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

[PeWe]

I create a build thread for this bike since it is an ongoing project with always something to modify. Most changes written in other threads since 2013.

My bike ended up in a much longer project as intended.
I was sure that I had rather clear plan what needed to do after the bike has been stored in a barn since 1990, to my garage sept 2009.

I was completely wrong!
I had no thoughts about all nice restorations and modification I should see and read about here on these forums.
Plus all very skilled and interested guys that brings tons of information. It is dificult to stop modding the bike! I have parts for another project, a K2-75. I have also some NOS parts for my K6. Maybe too good to be used, Seat, fenders, tacho&speedo, bar around seat, rear lamp + new replica parts for OEM looking front-end.

I pulled engine 2010 when I was curious about the status. Project started 2012 when I started to work with the engine.
The entire bike apart spring 2013 when frame has to be sandblasted and painted 2k black. Engine together summer 2013 and bike  completed fall same year, first version.

2014: Bike on the road
I spent long time with various problems never seen before on this bike, carb tuning with all problems possible, ignition caused by new Dyna wire with intermittent function and old front brake.

Tested different cams. Bike has frame kit so change cam is easy.
There are several replacements and improvements thanks to this forum, such as relays, Pamco with short lived coils, Dyna-S ignition with Dyna 5 ohm coils finally replaced by Points and Hondaman ignition module still Dyna coils..

2015: All intitial problems solved, IKON shocks replaced the old Marzocchi and new carbs. Better body set in Freedom Green Metallic under a short time soon replaced by a new set in Candy Sapphire Blue and finalized that year with 4-4 exhaust HM300 replica.
More cam tests during the season.

2016: More engine improvements with less time on the street 2016. Dual front brakes. Began the engine rebuild earlier with balanced and lightened crank with Carillo rods,

2016-2017: JMR Billet block with 71.25mm pistons (1005cc), head job (again) now with 5mm valve kit, still 34mm in valves and additional fine porting. Stronger starter motor (CB900).

Some photos of how bike looked when I brought it home and each year of progress. I should have started a build thread if I knew how much I should work and change. That thread should be very long and with hundreds of photos.

I have hundreds of photos describing all details made, remade and sometimes done again. 836, 900 and finally 1005cc.
CyxleX CX-7 cam followed by Action Fours SS-1, Megacycle 125-20, RC295 profile, DP315 with 900cc and 1005cc. 125-20 went in again and finally RC295 profile that won the street butt dyno.

It looked really nice with Yamiya no numbers followed by Lotus Root and finally replaced by Hindle 4-2-1 to get the power from the installed parts.
The Lotus Root pipes wait for an eventual comeback.

[PeWe]

End of last season at a carb test ride that hopefully are over. Future rides for pure happiness 

I'll update the clutch with F2 clutch to get the thicker anti rattle plate.
I have a complete F2 clutch with cover. Strange thing it came with 7 steel plate and 7 fibers. 1 extra steel that sat mounted first. It should have 5 std steel plates, 1 double riveted steel and 7 fibers.
The clutch cover need to get the black paint removed and get an extra breather installed as the cover has today

I have got a K2 clutch with also one extra steel plate sitting first. Anti rattling attempt?

I'll add photos when clutch goes out and F2 clutch goes in.
It's only the outer steel basket, alu center and one steel replaced by a double steel plate plus the clutch cover that differ.

[Korven]

Fun write up! Bikes are real neat in their original form and all but there seems to be something special with trying to go that extra mile for some extra performance.

[PeWe]

I had to start this thread since the bike project is still ongoing.
I have rebuilt some. Tank color and exhaust change the look.

Here from last ride October 27

[markreimer]

I had to start this thread since the bike project is still ongoing.
I have rebuilt some. Tank color and exhaust change the look.

Here from last ride October 27

Gorgeous bike pewe. Makes me miss my K4, which was set up fairly similar


Sent from my iPhone using Tapatalk

[PeWe]

Thanks!
These bikes are easy to make looking good. Close to stock, good paint and no rust.
An old bike can drain the wallet several times, but it's fun and will look good

[andy750]

Great summary write up PeWe and I for one always appreciate the wealth of info you give. I went with a K8 clutch in my K4 and this helped me with smoother clutch shifting and anti-rattle. of course I had to change the shift gears to K8 as well  . Your K6 looks amazing with the Hindle pipe - very inspiring! How much power release after switching from the 4-4 to the Hindle?

