ESE's works engine tuner

[wobbly]

The huge issue with any engine developed on the Yamaha RD case that started life as a 250, is its 102 bore centers.
This kills any thoughts of trying to make good power as the transfer ducts are squashed between the bores in the middle.
The stroke at 54 is easily capable of reving to 14,000 like a KZ, but as is the case with a 350 a bore of 64 makes for heavy pistons.

Thus in answer to your question, the best 350 I have simmed would be the LSR engine at 55Hp/cylinder at 11,000 with overev to easily 12,000.
This used a TZ250G - 3G3 cylinder and had reeds on the back.
That translates to around 100Hp at the rear wheel on a Dynojet.
It needed wasted studs and a bridged intake with a 3 port Exhaust and used a 58 stroke Banshee crank with 115 rods, and lighter 61.5mm H1 Kawasaki pistons.

CPI cylinders dont fit on the RD case due to the stud layout,but the RZ/Banshee has the same bore center width of 102mm.
The porting layout is 8 transfer ports with a bridged intake and 3 port exhaust, and they are easily capable of making the same or better power from a 350.
But you would have to get special castings done with the smaller bore, to get nearer to square, and the resulting much better STA numbers.
CPI will do this but want you to pay for 3 cylinders,to guarantee getting 1 good one - I did this with a 400 and got two usable castings at 66 bore.

[RomeuPT]

Parabéns Jan

Wob, I was searching but could not find, I remember that a lenght from reeds to carb mouth of 135 to 145mm was spoke about for a 125 with decent carb size making peak power at around 13k.

I am setting a pwk 38 for racing, and thinking if I should cut the mouth like it is presented in this pic so I can get that lenght closer or is there other reason for this to be like this?

Are the vents better be completly removed for a high end scenario?



Thanks

[wobbly]

Getting the intake short enough is hard.
Using the very short straight rubber manifold from the very early NF4 RS125 ( NLA ) that was built on MX cases is worth 1-2 Hp over the later longer
version,but the later RS125 short carb with the electronic powerjet is the shortest and best flowing.
If you dont want the powerjet then a PWM is by far the better carb for power everywhere.
Any carb with the guide plates on the floor is useless, even with them removed, I could not equal a PWM.
Also a shortened PWK wont make the power of the PWM or the short late model race carb.
No free lunch - again , sorry.

For the last little bit of power, filling in the slot for the choke, and filling in the slot in the floor of the bellmouth for the idle and main
air corrector circuits is for sure worth it.
But you MUST use small alloy tube inside the epoxy to allow the added tubes to be entering air at plain atmospheric pressure , or you will never get the jetting to work.
Here is one I did for an old Mikuni 38mm round slide on a TZ350.
This added around 3Hp in the twin at peak and double that in the overev at 11500.

[Flettner]

this would be better, no jets, vents or produding things into the gas flow. Just smooth, clean, short inlet, straight in with not even a reed block cage in the way. Long live the rotary valve engine. Injection, the way of the future, past.
I know, same old, but next generation on the way.
https://youtu.be/v5jLX4KtpXs

[TZ350]

.
Yep, rotary valve, inlet as short as, and fuel injection..... its the way ......

[wobbly]

It sure is the way TeeZee, but you and Suter and Cagiva seem to have had a little trouble along the way making the ECU do the right things at the right time
on a racebike.
MX has been done by Flet, and I did it with a Motec in a Champ Jetski , but a full noise racebike application has eluded everyone so far.
Really do hope you can find the key.

[husaberg]

It sure is the way TeeZee, but you and Suter and Cagiva seem to have had a little trouble along the way making the ECU do the right things at the right time
on a racebike.
MX has been done by Flet, and I did it with a Motec in a Champ Jetski , but a full noise racebike application has eluded everyone so far.
Really do hope you can find the key.

