reply #50 on:** April 13, 2011, 03:43:54 AM »

I did a mock up in an old K frame when I got home from work tonight, and the carb to frame clearances are not a problem.
There's a ton of room there.

Sam Green Racing · « **Reply #51 on:** April 13, 2011, 04:32:27 AM »

What about the carb to tank clearence Mick ?

Sam.

mick7504 · « **Reply #52 on:** April 13, 2011, 04:50:21 AM »

Quote from: SamCB750A on April 13, 2011, 04:32:27 AM

What about the carb to tank clearence Mick ?

Sam.

I'll have a look at that tomorrow night Sam.
I had all good intentions tonight to do that and also mount the air filters but the "troops" were getting hungry and it was my turn to cook tea so I had to down tools.
I'll put some more photos up tomorrow night and see how it all sits together.
Mick

Sam Green Racing · « **Reply #53 on:** April 13, 2011, 04:56:26 AM »

dragracer · « **Reply #54 on:** April 13, 2011, 09:29:03 PM »

Quote from: SamCB750A on April 13, 2011, 04:32:27 AM

What about the carb to tank clearence Mick ?

Sam.

Again, i don't have a K model but there are no tank issues with my F model using the 36mm flatslides. My neck has even been raked and the backbone was cut and rewelded which lowered the rear of the tank some. Still good to go. He should be good to go.

mick7504 · « **Reply #55 on:** April 14, 2011, 02:34:39 AM »

It's all good and nothing's too hard.

Retro Rocket · « **Reply #56 on:** April 14, 2011, 05:10:37 PM »

Man that billet block looks FAT....awesome.......Love the silver paint to Mick....

Hurry up and build that thing mate, i want to know what the RS carbs are like on the 1000. You are now my official "TESTER EXTRAORDINAIRE"

mick7504 · « **Reply #57 on:** April 14, 2011, 06:13:46 PM »

Thanks mate.

The tank and side covers are from the old Silver Bullet.
She's been with me for a long time now (longer than the missus come to think of it) and has been in the motorcycle retirement home for a while - the bike, the bike

but I've got some ideas a bit further down the track for it.

Funny thing happened the other night when I was mocking this thing up, my youngest daughter came down to the shed to see me and said "Dad, are WE going to be starting it up tonight?"

I think that I can confidantly say that females of all ages do like shiny expensive things.

Mick

Doctor_D · « **Reply #58 on:** May 12, 2011, 12:16:14 PM »

Mine have arrived.

Bench synched and did a quick accelerator pump adjust last night.

I need 50mm velocity stacks to get my 10.9" tuned intake length right, so those were ordered today from Sudco. Not sure if I want to run the CR31's or RS34's first... not a bad choice to have to make though.

Bit of nice news is that they have vacuum take-offs, so no need to put nipples on your spigots. (That sounds kinda kinky, don't it?)

Retro Rocket · « **Reply #59 on:** May 12, 2011, 04:12:27 PM »

My money's on the RS34's, they will be better for the street....

MRieck · « **Reply #60 on:** May 13, 2011, 05:22:50 AM »

Quote from: Retro Rocket on May 12, 2011, 04:12:27 PM

My money's on the RS34's, they will be better for the street....

i agree. I've had very good luck with RS's over the years. They are the small block Chevy of carbs.

Bill/BentON Racing · « **Reply #61 on:** May 13, 2011, 05:32:56 AM »

Let us know!!! Samauto has no carb issues!!!!!

,Bill
Mick,that is pretty...the Siver Bullet....cool!

mick7504 · « **Reply #62 on:** May 13, 2011, 07:15:34 PM »

Quote from: bellcow54 on May 13, 2011, 05:32:56 AM

Let us know!!! Samauto has no carb issues!!!!! ,Bill
Mick,that is pretty...the Siver Bullet....cool!

Thanks Bill
It's still the old sentimental favorite.
A few years under the belt now and a few wrinkles (Just like it's owner)

With a bit of TLC, I'm sure that she could still roar like a lion.

Mick

Spiider · « **Reply #63 on:** May 31, 2011, 05:20:14 PM »

So....how did they work out?

I'm wondering if these would be good for a stock motor? Or too much carb?

Retro Rocket · « **Reply #64 on:** May 31, 2011, 06:47:06 PM »

Quote from: Spiider on May 31, 2011, 05:20:14 PM

So....how did they work out?

I'm wondering if these would be good for a stock motor? Or too much carb?

Way too much....

Doctor_D · « **Reply #65 on:** May 31, 2011, 10:40:04 PM »

Trying to track down a problem with a non-running cylinder, but the carbs start easily, and have great throttle response.

Installation was a bear though. Really tight in older/harder carb boots. New, soft boots are highly recommended.

