Switching to dual carbs on a CB750. Thoughts??

[Hippie459MN]

I have a 1979 CB750 DOHC in an Amen hard tail frame and I have been really been considering a major carburetor modification and am looking for any thoughts or input.

I really love the look of twin carbs on the 4 cylinders and was wondering if anyone has ditched the 4 carbs for 2 carbs on the DOHC motors and had any good results. Cycle X has a SOHC kit but seeing I have a huge selection of carbs here I would be looking at just a 2 into 1 manifold option like the Cycle X Manifolds that can be found here - http://www.cyclexchange.net/Carb%20S...omp%20Page.htm

Its just a thought as I love the looks of the twin carbs over the 4 carb set up but if it wont work that well I will scrap the whole idea. I hate to spend a ton of money and time into something that is not going to work.

Here is my bike I will be working with. Its getting all new tank (The current amen tank in the pic will be for sale very soon if anyone is interested), rear fender, and ditching the rear 15 inch rim for a 17 or 18 inch rim this winter so just trying to plan out my direction with everything.



Any input or ideas would be great on this whole 2 carb set up idea on a DOHC.

[Guest]

Damn some of the dudes making manifolds are absolute dickwads, and I can't remember if these people are some of those... so if anyone wants to vouch the rep of that company that'd be cool.

Dual screw top carbs are going to be your easiest route... screw tops are easy to set and really reliable don't rely on vacuum shit, and fuel on demand when you twist. Cv's are ok but vacuum operated can be a pain though they have a nice power curve through the whole band if dialed in right... since you're dropping two carbs and changing things up, I'd avoid them simply because of the extra dynamics and tuning to get them just right, instead of just jetting, cable synch, and a/f screw on screw tops. Flat slides are great for power but, require periodic adjustment to stay tip top... best if you're a carb guy already type of carb.

[junkyardxl]

Nepil up here was running a lot of stuff from them on his single cam. Had nothing but good things to say.

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[ContractKiller]

Cycle X makes good stuff. I haven't run them personally but I've talked to several who have run their dual-carb setup and they've had good things to say about it. It's also been done, there's a few twin-cam CBs running around with them. Here's one that I drool over on occasion:

[junkyardxl]

Here's the only pic I can muster from joshes bike

[rigidchop]

I'm not sure about the DOHC's but on the SOHC's if the motor isn't in really good shape (good compression, electronic ignition) those carbs aren't the best.

[Hippie459MN]

Cycle X makes good stuff. I haven't run them personally but I've talked to several who have run their dual-carb setup and they've had good things to say about it. It's also been done, there's a few twin-cam CBs running around with them. Here's one that I drool over on occasion:

I like that! Guessing that is the Cycle X manifolds on that DOHC? Wasnt sure if the SOHC and the DOHC was the same as far as the intake locations and such. I have access to a bunch of flat and round slide carbs as a bunch of friends run snowmobile watercross and they always have a pile of them laying around in all different sizes.

Im still 50/50 on this idea but getting closer to going for it and just trying to see if and what anyone is running or has run and how well it worked for them before I fully commit to this. lol

Thanks for the info everyone and if anyone has anymore thoughts I would love to hear them.

[Guest]

Cycle X makes good stuff. I haven't run them personally but I've talked to several who have run their dual-carb setup and they've had good things to say about it. It's also been done, there's a few twin-cam CBs running around with them. Here's one that I drool over on occasion:

and I can see why you're drooling those have to be the nicest intakes I've seen yet.

[Alexander]

Avoid 2 stroke carbs.

I like that! Guessing that is the Cycle X manifolds on that DOHC? Wasnt sure if the SOHC and the DOHC was the same as far as the intake locations and such. I have access to a bunch of flat and round slide carbs as a bunch of friends run snowmobile watercross and they always have a pile of them laying around in all different sizes.

Im still 50/50 on this idea but getting closer to going for it and just trying to see if and what anyone is running or has run and how well it worked for them before I fully commit to this. lol

Thanks for the info everyone and if anyone has anymore thoughts I would love to hear them.

Don't try and use those freebie carbs. Those 2 stroke carbs have different emulsification tubes. I tried a big 2 stroke carb on my 1 into 2 XS650 and it sucked. Real shit performance because the vacuum characteristics are different between types of engines.

Use a VM34 or better. Aftermarket new carbs tune well.

I'm using a Mikuni HSR42 flatside carb on my XS1100 with a 1 into 4 intake. It works well on those domestic guys' 1200 Harleys.

~Alex

[johnnybarndrunks]

I have no hands on experience myself, but I've heard more people say they couldn't get these to work properly then I've heard people that actually have had any success with these.
My tip is to get in touch personally with people who are running these and ask.. Second hand widom is - well it is just that. Second hand.
It would suck to drop the dime on a setup like this just to find out it doesn't work 100% (or is a real PITA to dial in.)

[rigidchop]

DOHC and SOHC intake spacing is not the same.

[Hippie459MN]

Don't try and use those freebie carbs. Those 2 stroke carbs have different emulsification tubes. I tried a big 2 stroke carb on my 1 into 2 XS650 and it sucked. Real shit performance because the vacuum characteristics are different between types of engines.

Use a VM34 or better. Aftermarket new carbs tune well.

I'm using a Mikuni HSR42 flatside carb on my XS1100 with a 1 into 4 intake. It works well on those domestic guys' 1200 Harleys.

~Alex

Never thought of that. Good to know. Thank you.

DOHC and SOHC intake spacing is not the same.

Thats what I figured. I have never worked on a SOHC so I have never had any experience with them.

ContractKiller, any chance you could find out where that guy got that set up thats on the DOHC. Would love more info on it.

[Hippie459MN]

Found a little more info on that green bike but no contact info and looks like they guy made the intakes himself. Would love a set. Even converted it from shaft drive to chain so I guess it can be done!

http://www.bikermetric.com/2012/05/reader-rides-logans-1982-honda-cb900c.html

[ChopChuiey]

you should call the cyclex Wisconsin crew I call em all the time for tech support
I have the cyclex boxer motor and the dual carb setup on a Santee soft tail with chrome oem Triumph slim line tank

Ive had smooth bores 30mms, Cr's 31mm and stock carbs past hot rod setups which all takes time to synch dial in fresh builds run as should, but two carbs less time spent to dial in starts on a dime day or night. Cycle x in the buisness of cb750 why would you ask cb750 fitment on a knucklehead forums where they all dump their motor out side frame splat in the dirt haha

[ChopChuiey]

ps does anyone have any dellorto ss1 set of carbs 28 to 38 I can use for the cyclex dual carb manifold setup thanks