750 (810) Racer.

[Doc.]

Posted this in the 'New Member' section, thought I'd give it it's own topic, if that's OK(?).
Not everyone looks at the New Member section (I'm guessing).


A new friend of mine has an '82 'Kerby' Honda 500 single, and a '76 (I think) CB750 (now 810) Racer.

I've been working on them both in the last few weeks, to get them ready for the Belgian Classic TT in Gedinne, I'll be riding the Kerby.

This was at Brands last month, someone else riding it.

Nothing major needed doing, just a thorough 'going-over', with a few choice 'tweaks' and minor mods/adjustments.
Was hoping to take the Kerby to a track-day on the 9th, but a slipping clutch stopped that.
It was in a local Bike shop for a run on their Dyno, but the clutch was slipping while they were trying to start it!
The owner thinks they tried to start it on the roller, without taking it back against compression first, he thinks it probably just over-powered the Clutch.

We took the 750 instead.


Perfect day for it, pity it had an oil leak that stopped play   

Went out in the first session, and was impressed with how well it went.

I'd never ridden it before (or anything like it), and hadn't been on track for a few years, so took it fairly gently (luckily).
First three laps were 'sighting' laps, following a staff member.
Just after he pulled off, I felt my left Boot slipping on the peg, looked down to see Oil all over it.
Pulled in to check it over.

Looked to be coming from the bottom of the gear-change cover, so we whipped it off and found the gasket was broken at the rear lower corner.
As we didn't have a spare, we refitted it with some blue Hylomar, wiped the oil off the rear tyre, and I went out again.

Kept an eye on it, and after four laps or so it was doing it again.
Pulled in and whipped the Crank cover off.
Gasket was fine, as was the surface of the Crankcase.
Then I looked at the inside of the Cover itself, and there was the cause.

It's not got an Alternator fitted, and the gap in the casing where there should be a rubber bung (where the loom passes through), was just empty, no wonder it leaked!

[ChrisOnABike]

That looks like a fun ride!

[Doc.]

Indeed, it is.   
Despite it's age, it's obviously been well set up.
Handles very neutrally, doesn't drop in or want to sit up in the corners, just goes where you point it.

Engine's very strong, only real issue (other than the oil leak) was that the Tacho wasn't working, so I don't know what revs I was doing.
It felt pretty under-geared, but it may be I just wasn't revving it enough, being unfamiliar with it.

I'll see how it goes at the Track-day tomorrow . . .

[Doc.]

Got it all back in one piece and loaded in the Van with the Kerby, ready for tomorrow.
What a complete ba**ache it is getting the front Wheel in (or out).
You have to disassemble the Calipers, and completely remove the mount on one side, then slot the Wheel in place loosely, and re-fit the mount, then reassemble the Calipers.
There' just enough room to get the upper mounting bolts in, between the mount and the tyre.
I reckon it took us around half an hour to get it in and all locked up 

I've made up a stand to sit the lower Yoke on, it was on a front Paddock stand, which prevents the Fork Sliders being turned.
If it's supported on the Yoke, then with the mudguard off, you could spin the Sliders round, so the Caliper mounts will clear the Tyre.
Will still need to disassemble the Calipers though, but that's only four bolts to remove and refit, as opposed to seven.

[Doc.]

So, another perfect day for a Track-day, but another cut short by mechanical gremlins.

Took the 810 out first, just to check the oil leak was cured really, and to put a few more miles on it to make sure nothing else cropped up . . . well it did!
I'd cleaned the K&N filters since the last run, as they were filthy, and I suspected they were making it run rich.
It would start on the button with no choke and settle down to idle with minimal warm-up time.
I didn't re-oil them though, as the owner is thinking of running open bell-mouths next.

Anyway, it started only with choke, and wouldn't pull cleanly even when fully warmed up, in the end I had to run with the Choke slightly on, but it still wasn't right, obviously.
I decided to pull in early as it felt like it was overheating, I looked round to check it was clear to pull-in, and that's when I saw the plume of smoke behind me 
Fearing the worst, I coasted into the pits.
Only when I got off did I notice the big ball of fibre-glass fluff and melted rubber on the front of the mudguard 

 Phew! That's where the smoke was coming from.

I took it off to get more access when I fitted the Calipers and mounts, must have put it back a shade lower than it was originally, although it could be I was going a bit quicker (briefly) this time out, and there was quite a head-wind on one of the straights.
I reckon the long rear section was catching the wind, and forcing the front down onto the tyre.

I whipped the #1 Carb jet out to see what was fitted . . .

Is that an 'H' 12.5, or a 112.5, is it even a main jet?

[Bryanj]

Thats a Mikuni main let and 112.5

[Doc.]

Yes, thanks, can see it now.
We now have a set of 115s, 117s and 120s


Any suggestion on the setting for the pilot screws?
When I checked them they were only one half turn out from fully seated, seems off to me, aren't most set at around two turns or thereabouts, as a starting point?

[whiteylfc]

hi doc...you might be interested to know I had a v5 and frame for a cb750f2 with the reg no. DOC***V......

[Doc.]

Cool 

Had an absolutely blinding weekend at the Gedinne Classic TT in Belgium.
Just got back, 350-mile drive and a Channel Tunnel ride, and I'm still buzzing.
Owner doesn't like the 810 though, great engine, but much too heavy, he's more used to 'proper' lightweight race bikes!



I fitted the 117.5 jets, and set the pilots to 1.5 turns out, ran perfectly.

Circuit is beautiful, videos don't do it justice, you don't get a sense of the elevation changes for a start.

[Doc.]

Cool 

Had an absolutely blinding weekend at the Gedinne Classic TT in Belgium.
Just got back, 350-mile drive and a Channel Tunnel ride, and I'm still buzzing.
Owner doesn't like the 810 though, great engine, but much too heavy, he's more used to 'proper' lightweight race bikes!



I fitted the 117.5 jets, and set the pilots to 1.5 turns out, ran perfectly.

Circuit is beautiful, videos don't do it justice, you don't get a sense of the elevation changes for a start.

Edit; Oh, by the way, it's up fore sale now, he actually had a sign on it all weekend just to see what interest it got (none!), whereas he had three solid offers for the Kerby.
That's probably because the french have a four-stroke single race class, where the only rules are; 50bhp max power, 120kg minimum weight.

[K2-K6]

That looks like a really good trip and must be fun to ride it on track without the usual restriction of road riding.
Think that 1/1&half turn out is the starting point for most pilot screws generally and tweak from there if you need to.

[Doc.]

It really is a beautiful circuit, has a bit of everything.

Hundreds of pictures up on this website . . .
http://www.lamapix.com/php/pages/viewv3.php?code=HMJFASKKNC

Scroll down and click on the 'Diaporama' button.
You can then scroll through the whole lot.

[MarkCR750]

It's up for sale!
http://www.ebay.co.uk/itm/Honda-CB750-Post-Classic-Race-Bike-/171437255552?pt=UK_Motorcycles&hash=item27ea74eb80

[Doc.]

Keep up Mark, I mentioned that three posts back . . . 

Fingers crossed someone wants it, should be competitive in the right hands.
I'd like to have tried it, if only in one of the parades, but Stuart (the owner) wanted to ride it.

[MarkCR750]

Keep up Mark, I mentioned that three posts back . . . 

Fingers crossed someone wants it, should be competitive in the right hands.
I'd like to have tried it, if only in one of the parades, but Stuart (the owner) wanted to ride it.

Ha, hadn't noticed that, I'ts very definitely worth more than the current 4.5k trouble is a lot of people just don't realise how much these things cost to build!