Topic: 1975 Supersport, performance cafe

[Doctor_D]

Been lurking here a bit. New to CB's, but not to motorcycle repair, resto, performance, racing, etc.

After wrapping up my most recent project, 1971 Norton Commando Cafe, I was casting about for something new.


The availability of parts and bikes made the CB750 an easy choice, though the donor bike may make me live to regret that decision. 







It's a 1975 CB750F that was stored outside for 3 years in the wet Pacific Northwest.  Good thing it's getting a complete tear-down.

[Doctor_D]

Yesterday I finally had a few hours to head over to Twinline Motorcycles in Seattle to use the lift and work with Ian, the proprietor, to pull-down and inspect the beast.  Took us about 7  hours to strip, clean and sort salvageable bits.



Gotta love the grim reaper sticker on the oil tank. 



Except for the rust, and those horrible philips-head screws on the motor, things went pretty smoothly.









Wheels were broken down, hubs cleaned up and bearings pulled.  They'll be polished then they're off to Buchanans for ss spokes and Sunn rims.



Didn't quite finish breaking down the motor, but I did find a spider egg cluster beneath the cam towers.



The cam was badly worn, but most of the internals looked serviceable.

[HondaMan]

Didn't quite finish breaking down the motor, but I did find a spider egg cluster beneath the cam towers.

Well, now that you've got the bugs out, it should be easier! 

That's quite the collection of parts you have there. Almost anything you do to it will be a nice improvement! Are you going for more performance in the engine?

A suggestion: take a close look at the C5 gear's dogs (that's the one on the tranny's countershaft that you can pull out by removing the bearing retainer on the left side). The "F" is famous for wearing those dogs, which causes the tranny to tend to jump out of 2nd gear under power. They can be back-cut to square them up (with the C2 next to it) for a superior grip.

I'm also liking MCrider's cryo treatment of those gears, wish to do that with mine, now.

[Doctor_D]

The plan from here is fairly straightforward, but I'm trying to keep the budget under $15k with a July 1 finish date.

Standard durability modifications, 836cc kit, Web 63a cam, CR31's, programmable Dyna ignition, lighten charging system and crank, street-port head with 5mm valve-stem conversion and lighter valve-gear, e-start delete. I've got a set of LMP's 4 into 4 CR replica exhaust coming to round out the package.

Frame will go to M3 for most of the CR750 modifications, though I'm keeping the stock tank and sidestand tabs.  Planning on chroming the frame and swingarm after it's returned.

Already have Works rear shocks for it and will use Gold valve cartridge emulators with Racetech springs and new fork tubes and seals in otherwise stock front forks. Wipers will be swapped for gators.  I haven't settled on triple trees, gauges or controls yet.  Swingarm will be bronze-bushed.

Brakes aren't settled on, but I'd like some floating iron rotors if I can source them.  Ferodo pads, braided stainless lines, new master cylinders and overhauled calipers generally suffice for spirited road work in my experience.

Well, that's the plan.  Aesthetics are still very much up in the air, but I'm leaning toward trying to retain the overall character and lines of the 750 Supersport.  Suggestions are welcome.

Take care,
David

[Doctor_D]

A suggestion: take a close look at the C5 gear's dogs (that's the one on the tranny's countershaft that you can pull out by removing the bearing retainer on the left side). The "F" is famous for wearing those dogs, which causes the tranny to tend to jump out of 2nd gear under power. They can be back-cut to square them up (with the C2 next to it) for a superior grip.

I'm also liking MCrider's cryo treatment of those gears, wish to do that with mine, now.

Hondaman:

Yes, I'm planning on sending the gears out to be backcut.  I generally cryo and dry-film lubricant treat gearteeth in my project bikes, and will do that it funds allow here.  My projects have a way of getting way out of hand cost wise, and I've made a promise to myself that this one will be a little more conservative.

[HondaMan]

The plan from here is fairly straightforward, but I'm trying to keep the budget under $15k with a July 1 finish date.

Standard durability modifications, 836cc kit, Web 63a cam, CR31's, programmable Dyna ignition, lighten charging system and crank, street-port head with 5mm valve-stem conversion and lighter valve-gear, e-start delete. I've got a set of LMP's 4 into 4 CR replica exhaust coming to round out the package.

Frame will go to M3 for most of the CR750 modifications, though I'm keeping the stock tank and sidestand tabs.  Planning on chroming the frame and swingarm after it's returned.

Already have Works rear shocks for it and will use Gold valve cartridge emulators with Racetech springs and new fork tubes and seals in otherwise stock front forks. Wipers will be swapped for gators.  I haven't settled on triple trees, gauges or controls yet.  Swingarm will be bronze-bushed.

