Topic: JMR billet block build with RSC 970 transmission

[bigutah]

Decided it was time to build a thread on this monster!


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[Don R]

  Following. I would want a really nice rotating assembly to protect that lovely cylinder.

[denward17]

Following.....

Could you give us novices (me) some background on the RSC 970 trans?

[PeWe]

Which cam?

[newday777]

I sure do like them JMR blocks

[Tracksnblades1]

Which cam?

+1.

How it’s programmed is everything..🤔

[bigutah]

Which cam?

125/75


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[bigutah]

Following.....

Could you give us novices (me) some background on the RSC 970 trans?

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[PeWe]

Interesting trans graphs. I would like to have a 6th gear. I like the 17:48 drive sprockets with stock trans.

Your  clutch look strong.
(An extra breather hose from clutch cover is a good add-on too)

Beehive valve springs, right?

I use a late K/F2 clutch, EBC fibers, glass beaded metal discs.
I must use the harder Barnett springs for CB500 and smaller to not get  slipping clutch.
I'm not sure if clutch slips should not happen with a smaller rear sprocket.

125/75 or 125/70 (welded) is a good cam.  I was not sure about that cam, found a used one.
The result made me to order a new 125/70 (hardwelded) from Megacycle via Mike to have as a spare.

Work fine with my 970cc engine. Steady idle at 1000-1100 rpm if I want. 1200-1400 is better for take offs. The harder pounding compression need more rpm at take offs.
Compression is needed to get it over the 100whp barrier. Still ok with tap gas, Shell V-Power.

There is no sudden power that kick in as the bike had with 836cc and CX-7 cam after 6500 rpm when I almost lost the grip at ca: 7000rpm first time.

My billet block (71.25mm) is parked due to carb jetting issues that took time to get good from idle to top.

Did not want to cause abuse on the bores/pistons.

Got a NOS JE 970cc kit cheap I have used to get carbs right. Changed when I had it appart due to oil issues with too high sitting valve guides vs 125/75 lift letting oil to be burned. Got the  head fixed and 970cc on.

 It runs too well to be  removed.

Lets see when the billet block will return. Pistons have got gas porting that most likely will add some power.

I run it with Mikuni TMR32 carbs. Very quick throttle response, often too good. Need to be careful when riding on a bumpy road in 3rd gear,  50-100kmh. A bump moves my throttle hand just a little, a sudden hard short acceleration close to get me off the bike a few times.
 
Those carbs gives really hard deceleration at throttle offs too.  I guess this is typical for flat slides.

I have got a few rear wobbles when reducing too much in +160kmh. Had to give more throttle despite my brain said it is too fast for that situation

Safer to ride slow in 5th gear that the cam allows. Cruising from 2500 rpm is fine.

It is therefore really relaxing to ride my almost stock CB750 K2 with stock carbs.
I do miss the K6 when there is a long queue of slow going cars in front of me.  
Bigger bores, less needs of shifting down when passing cars when cruising around on nice country roads.

You will get a nice cruiser when your  bike is ready for the road!

- You will use RS34 carbs?

Below:
Mike's billet block looks very nice on the bike.

[MRieck]

Sending a crank out to Marine after Christmas for a 6mm stroke. Have 70mm Wiseco pistons with the raised piston pin which eases assembly. My final engine for my CB to celebrate it's 50th birthday in 2025.

[bigutah]

TMR’s have been my favorite carb for a while now.
GL clutch. All the good racing stuff in bottom end. Ken’s magic window upgrade. A well flowed head done by Mike helps with 33.5 intakes. RSC genuine Honda Team used kit 4-4 open megaphone exhausts. The same style ones dick mann used. I have a magnesium rear hub assy too.


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[PeWe]

Sending a crank out to Marine after Christmas for a 6mm stroke. Have 70mm Wiseco pistons with the raised piston pin which eases assembly. My final engine for my CB to celebrate it's 50th birthday in 2025.

69 mm stroke and 70mm bores make 1062,17cc  plus some additional torque I guess.
Also a billet block and a 125/70, right?

[PeWe]

TMR’s have been my favorite carb for a while now.
GL clutch. All the good racing stuff in bottom end. Ken’s magic window upgrade. A well flowed head done by Mike helps with 33.5 intakes. RSC genuine Honda Team used kit 4-4 open megaphone exhausts. The same style ones dick mann used. I have a magnesium rear hub assy too.

That will be something extra!
A race bike or street use with inspired riding?

Yoshimura MJN version or std TMR?
It took a while for me to find correct jetting.
My carbs had not the needles at delivery as I found later which work much better.

[bigutah]

100% race bike. No lights or anything. Upgraded suspension, titanium hardware everywhere. Spec Dunlop K124 race compound tires. And yes. They are the Yoshimura version.


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[bigutah]

Original Kit honda RSC oil cooler. CBX triples bored out to 37mm. Late model forks with air adjustments.


