Topic: Hi guys, I'm Evan from Electrosport, here with my new to me 74 CB750

[esport_evan]

Hi guys,

Wanted to introduce myself.
My names Evan, I run the Research & Development department at Electrosport Industries.

I'm not here to advertise (although I can answer any questions or help you guys with any of our products if you'd like...we do motorcycle charging systems, stators, rotors, CDI's, lighting, speedo/tachs, etc.)

Anyways, I've always been a big fan of 70's Honda CB's. I've had a few smaller displacement CB's, last one was a 73 Honda CB360.

I was checking Craigslist at lunch today, and came across an ad for a 74 CB750 that a guy had owned for 25 years. No pictures.
I give him a call, and his place is on my way home.
I pull out some cash, and head over there after work.

Turns out to be a super clean all original 74 CB750. Great, clean maroon tank and sidecovers, original pipes, full vetter fairing.
Runs great, all lights work, brand new tires.
Only issues are a non-functional front brake caliper, and a completely shot battery.

Here's a couple pics (dark when I got her home, I'll post up some better ones tomorow).

Gonna fix the front caliper, new battery, ditch the fairing, and 2-up seat w/ backrest,
Put some flat bars on it, probably one of our Acewell speedo/tach units and LED signals.

I'll keep you guys posted, just wanted to show off what I'm starting with!

[mrbreeze]

Looks to be a great project. Enjoy!!!!

[Retro Rocket]

Welcome to our little family.  Prepare yourself for a pile of questions on charging systems....     There's a few of us doing fuel injection conversions and other things that require a better charging system with more power. Do you guys handle this type of stuff or just stock replacements ?

Mick

[Staggerlee]

R&D, eh?

What's the poop on those 4000 series speedos; when do they become something more than vaporware? 

[J.Webster Designs]

Welcome to the forum. Looks like you have a nice starting point....

As Retro rocket already stated..... the guys on on this forum that are doing fuel injection swaps (this includes me) will probably be speaking with you about charging upgrades. Our old bikes aren't really up to the task of maintaining proper voltage at idle to run fuel injection.

you have joined the family.... now you owe us a favor.... (mafia reference for those that didn't get the joke)

[Jerry Rxman Griffin aka MuthaF'er]

Welcome aboard Evan. It would be great to have you here even if you weren't with Electrosport. BUT evan even better since you're with ES 

REAL nice starter bike! Lucky find. Hope we can help you too.

I'll be giving you some business as I progress with my restore. I fried my old style RR24 and will need a replacement.

Jerry

[dagersh]

Sweet find, Welcome to the madness!

[esport_evan]

Welcome aboard Evan. It would be great to have you here even if you weren't with Electrosport. BUT evan even better since you're with ES 

REAL nice starter bike! Lucky find. Hope we can help you too.

I'll be giving you some business as I progress with my restore. I fried my old style RR24 and will need a replacement.

Jerry

haha thanks Jerry! This was pretty funny.

Thanks to all of you guys for the warm welcome.
Feel free to give me a call anytime about any of our products or charging system questions.

The # is 760-842-8300, just ask for Evan.

I'll probably be bugging you guys about some of the specifics on this old CB.
I've had probably 30 motorcycles in the last 6 years (pretty excessive for only being 26 I think  ), but only 1 other CB, a 73 CB360.
I'm really excited to have a big 750 now, and I'm gonna have some fun on it.

First things first, what is the common cause of the front brake caliper not working? Didn't see any leaks, but it is completely non-functional.
Do the calipers lock up in the open position from sitting?

First order of business tonight is to get the Vetter Windjammer fairing removed.
It is immediately for sale! Just give me a call if you're interested. taking offers!

Here is some better pictures of the bike in the sun this morning:









More pictures here:
http://photos.octaneandelectrons.com/index.php/1974-Honda-CB750

[mrbreeze]

Whatever you do to it..............if you won't be using that gas tank....can I have first crack at buying it?

[Jerry Rxman Griffin aka MuthaF'er]

You should also be able to find a NOS seat to replace the Lazy Boy. 

That front brake is your main component on the bike. You can have either caliper sticking &/or master cylinder problems. If it were mine I'd take the whole braking system apart and clean repair. Pistons pit, seals go bad, system get gunked up. Get a Speed Bleeder and some stainless lines. We have someone here that makes some nice lines for a decent price. We have a guy that drills some nice patterns on rotors too.

Tell me how to adapt a 750A rectifier to all the other 750's K's and F's. I want to utilize a 750A field coil for increased output and know better than to try to use a standard 750 rectifier due to an increased output of +80W. AND, not or, I will personally be using another of your RR24's on MY bike.  Can it handle the increased output? In light of that I still want to know about the 750A rectifier.