Brakes aren't settled on, but I'd like some floating iron rotors if I can source them.  Ferodo pads, braided stainless lines, new master cylinders and overhauled calipers generally suffice for spirited road work in my experience.

Well, that's the plan.  Aesthetics are still very much up in the air, but I'm leaning toward trying to retain the overall character and lines of the 750 Supersport.  Suggestions are welcome.

Take care,
David

Very cool! I'm working on a kitbash of a K7 and an F3 for a customer, myself. He's selecting the cosmetics, I'm doing the under-hood stuff. Might I suggest: if you're going with Dyna's ignition components AND a lightened alternator rotor, maybe look into an HID headlight (35 watt) to both improve lighting and significantly reduce current consumption. Otherwise, you may find that you don't like the electrical performance: it will run short of power. If you retain the Honda RUN-STOP switch on the right handlebar and use Dyna's low-ohm coils, consider adding a relay to it for those high-current Dyna coils: over time, they can melt the contacts in that switch. 

[Jerry Rxman Griffin aka MuthaF'er]

David,

If I can help you source parts just let me know. I've been collecting mine for 3+ years. I can let you know availability and where you might find them. NOS masters are virtually unobtainable. PM me if I can help. I'm hoping to remove front and back ends and the engine in the next few weeks.

[Doctor_D]

RX:

Thanks for the offer of assistance.  I'm likely going to use a Lockheed or similar rear master cylinder, but I'm sure you and others will be called upon to offer guidance with regard to sourcing small bits or choosing the direction of the build.

Hondaman:

Good advice as always.  I'm a big fan of relays as a general rule.  With no e-start and led turn-signals and brake light - I'm hoping Mark McGrew's CR type charging system will be up to the task. (Absent any details on his website... but it looks nice.)  Either way, a HID headlight makes sense.  Do you have a preference for an easily retrofittable one?

[lordmember1969]

http://www.motorcyclehidlights.com/honda-cb750-hid-lights-c-97_680

Here is a set for the CB 750

[HondaMan]

http://www.motorcyclehidlights.com/honda-cb750-hid-lights-c-97_680

Here is a set for the CB 750

Yeah, that's the good one! The "other one" is Chinese and falls apart in a week or two. There's posts about it here on SOHC4.net.

[lordmember1969]

http://www.motorcyclehidlights.com/honda-cb750-hid-lights-c-97_680

Here is a set for the CB 750

Yeah, that's the good one! The "other one" is Chinese and falls apart in a week or two. There's posts about it here on SOHC4.net.

Have you tried them? Did you go for the standard or the digital slim?

[Retro Rocket]

If i were building an 836 i wouldn't be using CR-31's, they are basically set up for high revving engines and are useless around town, i would be going for the CR-29's even though they are far from ideal on the street, they are a much better choice than the 31's. A few guys on here run the 29's, the 31's are mainly used for racing or drag racing.

Mick

[jaguar]

try the DDM kit.  they are crazy cheap and work well.

http://www.motorcyclehidlights.com/honda-cb750-hid-lights-c-97_680

Here is a set for the CB 750

Yeah, that's the good one! The "other one" is Chinese and falls apart in a week or two. There's posts about it here on SOHC4.net.

Have you tried them? Did you go for the standard or the digital slim?

[Doctor_D]

If i were building an 836 i wouldn't be using CR-31's, they are basically set up for high revving engines and are useless around town, i would be going for the CR-29's even though they are far from ideal on the street, they are a much better choice than the 31's. A few guys on here run the 29's, the 31's are mainly used for racing or drag racing.

Mick

Mick:

Thanks for the input.  I'm used to working on twins, so carb sizes for 4's seen a little odd to me.

I'm not sure about your comment that CR's, in general, are not suited to the street.  I've run them on an XS650 and a T120R and their road manners are at least as good as Amals.

Finally, the target is 70rwhp.  If the 29's will suffice, then that's all I need to know.

[wannabridin]

for those that have ordered the HID kits, how do these kits overcome the quick flash problems with switching to highs to flash other drivers on the road?  i've thought about an HID kit for awhile now, but i haven't found one that leads to good reviews or usability with a high beam...  sorry to thread jack with this!

edit: just found this for use with a single bulb, like out bikes.  does anyone want to go halves on one of these since it's a 2 bulb setup?   

http://www.motorcyclehidlights.com/motorcycle-hid-c-99/bi-xenon-slim-motorcycle-hid-kit-p-227

great sounding project though, i think you'll have a REAL fun bike that will rip around town!!  hopefully you can get the CR's dialed in and get them running well for in town driving, i hear they're a little finicky for that...

one other thing, where did you get that poster in the back of the 2nd picture of the 2nd post???  that thing is awesome!!  more info is appreciated!  

