RH4 to RH10 JS Intake Port Sleeves

maaseyracer

maaseyracer

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I am going to make a new post on this as I think it is a completely different topic than my rebuild. I ran my rebuilt engine with JS pistons, rods, cam, BSA lifters, and beehive springs for about a week prior to installing these sleeves. I made sure I had a brown plug prior to installing these so I was at least in a reasonable tune. Install was done with loctite 510. Fit on these is very good and you can see the squeeze out on the tip of the sleeve in the photo. I added a sharpie mark at the top so I could line the shortest end on the tip of the sleeve up with the valve guide easier. I have since checked to see they were still locked in place and they are after half a dozen rides.

The difference is interesting at first it felt subtle, a bit more throttle response everywhere. I did have to adjust the needle clip leaner with these tubes. I am running 33mm Keihin CR carbs. I have been riding these around for a week and getting the feel of them. Here is where the big change is, when I checked on the sleeves i heated them up with a plumbing torch to see how hard it was to remove them, it was fairly easy with a glove. I then reassembled and took it out for a spin, the lack of throttle response was surprising, and it felt like I did not get on the cam until around 5000 or 6000 RPM. I reinstalled the sleeves and the difference is definitely there.

Very curious to get other opinions and thoughts here. I will check on them later this week after a few more rides to make sure they have not come loose, so far for the price I think it is a great improvement.

RH4 to RH10 JS Intake Port Sleeves
 
Maasracer,
Thanks for posting the results.

This kind of re-affirms Dynodaves Combat with the smaller ports, dyno testing run.
 
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If you want better throttle response, slower taper neddles might be better. With a quick taper the mixture richens faster as you wind the throttle on. The slightest bit too rich sloes the response. Quich taper needles favour heavy-handed riders. If you feen the throtlle on with a slower taper needle, the response is better than you get if you whak the throtle open with a quick taper needle. The taper compensates for loss of vacuum. Big ports lose vacuum more easdily. You now have smaller ports, so the taper on the neddles might be excessive.
Plug colour is not a good way to assess mid-range jetting - it is only used for setting the main jets. If you get a miss when you ride the bike, stop and rasise the needles one notch atv a time.
When the main jets are slightly too rich, the motor gets a reprieve when you use full throttle, rather than burning pistons. But in the midrange is where the jetting really needs to be correct.
 
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I use two 34mm MK2 Amal carbs on an 850 head with tapered ports, using methanol fuel, however the priciple is the same when using petrol. However with petrol as fuel, the differences are even more significant. I use 6D Mikuni needles, which are correct for that diameter carburettor. They are the slowest taper - throttle response is excellent.
My 850 is quick enough to stay with 1100cc CB750 Hondas in Period 4 historic races - mostly due to the jetting at part throttle openings. It is easy to getv right, when you knowc what you are doing. Yiou need to think if vacuum, jetting and fuel metering.
My brother races speedway sidecars. I had several arguments with him about this stuff. He now understands it and has won every race he has entered, for years.
It is not difficult but many people seem to believe that using more fuel means more power, when the opposite is often the truth.
 
Iirc on dyno testing Jim C said that the RH10 made about 2 hp more than the Rh4 at midrange and that they produced virtually the same power at top.
2 extra hp in the midrange , with no loss elsewhere, is a nice find!

Glen
 
The RH10 uses a tapered intake stub to go from 30mm at head to 32 mm at carb.
Is that how this arrangement is meant to work?

Glen
 
Lives up to the description. Good between the stop lights. Sweet 👍

My intake ports have 31mm entrances with my modified intake manifolds. (Commando Mk2 intakes modified and blended from 35mm for 35mm FCRs to 31mm for use on a straight up motor.) Older pre-Commando 750 head cleaned up by Fred B. Doesn't lack for throttle response. Same valve train as yours, but a one off 2 into 1 exhaust. That JS2 cam is strong and the motor is howling right around 7000RPM with the bigger carbonators. It would probably be a better than it is in the midrange with the 33mm CRS carburetors.

Irrelevant of course because my motor sits straight up, I changed a few things, and it is not an 850. I don't think the engine knows it is straight up though.
 
