Author Topic: CB750A Barn Build (Read 17028 times)

TurboD · « **on:** May 24, 2015, 01:29:55 PM »

I recently finished a couple Kawasaki builds and thought I would put a cool Auto build together. It was last fall when I put together my last modded SOHC bike and wanted to do something a little different.

I picked this 76 auto up a while back, it has not been ran in some time and looks like it was sitting in the mud before it was brought to me.

My plans are for a cool budget streetbike/dragbike. This will all be done with simple tools in a old barn (I'm outta room everywhere else Lol). It will get the usual Dragbike treatment, rake and stretch, bigger engine and maybe sneak in a little Nitrous for fun.

This project was started yesterday by getting it in the barn and stripping it in order to get it running just to see what I'm working with. In just a few minutes after sorting out some bad wiring I got it started and running, the carbs need cleaned to run properly but they will be discarded anyway so this is no concern. I will keep this thread updated as I make progress. Here's a few starting pictures.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #1 on:** May 24, 2015, 02:43:10 PM »

Nitrous A! Can't wait. Valdosta in November?

Old Scrambler · « **Reply #2 on:** May 24, 2015, 03:35:48 PM »

Before you tweak the converter.................a standard compression 836-kit with a 410 head for low turbo compression.........and a sidecar...........then run it at the Salt Flats

TurboD · « **Reply #3 on:** May 24, 2015, 03:54:23 PM »

I would like to make it to Valdosta this fall, I have a bike I built for the last one that I have not raced yet.

Valdosta is a long way for me.

The Salt Flats would be a lot of fun, I hope to make it out there some day.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #4 on:** May 24, 2015, 05:30:07 PM »

Carpool

Catch a ride with CycleX Kenny as he drives down with his bike (hopefully) from WI. Or Pops for that matter. Seems we're all hooking up somewhere along the way. Look forward to seeing you there.

TurboD · « **Reply #5 on:** May 25, 2015, 05:31:17 AM »

I would like to, we'll see what happens.

I started out yesterday by striping the bike down some and performed one of my rake jobs to get the ball rolling on the project. I'm not working on any certain order, mostly what I feel like tackling next or have parts on hand to work with.

I added 4 degrees to the front rake to give the bike more high speed stability, slightly lowering the front, more header clearance, along with the cool Dragbike look. I finished this job up in less than 2 hours, most of the time was spent measuring and checking, I like to take my time welding as to not over heat the headstock.

jweeks · « **Reply #6 on:** May 25, 2015, 10:17:33 AM »

Using the K head, 32 mm CV carbs with stock intake manifolds is the common route. The cheap Japanese intakes can be stretched to fit 34 mm CV carbs to a K head. Easiest way is with Seca 700/750 CV stockers.
Torque is what you need beyond stock at the rpm that you want to launch at. There are cheap converter stator modifications that can help if the motor makes more power at the rpm you want to launch at.
Gearing that's best for racing will have you buzzing around on the streets.
The DOHC 4 into 1 drag pipes look good but don't help you launch.
Mineral based oil is what you want to use. The rest has be covered before.
Good luck

TurboD · « **Reply #7 on:** May 25, 2015, 03:05:59 PM »

Jon I have a K8 head cleaned up and ready for porting, as well as a set of 750 Seca carbs. I ordered a new set of K intake boots from cruzin image. I already have a new VH sidewinder. I have been looking at all the current cam specs in an effort to choose a camshaft, there are a few different ways to approach this.

Not a lot to report work wise today. I cut the rear foot peg brackets off and ground down the welds. Then I sorted through my stash of DOHC swingarms to find a suitable one for this project, and then I started removing unwanted tabs and preparing it for extending. Hopefully tomorrow.

Retro Rocket · « **Reply #8 on:** May 25, 2015, 04:18:03 PM »

Tidy work on the steering head...

TurboD · « **Reply #9 on:** May 25, 2015, 05:18:55 PM »

Thank you, Sir.

jweeks · « **Reply #10 on:** May 25, 2015, 06:03:52 PM »

Quote from: TurboD on May 25, 2015, 03:05:59 PM

I have been looking at all the current cam specs in an effort to choose a camshaft, there are a few different ways to approach this.

The DP-295 cam has been used for a lot of the Hondamatic dragbikes. The other grind that I have been using is the Webcam #88 regrind. I don't remember the specs on that one. Nothing out there is perfect. Either cam will run well on the street.
Good Luck.

