Topic: CB750K6 -76 project back to life with more updates

[PeWe]

Last jetting was almost OK, not ok for me.
A little bit rich idle and lean on low lift at take off. 
More fuel screws fix the take off but richen the idle to worse.
It still have the very good throttle response the higher needle gave, from 2:6 to 3:6. Reach 100mph very quick!

Changed it yesterday/today, 2-3/11.
Smaller pilots and larger needle jets.
- Pilot 27.5 -
- Fuel screws 1
- Needle height: 3:6
- Needle jets : stock P1 -
- Main jet 145

Idling in garage test. Fuel screws can not be increased much.
Road test needed.

If this will not work as needed I'll change to almost as before except lower needle and larger needle jets.
- Pilot 32.5-
- Fuel screws 3/4
- Needle height: 2:6 -
- Needle jets:  P1
- Main jet 145

Also possible to place an M3 washer under the clip to get 2 1/2.
I'll see then if I have to decrease pilots back to 30.
Important to make notes.

Correct needle important for the good useful torque to happen between 4000-6000 rpm when twisting the trottle.

Correct dry idle important for the engine, too much fuel will make bad, not only carbonized pistons, chambers, valves and ex ports. Lubrication of the bores as well.

I know how well it can purr with stable idle.  Relatively hot cam and rather high compression no reason for bad idle

This must be improved and verified by road tests before next dyno can be actual.

[Stev-o]

Hey Per...looks like you are very close, but need to get it just right for "take off"!!

[PeWe]

Hey Steve,
Yes, I have been close before but to get it right I had to change more than expected like tuning on a parallel track which it will become when changing needle jet and try the other tried setting again.

It must be something like my plan. I do not want to mess with the air jets I never have changed before.

[PeWe]

Road test yesterday.
- Pilot 32.5
- Fuel screws 3/4 (1 1/8 better for 3000-4000 rpm, but Idle suffer rich)
- Needle height: 2:6
- Needle jets:  P1
- Main jet 145

More power than ever! Torque felt increased from low compared with dyno run. Stable constant torque thru all gears.

Cold wet roads, so I let it run up to around 100mph (160kmh) only which happened really quick.  A dyno run now should give higher numbers, that's for sure.

But idle and slow crusing under 4000rpm is not as it should. Too rich idle and lean later on up to 3500 something.
**********************************
Edit: May 2022 adjustments
### 2022 ####
 - Pilot: 35
-  Fuel screws: 3/4
-  Needle Jet: P1
-  Needle height: 2:6
-  Main jet: 145
*********************************
A jetting puzzle without loosing the good accelerating power with dry good idle by the fuel screws. Very sensitive settings.

[Stev-o]

Road test yesterday.
More power than ever! Torque felt increased from low compared with dyno run. Stable constant torque thru all gears.

The "butt dyno" tells all!

[PeWe]

Road test yesterday.
More power than ever! Torque felt increased from low compared with dyno run. Stable constant torque thru all gears.

The "butt dyno" tells all!

Yes!
Especially when the needle area get enough fuel followed by main jets.

[MauiK3]

Butt dyno is certified accurate..........until proven wrong by the dyno.
At one point I had to prove to a group of old school machinists that torque wrenches were a must and that hand feel was inaccurate. I took these folks down to our calibration lab and set up a blind test where they hand torqued some fasteners but could not see the calibrated machine tracking their work. They were all over the place and few were even close.
Not sure what this has to do with anything but the butt dyno reminded me that I like instruments.
Cheers

[PeWe]

Yes, torque wrench is a must and the feel how to use it. A torque wrench seller visited my job many years ago demonstrating how to tighten bolts, nuts and mistakes to be done. Lubed or not and where, which lube vs torque chart.

Last dyno run was done recently, October 26 where possible power to gain is visible on the AFR plus the words from the dyno operator.  So my butt is like a very well calibrated wrench with memory!