For whaterver revs your motor does, if the comp ratio and ignition timing do not change, - there is an optimum fuel/air ratio in the mixture to deliver maximum energy. It does not change., unless you change the fuel. When you reduce the port size, you create more vacuum. The depresssion on the jets and the shape of the needle determines how much fuel is deliverd. The slightest deviation from the optimum fuel mixture towards richness will reduce the energy which is produced by the combustion process. However the usable rev range of the motor determines the optimum size of the inlet ports. If the port is too big for the usable rev range, there is less depression on the jets, so a quicker taper needle is used. When you wind the throttle on fast with a fast taper needle, you can often exceed the optimium amount of fuel.
When the port is smaller, it is easier to maintain vacuum. But if you whack the throttle open you can sometimes get insufficient fuel.
If you wind the throttle on slightly slower with a slow taper needle,and use a small port, the mixture can be maintained closer to the optimum, and the motor will deliver more power, than if you whack the throttle open and get more fuel into a bigger port.
The optimum mixture depends on comp, ratio. ignition timing. octane ratio, and jetting. The port size affects the jetting. The revs affect the advamce curve.
Fuel injection and programmable timing offer more control.

One of the reason I don't like two strokes, is this stuff - errors cause seizures. If you do seize a Suzuki GT750, one stuffed cylinder means you replace them all. A Commando is much nicer.
 
maaseyracer said:
I am going to make a new post on this as I think it is a completely different topic than my rebuild. I ran my rebuilt engine with JS pistons, rods, cam, BSA lifters, and beehive springs for about a week prior to installing these sleeves. I made sure I had a brown plug prior to installing these so I was at least in a reasonable tune. Install was done with loctite 510. Fit on these is very good and you can see the squeeze out on the tip of the sleeve in the photo. I added a sharpie mark at the top so I could line the shortest end on the tip of the sleeve up with the valve guide easier. I have since checked to see they were still locked in place and they are after half a dozen rides.

The difference is interesting at first it felt subtle, a bit more throttle response everywhere. I did have to adjust the needle clip leaner with these tubes. I am running 33mm Keihin CR carbs. I have been riding these around for a week and getting the feel of them. Here is where the big change is, when I checked on the sleeves i heated them up with a plumbing torch to see how hard it was to remove them, it was fairly easy with a glove. I then reassembled and took it out for a spin, the lack of throttle response was surprising, and it felt like I did not get on the cam until around 5000 or 6000 RPM. I reinstalled the sleeves and the difference is definitely there.

Very curious to get other opinions and thoughts here. I will check on them later this week after a few more rides to make sure they have not come loose, so far for the price I think it is a great improvement.

RH4 to RH10 JS Intake Port Sleeves
Click to expand...
A common mistake which many road racers make, is enlarging inlet ports. I did it myself when I was young and stupid. My short stroke Triton used to power on forever, but with high gearing could not pull the skin off a rice pudding.
 
worntorn said:
Iirc on dyno testing Jim C said that the RH10 made about 2 hp more than the Rh4 at midrange and that they produced virtually the same power at top.
2 extra hp in the midrange , with no loss elsewhere, is a nice find!

Glen
Click to expand...
I recall him saying the difference was much greater Glen. The velocity in the low and mid range was much higher with the RH10 but the increased flow of the RH4 was more than the engine needed, hence they performed (more or less) the same at the top end.

Different engine sizes, and tunes, will of course behave differently though.
 
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I like the mod, but I'm not clear on this.
Is your head an RH4 or RH10 with RH4 sleeves?
 
You could probably do it to a 72 combat head as well.
I have one combat with 32 mm intakes and one with 30 mm.
I have an RH4 head on my 73 850 so I might be in the market for this mod.
 
Anything that puts power back in the midrange (where most of us ride) without a loss elsewhere has got to be good
Shame it doesn't beef up the week area around the valve guides too
That'd be perfect
 
In my experience (always subject to extreme criticism) midrange moves up a few RPM with slightly larger intake ports and higher lift and longer duration cam profiles. Sensible short shifting street riders relying on torque and trying to make their motors lope along and last forever would probably get the most out of this sleeve modification. I doubt many road racers would see any huge benefit unless they only raced on racetracks with Winton turn 2's in them. Or only raced in a field filled with overweight out of shape retirees going a lot slower.

You can also get slightly better midrange spending countless hours tuning carburetion, exhaust, and making intake track modifications, as well as using smaller diameter carburetors at the cost of top end. A lot of parts can be touched up to improve flow. The sleeve is certainly cheaper than buying new carburetors and taking all that time to tune though.

Comnoz is a sharp tuner, but I seriously doubt his racebike had 30mm intake ports.
 
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