Topic: Ross’s 1975 CB750 K5

[spotty]

^/Thread drift

What kind of paint do you use on the seat stencil?

I too was wondering this very thing last night

[Galactica]

Yesterday a friend showed me his original 76 CB750 seat cover.  It is a grey colour.  I believe elsewhere on this site it was posted that a correct paint would be Krylon Fusion (for plastic) 42338 Nickel Shimmer.  That would jive with the grey colour I saw on my friend’s seat cover.  The difficulty then is finding it.  I’ve not yet found any here locally in the lower mainland BC.

[BenelliSEI]

I got a close match in a ”Fabricland” store where my wife shops, here in Ontario. Not sure if they have stores out west?

[Galactica]

Yes we have Fabricland here.  There is one not far from my home.  Do you remember the brand and colour name of the paint?

I have finally got the front brake to acceptable operation.  Not quite 100% happy with it, but it will have to do. 

When I had the swing arm removed, I reinstalled it with a couple of items that still needed doing.  The rear brake shoes still had some material on them, but not much.  I’ve since obtained a new set.  Also when I was pressure washing the swing arm, I must have washed away one of the felt washers.  I’ve since also obtained a new set of those.

 Probably next week I should get all of that work done.  Then I’ll put a plate and insurance on it, and get the carbs dialled in.  Hopefully there won’t be too much more that needs doing.  All I have left to obtain before paint is a stripe kit for the tank, and of course seat decal and paint. 

[BenelliSEI]

Yes we have Fabricland here.  There is one not far from my home.  Do you remember the brand and colour name of the paint?

I have finally got the front brake to acceptable operation.  Not quite 100% happy with it, but it will have to do. 

When I had the swing arm removed, I reinstalled it with a couple of items that still needed doing.  The rear brake shoes still had some material on them, but not much.  I’ve since obtained a new set.  Also when I was pressure washing the swing arm, I must have washed away one of the felt washers.  I’ve since also obtained a new set of those.

 Probably next week I should get all of that work done.  Then I’ll put a plate and insurance on it, and get the carbs dialled in.  Hopefully there won’t be too much more that needs doing.  All I have left to obtain before paint is a stripe kit for the tank, and of course seat decal and paint.

No sorry…. I went and one of the ladies sold me an aerosol can of “vinyl paint”. It was a light silver and looked great.

[Galactica]

Ok, thanks.  I may borrow my friend’s seat cover and take it along when I really get down to shopping for it.  Then I can sorta compare the cap colour with the actual seat stencil.

[Galactica]

So I’ve had the bike running a couple of times and rode it up and down the back lane to check the front brake.  It sure won’t stop the bike all that well in a panic stop. 

It ran ok but smelled really rich.  Initially I had the air screws out 1 turn from seated.  The second time I ran it in the lane I turned them out 1 1/2 turn from seated.  Still smelled really rich and was really hard to start.  So I pulled the spark plugs for inspection.  All black and sooty. 

I wondered if the fuel level in the bowls was too high.  I’d set the floats dry at 26mm.  I found this procedure a bit odd.  The only other carbs I’ve done have been Mikunis on my Kawasakis using the clear tube method.  I’d sold all of my old Zeds along with all parts and special tools in favour of a modern bike.  My thinking was that I was done with old bikes.  Then I came across this current ‘75 CB750 project.

I wanted to visually check the float bowl levels so I borrowed a friend’s clear tube tool.  With the carbs in situ, the fuel levels are all exactly the same. At least it shows that I was consistent in setting them when dry. 

The clear tube showed the level being about 1/4” below the carb body flange.  Does anyone know if that’s correct for these carbs? 

Cheers,
Ross

[newday777]

Ross
Did you put in aftermarket carb kits and their brass jets and float valves? 🤔

What exactly did you do so far to the front brakes? 🤔

[Galactica]

I reused the original carb jets.  Float needles and seats I got from Vintage CB750.

I got a master cylinder rebuild kit, brake hoses and brake pipe from Vintage as well.  I got an aftermarket complete caliper from Dave Silver Spares. 

[Galactica]

A couple of things I neglected to say.

When I got the bike, of course, the previous owner said it had been running well when parked, some 10 or so years ago.  I did the usual checks.  Valve clearances, compression, spark, rebuilt carbs, cleaned fuel tank, new fuel lines & filter.  I looked at the points, they looked quite good, but was lazy and didn’t check gap or ignition timing.

After I pulled the plugs and saw their sooty condition, I decided to check the points gap and timing.  The timing was fairly close, a few degrees advanced.  The points gap was a bit tight at .010 so I set the gap at .014 and the timing dead on F. 

When I used the clear tube to check the float levels, of course I had to drain the bowls.  I was quite surprised at the fuel in them.  It was quite cloudy and yellow/orange with quite a bit of water as well.  I drained the fuel tank and put in fresh gas.

No surprise, I guess, it now starts and idles well and the plugs look good.  I’m going run it like that for now, if it ever stops bloody raining.  We’re expecting 300mm this week. 

I was just wondering though, if anyone had used the clear tube method to set float bowl levels, and what that level should be. 

[newday777]

I haven't done the clear tube method but I think the general consensus is 3-4mm from the gasket surface.

http://forums.sohc4.net/index.php?topic=138594.0

[Galactica]

Ok, so it seems my levels might be a bit low.  Probably about 7mm below the gasket.  Thanks.