Happy New Year!
Andy

[PeWe]

I have not done any dyno jet. I expect > 100whp. 105 a nice goal

[PeWe]

I have a complete 1975 F transmission in really good condition.I'll change the final shaft to a K model I have. Remove the final gear and put it on  r
The K shaft together with 2 new ball bearings. To be used in a K2-K6 crank case.
I think I'll change the primary hub cush rubbers by age, not by use.
There is a complete crank from same source.
Always something....

[PeWe]

Have done the planned winter jobs on this bike.
Changed needle jets and needle heights. Need test ride to verify. If OK, dyno.

New front and rear tires. Replaced brake shoes.
Adjusted charging regulator and installed the voltmeter as my K2 got last year. Work perfectly to verify how the charging system work, regulator especially.

Did the clutch yesterday after work. Later deeper with double metal disc for less rattle placed in the middle of the pack. The only rattle my engine had was when u-turning bike to left when taking off, especially when warm.

Splined shaft on primary hub in the thicker range making basket to sit very tight. Puller needed to take basket off. No play at all when basket is mounted on the splined shaft.
The snap ring holding basket on splined shaft took time to get in its tight place. I finally got it right with help of 2 small screwdrivers to bend with as wrenching on a tire.

I flipped snap ring  (circlip) with rounded side inwards, so the sharp edge grip the groove better for outwards movement. Basket can not move inwards.

 I think my K2 has a combo with play since it rattles when idlling. Disappear when.using the clutch

I had a complete F2 clutch since a few years.
It was only the outer steel basket and inner alu hub that differ from K6 clutch. These parts about 2 mm deeper. The pressure plate with 4 towers for springs is the same.

I had prepared an F2 cover since I knew it must have space enough for the wider clutch.

Surprise!! I could not measure any difference on my F2 cover I had removed the black paint on and the cover my bike had before. Even the old stock K6 cover look the same. I searched the forum and found the answer.

It is only a casted nob sticking up beside the kick shaft. A boss for cover screw.
Early has a higher rounded tip while later has a flat and little bit lower.
I have NOS early cover I could compare with.

Honda must have used later cover on K6 that has the lower steel basket and lower alu hub.

 I prepared the F2 cover when not needed. It has no paint, extra breather and new oil seals. For my other engine build getting 900cc.

[PeWe]

I noticed more oil splash than expected when doing the clutch.
I have seen that before which I blamed big bore and lack of breather. Engine got an additional breather in clutch cover which helped then.

I realized that the oil filter cover has a bad o- ring. Changed oil.and filter. Old o-ring too soft. The new o- ring not much harder.

I tightened oil filter bolt less this time to not weaken the o- ring.

Engine cases are clean now, let's see in a few months when bike will hit the road.
Ordered 89x4.5mm NBR 70 o- rings that hopefully is as good as or better than stock Honda.

[PeWe]

Replaced the ignition switch today. From cheap aftermarket my bike got at the rebuild 2013 to a Honda set with seat and steering locks.
My seat lock lost the protection cover last year. Ordered a kit then.

I noticed that voltage changed on my newly installed voltmeter when I wiggled the switch key. It is connected to black and green wires inside headlight bucket

 Voltage drop of around 0.5V.
Now stable with stock Honda switch. 1 key for ign switch and seat. I do not change steering lock which should be different on EU bikes.

Old switch visible on photo st lower left

[PeWe]

Installed vent tubes on my carbs, Mikuni TMR32.
These tubes seems to be a kind of tuning (dampening) for the carb ventilation, not only keep dirt away. Not too good vent letting air in that way.

It sounded OK when I let it Idle 6-7 minutes to ensure no need of choke.

Here rather big tube connections on carbs, OD 8mm. PVC hoses ID 8mm added. Around 18" long.

Carbs cleaned sfter pics were taken

I look forward to a ride when the comeback of the winter has returned to hell!

Carbs have Pods!!! Garlic and a cross will keep the dark forces away!!!!

I guess it will run very fine now, despite no countermeasures for the dark forces.

The only force I need to care about is my right hand twist!!

