Topic: CB750 K3 Chopper Build

[budman]

I picked up my new project after work tonight.  It's a craigslist find.  The guy I bought it from is an older version of me.  He bought the bike at a garage sale several years ago and started chopping.  He said he doesn't have time to complete it.  He has too many other projects.  It's pretty rough, but so was my last build when I got it.  I can see the potential.  I was attracted to the stance in his photos.  I've been wanting a chopper for years.

The only real hiccup is it didn't come with a title, but the guy did give me a report from the DMV.  The bike hasn't been registered since 1990.  I'm pretty confident I can get a bonded title for it.

The gears are already turning in my head.  The first thing I'm going to do is to put it back together to see what I've really got before blowing it back apart.  The guy made a lot of parts himself, which right now I'm thinking I probably won't use.

The frame looks straight after the hard tail job.  After I decide what parts of his I want to use I'll need to blast all that Nitro-Stan putty off and see what's underneath.  I hope the surprises are minimal.

At this point I know I'm going to use the frame, the front end, the wheels, the engine and probably the rear fender.  For the engine I'm thinking an 836 with twin Mikunis from Cycle X.  Gonna try to keep the cosmetic side of the engine within a lower budget.  No chrome, probably mostly paint and a few polished parts.

I'm gonna ditch the small peanut tank and go with a king Sporty tank I already have.

I'm pretty sure the wheels are AMF Harley.  I'm going to use them, just have them powder (re)coated.

I could go on an on...

For now here's some photos pics of the bike before the guy pulled it apart for paint.

[budman]

Here's the actual pile of parts I got.

[Stev-o]

Congrats, great project Bud, you didnt waste time!
I love the stance too.  Exhaust looks to be custom made, will you use that?
The points cover is custom too?

[budman]

Congrats, great project Bud, you didnt waste time!
I love the stance too.  Exhaust looks to be custom made, will you use that?
The points cover is custom too?

Thanks, Steve.  Should be fun.

I'm not going to use the exhaust.  Probably go with a 4 into 4 drag exhaust if there's clearance.

The guy I got it from made the points cover.  I'll probably use it.  He made a lot of parts for it, like an adapter on the front wheel for the speedo drive.  He made an oil tank for it too, but I don't think I'm going to use it either.

[palepainter]

Ooooh.  That is cool.  Just right on the rake and stretch. Not too long, but not short and squatty.  Perfect.  Looking forward to it.

[budman]

Ooooh.  That is cool.  Just right on the rake and stretch. Not too long, but not short and squatty.  Perfect.  Looking forward to it.

My thoughts exactly.  I couldn't pass it up.

[Stev-o]

Have you assessed the motor yet, Bud.  Any idea why he pulled it apart?

I have a lot of spare engine parts if needed.

[mscuiletti]

Looking forward to this! Very cool.

[Lostboy Steve]

Very cool! If it were mine I would have just left it. Looks cool with all the patina and 70s styling.


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[budman]

Have you assessed the motor yet, Bud.  Any idea why he pulled it apart?

I have a lot of spare engine parts if needed.

Just a quick visual.  I'm pretty sure the bottom end is OK.  Head and cylinders look good.  No broken or bent fins that I can see so far.  The PO took it apart because of a stuck piston.  He couldn't turn it over.  He told me it only had 11k on the speedo.

I'm thinking 836 with dual carbs right now, but that could change.  I'll probably split the cases and pretty much repeat the process I did on the Cafe Tracer.  Probably no chrome on this engine.  I think I want the engine to look something along the lines of the engine in palepainter's cafe...dark.

Thanks for the offer.  I'll keep in mind.

[budman]

Very cool! If it were mine I would have just left it. Looks cool with all the patina and 70s styling.

The PO blew it apart.  I wish it would have been together because he made a lot of parts for it.  It'll take me a while to figure out what he was thinking, then I'll have to decide what stays and what goes.

[budman]

Looking forward to this! Very cool.

Thank you.

[budman]

I spent almost all day yesterday cleaning up the shop, getting it ready for the chopper build.  After I was finished I dug out the king sporty tank I used to run on my bobber.  It had been sitting on the shelf collecting dust since I replaced it with the current bigger tank in 2011 before I rode the bike to Sturgis that year.