Can't wait to give 'em rip on the dyno. Soon, very soon.

Doctor_D · « **Reply #66 on:** June 05, 2011, 06:53:01 AM »

I've been trying to get a run on the dyno, but I have a mysterious problem cropping up. A random cylinder is dropping out. First it was cylinder 1, then 1 ran and it was number three, then number 2... Seems like my ignition, Dyna 2000, is the issue.

Honestly though, I am trying to get a report to you folks.

MRieck · « **Reply #67 on:** June 05, 2011, 11:15:58 AM »

Quote from: Doctor_D on June 05, 2011, 06:53:01 AM

I've been trying to get a run on the dyno, but I have a mysterious problem cropping up. A random cylinder is dropping out. First it was cylinder 1, then 1 ran and it was number three, then number 2... Seems like my ignition, Dyna 2000, is the issue.

Honestly though, I am trying to get a report to you folks.

Any access to another module Dave?

Sam Green Racing · « **Reply #68 on:** June 05, 2011, 01:51:18 PM »

Sounds like there are a lot of Dyna 2000 modules going duff just latley.

Sam.

MRieck · « **Reply #69 on:** June 05, 2011, 04:56:16 PM »

Quote from: SamCB750A on June 05, 2011, 01:51:18 PM

Sounds like there are a lot of Dyna 2000 modules going duff just latley.

Sam.

Yes.

jaguar · « **Reply #70 on:** October 03, 2011, 10:00:14 AM »

any updates on these carbs and how they are running?
what are people running these on?
im on the hunt for carbs for my 812 yoshi motor

Doctor_D · « **Reply #71 on:** March 31, 2012, 10:12:25 AM »

Dredging up this old thread to give a quick update.

I took the carbs off to put larger pilots in and to go over them thoroughly once more as carb 3 still wasn't reading on the sniffer at idle. Sort of the standard approach, took everything apart, blasted all the ports with PB Blaster, poked them with guitar string, blew them out with compressed air... One float was a little low, but clearly not enough to cause an issue.

It wasn't until I got to the idle fuel orifice, a tiny hole on the bottom of the engine side of the carb body, that I noticed an issue. The guitar string only went through one of the ports.

Seems someone, odds are it was me, over tightened the pilot fuel screws on 3 of 4 carbs causing the delicate tapered tips to jam in the idle port and shear off. In my defense, the springs and o-rings on the screws create some resistance, making it hard to know exactly when the screw has bottomed out.

Never having had all the screws off at the same time, I didn't notice that the tips of the screws looked different. Pretty obvious once they're on the table together though.

It's not an unusual problem, so I'm not beating myself up too badly. However, getting the broken off tips out of the carb bodies isn't the most fun I've ever had.

In any case, this explains some of the problems I was having, and new screws are on the way.

The other issue was one of the accelerator pump sticking. This was solved by using a felt polishing bob on a Dremel, and some Mother's to clean out the pump piston bore. Much nicer now and it returns fully every time.

As for jetting, the needles that come with the carbs might be fine for a stock GS750, but on a modified 836 they're too lean. 9DZH03's are much better, curing the huge lean-out that was occurring right after the end of the accelerator pump stroke finished. 127.5 mains were too lean with my open 4 into 4's and 50mm velocity stacks, but with balky pilots and a lean needle it's not an accurate measure. As soon as the new screws are in hand, we'll get back on the dyno and try again.

Retro Rocket · « **Reply #72 on:** April 01, 2012, 06:46:31 PM »

Thanks for the update Dave....

Doctor_D · « **Reply #73 on:** April 15, 2012, 08:19:15 AM »

I've now entered full head-scratcher territory.

Dyno run from a few weeks ago, A/F shows all sorts of problems. Both the needle and the main were too lean. Down about 10hp from by previous best with the CR31's.

Now here's the part that's got me tearing my hair out, yesterday we ran it in perfect conditions, 60F, 28% humidity. A/F is not perfect, but much better. Only picked up 2hp from the prior RS34 run. Acceleration curve looks very good, much more linear - but I'm not happy leaving 8hp on the table.

I overlaid the RS run (blue) with my best CR31 run (maroon, burgandy). After 4500 rpms, the CR31's walk away from the RS's.

The CR's were a bit richer, but I have a hard time believing that's the only thing going on here. As for ignition, with the CR's, the bike ran best on program 4 with 30-deg of total advance. That and the plug heat range are next on the check-list. (Currently Denso IX27's, 24B's are on-order.)

I'm happy to take suggestions.

MRieck · « **Reply #74 on:** April 15, 2012, 10:37:38 AM »

The curve does look good but the loss of 8HP is unacceptable. What was the AF Dave?

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Author Topic: Mikuni RS34's & CB 750 (Read 40651 times)