Author Topic: My twin carb setup (Read 7875 times)

De250r · « **on:** April 17, 2013, 09:29:24 PM »

I'm building an 81 cb750 bobber and just finished mocking up my twin carb setup. I'm using 36 mill mikuni flat slides but my manifold is built so it will debore them to 34 mm.

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De250r · « **Reply #1 on:** April 17, 2013, 09:33:34 PM »

I'm gonna build a air filter or run pods.

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De250r · « **Reply #2 on:** April 17, 2013, 09:47:07 PM »

Ill prob build a support under the carbs. I think it will all fit in what's left of the stock frame but still might chop more off. We shall see.
I bought 2 750 from a guy who started chopping them then lost interest for 200. Could almost put two complete bike and another parts bike together out of what I got. Trying to see how little more cash I need to put in to get a decent rat bobber to cruise around on. I can fabricate and machine thing s and my buddie had the carbs. I've got a lot of parts to choose from so I'm interested to see what it comes out like.

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De250r · « **Reply #3 on:** April 18, 2013, 05:14:25 AM »

I'm hoping to machine a lot of brass tidbits for it exhaust tip pegs grips etc. want to run stock geometry in the front maybe struts out back for cruising around town and get some air shocks if I wanna ride to bike week or some where.

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iron_worker · « **Reply #4 on:** April 18, 2013, 07:08:36 AM »

Do you think think the twin 34-36mm will be enough for the 750? Seems like it might be a bit restrictive at the top end? Although you'll probably have really nice throttle respsonse and acceleration at low end.

Cycle X makes a twin carb kit for these bikes. However, this is very cool that you're doing it yourself.

IW

De250r · « **Reply #5 on:** April 18, 2013, 07:38:23 AM »

They use 34mm in there kits as well. I read that 36 mm will pull good top end but throttle response on bottom will b slower. That's why I debored the carbs to 34 using the manifold. It's actually an oval carb opening now I dint want to alter the idle/pilot/1/8 throttle fuel circuit so my de bore is from 1/8 opening up.
I saw a video of a cb750 running on a single old over grown lawn tractor carb so I'm sure these will work. How well I'm curious to find out.

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De250r · « **Reply #6 on:** April 18, 2013, 07:45:39 AM »

In the pics above the manifold needs to be sucked in to the boots still so there won't b a gap. I'm also gonna grind it buff it polish it. Might powder coat it tho.
Gonna use these for my exhaust tips run 1 on each side y 2-1 put a little baffle insert in it to make Johnny law happy

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lwahples · « **Reply #7 on:** April 18, 2013, 08:27:44 AM »

Be neat to see how this works out, What part of VT?

De250r · « **Reply #8 on:** April 18, 2013, 09:28:48 AM »

Northeast kingdom. Saint johnsbury area. I spend the majority of my riding time on my dual sport. I traded my Harley last year for a yamaha rhino because I put less and less miles every year I had the Harley. I've always been into building customizing snowmobiles four wheelers mud trucks whatever. This will b my first street bike so I'm stoked. Now if I can just stay off my dirtbike long enough to work on the cb
The other cb I have is a 75 I believe might build a dual sport/scrambler style bike out of it. Or a snow chopper

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De250r · « **Reply #9 on:** April 18, 2013, 10:05:11 AM »

I've also got 4 of these black anodized aluminum parts that would make nice exhaust tips as well. Just thought of this brass flappers covering these

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lwahples · « **Reply #10 on:** April 18, 2013, 11:53:55 AM »

If you decide to do something different and want to trade the 750 for something, I'm in Barre. Good Luck.

De250r · « **Reply #11 on:** April 18, 2013, 03:06:12 PM »

Prob gonna keep both. I got so little in to them. Thanks
I got the rest of the bike stripped of wiring and my shop cleaned up a bit. Gonna take my son up and tinker some more here in a bit. I took some measurement of the newer yamaha wheels I've got and I think I can get them to work.

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De250r · « **Reply #12 on:** April 18, 2013, 04:44:46 PM »

Just mocked up the wheels and the new ones are so much lighter and more modern looking. The front rotors are the same size. The tire itself is 24 inces tall compared to the stock 26 but its quite a bit fatter than the stock. The rotors will line up with 3/16 spacers or so. Will have to get dial indicator out and fugue for wheel spacers and cut new ones. The rear fell right in. Ill have to make a big spacer/caliper bracket and the other spacer.
I got the manifold sucked in with a Ratchet strap and the carb fits in real nice and clean. The radius even lines up with the motor as your looking down.
Thinking about low rise drag bars. Maybe build some of those too. I like how much cleaner it looks today after finally workin on it.

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De250r · « **Reply #13 on:** April 18, 2013, 04:46:40 PM »

The boss was out supervising tonight as well. So I gave him a real saw to cut all my stuff up with.