The tricky thing is to combine that nice power with clean not too rich idle and smooth running not hesitating nor stumbling rich on the first few mm of throttle lift. The important needle area is affected by the pilot circuit and vice versa. So this can go on for a while.
I hope I can find a good combo without changing needles that cost some or involving air jets replacements.

The Mikuni TMR flat slide carbs are very direct. They give really good direct response on correct settings, but also not forgiving when just a little wrong somewhere.

Injection would be easier. Just leave the bike at a tuner with dyno that can make it perfect, a straight line on the AFR chart.

But the charm with carb tuning is another reason for a test ride

[PeWe]

Clutch got their metal discs refreshed. Glass beaded except for the double plate that can be really tricky to clean with risk to get media in engine.
Glass media very small.
So the double plate got another surface refresh by grinding it a little.

Clutch hopefully no slip when not really warm. I had to start and idle engine after assembly to warm up oil and adjust again the bottom lever play to the better.

https://www.#$%*ute.com/video/q8LxCXNACZAO/

[seanbarney41]

Mercy!  That sound is very un-honda-like, sounds like when a very large dog sits on his haunches, bares his teeth, and growls.

[PeWe]

The Hindle 4-2-1 give it a darker tone.
I like the idle posted today.
Around 1000rpm with the Megacycle 125-75 cam.

I prefer 1200rpm which is easier when riding. It might increase to that when really warm.

The dyno run was October 2020 where it got 101whp with 1005cc build. Also 125-75 cam but another head.

I have a later dyno October 2021 with 970cc build where it got 104whp despite a little lean after 6500rpm. Not published
I adjusted carbs to the better after that so hopefully a few more.
It idles well now, hopefully still good midrange as it had at the last ride when it ran better  than dyno before, especially midrange. I have fiddled with the carbs after that.

I smell the difference in the garage when idling and after, not stinking rich which is a good sign

The engine is like an orchestra, all individual upgrade parts are instruments that must play the same song at the same time!
They start to do that now which give the good power and response.

[seanbarney41]

I was figuring that nearly 1000cc is what gives that darkness, not the Hindle

[PeWe]

Yes the bigger bore make it to sound bigger, compression involved.
CB750's in general has a special sound, really easy to like.

The flat slide carbs sounds too, at idle a clattering sound, accceleration a whistling sound.

Here another video at first start of the 1005cc build. It had DP315 cam, Yamiya No numbers 4-4. Dyno 93 whp as  best.
Lower compression than now.

Here more as it has sounded back in the 80's. 836cc with nice screaming slim Alfa 4-1, modest and valve train friendly Action Fours SS-1 cam.  (After dyno RC295 wich gave better torque from 4000rpm, SS-1 woke up a little bit later)
Dyno done 2015, 80 whp. Another dyno with 125-20 cam 83whp.

Edit: 836cc was with stock rods so I waited for a rod to pop out when standing beside when revs passed 9000 rpm.
But I realized that I often enter 9500 on 2nd and 3rd.
That helped me to replace the crank soon after, APE crank with Carillos.

[SOHC4 Cafe Racer Fan]

93 hp at the rear wheel!  That's impressive!

[PeWe]

93 hp at the rear wheel!  That's impressive!

It felt OK with the bigger bore that has a good torque from low.
The 4-4 made bike to look at best but restricted the revs over 8000rpm.

Bike feels much more responsive with the 4-2-1, higher compression and cam that all together raise the power 11whp further

I'll see coming spring if I get more power and correct fuel ratio which is more important, not creating carbon or too lean. Earlier both.
Maybe I'll make a quick exhaust swap, Yamiya "Lotus Root" 4-4 for the look.

[PeWe]

Bike is waiting for spring with a rear tire that has around 1000km left, plus a dyno run.

I have not yet tested the new rear wheel I built one year ago with 3.0-18 rim. Had to use up a tire on stoch rim first.

Tire in garage  not yet mounted and I already look forward for next change.

Tire to be used first Metzeler Roadtec 01 120/80-18 diameter close to stock 4.0-18

Next rear tire wider 130/80-18.
Matching front 100/90-19 on 2.15-19 rim as has 90/90-19 now.