Yeah, good to have you as one of our guys now!

[MCRider]

Agree with jerry. You'll ned to set aside time to go thru the whole system. Direct to your problem, I vote that the master Cylinder is plugged. What happens is that the you can pull the lever engaging the pucks against the disc. Then release the lever. The only thing mechanical to withdraw the puck from the disc is the flexibility of the ORing in the caliper, not much. Any plug in the master cylinder which does not allow an easy return of the fluid to the reservoir, will keep the disc engaged. The ORing flex cannot overcome the resistance.

A check for this is to loosen any joint in the line or the bleeder, and tap the caliper, if that frees up the brake then its the MC. Then tighten up the joint/bleeder and pull the lever again. If the brake locks, then its confirmed.

Open the reservoir and see if its full of nasty fishoil. Another giveaway.

This is a very common problem, lots has been written here on the subject.

Check your PM for a question.

[1974CB750rider]

Welcome Evan, I vote strip the whole brake system off the bike and go through it. If the bike has been sitting for a while the front brake issue is a usual problem. Check with Matt at TAS Motorsports for a master cylinder kit. Those guys are great and don't care to take the time to answer any questions you may have. Thats a beautiful bike you got a hold of, can't wait to see it with a new seat and no vetter fairing. How many miles does it have on it? My 74 has almost 49000 now. Welcome to the forum.

[esport_evan]

Whatever you do to it..............if you won't be using that gas tank....can I have first crack at buying it?

Hey MrBreeze, sorry I will definitely be keeping the tank! I'm a big fan of em.

[esport_evan]

Thanks for the info on the brake guys.
I will pull it apart next week (headed out to Vegas for the weekend, so no work getting done!)

I will pull it off the bike and check the caliper and the master cylinder and see where the problem is.
I'll post up with the results next week.

I have the fairing and the seat off the bike now, heres a pic:





I'll answer your questions in another reply about the r/r.

[esport_evan]

Thanks for the info on the brake guys.
I will pull it apart next week (headed out to Vegas for the weekend, so no work getting done!)

I will pull it off the bike and check the caliper and the master cylinder and see where the problem is.
I'll post up with the results next week.

I have the fairing and the seat off the bike now, heres a pic:





I'll answer your questions in another reply about the r/r.

And the seat/backrest & Vetter fairing are for sale ASAP.
Give me a call and make an offer!

(760)-274-4913 cell

[esport_evan]

You should also be able to find a NOS seat to replace the Lazy Boy. 

That front brake is your main component on the bike. You can have either caliper sticking &/or master cylinder problems. If it were mine I'd take the whole braking system apart and clean repair. Pistons pit, seals go bad, system get gunked up. Get a Speed Bleeder and some stainless lines. We have someone here that makes some nice lines for a decent price. We have a guy that drills some nice patterns on rotors too.

Tell me how to adapt a 750A rectifier to all the other 750's K's and F's. I want to utilize a 750A field coil for increased output and know better than to try to use a standard 750 rectifier due to an increased output of +80W. AND, not or, I will personally be using another of your RR24's on MY bike.  Can it handle the increased output? In light of that I still want to know about the 750A rectifier.

Yeah, good to have you as one of our guys now!

Rxman,

Can you give me the specifics on a 750A regulator?
I'm not super familiar with them, do you mean the regulator from the Automatic trans model of these CBs?
I wasn't aware they had a different reg and field coil in those models vs. the standard trans bikes.
Or maybe I'm way off and 750A is a part number?

I believe you are referring to our ESR240 regulator/rectifier unit?
The ESR240 can absolutely handle the increased power output of either field coil you decide to run in your bike.
We use the same heatsink housing in all our regulators, as well as the same rectifier diode bridge and regulator circuit.
Our diodes are spec'd at 60Amps (which would mean 780W power handling at 13VDC out of the regulator), as well as high temperature solder and an efficient heatsink. The regulator is spec'd to handle this high power as well, with a firm regulation point at 14.2VDC out. (+/- 0.4V or so due to component tolerances).

You can use this regulator to completely replace the unreliable OEM mechanical voltage/current regulators that came on the bike. I would recommend it and I plan on doing it on my CB.
I will post a writeup with pictures when I do the conversion on mine.

[Jerry Rxman Griffin aka MuthaF'er]

Damn, that ESR240 can handle a big ass battery!    I haven't checked your stuff lately but is the RR24 the same as the ESR240? My old RR24 was the old "homemade looking" style that I got MANY moons ago. Differences?

