ESE's works engine tuner

[TZ350]

Good One Wob .....

[diesel pig]

I have been using the 36mm keihin with TPS and the wobbly powerjet mod with some success over the last six months on my 100cc bucket. Now the bucket is starting to go well I am going to start working again on a larger capacity Two Stroke project and since I am going to use a igntec on it I would like a 38mm or 39mm keihin with TPS and a solenoid powerjet to go with it. So before I go looking on e-bay is there a particular dirt bike that has a carb like that?

[husaberg]

I have been using the 36mm keihin with TPS and the wobbly powerjet mod with some success over the last six months on my 100cc bucket. Now the bucket is starting to go well I am going to start working again on a larger capacity Two Stroke project and since I am going to use a igntec on it I would like a 38mm or 39mm keihin with TPS and a solenoid powerjet to go with it. So before I go looking on e-bay is there a particular dirt bike that has a carb like that?

97-98 Honda cr250 has a tps PJ carb. from memory the Kawa KX250 (Added later from 99 actually)
yams and ktm from around the same era has the flatslide tps PJ but why so big?

For best results do a picture search or have a look at the Parts Fiche.
From memory later hondas went to Mikuni TMX with no pj and later Kawas ditched the Powerjet.

I think the Kawa carb (99-2000ish )and some of the KTM were shorties. (as you have noticed the 36mm is rather smaller than most others i guess)
But won't the KX125 36 bore to 38 anyway?

Maybe what you may want is the late Honda RS125 Carb Wob will ad what its called i can't remember had an S though?

After a bit of Net research it seems (if you can trust the net) that the KTM may be able to stand a higher level of down draft std and has a different bowl pick up but unconfirmed only

[dinamik2t]

YZ250 's -past '99- are Keihin PWK 38 with TPS/PJ. Also RM250's, but I don't know which years.
The same carb is also on KX125 I think. -edit: on 98~00 models, in 36mm diameter
All are short PWM bodies, some with Shindengen solenoids, others with Keihin solenoids. Some PJs have a cutout at the end of the tube, some have a hole at the rear, near the end of the tube.

The PJs can be removed, as Wob said in the past, with a 3 or 4 mm drill, pushing from the side towards the bore. It's just press fit.
Even if you damage the brass tube you can cut and insert a new one. If I remember correctly, the tube has an OD of 3mm and and ID of 1.8mm.

[RMS eng]

Plus the atleast 10kg of stuff/fluids you still need to add. Looks good though. I was hopeing to be the first to do a 4 stroke NX4 bike.


That is about what I think the finished weight will be.
If our (latest) project actually happens (see Chris Pickett) we are hopeing for around 78kg as the CBR motor is a few kgs lighter than the FXR.

CBR150 motor in the NX4 frame will take a bit of work to keep it under 80KG ,but i think we can get it done with alot of light parts,but if you can get a FXR150 motor in a NX4 frame down to 70 KG,that is well done,but that means if i put my RG50 motor in the NX4 RS125 frame to get some track time and try to beat Dave T ,it would be around 56KG.RG 50 14KG FXR150 28KG =14kg ,70 -14=56 kg

[quallman1234]

Darkside project

Attachment 279362

Its pretty funny, how obvious where these frames came from... With the painted wheels etc
Cool project.

[F5 Dave]

CBR150 motor in the NX4 frame will take a bit of work to keep it under 80KG ,but i think we can get it done with alot of light parts,but if you can get a FXR150 motor in a NX4 frame down to 70 KG,that is well done,but that means if i put my RG50 motor in the NX4 RS125 frame to get some track time and try to beat Dave T ,it would be around 56KG.RG 50 14KG FXR150 28KG =14kg ,70 -14=56 kg

My 50 actuallly got slightly heavier when I put it in the RS (was 59.5 in the RG50 or what was left of it).

All a bit spoiled as I'm almost 80kg now. I could get back to 75 if I avoided the beer wine & weekend pies, but feck it.

[TZ350]

Model aero engine carburetor, about 9mm bore.



I have been having trouble with detonation in over rev and I hope to cure it by bleeding some of the pipe pressure off when the engine is running in the detonation zone.

Sometimes stingers/mufflers have been attached here at the fattest point on the pipe because the pressure wave is at its lowest amplitude and quietest so I guess I can bleed pressure of from here without upsetting things and being to noisy.