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De250r · « **Reply #14 on:** April 19, 2013, 01:49:40 PM »

Did some more today got my seat mocked up into place. It's the passenger pilon from a stock Harley seat. It fits nicely. Think it will bolt in the front and strap it down in the back. Think I'm gonna run the front fended in the back mounted on swing arm.
My gas tanks I got rnt worth the effort. So in looking for one off? Put the stock bars on just for reference. I like the way it feels with the little seat

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De250r · « **Reply #15 on:** April 20, 2013, 05:58:28 PM »

Did a bunch of little stuff today.mounted the fri. Calipers. Well tried to. Had to unbolt the rotors from the wheel slide the rotor in caliper then replace rotor in order to clear the rim. No biggy. Then the rotor bolts hit caliper bracket. Little grinding they will clear. Then I can measure for spacers.
I got the rear axle all tight did some serious sitting back and visioning. I think I'm gonna run just some dirtbike bars like the look and feel.
Think I'm gonna hard tail it with struts and run one shock under the seat. Was thinking about cutting the passenger peg wings off but have decide that's a good spot for rear set control with another farther forward peg.
I might use the sides of the stock tank and Remake the center. There r some cool curves in the stock pinstriping that will make nice cut outs for my knees.also have some stainless sheets and wire for my welder. Have a aluminum diamond plate tool box that has been cut apart I could make a tank out of as well. The carbs aren't in the way anymore so it opens up under the tank.
The air filter will b pretty easy using the airbox opening from the snowmobile cut and epoxied to a piece of aluminum with a filter bolted to it.

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De250r · « **Reply #16 on:** April 21, 2013, 05:41:00 PM »

I got some more parts from my brother today. All the brake setups from an fz600 where the wheels came from. I will have to run the calipers in front of the wheel instead of the back but I have to build wheel spacers anyway so ill build brackets into them to mount both calipers. They r smaller than the cb but 12 years newer.the rear caliper will mount behind the wheel with a spacer as well I also got the little speedo from the bike and the rear shock. The speedo will work and look good its pretty small so I can hide it somewhere. The rear shock hides and fits perfect under the seat and dual air intakes beside it. The shock will start its travel at the height it is at in the last pic. The shock will b mounted without linkage so it should b real stiff riding but it will give some. No new pics tonight but a lot of ideas and progress.

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bjbuchanan · « **Reply #17 on:** April 21, 2013, 07:05:48 PM »

I like what you are doing here it is pretty cool. Hopefully your thread gets some more traffic, you are doing cool stuff and I think the overall feel of the bike so far is great

What about maybe supermoto bars if you don't want just flat bars

De250r · « **Reply #18 on:** April 21, 2013, 07:18:00 PM »

Thanks for the reply. Supermoto bars are about the height I'm after we will see when it comes time to order some.

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iron_worker · « **Reply #19 on:** April 22, 2013, 09:42:01 AM »

That should would be way too stiff for just under the seat. It's designed to take the weight of the rear of the bike + your weight + a passenger.

IW

De250r · « **Reply #20 on:** April 22, 2013, 11:52:49 AM »

In gonna have it mounted to the swing arm. No longer gonna hard tail it. I would use one cb750 to do just the seat. Sorry I didn't clear that up. Nothing is permanent yet so who knows how it will end up.

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De250r · « **Reply #21 on:** April 22, 2013, 01:07:19 PM »

Took down all my dimensions for caliper brackets. A lot of numbers. What did people do b4 zip ties. It's the perfect thing for hanging things right where you want them. Hopefully get some more done tonight.
I like hearing others opinions ideas and comments.

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De250r · « **Reply #22 on:** April 22, 2013, 07:20:01 PM »

After a lesson in trigonometry I think I've got the caliper brackets figured out hopefully. I forgot how much I didn't pay attention in math class.

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De250r · « **Reply #23 on:** April 25, 2013, 06:17:02 AM »

I got the first operation of caliper brackets done and my math was correct Now as long as I don't mess them up finishing them. Lets hope. I got it figured out how I'm gonna build the rear caliper bracket. The rear sprocket lined right up with the front sprocket by using the spacers from the fz
I crushed some empty .270 casing and came up with a speedo mount for the one off the fz600.
It is a rolling chassis again so I pulled it out of the shop yesterday and cut ground off most of the extra tabs. It made it look alot better
I'm thinking about cutting the bottom out of stock tank and rebuilding the top. Hopefully find some more time today to go work on it some more.

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De250r · « **Reply #24 on:** April 26, 2013, 04:27:30 PM »

Caliper brackets just need to figure final wheel spacing so I can cut the last 2 pads into them. Speed holes as well to cut weight

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Author Topic: My twin carb setup (Read 7875 times)