I figured the king sporty tank would make a great tank for the chopper.  It'll be better than the 1.5 gallon sporty tank that came with it.  I painted the cheesy flame job around 2010.  I figured I'd try my hand at ratting it out.  I guess I've been watching too much "Vegas Rat Rods".  Like it or not I think I'm going to run with it.

Here's what I started with.


Here's what I ended up with.




I guess that makes the first piece of the puzzle finished.  Only cost me $5 for a can of flat clear.

[SOHC4 Cafe Racer Fan]

Have you assessed the motor yet, Bud.  Any idea why he pulled it apart?

I have a lot of spare engine parts if needed.

Just a quick visual.  I'm pretty sure the bottom end is OK.  Head and cylinders look good.  No broken or bent fins that I can see so far.  The PO took it apart because of a stuck piston.  He couldn't turn it over.  He told me it only had 11k on the speedo.

I'm thinking 836 with dual carbs right now, but that could change.  I'll probably split the cases and pretty much repeat the process I did on the Cafe Tracer.  Probably no chrome on this engine.  I think I want the engine to look something along the lines of the engine in palepainter's cafe...dark.

Thanks for the offer.  I'll keep in mind.

Bud,

What are the advantages to the dual carburetor set up?

[Stev-o]

Tank looks cool Bud, I like it...

[budman]

What are the advantages to the dual carburetor set up?

There's the obvious...two less carbs to futz with.  Also more horsepower and better performance.  The visual appeal is more chopper-like.

[budman]

Tank looks cool Bud, I like it...

Thanks, Steve.  I won't have flames on the rear fender, but I've got some ideas on how to make it match the tank.  I'm also thinking of making some air intakes for the dual carb setup that will have the same look.

[SOHC4 Cafe Racer Fan]

What are the advantages to the dual carburetor set up?

There's the obvious...two less carbs to futz with.  Also more horsepower and better performance.  The visual appeal is more chopper-like.

I get the two less advantage and the visual difference.  What type of performance gain to you get from the 2 carb set up?  Is it just top end hp or more torque?  Any idea of number gains?  I was wondering how they compare to CRs or Mikunis.  In other words, why are they not more prevalent as a performance mod?

[budman]

What are the advantages to the dual carburetor set up?

There's the obvious...two less carbs to futz with.  Also more horsepower and better performance.  The visual appeal is more chopper-like.

I get the two less advantage and the visual difference.  What type of performance gain to you get from the 2 carb set up?  Is it just top end hp or more torque?  Any idea of number gains?  I was wondering how they compare to CRs or Mikunis.  In other words, why are they not more prevalent as a performance mod?

Having never done a dual carb setup I would think (hope) to get more top end up and torque when coupled to an 836, which is the direction I would like to take.

I've only found two kits that are available so far,  Speedmoto and CycleX.  Both use Mikuni VM34's.  The Speedmoto manifolds look kind of homemade and I don't really dig the big mounting flanges, but it will fit a stock frame.  The CycleX manifolds look cleaner, but there are some fitment issues with a stock frame, but from some research I've found there are some workarounds.

Having no experience I can only gauge things by what I read.  There are some testimonials on the CycleX site and elsewhere.  Their kit seems to be the ticket.

I would guess you don't see many dual carb setups is because of the expense.  Some guy like me gets his hands on an old clunker which already comes with a rack of carbs.  It's much cheaper to rebuild what you already have and spend the money on some other needed parts.

[SOHC4 Cafe Racer Fan]

What are the advantages to the dual carburetor set up?

There's the obvious...two less carbs to futz with.  Also more horsepower and better performance.  The visual appeal is more chopper-like.

I get the two less advantage and the visual difference.  What type of performance gain to you get from the 2 carb set up?  Is it just top end hp or more torque?  Any idea of number gains?  I was wondering how they compare to CRs or Mikunis.  In other words, why are they not more prevalent as a performance mod?

Having never done a dual carb setup I would think (hope) to get more top end up and torque when coupled to an 836, which is the direction I would like to take.

