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

[PeWe]

Engine updated with other ported head, cam and new carb boots.

It started with bike ran different. Carb jetting felt as working against a moving target.

I looked closer and noticed that carb clamp 2 and 3 sat strange on head side. Opened clamps, moved them aside and saw long cracks all the way thru. 3 was worse almost half side open, 2 only a 20mm wide crack.

Plugs in 2-3 white- grey.

Compression check showed  15-20 PSI less than before.

Opened engine, worked hard to get off the head. Nuts were loose on EX side. They had sunked down into head's soft alu.
Got head off and could clean pistons that had got some oil due to the loose nuts.

All pistons and bores looked fine!

I had in parallel worked on another ported head, not only as replacement, upgrade with less chamber volume, thinner gasket cranking up the compression.

Also 34mm inlet valves but not 5mm stems as the old one.

Cam has almost same numbers as the old RC295 but different lobe shapes.
New cam has 0.2mm more lift on EX and a degree or 2 different.

The new carb boots got wider clamps. The old Honda boots were very soft. I remember that when I could tighten them more.
Important to not tighten these boots too hard, they will crack within 4-5 years/~20.000km.

Now back to sync carbs again. Will have some road tests first. I started it yesterday and it seems to be OK.
I'm curious about the head will work.









Restore, clean pistons that look like new







The "new" cam has different position of the notch that usually is faced upwards at 1:4 TDC. The horisontal line is as usual.

Right is old cam
Lift In/Ex: 9.93/9.18mm
Open close at 0 lash, 1mm lift:
25/54  dur:259
56/21 dur: 257

"New" cam:
Lift In/Ex: 10.0/9.4mm
Open close at 0 lash, 1mm lift:
26/55    dur: 261
55.5/23 dur: 258.5

Started engine yesterday.
Road test next.



The "new" head chamber upgrade. Ported earlier head, 6.5mm stem valves 34/28mm.
Old head here was a K6 head with 5mm valve kit, 34/28mm

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[PeWe]

+200km long ride today after work.
It runs very smooth in higher speeds. An even power from 4000 rpm and up.
Not a sudden kick after 7000 rpm as similar cam CX-7 gave when bike had 836cc.
Rather good throttle response from 160-170km/h just enter the red area on 5th gear, 8500.

Washer under needles (+1/2 notch richer) and synch carbs, hopefully tomorrow.

Edit: Another +200km ride today Thursday.
Bike runs much better now. Better response from 4000 rpm and up with raised needles. Idle and take off better after carb synch.
(Easy to open fuel screws when carbs are not in synch)

-Needles raised by an M3 washer, before 3rd fom top.

Correct jetting found and verified on Dyno October 2020 and road tests later.
Fuel from Needle area moved to Pilot area, less fuel screws.
- Fuel screws 3/4
- Pilots 35
- Needle jets P-0
- Needle height 2
- Main jet 142.5

Good stable idle.
Dyno and road tested - OK

Edit: A 200km/h ride today Friday. I looked for another gear at 8500 rpm on 5th gear!
- How to install a 6th gear?

Yes, the 125-75 make the speedo and tachometer happier with an even power from 4000 rpm and up.
Not bad before either. Idles fine,  I can cruise in 2000 rpm on 5th gear, then increase without hickups.

[andy750]

I always enjoy your updates Per. So detailed and precise and interested in hearing about these different cams. Any chance of getting a ride video one of these days so we can hear the engine as you shift up? 

[PeWe]

I have a small video camera, GoPro copy
It need a good and stable attachment.
Maybe....

[PeWe]

Dyno video! Road video might end up in speeding ticket or worse

Idle rather OK. I have reduced fuel screws a little afterwards making idle a little bit better, drier.

[andy750]

I like the Dyno video bike sounds good. What did you get for hp? Torque?

I looked back at an earlier post on carb boots and saw you are using the plumber clamps. I tried those but felt they were not good for the Honda boots in terms of a consistent seal and changed back to Honda clamps instead - this helped my runaway idle. I am guessing you can tighten the plumber clamps more which may cause the tear you describe.

Anyway next question - what gloves did I see in the Idle video - are they good Fall gloves? Look interesting. I just bought some Five gloves from FC Moto and they are good but one of the fingers is a little tight.

Thanks
Andy

[PeWe]

Finally the minimum result achieved for those parts!
Around 100whp and a nice torque and hp graph that continue to 9000 rpm! See result in blue.
Carb jetting is better here too.

Edit: I just got an idea to test 1 step bigger pilot jets. Now 32.5, change to 35. That might make the hesitation at 3500-4000 (after acc pump) to disappear. Fuel screws a little bit less.
Needle height hopefully still OK (not too rich), now 3rd notch + an M3 washer making 3.5. Washer to be removed with pilot 35.

The hp need to continue for another 1000 rpm or just higher since lower rpm need too!!
Head need more air, still have good torque and low rpm response. Min 5hp more!!
 


But the biggest jetting improvement not visible.  Before way too rich idle and too lean between 2000-3000 rpm on 5th gear. Several steps bigger pilots helped to reduce fuel screws rather much.