[seanbarney41]

Unlike Mikuni, Keihin never really specified a fuel level in bowl spec, only the float measurement.  I think the 26mm float spec usually results in about 5mm below the top of the bowl.  I like to set 'em at 26mm (or whatever the factory service manual calls for) and then fine tune with the clear tube if 26mm does not result in 3-5mm.

[Galactica]

Ok.  I know  from personal experience on my old Zeds that having float level high results in a rich condition that no amount of adjustment will change.  Especially when the weather gets really hot. 

So here’s a question.  At what it’s the reverse true?  I wonder how low the level would have to be to induce an overly lean condition.

[lash]

Try 3/4 on the air screws..and new plugs..

[Galactica]

Try 3/4 on the air screws..and new plugs..

It’s tough to diagnose when you do more than one change at a time.  I did a couple, so my bad.  Putting the timing and points gap spot on should help the spark I would think. 

But the fuel I drained from the bowls was really skanky.  It was quite cloudy and dark with quite a bit of water as well.  Not sure why.  It wasn’t all that old. That, I think would have been an issue.

So I’m going to go back to square one.  I’ve all new gasoline.  Timing, points, valves all set.  Plug are cleaned (they are new plugs).  Floats set dry as per spec (I suspect they’re a bit low).  Carbs bench synched.  And I’ve put the air screws back to spec. 

Now I’ll wait for weather to at least ride it up and down the back lane.  Forecast is rain all week, clearing but cold(5C) on the weekend.  Idling in the garage is good though.  Starts really easy now and plugs seem to be remaining clean.  Fingers crossed 🤞.

[Galactica]

Caught a break in the rain this morning.  Ran the bike up a down the lane 5 or 6 times.  Starts and runs really well (at least up to 20mph).  Plugs look good.  GPS says the speedo is correct up to 20mph.

But man, is the front brake ever weak.   Have to squeeze pretty much max to get it to stop.  None of my Zeds were ever like this, and the setups are pretty much the same except for the caliper bracket on the CB whereas on the Zeds the caliper is fork mounted. 

[lash]

I had a big improvement in braking by going to stainless steel brake lines.

[Galactica]

I had a big improvement in braking by going to stainless steel brake lines.

Ya, that’s my next option.  There’s a local place I can go.  This week, I’ll take the original lines in and get a price on matching black vinyl coated braided lines.  If it’s near the price I can get them online, I’ll get them.  And I’ll try the original caliper.  Problem is that the bleeder screw seat was really corroded and leaking.  I had friend try to machine it, but it’s a difficult repair.  We think it’s ok, but won’t know until it’s under pressure.

[seanbarney41]

These brakes are always gonna be far inferior to the Kawasaki's...dual disc set-up and a real master cylinder can compare

[Galactica]

Of the Zeds I had, only my 79 LTD had dual discs.  My Z1, 2 KZ900s, and 2 KZ1000s all had a single disc. 

Early last year I had a ‘78 CB 750 that I resurrected and then sold on.  I was never happy with that brake either.  The only other CB750 I’ve ridden was a ‘75 CB750 that I had from ‘77 to ‘79, and I have no memory as to its braking power.  So perhaps the brake on this bike is as good as I can expect.

In 2020 I sold my remaining Zeds in favour of a new Tracer900, thinking I was done with old motorcycles.  The braking on that bike is stupendous.  Two fingers can stop it on a dime.  Perhaps I’ve just gotten too accustomed to that. 

My intention is to keep this CB until I give up motorcycles all together.  So I’ll try to get the best braking I can with it, while keeping as close to stock as I can, and stay within collector plate perimeters.

[BenelliSEI]

I ride a newer Honda Varadero XL1000 and for sure the linked brakes (triple discs with ABS) are significantly better than my stock cb750’s, but honestly not that much. My K0 and K3 have good brakes. I do have a drilled disc and Teflon/metal braided lines on the K3, but the K0 is stock. They are well maintained and I bleed in fresh fluid every three years. If you think your brakes are that poor I suspect your master needs a rebuild, or the caliper  (or pivot) is siezed, or the lines are collapsing internally. To be that bad, something is not right.

[Galactica]

Ya, there’s something not right in the front brake.  I’ll pick away at it. 

Here’s a couple of pics showing fuel levels.  The floats were set dry at 26mm from the cutout on the carb bodies.  A bit lower than I had estimated earlier. 

I suspect that even though they are set to spec (26mm, right?), I think they’re a bit low.  I think I’ll remove the carbs, set #1 to 5mm below the gasket service using the  clear tube, measure that one dry, then set the others to match dry, then check all using the clear tube. 

I hate dealing with gasoline.  I always manage to spill it several times.

[Galactica]

So I removed the carbs to adjust the float levels.  And I only spilled gasoline once so far! 

I set the fuel level 5mm below the gasket mating surface.  This turned out to be a dry float height of 23mm from the carb flange cutout.

I’ll reinstall the carbs after I’ve had some lunch and attempt fine setting the air mixture screws.  I’ve never really been very good at it, gut I’ll give it go.

[BenelliSEI]

Ross…… Where did you get that fitting for the clear hose?