[PeWe]

Test rides to ensure regulator adjustment for correct max charging voltage - OK
  Sept 02- Road tests after A/F result on dyno have resulted into this jet setup:
Dyno delayed months due to Covid 19. Idle too rich, too lean under 100kmh with old setup
Below the updates fixing it.
Needles adjusted (leaner) after last dyno Oct 27 -2020. Winter job 20-21 lifting head, pistons verified rich
Pilot jets: 35 (Smaller pilot jets demands much more fuel screws causing stinking rich idle)
Fuel screws: 3/4  turns out
Needle jets: P-1
Needles: 9E11-52 (as delivered)
Needles height: 1 1/2 (1+ M3 washer) :6 
Main jets: 145
 
Air filter: KN oval pods
Exhaust system: Hindle 4-2-1 with long baffle.
Fuel: Shell V-Power
Ignition: TEC points with Hondaman ign module.
From sept 2020: Dyna-S

If fuel screws need to be opened much, idle will suffer going rich. Here too lean needle jets and pilot jets causing fuel screw to enter the 2-3+ turns open area.
Correct needle jet helped to start with. Still too much fuel screw due to too small pilot causing rich idle when fuel screws had to compensate for missing fuel delivery at very low lift.

Going bigger on pilot jets reduced the rich idle at each step up. 17.5, 20, 22.5, 25, 27.5 all needed much fuel screw between +3 -->2 1/8 to not sputter too much at take offs and low lifts.
Pilot 30 hit the better range, suddenly reducing fuel screws to 1 1/4 turn.

Jets in correct order
- Idle need fuel screws 3/4
- Pilot must then be 35 to run OK 2000-4000rpm
- Needle jet must be P1.
- Needle height max 2:6
- Main jet 145

Edit:
Needles were wrong and made the jetting impossible.

Correct needles with good jetting:
9D3-52   (aka 9D03-52/ J8-9D03-52)

Height:4:6

Fuel screws:   3/4
Pilot jet: 27.5   (del with carbs)
Needle jet: P1  (del with carbs)
Main jet: 142.5
Air jet: 130   (del with carbs)

[PeWe]

Switched seats after the ride today. I have now a reason for another 200km ride very soon.
It will get Honda painted on its rear when I have a stencil.

[andy750]

I may have missed it but what shocks are you using? On my K4 I have Hagons (stiff but very good for my weight) and on the K2 I have MikeRs old Hyperpros with new springs. No problem with butt fatigue after 300+miles on made-to-order seat and DSS K2 replica seat.

[PeWe]

Ikon shocks. They work fine.
My K6 here has progressive springs. My K2 has also Ikons but std springs.
The progressive is my favourite.

With previous setting with spring pretension at the middle, bike had a nice attack and good handling. (Damping 2)
One step lower spring, a little bit laidback stance of the bike, but more comfortable for longer rides. Still OK handling.

The seat and tire pressure  make difference. I  have recently tested higher pressure (again), around 2.7 BAR, 38-39PSI.

Same result as before, pressure on the CB750 stock label feels better. 2.1 BAR (30PSI) front, 2.4 BAR (34PSI) rear.

I have worked from home the last 3 months, sitting on my sofa from 05:30-3:00 pm. After that a 200km ride.  
A lot of sitting

[PeWe]

Tire wrestling today. Changed tire on my extra wheel.
Metzeler Roadtec 01 size 4.0-18.
Metzeler released this for old bike sizes and types too. X- Ply.
Over 150mm radial.

I'll see if it will live longer. Tire grinding carb testing is completed, now just riding the bike.

I'll change it within a few days even if old tire has 1-2 mm left to flat. Handling is affected in corners and passing painted road center lines when really flat so safety comes first.

The old 4.0-18 tire has not as bad handling as 120/90-18 tires had after same milage. The wider got bad handling at 3500km. 4.0-18 not that bad at 5000km. On stock 2.15 rims.

[PeWe]

Bike got the extra rear wheel with new tire.
Did an oil change with new filter too.
This time my home blended semi synth.
2 Spectro HD 20W-50 mineral
2 Q8 SBK Racing 10W-50 synth
1 Red Line 20W-60 Esther synth.

I used 2.5 L of my home blended semi + around 0.3L Red Line 20W-50.
Will adjust to max oil level with Red Line 20-50 after a longer ride.
Edit: no need to add more, dipstick at max plus a few mm more direct after a long ride.

Spark plugs need to be indexed  so gap is oriented for best and equal burn on all chambers.
Photos how the gap face now without shims.

