Street Tracker/Scrambler BigBore Yamahawesome

txrenegade

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After spending the better part of far too much time on a 1973 CB750..

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I finally decided it was done. So what now... Start a new project!

Limey bikes up in Austin sold me a titled 1975 frame and did a big bore build for me with a NOS Yamaha Factory 750 kit that he had sitting around. From what I understand, those kits are very rare, but I love the nostalgia of basically running a racing engine from the 70's! I don't have a garage, so as the pictures show, this thing is built in a bedroom of my house as was the CB750.

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The frame was quickly de-tabbed and chopped up to get ready for what I had in mind....

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The tail of the frame was cut off and a new hoop from Cognito Moto with integrated tail light was welded up along with a pan underneath. I am running an XS750 gas tank so my buddy and I got new mounts taken care of for that as well. It's a section of pipe with washers welded on so the rubber pucks pop right on.

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This thing is running some GSXR forks up front with 18" rims front and back with Buchanan Spokes too. It was my second time to lace and true the rims and it still sucked.

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I caught it trying to take a nap one day... (actually I forgot to latch the lift) but luckily nothing was messed up.

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I was worried about the overall seat shape with the height of the hoop so I used some florist foam to mock up an overall seat shape just to be sure.

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My next step was the headlight plate and dash. I had seen a few cool ones floating around and after mocking it all up with foam board, my architect buddy drew up my parts in CAD and I had it all laser cut from 5ga. aluminum. I think it came out pretty good. The Motogadget Mini along with the idiot lights and switches and "key" (more on that later) will be in the dash as well. I'm pretty excited with the way this is coming together.

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The headlights required some trick brackets to get them mounted but I was glad to get that sorted out.

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So that's where it sits right now... I just ordered some shocks from Works Performance and I'm still in the process of getting the front end right.

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I'm also still sorting out the rear brake setup with the stretched swingarm but hopefully will tear it down in a few weeks and send the pieces and parts to powder coating. Then the real fun begins...
 
Christonastick that's some good looking stuff there...and all in a bedroom. Good work. I'll be following.

If you don't mind my asking, did you do the front end Gixxer swap on your own? Or did you have Cognito do it? Thinking about going that direction myself...was curious...
 
I got the parts from Cognito. Front hub, steering stem, top triple and bearings. Thanks for the kind words. It's slowly coming together but I'll try to keep this updated.
 
I really like your work so far and appreciate the asymmetrical lights.
Does your 750 cylinder have a factory cast in 750 cc marking, or does it still say 653cc?
 
I really like your work so far and appreciate the asymmetrical lights.
Does your 750 cylinder have a factory cast in 750 cc marking, or does it still say 653cc?

It still says 653cc on the bottom front of the left cylinder. I haven't been able to find much info on the kit but the shop that did the build is very reputable and said that's what it was.
 
Back in the mid-70s, Rocky Cycle acquired the stock of Yamaha's 750 kits, sleeves/pistons/rings/pins/clips/gaskets. I got their 256 version. Your shop probably got their 447 version. These factory sleeves are thinner than other aftermarket sleeves, and included the dowel pin cutouts. They easily slid into the existing crankcase openings.

Warning: Highly questionable insider info here.

I've never revealed this before, mostly because I've never found any other confirmation stories.
So, take it with a grain of arsenic.
Or, please confirm this crap. It's been driving me nuts.

According to the Yamaha and Rocky reps I talked to back then, their story was that Yamaha had originally planned the XS1 to be a 750cc engine, but their marketing group talked them into downsizing it to 650cc, to avoid competing in the highly competitive 750cc market, and be more successful in the 650cc market. But, a lot of the 750cc stuff had already been produced, so it was just shelved, and the engine adapted for 650cc. They also claimed that's why the wristpin was originally larger, at 22mm. Then, when it was decided to discontinue any factory 750cc options, the piston/wristpin/conrod design settled to 20mm, to more appropriately match the 650cc power level.

Similar story with the Pinto and Vega.
Ever wonder why you could easily shoehorn a V8 in those?

Edit: After reading the stories about the XS2's limited 750cc production, I believe that THIS was the more likely actual source of the 750cc kit parts, and the reps twisted the story.

Anyway, there's a major eBay vendor just east of you, in Lockhart, with a warehouse full of NOS parts, including some of those Rocky XS650/750 acquired kit parts...
 
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Love the shape of the seat/hoop!

Oh and how'd you get that harbor freight rear stand to work? Mines a POS
 
Well, I certainly did not update this thread like I wanted to, but the bike is finally on the road. The tank is currently at the painter and some other odds and ends need to be powder coated before it's completely done, but I figured I would post some photos of where it's at. The bike is running pretty good but I am still messing with the VM34s and getting some things dialed in. Let me know what y'all think!

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Really nice bike man!
This is exactly the idea I had for my seat. Kind of mix between scrambler and tracker.
Why did you change from the oil lines on top of the clutch and pump to reservoirs?
Too small?
 
Really nice bike man!
This is exactly the idea I had for my seat. Kind of mix between scrambler and tracker.
Why did you change from the oil lines on top of the clutch and pump to reservoirs?
Too small?

I'm not exactly sure what your question is. The clutch and front brake are both hyrdaulic. The reservoirs are bulky and I like the look of the smaller little tubes with the extra instead of the large cups.
 
They are some cheap foglight things for cars from eBay. I run one for low and both for high. Nothing spectacular but they work.
Hi txrenegade,
my night vision ain't what it was, which prompts me to ask, as there's room to add the matching spotlights on that front panel, why dontcha?
 
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