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[Jerry Rxman Griffin aka MuthaF'er]

Very nice set up Utah

Great golden birthday present Mike

[bigutah]

TMR’s have been my favorite carb for a while now.
GL clutch. All the good racing stuff in bottom end. Ken’s magic window upgrade. A well flowed head done by Mike helps with 33.5 intakes. RSC genuine Honda Team used kit 4-4 open megaphone exhausts. The same style ones dick mann used. I have a magnesium rear hub assy too.

That will be something extra!
A race bike or street use with inspired riding?

Yoshimura MJN version or std TMR?
It took a while for me to find correct jetting.
My carbs had not the needles at delivery as I found later which work much better.

The best part about Utah, is with a full spirited race bike. It does have a shock bolt mounted plate, and highway patrol leaves me alone. So I do enjoy my fair share of canyon runs on it. Just have to ride while the sun is still in the sky and put her away before dark.

I think cops think it’s a “cafe” and has hidden lights or something. Either way, I’ll continue rolling with that!

[PeWe]

A very beautiful bike that will run better than the old famous RC750's back in the days, that's for sure!

[bigutah]

A very beautiful bike that will run better than the old famous RC750's back in the days, that's for sure!

That’s the end goal.


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[bigutah]

Interesting trans graphs. I would like to have a 6th gear. I like the 17:48 drive sprockets with stock trans.

Your  clutch look strong.
(An extra breather hose from clutch cover is a good add-on too)

Beehive valve springs, right?

I use a late K/F2 clutch, EBC fibers, glass beaded metal discs.
I must use the harder Barnett springs for CB500 and smaller to not get  slipping clutch.
I'm not sure if clutch slips should not happen with a smaller rear sprocket.

125/75 or 125/70 (welded) is a good cam.  I was not sure about that cam, found a used one.
The result made me to order a new 125/70 (hardwelded) from Megacycle via Mike to have as a spare.

Work fine with my 970cc engine. Steady idle at 1000-1100 rpm if I want. 1200-1400 is better for take offs. The harder pounding compression need more rpm at take offs.
Compression is needed to get it over the 100whp barrier. Still ok with tap gas, Shell V-Power.

There is no sudden power that kick in as the bike had with 836cc and CX-7 cam after 6500 rpm when I almost lost the grip at ca: 7000rpm first time.

My billet block (71.25mm) is parked due to carb jetting issues that took time to get good from idle to top.

Did not want to cause abuse on the bores/pistons.

Got a NOS JE 970cc kit cheap I have used to get carbs right. Changed when I had it appart due to oil issues with too high sitting valve guides vs 125/75 lift letting oil to be burned. Got the  head fixed and 970cc on.

 It runs too well to be  removed.

Lets see when the billet block will return. Pistons have got gas porting that most likely will add some power.

I run it with Mikuni TMR32 carbs. Very quick throttle response, often too good. Need to be careful when riding on a bumpy road in 3rd gear,  50-100kmh. A bump moves my throttle hand just a little, a sudden hard short acceleration close to get me off the bike a few times.
 
Those carbs gives really hard deceleration at throttle offs too.  I guess this is typical for flat slides.

I have got a few rear wobbles when reducing too much in +160kmh. Had to give more throttle despite my brain said it is too fast for that situation

Safer to ride slow in 5th gear that the cam allows. Cruising from 2500 rpm is fine.

It is therefore really relaxing to ride my almost stock CB750 K2 with stock carbs.
I do miss the K6 when there is a long queue of slow going cars in front of me.  
Bigger bores, less needs of shifting down when passing cars when cruising around on nice country roads.

You will get a nice cruiser when your  bike is ready for the road!

- You will use RS34 carbs?

Below:
Mike's billet block looks very nice on the bike.

I gotta know, any videos floating around of your beast running? would love to hear TMR’s with a 4-1


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[MRieck]

Sending a crank out to Marine after Christmas for a 6mm stroke. Have 70mm Wiseco pistons with the raised piston pin which eases assembly. My final engine for my CB to celebrate it's 50th birthday in 2025.

69 mm stroke and 70mm bores make 1062,17cc  plus some additional torque I guess.
Also a billet block and a 125/70, right?

Correct Per....have just about all the parts on hand.

[MRieck]

Very nice set up Utah

Great golden birthday present Mike

I agree Jerry. My F hasn't seen as many wives as your bike BUT we have been through thick and thin.

[PeWe]

****
I gotta know, any videos floating around of your beast running? would love to hear TMR’s with a 4-1

No video recording while riding.
TMR's gives a nice whistling sound when giving an even throttle.
The slides rattles when idle is right, like castanets.

Slowly increase throttle on 3rd gear up to 5000rpm, WOT from there followed by throttle roll-off gives a nice race sound that trigger horns to grow.