The CB750A automatic apparently required a higher capacity rectifier due to the increased output (290W vs 210W I believe) from the field coil on it vs all the other CB750's. The regulator is the same as the other CB750's. The CB750A field coil  I just tested  is 4.1 ohm vs 7.2 ohm for a standard 750 field coil. Obviously larger gauge wire. No real differences in rotor or stator. The rotor I received is the same style as the early CB750 (now updated smaller/lighter) with the rear "lip" and uses a longer bolt (heavier longer center post) and 1 lb heavier overall. The 750A rectifier has a more "solid state look" to it than the standard CB750 rectifier, much like the appearance of the more modern R/R units. It also has more wires - 3 yellow as expected, 2 red/white and 2 green. The wiring schematic appears to just have the R/W doubled up to carry more current from the main fuse through the starter solenoid then on to the rectifier. The green seems to be redundant also. Looks like it may just need to have the wires within the connector terminals doubled/matched up.
Sounds like in lieu of that I could use the 750A field coil along with your ESR240. I'll explain to you the reason for my madness later.

Jerry

[754]

Evan just a question about the bike, when you say 74, I am thinking Sept or later.. build date/month is on neck tag.

 Curious as I thought 74 still had small signal lights, or the cutoff was during 74.
 Also is there a shift pattern cast into the left side tranny cover? (the one your shifter comes out of), they are usually on 75 and up.

 You have a mod I spotted on your bike, your side cover emblem is script and a diamond.. those look the best I would leave it (someone took the fat emblem off, looks like..) (script ended in 72)

 Oh yes, almost forgot... Welcome aboard...

[bucky katt]

i just got one of your regulator/rectifiers for my k4 750, nice piece. welcome to the forum!

[RRRToolSolutions]

I think it's a 1975 too since the gauges have the offset on the odometer for the 1/10ths - this was not there in 1974. Combine that with the turnsignals and it must be a 1974 late build, making it a K5 model. I can't do it now, but I will look for paint codes to see if the color and stripes match for the 1975 year.

Best Regards,

Gordon

[andy750]

Its a 75 alright - left-hand petcock (74 was right-hand side), large turn signals, and orange paint (not flake sunrise orange but called something else) - a friend has one here in Boston and looks quite different from my 74.

cheers
Andy

[esport_evan]

Hey guys,

Sorry for the delay, I was out of town until last night.

Thanks for the updates, sounds like it is a 75!?
I'll check the neck tag tonight and see what it says.

Gonna get started on the brakes and carbs this week, do a little tuneup and get her ready to ride.

[esport_evan]

Damn, that ESR240 can handle a big ass battery!    I haven't checked your stuff lately but is the RR24 the same as the ESR240? My old RR24 was the old "homemade looking" style that I got MANY moons ago. Differences?

The CB750A automatic apparently required a higher capacity rectifier due to the increased output (290W vs 210W I believe) from the field coil on it vs all the other CB750's. The regulator is the same as the other CB750's. The CB750A field coil  I just tested  is 4.1 ohm vs 7.2 ohm for a standard 750 field coil. Obviously larger gauge wire. No real differences in rotor or stator. The rotor I received is the same style as the early CB750 (now updated smaller/lighter) with the rear "lip" and uses a longer bolt (heavier longer center post) and 1 lb heavier overall. The 750A rectifier has a more "solid state look" to it than the standard CB750 rectifier, much like the appearance of the more modern R/R units. It also has more wires - 3 yellow as expected, 2 red/white and 2 green. The wiring schematic appears to just have the R/W doubled up to carry more current from the main fuse through the starter solenoid then on to the rectifier. The green seems to be redundant also. Looks like it may just need to have the wires within the connector terminals doubled/matched up.
Sounds like in lieu of that I could use the 750A field coil along with your ESR240. I'll explain to you the reason for my madness later.

Jerry

Your old RR24 must've been one of our old production models.
The ESR240 is physically/fitment wise the same, with upgraded and improved regulation/rectification circuitry.

I'll have to look into the differences between the 750 & /A field coils?
I supposed they would be interchangeable, but I'm not sure how you would possibly split the rotor halves apart, get the new coil cemented in place, and then press it back together perfectly aligned.
Let me know what you're trying to do, and I might be able to help.

We do have external stators and complete rotors available for the DOHC 4 engines.
I'm not sure if they're interchangeable with the SOHC parts?
Any insight into this you guys?

[mystic_1]

Field coil on a 750 is not inside the rotor itself, but is a separate stationary component that mounts to the alternator cover.

#9:



mystic_1

[esport_evan]

Thanks Mystic.

See what happens you assume!? haha
I was thinking it was the same setup as the internal field coil rotor as on the DOHC engines.