Might get a chance to try it out in a day or two.

[wobbly]

I simply dont get it TZee.
A million 2 strokes have run at seriously high Hp levels without silly bleed systems needed to stop deto at high rpm.
The basics are combustion control and ignition advance.
With a properly designed toroid, or bathtub chamber, then deto is kept in control as good as it can be.
If that dosnt have the desired effect then pulling out advance is the next step - with the aside of needing at the minimum a 10.5 plug due to the high inherent temps being used, at 30 Hp levels.
But again, pull out advance and the EGT will rise, thus needing richer jets to keep the temps in the ball park.
This all assumes you have the correct com for the fuel quality - just another variable.
Get it all right and the effects are synergistic, lots of HP,get one wrong and it will all turn to sheeeite.
Helpful eh.

[TZ350]

We did ignition timing, air correction and main jet size to death on the dyno and at Taumaranui without success.

2 strokes have run at seriously high Hp levels without silly bleed systems needed to stop deto at high rpm.

Frits proposed this bleed system, thought I should at least give something like it a try.......

Its not something I dreampt up without thinking about it, and this is what influenced my thinking.

Kel sent me this ......

jan thiel on part throttle deto

"I am 100% convinced our engine could have run for 6 hours at max power without seizing.
The problems arise when you close the throttle, or run part throttle!
The piston is mainly cooled by the transfer flow.
And at part throttle there is less transfer flow, causing detonation (auto ignition)
The entering fresh charge is ignited by the remaining, hot, burned gases!
You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? I did not find a solution before I retired.
And nobody else was really interested.
At 100% throttle the engine was undestructible!
By making the transfer ports as wide as possible we had very good piston cooling."

No answer here but at least we are not alone with engines that fail on part throttle

I scraped the full coversation below from here:- http://www.pit-lane.biz/t3173p60-gp1...vermars-part-2

Brian Callahan
Jan or others, how did you control the tuned pipe wall temperature (or EGT directly?) when testing on dyno? This seemed the most difficult thing to mimic when testing either the GP engines at QUB or my R/C boat engines, in the lab. The inertial dyno or computer controlled brake seem to work best because we can match the test engine's acceleration with reality. On steady-state testing, EGT would simply climb 500, 600, 700, 750 °C until way past reality and the piston would seize.

Frits Overmars
This has always been one of Jan's greatest handicaps. He has asked for an inertial test bench over and over, but Aprilias race director Witteveen, or The Great Leader as we call him, never deemed it necessary....

Jan Thiel
When EGT goes up and up there should be some serious problem with the engine.
We never had pistons seize during our steady state tests.
Working on the dyno continuously 5 days a week!
I am 100% convinced our engine could have run for 6 hours at max power without seizing.
The problems arise when you close the throttle, or run part throttle!
The piston is mainly cooled by the transfer flow.
And at part throttle there is less transfer flow, causing detonation (auto ignition)
The entering fresh charge is ignited by the remaining, hot, burned gases!
You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? I did not find a solution before I retired.
And nobody else was really interested.
At 100% throttle the engine was undestructible!
By making the transfer ports as wide as possible we had very good piston cooling.

As Frits has written, I would have liked to have also a dynamic testing possibility, with a flywheel.
In my opinion you should simulate a straight, starting at around 10.000 rpm, and shift through the gears
until you reach top speed. And with the airbox as used on the bike, with a ventilator that simulates the raising
air speed as it would be on track! Maybe it is interesting to know that without a ventilator the engine gave
less power with the airbox fitted.

I was told that such a testing system was too expensive.
And unnecessary as we won anyway!

I can also see a disadvantage of 'dynamic' testing.
Because the duration of the test is so short you can get away with very extreme (too extreme?) settings,
without damage.

GrahamB
Remember that retarding the ignition is used at high rpm to increase exhaust temps and effectively shorten the pipe. So it's likely to increase the heating of the front edge of the piston...

Haufen
Yes I know, but part load egt is usually lower than full load egt. And I think most of us would prefer higher part load egt over part load detonation. Of course, how far one could go and how far one would need to go would have to be tested, and how much would be needed would depend on the engine.