A little bangs from exhaust like drums. If it bangs with sharp sound, more like explosions the pilot circuit is too lean.
Too silent is rich.
All carb adjusting rides have taught me how it sounds

Direct follow up with WOT again must be heard. The Hindle 4-2-1 has a nice tone.
Mostly idle here. 970cc setup.

My 71.25mm pistons for my billet block got these holes for top ring I really want to test.

[MRieck]

****
I gotta know, any videos floating around of your beast running? would love to hear TMR’s with a 4-1

No video recording while riding.
TMR's gives a nice whistling sound when giving an even throttle.
The slides rattles when idle is right, like castanets.

Slowly increase throttle on 3rd gear up to 5000rpm, WOT from there followed by throttle roll-off gives a nice race sound that trigger horns to grow.

A little bangs from exhaust like drums. If it bangs with sharp sound, more like explosions the pilot circuit is too lean.
Too silent is rich.
All carb adjusting rides have taught me how it sounds

Direct follow up with WOT again must be heard. The Hindle 4-2-1 has a nice tone.
Mostly idle here. 970cc setup.

My 71.25mm pistons for my billet block got these holes for top ring I really want to test.

FCR's make that same whistling sound Per.....you got to love it. Carb tuning is half science , half voodoo when it comes to high performance set ups. I've found the best indicator of the idle...or pilot circuit.... is cruising around not really cracking the throttle open for an hour or so. When you're cruising on the highway you are basically on the idle circuit 90% of the time. Once you get the idle circuit correct you can work one the other circuits. Fact tom remember is that fuel curve is very fluid and each one effects the other...that's why I have always used the idle circuit as  the foundation of my carb tuning.
 Per.....just to let you know there are no more 71.25 ring packs available....the closet I've found are Suzuki XA rings for the 71mm piston.

[PeWe]

FCR's make that same whistling sound Per.....you got to love it. Carb tuning is half science , half voodoo when it comes to high performance set ups. I've found the best indicator of the idle...or pilot circuit.... is cruising around not really cracking the throttle open for an hour or so. When you're cruising on the highway you are basically on the idle circuit 90% of the time. Once you get the idle circuit correct you can work one the other circuits. Fact tom remember is that fuel curve is very fluid and each one effects the other...that's why I have always used the idle circuit as  the foundation of my carb tuning.
 Per.....just to let you know there are no more 71.25 ring packs available....the closet I've found are Suzuki XA rings for the 71mm piston.

Yes, the sound of the carbs is nice. I'll hear when idle is good

§ Bigutah will hopefully have use of the pilot circuit talk...

Pilot circuit cover the legal speed area.
The jetting much easier when I found the correct needles.
MJN has only 2 if I have understood it correctly, small and large carb bodies. 32mm is small.

Most of my rides have been pilot circuit related
See documented rides in the Open forum, Frank memorial....
The TMR std filter adapters did not cover Pilot Air Jet as Yoshimuras do.

So, my carbs got some dirt inside during 30.000km.  PAJ got filter added 2022.

I used fuel additive in high dose last fall that allowed me to reduce fuel screws 1/4 turn after 200km of my 300km ride.  Cleaned the pilot circuit.

Plugs rings still looked too black so I did some more pilot rides. Downhill in low speed, up to max 80kmh where I slowly reduced throttle revealed a rich sound. Downhill to reveal the smallest too rich.

I reduced the pilot from 27.5 to 25 and fuel screws from 3/4 to 1/2+1/8. 1/8 turn is much on these carbs. I guess carbs need choke longer time now and a longer warm-up to work well when fully warm.

Reducing pilot need higher needles and more main jet to compensate for the total fuel. (If needle and main atea was OK before)
I raised needles 1/2 notch (0.5mm thick M3 washer) (I have seen that before, 2 steps of pilot need 1 notch (1mm) needle to compensate)
 + main jet 1 step (2.5).

When I pinched 1 oil rail for 8 years ago fitting the billet block was a strike of luck then.

The shipping cost was crazy for one small package of rings, initially $,72US + 30% VAT, customs.
Neither Dynoman nor Summit racing could put a set in a jiffy bag, around $5US shipping.
$36US the lowest possible by Dynoman so I ordered a full set of rings, 4 sets of $25US each.

So I have a full set minus one oil rail.
Summit racing does not have today when I searched.
Dynoman can not find either? A forgotten box on a shelf somewhere They sold 71.25 mm pistons for a while.

I'll measure my used rings gaps, if I must use my new set
0.25mm gaps might be enough for top ring and 2nd?
I think it was +0.30mm, 0.35mm  (0.012" vs 0.014") for the 2 rings. I had to file some.
Oil rails 0.25mm.
The bores will live looooong time.

I'll change oil soon so I can start the bike,  use up the fuel in carbs. A video to hear the sound when revving it a little

My new set of rings ordered 8 years ago. Time flies by...

Boxes marked JE on outside, rings in plastic bags inside marked Wiseco.