I've only found two kits that are available so far,  Speedmoto and CycleX.  Both use Mikuni VM34's.  The Speedmoto manifolds look kind of homemade and I don't really dig the big mounting flanges, but it will fit a stock frame.  The CycleX manifolds look cleaner, but there are some fitment issues with a stock frame, but from some research I've found there are some workarounds.

Having no experience I can only gauge things by what I read.  There are some testimonials on the CycleX site and elsewhere.  Their kit seems to be the ticket.

I would guess you don't see many dual carb setups is because of the expense.  Some guy like me gets his hands on an old clunker which already comes with a rack of carbs.  It's much cheaper to rebuild what you already have and spend the money on some other needed parts.

Interesting.  I know I saw one guy who did a single Weber for the entire motor.  I am not sure how it runs though.

[Terry in Australia]

That's a great looking chopper Bud, great score! I doubt that you'll get any exhaust to fit underneath unless you lift it up, but I really like that "High pipe" exhaust too, if you don't use it, I'd be interested in buying it?

Re: the twin carb set up, the Speedmoto items are made by Murray Feldman in North Carolina.  Cycle X's system is designed for choppers like yours, it's not great with un-equal length intake runners, but fits your frame, whereas it's a bad fit on a stock 750 frame.

I'd bought a set of Murray's Mikuni's for my CX500 which worked great, so I asked him to make me a set for a CB750. I received the first set he made, but they were unimpressive. To be fair to Murray, who's a nice guy, I probably didn't spend enough time trying to set them up, and it didn't help that the manifolds were too long, meaning that there was no room between the carb and the frame for an air filter, so I put them back in the box, threw some stock carbs back on, and rode it like that until I traded it for my RC51. Murray did modify his design and sent me another set of manifolds, but I never attempted to use them.

There are a lot of claims out there about "More Power" from the 34mm Mics, but logically, an engine designed to run four 28mm carbs will not produce more power with two 34 mm carbs, ever, unless there's a turbo attached. They should, however, produce noticeably more torque due to the extra length of the intake runners, and they should be pretty fuel efficient too. Murray's CX500 setup works really well compared to Honda's miserable CV carbs, which are possibly the worst carbs ever made.

I'm building a stock(ish) CB750 "Bitsa" and looking thru my stash on the weekend I found Murray's twin carb setup again, and thought, "why not", new carbs generally work better than 45 year old carbs, so I'll install them on my bitsa, and this time I've promised to spend a bit more time setting them up , so it'll be interesting to see how well they really work compared to stockers, all marketing bullsh1t aside. I'll be interested to see how you go with the Cycle X setup! Cheers, Terry.

[SOHC4 Cafe Racer Fan]

Thanks for the insight Terry.

[budman]

Terry, it's all an experiment, or an educated guess.

The frame on my chopper, while it certainly is modified it's pretty much untouched around the oil tank area.  I'm pretty sure I'll run into air intake fitment issues at the very minimum.  I have some idea though.

As far as the exhaust goes I'm looking at something like the CycleX Low Boy Super Drags.  They appear to tuck up close to the frame.  I don't know if they'll fit a stock frame, but they might make a good starting point.  I may end up building my own exhaust.  The pipes that came with the bike aren't very well made.  I think the tips are made from galvanized fence post.

A full mock up is in order before any paint work is attempted.

[budman]

I blasted the frame this morning.  It only took about 20 minutes to remove all that nasty Nitro-Stan putty, primer, rust and whatever else that was stuck on the frame.  kmb69 came out for the festivities.

The frame is already back home on the lift, awaiting a coat of epoxy primer which it will get in the morning.

Lots of fab, mods and cleanup to do from here.

[kmb69]

I blasted the frame this morning.  It only took about 20 minutes to remove all that nasty Nitro-Stan putty, primer, rust and whatever else that was stuck on the frame.  kmb69 came out for the festivities.

The frame is already back home on the lift, awaiting a coat of epoxy primer which it will get in the morning.

Lots of fab, mods and cleanup to do from here.
.....

Yep, Bud made short work of cleaning that frame off to bare iron! Thanks for the invite.

Looking forward to Bud's build on this one.

Really think Bud needs to go at least 915cc on this one - especially for Stev-o's benefit!