Author Topic: CV Carbs for 750 (Read 15557 times)

TurboD · « **on:** April 08, 2014, 06:36:31 PM »

I am wanting to put some CV carbs on my 750 F2. Anyone know what carbs will fit? (direct fit hopefully)

raymond10078 · « **Reply #1 on:** April 08, 2014, 06:49:45 PM »

Yamaha XJ750 carbs will fit using 76/older carb rubbers.

TurboD · « **Reply #2 on:** April 08, 2014, 08:59:33 PM »

I don't think the early boots will fit the f2 head.

raymond10078 · « **Reply #3 on:** April 09, 2014, 03:33:33 AM »

TurboD I think you are right about that, I spoke too soon.

jweeks · « **Reply #4 on:** April 09, 2014, 04:41:19 PM »

Ok, right carbs (32mm), wrong manifolds. Try these:
http://www.vintagecb750.com/products/73/featured-products
Should work with only a main jet change if running on the street.

Honda 80's Nighthawks from outside the USA (ie: 750's not 700's) fit (34mm). I'm told that with a jet kit and a little massaging for your combination they run fine. Bear has sent Bill a set to play with. I've bought a Canadian set through Ebay.ca

The CV carbs run small compaired to mechanical linkage carbs. This means that you could run a larger CV carb than say CR's. Since the automatics have to run CV's for full throttle launches at reduced rpms, we've played with most of what's out there. 34 mm CV's are the largest that will fit your unmodified manifolds. Machining manifold id's for bigger carbs has limited gains due to port limitations. Sam's Hondamatic runs older Suzuki 750 carbs (32mm?) with a jet kit and dyno tuning. I had them reracked to fit. Pops likes STP as the carb to manifold lube. First time in is always a tight fit.....

What's the application?

TurboD · « **Reply #5 on:** April 09, 2014, 05:44:07 PM »

I am ultimately building a blow thru turbo system, I just got the bike together and running it NA to break it in and sort out any problems. I got this one a couple months back as a complete basket case, I brought it home in my car.

I picked up a nice set off of a mid 80's 650 only to find out the spacing is wrong.

raymond10078 · « **Reply #6 on:** April 09, 2014, 05:53:02 PM »

Hmm. Then maybe the turbo seca carbs would work then too - just a thought.

jweeks · « **Reply #7 on:** April 09, 2014, 07:27:31 PM »

Would fuel injection be too scary a thought?

dusterdude · « **Reply #8 on:** April 10, 2014, 12:04:34 PM »

Its been done but expensive.who on here did an fi setup?i forget

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dragracer · « **Reply #9 on:** April 10, 2014, 02:34:13 PM »

A member of Hondachoppers installed fuel injection on his bike. I also saw a member on this site that tried it with success. Used Suzuki GSXR fuel injectors and throttle bodies. A microsquirt ECU was used to control fuel at first and then I believe they converted it for ignition also.

jweeks · « **Reply #10 on:** April 10, 2014, 02:54:56 PM »

http://forums.sohc4.net/index.php?topic=30624.575

It takes some time to get it running right but parts are boneyard available. Once you understand the megasquirt software, you should be able to tune it a lot closer than with the carbs.

An airbox for the carbs with some fuel pressure enrichment when on boost won't be that easy either in my opinion. If you can get any method to work, we'd like to see the process.

TurboD · « **Reply #11 on:** April 12, 2014, 08:01:27 PM »

I bought a set from a 84 750 Nighthawk from Canada, hopefully they will fit.

Mitchell · « **Reply #12 on:** April 15, 2014, 06:37:15 PM »

1983 to1985 cb650 cv carbs fit right up with round top carb intake boots. Thats what i used for my blow through setup. I think the cb700 and cb550 from those same year models will work too.

TurboD · « **Reply #13 on:** April 15, 2014, 06:44:30 PM »

Do you mean the round top hat style? the set I have are from a 84 85 650 and the center two carbs are clearly too wide.

Mitchell · « **Reply #14 on:** April 17, 2014, 05:49:26 PM »

I mean the round top cb750 carb intake boots 69-76. My motor is a 73k im not sure if the f3 head intake ports have the same spacing but I know the carb intake boots and carbs are differant. i think you need to get a set of early model carb intake boots and the 650 carbs will fit. That thing is going to be sick with a turbo setup are you going to use the four to one header to pipe it all together? and on a side note the cv carbs with a turbo tune really easy just get the jetting right with out the turbo and you should be dead on when you boost it up as long as your reffrence tubes are not to big or to small, mine are about 3/16'' i.d.

TurboD · « **Reply #15 on:** April 17, 2014, 06:34:18 PM »

Yes the F2-3 heads have a larger intake runner and use a bigger intake boot. I am going to build a header, the turbo will be mounted behind the front wheel.

Mitchell · « **Reply #16 on:** April 17, 2014, 07:10:23 PM »

I knew there were some differances in the heads but I have never owned an f3. I knew the carb side of the intake boots are bigger but I thought the head side could have been the same.

There was a guy on here that built an f3 with stock carbs blow through.