I think Honda won the all japan championship with a Fuel injected NSR250 in the early 90's a couple of years prior to Itoh being the first ever 500 GP bike to go over 200MPH.
Not sure where I found that morsel but think it was in Motocourse.
Edit
Oh well maybe not
okay they just raced it

[RomeuPT]

Getting the intake short enough is hard.
Using the very short straight rubber manifold from the very early NF4 RS125 ( NLA ) that was built on MX cases is worth 1-2 Hp over the later longer
version,but the later RS125 short carb with the electronic powerjet is the shortest and best flowing.
If you dont want the powerjet then a PWM is by far the better carb for power everywhere.
Any carb with the guide plates on the floor is useless, even with them removed, I could not equal a PWM.
Also a shortened PWK wont make the power of the PWM or the short late model race carb.
No free lunch - again , sorry.

For the last little bit of power, filling in the slot for the choke, and filling in the slot in the floor of the bellmouth for the idle and main
air corrector circuits is for sure worth it.
But you MUST use small alloy tube inside the epoxy to allow the added tubes to be entering air at plain atmospheric pressure , or you will never get the jetting to work.
Here is one I did for an old Mikuni 38mm round slide on a TZ350.
This added around 3Hp in the twin at peak and double that in the overev at 11500.

Thanks

The issue...


Yep, I wish I could use the PWM but there is no room, for the pwk to be closer has possible I already grinded a bit of the engine case support and the carb is angled enought too. Guess I can get with 135mm with worked pwk, maybe far from the best, but without cuting cases and major rumble is pretty much where I can get on my engine...

[_____]

Thanks

The issue...

.

I'd cut the section where the bowl needs to be, fit helicoils in the airising outer two ears and screw it to the frame with two short screws.

[wobbly]

Will a carb bowl clear the rear mount if it is dead straight on the manifold - with the plus of making a couple of extra Hp for free.
Most carbs would be way too downdraft and would spew fuel out the pilot system under brakes.
But a Lectron can be run very steep with no issues at all.
What is that motor you are working on ?

[husaberg]

Will a carb bowl clear the rear mount if it is dead straight on the manifold - with the plus of making a couple of extra Hp for free.
Most carbs would be way too downdraft and would spew fuel out the pilot system under brakes.
But a Lectron can be run very steep with no issues at all.
What is that motor you are working on ?

Its a NSR125 or 150 Wob
........
He might have to go Mikuni TDMR or a Keihin FCR or a Keihin of a NSR250 or RGV TMSS Mikuni
That rear upper mount is in the way.

[RomeuPT]

Will a carb bowl clear the rear mount if it is dead straight on the manifold - with the plus of making a couple of extra Hp for free.
Most carbs would be way too downdraft and would spew fuel out the pilot system under brakes.
But a Lectron can be run very steep with no issues at all.
What is that motor you are working on ?

I'd cut the section where the bowl needs to be, fit helicoils in the airising outer two ears and screw it to the frame with two short screws.

Its a NSR 125 engine.

yes it has a straight manifold and the front bolts of the carb bowl are already touching the mount.

The carb is not very angled down to be a problem, or at least that I have noticed.

I had a shortened tmx 38 already touching the mount, but the keihin works better at lower ranges, does not bog... I am trying to improve

Dont know what to do, maybe just grind the the mount some mm and work the pwk

Inside the engine mount is where air circulates in/out the engine, I dont think removing it is a good idea :/

[TZ350]

.
The mount looks like it also serves as the breather tower for the gear box.

I wouldn't hesitate to cut a big scoop out of the middle of that mount to clear the carb.

If you break through just glue in some hard foam, 1mm alloy sheet or similar to stop the gear box oil splashing out.

Leave some of original mount on the outsides. You don't have to crush it up tight in the frame for it to still hold the engine up.

Any way do you even need all three engine mounting points, the lower front and rear may be enough.

[wobbly]

That intake rubber is huge - the old NX4 one is only around 25mm overall,so that pulls the whole carb and bowl way closer.
16210-NX4-000 - hard to find though.
A downdraft oval bore Keihin carb off a NS400 would be the go,its been done before.
As would a 36mm downdraft off an Aprilia RS250 road bike.
But the Lectron would work to.

[jonny quest]

https://www.bbc.com/sport/motorsport/44176061
Watch the NW200 highlights around 18 seconds, the green bike blows past the other bikes like they're standing still!

Did the RSA125 act like that? With around 5hp more than the competition, how did it not?