Mic
How about much larger travel on the exhaust power valve.
With a shorter exhaust port duration power is lower. And this is already controlled with the stepmotor over the ECU.

Jan Thiel
This causes detonation (auto ignition)
The problem is that the burned gases do not exit the cilinder!
Retarding ignition also does not make sense.
As you have an AUTO-inition problem!
So the engine does not 'listen' to its ECU anymore!
What you would need is the same fresh gas flow, but with less HP!
Not easy to achieve!
A variable tailpipe might help.

Jan Thiel
Haufen, We also had such a test bench at Aprlia.
The prototype of this test bench was developed by Apicom in collaboration wit Aprilia.
So we had it first, and now anyone can buy it.
It was helpful but not what I wanted.
A so-called step test.
And without the airbox!

Frits Overmars
Like Jan wrote, a shorter exhaust duration will worsen the detonation. What happens is this:
During normal operation, the blowdown time.area of the exhaust ports is sufficient to drop the cylinder pressure below the crankcase pressure before the transfer ports open, even at high rpm.
At part-throttle that cylinder pressure will drop to the same level, but now the crankcase pressure is much lower and exhaust gases will enter the transfer ducts, contaminating and heating the fresh mixture even before it enters the cylinder.
A theoretical solution would be a power valve that enlarges the normal exhaust timing instead of lowering it. But that is impractical as it would ruin the shape of the exhaust duct and it would cause cooling problems in the cylinder's exhaust area.
A variable tailpipe area, like Jan says, can be a more practical approach. I designed a simple solution, shown in the drawing below, but then two-stroke development at Aprilia was terminated because of Dorna's ban on two-strokes

Howard Gifford
Another way to lower HP without sacrificing piston cooling would be to richen the mixture when you want to lower the power. With a signal to a fuel enrichening solenoid you could achieve a power range. It would then be instantaneous and programmable. Not enviornmentally friendly but would work for racing. The mixture ratio difference from high power to low power would need to be just rich enough before a misfire and just lean enough for sustained high power.

The variable tailpipe idea will work but I suspect the pipe temperature would drop off and it would take several seconds to regain full power. But then again rich mixture may have the same problem.
Two strokes are like redheads. Hard to figure out and very temperamental. But when they are happy they are a lot of fun!
HG

Jan Thiel a écrit:
The entering fresh charge is ignited by the remaining, hot, burned gases!
You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? I did not find a solution before I retired.
And nobody else was really interested.

Institute of TwoStrokes
On aftermarket ignitions I use there is a mode I can switch on where a number of indivdual sparks are cut, depending on throttle position. It is now only configured for cutting 1 in every 3 sparks on over run(tps <10% with high rpm). Would that sort of system solve the part throttle detonation? If the number of sparks cut could be varied along with TPS for this to begin and end? If it would be helpful I'm certain the manufacturer would only need a software change to do this.

Jan Thiel
I certainly thought about cutting sparks.
But remember: the problem was AUTO-ignition!

GrahamB a écrit:
Remember that retarding the ignition is used at high rpm to increase exhaust temps and effectively shorten the pipe. So it's likely to increase the heating of the front edge of the piston...

Jan Thiel
Indeed, retarding too much caused detonation!

Institute of TwoStrokes a écrit:
Jan Thiel a écrit: The entering fresh charge is ignited by the remaining, hot, burned gases! You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? On aftermarket ignitions I use there is a mode I can switch on where a number of individual sparks are cut, depending on throttle position. Would that sort of system solve the part throttle detonation?

Frits Overmars
As Jan pointed out, once you have auto-ignition, the engine does not listen to its ECU any more. So you would have to start skipping sparks well before the onset of detonation.
In a foul-stroke your proposed system does work, but a two-stroke would react far from linear. For example, if you skip 1 in 4 sparks, you will loose much more than 25% of engine power because that one missing spark will cause the gasdynamics processes to collapse. The main problem would be to realise a smooth transition from intermittent to full ignition.


Jan Thiel a écrit:
Retarding ignition also does not make sense.
As you have an AUTO-inition problem!
So the engine does not 'listen' to its ECU anymore!
What you would need is the same fresh gas flow, but with less HP!
Not easy to achieve!
A variable tailpipe might help.