Thats how I built my header set up with the turbo right infront of the engine just keep an eye out for cleareance for supension travel, I had to cheat mine to the side so it would clear. it looks like theres alot of room but onece you get to building the room disapears quickly. You could run the 4 to 1 and put the turbo right inbetween the shocks. building the header was the hardest part of the build for me because the location of the turbo, however I think in the long run it was worth it because heat helps spool the turbo and its as close to the motor as it could get and high so the oil drains good right into my stator cover

TurboD · « **Reply #17 on:** April 21, 2014, 07:50:29 AM »

Now after buying a set of Canadian 750 Nighthawk Carbs and waiting for them to arrive. They do NOT fit, they are exactly the same spacing as the 650 Nighthawk set that I bought before these.

dragracer · « **Reply #18 on:** April 21, 2014, 08:23:05 AM »

I thought I read they were a close fit but have to be tweaked on the racking?

dragracer · « **Reply #19 on:** April 21, 2014, 08:37:04 AM »

By the way, I used 85/86 Ninja 900/Yama FJ1100 flatslides on my F model. I tried a set of stock CV's from the Ninja but they were in such bad shape, I went with new Mikuni instead. The spacing was darn close but not quite exact- you can go on Mikuni's website and all of their applications with spacing are listed- that's how I decided on which model was close to the Honda spacing. Sudco is a resource for those specs also. Since the OD of the carbs was smaller the ID of the boots, I used a coarse sanding drum on my die grinder to offset grind the boots some. It made one side of the boot a bit thinner than the other but after 17 years, I haven't noticed a leaking issue yet. I then used my heat gun to soften up the boots, lubed them a bit and slide the carbs in place with some effort. It was a long day of grinding and fitting but in the end, it was well worth the effort. Glad I had the patience in order to taste the rewards. Yes, its a 10 second Honda on a street tire with no wheelie bar.

Missingparts · « **Reply #20 on:** April 21, 2014, 05:16:38 PM »

The 84 through 87 CB700sc uses a cv carb that has the same spacing and matches up really well. The stock throttle cable even bolts right up.

jweeks · « **Reply #21 on:** April 21, 2014, 05:32:02 PM »

Am I the only one confused here? I've read on this forum about the Canadian 750 Nighthawk carbs fitting the CB750 (K) head. That's why I purchased a set that I haven't yet tried to use. Bear stated that the Australian equivalent to the Nighthawk carbs get used down under on our SOHC CB750's. He sent a set to Bill Benton to try. Mitchell has fitted a set of CB650 carbs to a 1973 K 750 head. TurboD says the CB650 and Nighthawk 750 carbs have identical spacing with the center two carbs having too wide a spacing to fit.

Can the manifolds be mixed to give us altered mountings? There are two different ones in use. On the Mikuni RS34's & CB 750 topic Johno on page 4 has found Japanese aftermarket manifolds for K heads that are softer and more flexible for larger diameter carb ends. I've messaged him for more source information.

The FJ700/750 carbs also have been recommended previously on the forum. Pops has purchased a set and mounted them to a CB750 SOHC K head without problems.

There's not a lot of information about successful CV carb mountings to SOHC 750F heads. I've already posted the only source that I know of for aftermarket F manifolds. Dimensionally, I've never heard of any difference between F and K carbs for spacing or mounting. I've got a set of Mikuni 34 mm CV carbs reracked to fit my F headed SOHC 750 based motor. The mounting of the carbs is easier than finding the tuning needles and idle circuit changes to make them work with our motors. My Mikuni's got custom needles from Dyna-Jet in the early days. I don't know where to look currently for that kind of parts for obsolete carbs. The "performance" jet kits that are available usually include new needles for "modified" motors. That's what I used on Sam's K head Hondamatic - old 750 Suzuki CV carbs reracked and the stage 3 jet kit applied. Dyno time to get the right notch and main jet and you're down the road of your choice.

Do we measure everything for carb spacing and take pictures of our successes? Right now, I'm confused by one who has made it work and one who says it can't work. Anybody got some ideas? $:-\$

TurboD · « **Reply #22 on:** April 21, 2014, 05:41:51 PM »

Earlier today I found a seller on feebay with some xj650 seca turbo carbs, he was nice enough to measure them for me. They do not appear to be a good option as the center spacing is wider as well.

I just emailed a Feebay seller with a set of 84 cb700sc carbs (as per MP's post), we'll see what he comes up with.

jweeks The spacing on the K and F heads are the same, the later F uses a shorter and bigger intake boot.

Missingparts · « **Reply #23 on:** April 21, 2014, 05:47:16 PM »

I did some further research after finding the thread below a while back
http://forums.sohc4.net/index.php?topic=28898.msg522785#msg522785
It turns out the 84 cb700sc carbs are pretty much the same as the ones in the link above but with a larger venturi.
I have a set that I am rebuilding right now. I compared them before dis-assembly and the spacing was the same.

TurboD · « **Reply #24 on:** April 21, 2014, 05:50:23 PM »

My 650sc and 750sc have the same spacing, the 750sc are bigger.

The seller with the 84 700sc carbs just emailed me and said that he will measure them tomorrow when he gets back to his shop.

News:

Author Topic: CV Carbs for 750 (Read 15557 times)