ESE's works engine tuner

[husaberg]

As you have gone 1/2 way and put in the bore/duct radius you may as well go all the way and epoxy fill the B port front wall
as Jan did as a successful test on the Aprilia.

I notice Yamaha regressed in that detail. Compared to the earlier reverse cylinder
https://www.kiwibiker.co.nz/forums/a...8&d=1481884812

[41juergen]

But you want the flow in the desired direction, that would be (a least a little) influenced by the grinding....
One other point came back into my mind: Wob I think you mentioned some when before that the aux ex ports shall be some °CA lower as the main ex port, otherwise one would loose some significant power in the lower power band. Is that valid also for aux ex ports which are connected to the PV (as the Yamaha drum type is)? If not I can get some more blow down there...

Wob, do you have any comment / recommendation on the height of the aux ex ports?

[philou]

Even if it's not needed to guide the rings back into place, isn't there still some benefit to airflow? I had always thought sharp edges were the enemy of good aerodynamics.

Jean or Frits indicates that the chamfered intake ports were harmful. It helps the exhaust gases to come in when the intake ports open.

[Frits Overmars]

Jean or Frits indicates that the chamfered intake ports were harmful. It helps the exhaust gases to come in when the intake ports open.

Philou, we must be careful with our terminology here. I was talking about the transfer ports: the ports that transfer the mixture from the crankcase to the cylinder.
For me, intake ports are the ports that allow the mixture to enter the crankcase.

[philou]

Yes Frits, you're right. I'm sorry.

My English is not yet very good :cri:

I want to participate in the discussions.

Not only take information

[SwePatrick]

Is there someone that have successfully converted an Keihin FCR carburetor for use on Twostroke?
I´ve got an FCR 41 tapered bored from 43.4 and upstreams to 46mm then a short nice velocitystack.

If so, what were your mods?

I plan to use this with methanol.
And one idea i have is to modify the throttle.
As is, it has a big cavity from underside and up inside instead of viceversa as normal on twostrokes.
This will lead to modify the 'venturi' to look as an normal twostroke carb like PWK/PWM.
And ofcoarse delete the pumper.

Rgds
Patrick

[Frits Overmars]

Yes Frits, you're right. I'm sorry. My English is not yet very good. I want to participate in the discussions. Not only take information

You are very welcome Philou. And don't worry about languages; I suppose that your English is a lot better than my French .

Is there someone that have successfully converted an Keihin FCR carburetor for use on Twostroke?

Yep, 25 years ago, so I don't remember many details Patrick.

[jfn2]

Has anyone tried this setup from Yoshimura yet? They are using TMR, FCR's,TM's and YD's for their setup.
http://www.bikebros.co.jp/vb/sports/...carburetor-en/
MJN stands for 'Multiple Jet Nozzle'
Also check out their Dual Stack Air Funnel setup.
Comments?

[peewee]

You gotta love those paddle tires! Sounds pretty good.

i dont normally ride in dirt with that tire , i just wanted to see if the engine would run so i went just barely out of city limits. it did get good traction as the front tire lifted up rather quickly

[Grumph]

Is there someone that have successfully converted an Keihin FCR carburetor for use on Twostroke?
I´ve got an FCR 41 tapered bored from 43.4 and upstreams to 46mm then a short nice velocitystack.

If so, what were your mods?

I plan to use this with methanol.
And one idea i have is to modify the throttle.
As is, it has a big cavity from underside and up inside instead of viceversa as normal on twostrokes.
This will lead to modify the 'venturi' to look as an normal twostroke carb like PWK/PWM.
And ofcoarse delete the pumper.

Rgds
Patrick

My experience with FCR's on methanol is on fourstrokes but I hope some of it will help.
Float needles and seats - standard petrol sizes will work - but only with a pump supply. I used around 1.2lb pressure with good results. If you're gravity feeding, you'll need bigger float needle and seat assemblies.
Pilot/slow run jets - with a bore size that big, petrol slow runs would be around .50mm bore. Meth, I'd start around .65mm bore.
Needle and needle jet - You can get Methanol needles i believe but a rich petrol needle will do. Needle jet should go to around 3.2- 3.5mm bore.

I wouldn't modify the slide. try it as it comes first. The pump is adjustable, if you do have response problems, it's worth trying a small pump shot.
Remember that you can happily run Methanol up to 20% rich and never notice...This fills in a lot of holes in the jetting, LOL.
Wob's already said quite a bit about EGT's for Meth, he knows that side better than me.

[oldjohnno]

Has anyone tried this setup from Yoshimura yet? They are using TMR, FCR's,TM's and YD's for their setup.
http://www.bikebros.co.jp/vb/sports/...carburetor-en/
MJN stands for 'Multiple Jet Nozzle'
Also check out their Dual Stack Air Funnel setup.
Comments?

I can't help but think all this has as much to do with marketing as it does with engineering. The late great Harry A Miller was producing progressive multi-hole-discharge carbs in the 1920s. And there were no 4 into 1 exhausts before Yoshi "invented" them in the 70's?

[wobbly]

Re the height of the Aux ports.This is a simple case of swings and roundabouts - the higher you go the better the peak power ( more STA at opening )
but this comes at the expense of power at the low end, and in the overev ie it creates a narrower band of peakyer power.
So,to get the best of both, once the width has been maximized,and that seems to be limited to around to bore center,then the height is dictated by the power needed and
the width of the powerband.
This is helped of course in the bottom by a PV, but the Aprilia had around 2mm of height difference on a 54.5 stroke,and thus was biased somewhat toward band width,allowing
good overev capability.
KZ2 engines have no PV and need plenty of bottom and overev,but the width is nowhere near bore center ( no piston plugs ) but have around 1.5mm stagger, so i believe there is
alot to be gained in tests with plugs and much wider/lower Aux.