TurboD · « **Reply #11 on:** May 26, 2015, 06:36:56 PM »

Thanks Jon

Today I got the swingarm extended, added 6 inches. I used 1 1/2 inch chromoly tubing slightly flattened or ovaled in a hydraulic press to match up with the tubing on the DOHC swingarm.

jweeks · « **Reply #12 on:** May 26, 2015, 06:51:07 PM »

The longer swingarm usually is for keeping the front end down. You'll have a very big motor with the 295 cam before that would become an issue.....

The #88 grind will power wheelie going down the track when it hits the right powerband spot. On my 10 second dragbike the bike is about 150' out in low gear when the front end comes up. It hits the wheelie bar and goes right back down for the rest of the ride. On the street with a sane throttle hand, I doubt you will have the rubber and the desire to break 7k at wide open throttle with a big cc Hondamatic motor. (My motor is around 1180 with the 900F crank) And my wheelbase isn't much different than what you're building.

TurboD · « **Reply #13 on:** May 27, 2015, 05:15:05 AM »

I'm pretty sure that extending a Hondamatic is not needed, but looking good and looking the part is half the fun of it. Lol

I got my cruzin image intake boots yesterday, I ordered them on the 21st and they got here on the 26th, and this was over a holiday weekend. Always great service, highly recommend.

Guys, I am looking for a good usable left cover for this bike. Anyone have one??

johno · « **Reply #14 on:** May 27, 2015, 06:11:42 AM »

Hi Turbo,
you need to visit my shed soon, got a few dozen little fabrication jobs for you

Enjoying your project., re your rake job, just curious looking at the pics the amount of material at the top cut looked about 4mm, if so 1mm =1 degree ? is that how your calcs rolled out Turbo ?

LAST SUGGESTION, yellow would look nice

cheers Johno

TurboD · « **Reply #15 on:** May 27, 2015, 05:30:04 PM »

Johno I will be right over to help.

I'm going to say it was closer to 10mm total, I can check it tomorrow. I have found it easier to sometimes make the cut ever so slightly wider, adjust to the amount rake wanted, then tack into place. On some of my first jobs I did not cut enough out, then found it to be harder and more time consuming to widen the gap.

TurboD · « **Reply #16 on:** May 30, 2015, 02:19:10 PM »

I'm getting a little closer all the time, I have the swingarm finished and the rear axle spacers sorted out. I have the head off, disassembled and flow tested. next I need to start porting work on it, and order a cam.

Bill/BentON Racing · « **Reply #17 on:** May 30, 2015, 03:09:19 PM »

Come to Memphis if possible!

Some motivation, lol, Bill

Jerry Rxman Griffin aka MuthaF'er · « **Reply #18 on:** May 30, 2015, 03:41:06 PM »

ONLY 10.90?

TurboD · « **Reply #19 on:** May 30, 2015, 03:44:13 PM »

Bill I will be happy to post some numbers on it. Hehe. When is the Memphis race? I'm afraid I may have a Top 10 list race that weekend.

Bill/BentON Racing · « **Reply #20 on:** May 30, 2015, 04:16:12 PM »

June 20,21st

TurboD · « **Reply #21 on:** June 05, 2015, 06:59:57 PM »

Getting closer everyday, I'm pretty much down to finishing the head and then putting the top end back together.

POPS 911 · « **Reply #22 on:** June 06, 2015, 02:41:41 PM »

Finally someone who says they can run 10 anything will be in the lanes on a CB750A HONDAMATIC , this will be worth the drive ...... Got to see this Turbo wick up and pull off the line = good thing you only shift one time with this SLIDER from the old dayz. With them struts on Bills bike maybe the bounce on the bumps will not affect the ride when the boost is full on ..........

dragracer · « **Reply #23 on:** June 06, 2015, 09:41:30 PM »

Quote from: POPS 911 on June 06, 2015, 02:41:41 PM

Finally someone who says they can run 10 anything will be in the lanes on a CB750A HONDAMATIC , this will be worth the drive ...... Got to see this Turbo wick up and pull off the line = good thing you only shift one time with this SLIDER from the old dayz. With them struts on Bills bike maybe the bounce on the bumps will not affect the ride when the boost is full on ..........

Richard,
I'm planning to be on the sidelines with my bag of popcorn.

Bill/BentON Racing · « **Reply #24 on:** June 07, 2015, 06:05:53 AM »

I hope to be in the lanes on Cobra Girl. No turbo's til shoulder fixed, surgery, I'm afraid. Bill

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Author Topic: CB750A Barn Build (Read 17028 times)