Metzeler  Roadtec 01 size 4.0-18






Cyl 1 plug orientation by red thin marker pen


Cyl 2 plug orientation by green marker pen


Cyl 3 plug orientation by green marker pen


Cyl 4 plug orientation by thin redmarker pen


Plugs to be mounted same way in another head to see the orientation from chamber side.
This will help to calculate shims thicknesses.

Plug thread has 1.25mm pitch.
360 degrees turn is 1.25mm
180 degrees half of that.
All 4 plugs need of orientation change easy to calculate which give the shim thickness

[PeWe]

Verified plug orientation on a spare head.
They are all oriented towards the plug cavity "corners" as seen here with green marker pen. Gap  facing In valves center.

Cylinder 4


Cylinder 3


Cylinder 2


Cylinder 1


All properly oriented from chamber side


Head with plugs bottomed facing mostly to exhaust. So indexing is a good detail for even firing I suppose.
I have not checked other plugs. I doubt the threads are equal, plugs can probably be very different.

Here where plugs are just tightened.



They can orient as on a lottery. My K2 had 1-3 correct, 4  180 degrees wrong. Changed that sparkplug to one that landed correct found after testing 4-5 plugs. Bike runs very smooth with really nice throttle roll-on and off.

My K6 had most plugs wrong.

[PeWe]

Indexing spark plugs, matching plugs!

I could orient plugs properly without washers.
I marked some lightly used and clean plus used during recent carb jetting. Washers were flattened and easier to see how the bottom up.

I had to test almost 10 plugs in cyl 3 to find a plug with correct angle, same with cyl 2.
1, 4 easier.

As a clock: head edge at ex side is 6 o'clock when standing in front of engine in plug changing position.
Something like this as earlier photos show.
Cyl 4: marked plug 1:00
Cyl 3: 11:00
Cyl 2: 1:00
Cyl 1: 11:00

Good idea to have extra plugs to find matching plugs.

The plug is ok, hole ok too but it does not ignite as same plug in another hole. I have to try several....
Feels familiar!

Update after a test ride:
Engine feels smoother from taking off to up in revs.
Sneezing carb came back, this is usually fixed by more fuel screws, opened 1/16 turn more.

Changing plugs earlier can be the reason of going up down on fuel screws due to different plugs are differently oriented in chambers.

[PeWe]

The bike's old cut and modified original K6 seat got its name back at the rear. It looks better. Thinner coat of paint might have looked more like stock.

[PeWe]

Test ride today to verify last rear shock settings. Ikon shocks.
Success, now better and more ergonomically comfortable!!

Springs at highest setting much better for my hips and knees. Before pain during hard acceleration.
The bike's stance feels much better too.  My ass does not complain either

Damping on lightest setting (1).

Same setting verified on my K2, also Ikons, not progressive springs on that one as this K6 has. Alone and with wife.

I had looked too much into Ikons recommendations that does not fit me.
I understand why some see the spring pretension as ride height only.

From Ikons webpage:
Damping force
1. For very smooth damping under modest loading.

2. For solo and pillion passenger use on average to good roads.

3. For sporting solo riding or for use with pillion passenger and luggage.

4. Heavier adjustment than strictly necessary for use with pillion passenger and luggage.

Springs:   
- lower position for solo use. 
- centre position for pillion passenger use.
- top position for heavy pillion passenger use.

[PeWe]

Plan B head project started. Trusted longetivety...

392 head look almost ported as stock.
Chambers must be max 24.4cc as my K6 head. Less is better.

EDIT: I have measured the chambers that are more like earlier stock. 22.5- 22.9cc. strange head. This opens for alternatives.

Maybe open a little to ensure JE 71.25 pistons CR 11:1 for stock head getting OK with 24.4cc chambers.

K6 chambers opened to 65mm. 392 head +60 mm.

In valves will be KPMI 33.5mm 6.5mm stems so ports must be better to not loose power compared with my K6 head with 5mm stemmed 34mm in valves.
EX KPMI 28.5mm.
KPMI springs.

Before photos.


All EX guides are shot as usually in a used CB750 head.  2 In guides a little too wide so all guides will be replaced.

I have new stock steel guides. I do not trust bronze in the long run.

I have a set of oil orifices to use.

[PeWe]

Ex studs, all removed by double nut method.

Plan B parts parting up..
Kibblewhite IN valves and springs. Good total price from a seller on eBay UK.

Ex valves and APE retainers incoming. Quality needed, I have heard about valve drops and consequenses.