I have used that kind of clamp before without any problems, 9mm wide. On old stock boots from early 80's.
The rubber today is much softer. A mistake was to retighten them after a while.

I had wider clamps home, did not realize they where 12mm wide when ordered a few years ago. I think they will work better, less risk they dig into the rubber as the old. I also aimed the boots a little bit more upwardd. I'll not retighten the clamps.

Carbs and filters fits exactly, not much clearance against frame.

I'll check my K2 and see how the rubbers look like. I'll order an extra set of Honda bagged boots. I suspect that Honda boots are not good anymore.

The gloves for colder part of season. I needed a warmer set. These are rain gloves but still not causing hands to sweat like others with bad insulation.

Difficult to find gloves with wide enough sleeves cover the thick leather jacket sleeves.

Dainese X-Tourer D-Dry.
https://www.dainese.com/gb/en/promotions/promotions-moto/gloves/x-tourer-d-dry-gloves-201815896.html#

[SOHC4 Cafe Racer Fan]

Wow! Those are some great numbers!

[PeWe]

Thanks!
Aiming for more! 105hp would be better

I did not test different ignition settings on the dyno. Maybe a couple to be found there.

[SOHC4 Cafe Racer Fan]

That thing is the very definition of a sleeper.

[754]

Really great numbers, lots of torque..

[PeWe]

Yes, torque curve is rather flat, good numbers very early.

[SOHC4 Cafe Racer Fan]

Yes, torque curve is rather flat, good numbers very early.

 

Unbelievable torque number!  Did you brace or gusset the frame to guard against any twist from all that added grunt?

[PeWe]

No reinforcements at all.
Frank's frame kit!
Steering damper at front. Ikon shocks, K2 swingarm with needle bearings.
I have a fresh K6 swingarm to make it more stock like.
Strong X-ring chain in need of replacement.

I had a ride today after fiddling with the carbs.
It felt strong and extra alive.
1 step bigger pilots, needles a little bit leaner by removing the washers I had added. This action based on last dyno visit.

Felt like more power so I called for a dyno time. Maybe possible end of next week if lucky.

I will take engine apart in winter so I must know if it was just good oxygen rich air today or more hp after carb adjustments.

[PeWe]

A 160km ride today to verify last adjustment of fuel screws, reduced 1/8 from 1turn out. Success!!
Finally good from idle and all way up without any hesitation when slowly twisting and reducing throttle during the entire rpm range. Quick WAT works as good as it can.

Clean plugs and Dyno next if getting a time.

[Chetterooski]

Your bike is simply amazing.  Looking forward to updated dyno results.

[PeWe]

I hope chain will make it.
A softer attack on dyno.
I have new chain with sprockets to be installed this winter.

[PeWe]

No Dyno run.  Very small chance next week.
It would be fine to get the extra power on graphs before winter total engine tear down with service, reseal cases, maybe new primary chains and tensioner.

Plugs after last ride yesterday were mirrors of how fuel screws were adjusted.
1, 4 OK, 2 lean, 3 rich.
I had brushed them clean before, ring and ground strap.

2 got more and 3 less to be equal as 1,4.
The screws are PITA to adjust when screws are not visible as stock carbs and smoothbores  air screws. More feel than visibility, 1,4 rather visible.

1/8 more or less make a difference.

[PeWe]

Dyno today.
Blue graphs. Bad weather and bad chain probably the reason for 1.5hp less after 8000 rpm.

The fun area and most important for street bike, 4000-6000 rpm improved, better torque which I have noticed on road test. Now a cleaner running engine, plug color better.


Will lower the needles just a little to reduce fuel.
I found 0.8mm washers on eBay from China. I'll know next year if that will help. I need to measure on a needle if it really will lower by 0.2mm.
2nd notch with additional 0.8mm washer under compared to 3rd notch.

[PeWe]

Got the beginning of next season today. Rear tire, very well packed.
I'll try how this tire look and work in 120/90-18. Before 4.0-18 that worked well, very stable.

[seanbarney41]

What brand tire is that?

[PeWe]

Metzeler Roadtec 01.
Available for our old bikes sizes and non radial.
There are really fat radials too

[seanbarney41]

I think i will try a set of those.

[PeWe]

I'm sure you'll like it.
There are cheaper tires.
I like the handling I experienced last season on 4.0-18.

https://www.metzeler.com/en-ww/products/tyres/roadtec-01

[PeWe]

I could not resist to adjust needles a little.
Dyno guy told me that it runs a little rich in the 120-130 kmh range. Enough for lower the needles.

Adjusted around 1/3 notch lower.
From notch 3 to notch 2 with metal washer of 0.65mm
- Lower by 0.35mm
 (1mm is the difference between  2 notches).

It would be nice with a 70km testride in constant 120-130kmh, kill switch  and check a plug beside the road.
 
I have cleaned the base ring on plug 4, easy to access. I'll might clean plug 1 too.

Weather is not too cold, only wet. Need dry roads for a test this week

Photos with the TMR stock nylon washer.