Metzeler has not the Roadtec 01 in 130/80-18.
Michelin has, Road Classic.

So I need to ride up the existing tire on bike.
New 3.0 wheel with Metzeler 120/80-18 and ride it up too.  Cannot use it on another bike when 120/80 need wider rim than 2.15.

Then time for the Michelin 130/80 tire.

Later change Metzeler front to Michelin too, 100/90-19.

So I have rides to be done.

Metzeler Roadtec 01 is a good stable tire. Like it, 2 rear done. 4.0-18 and 120/90-18, the latter no longer available/produced. 120/80 on their list.



Next tire I look forward to test as wider rear. Rather new model. Front will come too.


I have compared the rear wheel radius. I choosed 120/80 since it was closer to stock 4.0 than 120/90.

        4.0-18 - 326.39mm
120/90-18 - 336.6mm

120/80-18 - 324.6mm
130/80-18 - 332.6mm

My thoughts now is that a 130/80 might live longer and handle the power better.
 3.0" rim allow that width.

[Stev-o]

The Metzeler Roadtec 01 tire looks awesome!   Obviously not a vintage tread pattern but great for a rocket bike with 93 hp!!  Great job

[PeWe]

Thanks Steve-o.
I agree the, Metzeler look really good and is very stable, even when rather flat.

Power has passed the 100....
104 whp at last dyno

I ordered Michelins today, Metzeler has not that size, 130/80-18.
Road Classic is a newer design so I hope they must be good. More km on rear is needed.

I'll change direct when I get the tires now when there is no bike weather anyway. Front too, 90/90 is a little bit small. 100/90-19 soon here.

The front caliper bracket holders need to be shimmed when there is a vertical play of the entire caliper bracket.

[PeWe]

I got one of the Michelin tires today, rear 130/80-18.

I compared its width with the Metzeler 120/80-18 also not yet mounted and the old 120/90-18 sitting on bike with stock 2.15 rim. Inflated tire is not wider, maybe max 1mm.
Drive chain guard will stay clear from the tire that is around 3mm wider to that direction.

I must remove (or lift) the chain guard anyway to lift chain off the sprocket.

Endless riveted chain, no need to open it for wheel off or pull engine. Lift front sprocket with chain on and let it go backwards to give extra slack to lift chain off rear sprocket.

Old rear tire with some life left. Here why stock 2.15 rim should not use wider tire than 4.0-18.
This very tire cause not that bad handling as previous 120/90 tires.


I changed my mind again. I'll start with the 120/80-18 tire on my new 3.0"-18 wheel. 130 later on.
Front calipers need to be shimmed. Shims ordered from China that will take a while.
I guess 0.5mm will fix it. Do that when replacing front tire

[MauiK3]

Great sounding bike,

[PeWe]

Thanks! :-)
It sounds even better in reality, chain rattle sounds more on indoor video. It has a more even idle now when not running too rich.

New brake fluid in front brakes. Probably no change since it got dual brakes 2016.
Sucked out the old fluid in the MC with a syringe, refilled with new and bled both calipers some times with additional refills.

Just waiting for spring rides. 5 months of waiting make the spring rides to very special events!

[PeWe]

Feeling tired!
Something for tomorrow daytime.

[PeWe]

Tire is on, soon ready for a ride.

I'll verify the balance another day.  Hopefully not that much wrong. Lightest part of tire sit at the valve.

I like the straight tire profile, not the bulbing profile as 120/90 on 2.15" rim
Let's see what the bike will say

.

I had to rotate tire for better balance. I understand why the pros do not bother. They fix it with their machine.

[Stev-o]

Looks great Per.

Let us know what the bikes says! 

[PeWe]

Thanks Stev-o,
I need to wear out the old tire. So hopefully a report in April.

The old tire is rather flat so wheel change might happen earlier.
I hope I'll get a dyno time early April if weather is OK.
Dyno on old tire.

The new wheel look good and I'm curious about next tire which is a little bit wider so I need to ride the bike often and long to wear the new tire down for another change.