[Doctor_D]

Wanna:

That isn't a poster.  It's a drawing of a CB750 Twinline built for a customer.

Twinline does quite a few "ratty cafes" and streetfighters, but from time to time a customer comes along with the budget and patience to have them do a full custom job.  There's a picture of it on their Completed Bikes page.

http://www.twinlinemotorcycles.com/

[wannabridin]

sweet!  thanks for the reply!  now if i can only get the website to work...

[fasturd]

Brembo makes a nice rear master that is still available. Lots of old Guzzis and Ducs use them. I have one on my 400F If the Honda one is not available you might want to look at the alternative.
I got parts for mine from Beval Heaven. Another SOHC'r hooked me up with them.
Good luck on the build it should be VERY interesting!

[Retro Rocket]

If i were building an 836 i wouldn't be using CR-31's, they are basically set up for high revving engines and are useless around town, i would be going for the CR-29's even though they are far from ideal on the street, they are a much better choice than the 31's. A few guys on here run the 29's, the 31's are mainly used for racing or drag racing.

Mick

Mick:

Thanks for the input.  I'm used to working on twins, so carb sizes for 4's seen a little odd to me.

I'm not sure about your comment that CR's, in general, are not suited to the street.  I've run them on an XS650 and a T120R and their road manners are at least as good as Amals.

Finally, the target is 70rwhp.  If the 29's will suffice, then that's all I need to know.

Cr's are basically designed for racing so their characteristics aren't generally suited to the street but i didn't say they shouldn't be used, there are a few members on here that run the 29's on the street and i was going to use them as well until i decided to go with fuel injection. I have a set of 31's i was going to use and was told that they are no good for the street, they are all top end and nothing down low and very hard to set up for the street and my engine is 1000cc. My 31's are the older type with ticklers, {primers}, they are going to be sold to fund other goodies for my bike...

Mick

[jaguar]

Brembo makes a nice rear master that is still available. Lots of old Guzzis and Ducs use them. I have one on my 400F If the Honda one is not available you might want to look at the alternative.
I got parts for mine from Beval Heaven. Another SOHC'r hooked me up with them.
Good luck on the build it should be VERY interesting!

do you have a link to that?

[Doctor_D]

He's talking about these: http://shop.bevelheaven.com/detail.aspx?ID=1275

They're easy to adapt, cheap, well made and work great.

[jaguar]

how do you adapt them?

[HondaMan]

If i were building an 836 i wouldn't be using CR-31's, they are basically set up for high revving engines and are useless around town, i would be going for the CR-29's even though they are far from ideal on the street, they are a much better choice than the 31's. A few guys on here run the 29's, the 31's are mainly used for racing or drag racing.

Mick

Mick:

Thanks for the input.  I'm used to working on twins, so carb sizes for 4's seen a little odd to me.

I'm not sure about your comment that CR's, in general, are not suited to the street.  I've run them on an XS650 and a T120R and their road manners are at least as good as Amals.

Finally, the target is 70rwhp.  If the 29's will suffice, then that's all I need to know.

Cr's are basically designed for racing so their characteristics aren't generally suited to the street but i didn't say they shouldn't be used, there are a few members on here that run the 29's on the street and i was going to use them as well until i decided to go with fuel injection. I have a set of 31's i was going to use and was told that they are no good for the street, they are all top end and nothing down low and very hard to set up for the street and my engine is 1000cc. My 31's are the older type with ticklers, {primers}, they are going to be sold to fund other goodies for my bike...

Mick

The biggest issue with the CR carbs is the cutaway on the slides. They are meant for good control in the 2/3 to full throttle range, where the street carbs are meant for good control in the 1/8 to 7/8 throttle range. Typically, the street carbs do nothing between 3/4 and full throttle: the CR carbs do nothing between 1/8 and 1/2 throttle, making them dodgy on the street. The poor-man's CR used to be the street Keihins with the slides cut up to 3.0 or 3.5, like the real CR. 

[Doctor_D]

how do you adapt them?

KB02 has good pictures of using them with his rearsets here: http://forums.sohc4.net/index.php?topic=22216.0  Look near the bottom of page 15.

[MRieck]

If i were building an 836 i wouldn't be using CR-31's, they are basically set up for high revving engines and are useless around town, i would be going for the CR-29's even though they are far from ideal on the street, they are a much better choice than the 31's. A few guys on here run the 29's, the 31's are mainly used for racing or drag racing.

Mick

Mick:

Thanks for the input.  I'm used to working on twins, so carb sizes for 4's seen a little odd to me.

I'm not sure about your comment that CR's, in general, are not suited to the street.  I've run them on an XS650 and a T120R and their road manners are at least as good as Amals.

Finally, the target is 70rwhp.   If the 29's will suffice, then that's all I need to know.

  You will easily achieve that #