FCR carbs were designed for 4T, and the biggest issue on a 2T is that the slide is set at a 1.5,whereas a normal 2T Keihin would be a 5.
This gives very rich transition response,and cant be tuned out - but on Meth this may not matter.
For simple gravity feed you need at least a 4.2 float jet,and I believe that Meth needles are available, but the tube is fixed,so will have to be drilled or be part of an alky kit
to get sufficient flow at 1/4 to WOT with a thin point on the needle tip.

[peewee]

patrick have you checked ebay for used kiehin, mikuni or lectron ? these may be easier options

juergon i left my aux about 3* lower than the main. seems like standard 250cc cylinders such as ktm were about 8* lower if i remember correct

[SwePatrick]

My experience with FCR's on methanol is on fourstrokes but I hope some of it will help.
Float needles and seats - standard petrol sizes will work - but only with a pump supply. I used around 1.2lb pressure with good results. If you're gravity feeding, you'll need bigger float needle and seat assemblies.
Pilot/slow run jets - with a bore size that big, petrol slow runs would be around .50mm bore. Meth, I'd start around .65mm bore.
Needle and needle jet - You can get Methanol needles i believe but a rich petrol needle will do. Needle jet should go to around 3.2- 3.5mm bore.

I wouldn't modify the slide. try it as it comes first. The pump is adjustable, if you do have response problems, it's worth trying a small pump shot.
Remember that you can happily run Methanol up to 20% rich and never notice...This fills in a lot of holes in the jetting, LOL.
Wob's already said quite a bit about EGT's for Meth, he knows that side better than me.

Thanks, Yes i´ll wait with modifying throttle then.
And yes, the rich situation is one of the parameters why i want to go methanol.
'Less adjusting at the tracks as it still produces power slightly rich'

As is, the engine it will sit on is 211.6cc and produces at this point quite well already on Avgas100ll.
I have to redesign the pipe a bit i guess thou, the powerpeak is very high(73.29hp, corrected), but very short.(i got a quite hard angle on the end converging cone)
Peakpower is at ~12400rpm and roughly 500rpm wide
The powerband is average ~40hp as is(9000-13000rpm), quite sad actually.
Made an powerjet the other day to try to widen the curve a bit, i need a carb that is a bit leaner just before and after the torquepeak, i figure the powerjet will do just that(not fully tested in dyno yet)
But on Methanol this would play a minor part i guess
At this point(on avgas100ll) i run an bored out(41mm) Keihin PWM.
It screams for a bigger carb also as just boring the carb 0.5mm gave me 3hp

And Frits, Try to remember

[Nath88]

Hi All,
Thought I’d drop by to share the findings of my YZ250 EFI project. It has a 2009 CRF450R 50mm throttle body, 3D printed polyurethane throttle boot to a Boyesen RAD valve. Fuel system is returnless with a Walbro GSL-414 pump controlled by a Madhu PWM pump controller/pressure sensor. Fuel filter is a Sytec mini bullet. Injector is the CRF450R 12 hole injector (440cc/min @ 4 bar). It’s controlled with a Microsquirt V3 running MSextra code, triggered by a 20-1 tooth wheel welded to the ignition rotor and a crank sensor from a YFM350.

It’s tuned in Alpha-N strategy (TPS vs. RPM table), with barometric pressure sensor and intake air temp sensor for compensation. It uses a Wideband O2 and logs either EGT or Fuel pressure.
First start was about a month ago, have put 3 tanks of fuel through it so far. Most of the tuning has been automatic based on AFR targets, except idle, light throttle and overrun where it needs to be tuned manually. 50mm throttle feels just as linear as the 38mm carb. I haven’t used any accel pump fuelling yet, so I’m hoping that will sharpen the throttle up a bit more.

Throttle transition at high rpm has been the main tuning issue. When closing and reopening the throttle, the motor would flood and not refire until the revs dropped, so I figured the airflow must drop off at some throttle value. I tried tuning a ledge into the fuel map, it was better than before but still hit and miss, fast roll on was ok, slow roll on or steady part throttle would still flood.
Then I figured that the airflow wasn't just related to the throttle, but when the engine is firing, the airflow is significantly higher than when it isn’t firing, due to the exhaust vacuum after blowdown pulling charge through the engine.
Therefore the fuel required for a cycle can be predicted by whether or not the engine fired on the previous cycle, in addition to engine speed and throttle position.
So my solution is to check whether the cylinder has fired, then adjust the fuel table for the next cycle. The throttle body MAP sensor is connected to the exhaust port and samples the pressure during blowdown. I’ve set up a 2nd fuel table in the ECU with a multiplier for when the pressure is above a threshold, corresponding to the cylinder firing. When the exhaust pressure is high, the main fuel table is unchanged, when low, it is reduced by 50% (will need to be dialled in for various RPM, but seems to work so far). The main fuel table is tuned with the wideband when the motor is firing, then extrapolated into the non-firing low throttle/overrun area. On closing the throttle, once the motor stops firing, fuel flow drops to match the airflow, so the motor doesn’t flood. On opening the throttle, the mixture is correct to initiate firing, then after the first fire fuel flow goes back to the main table value.

I think with some tuning I should be able to get the transition pretty much seamless. At the moment I'm working on getting the fuel table just right around the transition area, then I'll work on the switch threshold and multiplier values. That said, it's pretty decent already, but I'm a perfectionist.

Nathan

https://www.youtube.com/watch?v=4Zsz26QmfAU