Haufen
I think I expressed myself unclearly. What I meant was the following:
Imagine your engine with the throttle opened just above the auto-ignition range. Then you have sufficient transfer flow, but too much power. To lower the power, now retard the ignition. Then you still have sufficient transfer flow, but with less power.

I think Honda used auto-ignition to their advantage on two-strokes. As far as I remember they did it with a (very) variable exhaust power valve.

Frits Overmars a écrit:

Mic a écrit:
How about much larger travel on the exhaust power valve. With a shorter exhaust port duration power is lower. And this is already controlled with the stepmotor over the ECU.

Frits Overmars a écrit:
Like Jan wrote, a shorter exhaust duration will worsen the detonation. What happens is this:
During normal operation, the blowdown time.area of the exhaust ports is sufficient to drop the cylinder pressure below the crankcase pressure before the transfer ports open, even at high rpm.
At part-throttle that cylinder pressure will drop to the same level, but now the crankcase pressure is much lower and exhaust gases will enter the transfer ducts, contaminating and heating the fresh mixture even before it enters the cylinder.
A theoretical solution would be a power valve that enlarges the normal exhaust timing instead of lowering it. But that is impractical as it would ruin the shape of the exhaust duct and it would cause cooling problems in the cylinder's exhaust area.
A variable tailpipe area, like Jan says, can be a more practical approach. I designed a simple solution, shown in the drawing below.

Attachment 269228

Haufen
I think I have not gotten behind the variable tailpipe idea, yet. What would you like to vary with it and to achieve which effects? At little throttle openings the pressure inside the exhaust pipe is already very close to atmospheric pressure (if not even) on most engines. And if you had say 100mbar inside the pipe at the critical throttle opening, then the engine might have had more power with a bigger tailpipe.

Attachment 269228

Frits Overmars
'Opening' the end of the reflector will cause a substantial weakening of the reflected pulse and thus less charging of the cylinder. Izze simple, no?

Haufen a écrit:
Variable transfer timing would be nice also, if feasible.

Frits Overmars
That would be my ideal. Lowering all the transfer roofs would shorten the transfer timing and lengthen the blowdown timing, so the cylinder pressure would drop further before the transfers would open. It would cure the hig revs/low power-detonation and it would improve the power band because a too early-returning exhaust pulse would have less opportunity to push the fresh cylinder contents back into the crankcase.
A controllable transfer height would even make a throttle valve unnecessary.
There's only the little problem of how to build it...

Jan Thiel
Haufen, Auto-ignition usually occurs between 10 to 40% throttle at high revs.
In fast, non full throttle corners.

Retarding the ignition was tried to diminish power.
This makes the exhaust very hot.
Then, when you need full power, it is not there because the exhaust temperatures are wrong.
This takes a little time, when the engine is back to full power you are already at the end of the straight!
The same goes for water injection in the exhaust.
It was tried by Rotax about 25 years ago.
There was a LOT more power at low revs, so the rider had to take it easy when opening the throttle.
But the engine revved a little bit less, because the exhaust temperature did not recover at high revs.
And lap times became actually slower.
After a day of testing the system was switched off.
Lap times immediately improved!

A very important thing when accelerating is the power you have after changing gear.
Spark interruption may be not so good for this!
As I did not have the dyno I wanted this gearchange effect could not be tried on the dyno, very regrettably!
Retarding the ignition and weakening the mixture by powerjet can also have a negative effect on this.
The exhaust temperature should be 'Right' for the No. of revs after you change gear.
If the temperature is too high there will be less power!
So it is REALLY complicated!

[Neal]

It would be interesting if you pinpoint the cause of the detonation and it points to part throttle at high revs . When i raced small bikes on kart tracks the style was either full throttle to your brake marker , shut off , change gears , lean for the corner and bang on the throttle again . No 1/4 - 1/2 throttle anywhere on the track . The corners are so quick that if you blink you are exiting the corner already .
Kinda like riding a skateboard in the bath .

I am sure you will find the cause of the det , rather sooner than later !

[kel]

It would be interesting if you pinpoint the cause of the detonation and it points to part throttle at high revs . When i raced small bikes on kart tracks the style was either full throttle to your brake marker , shut off , change gears , lean for the corner and bang on the throttle again . No 1/4 - 1/2 throttle anywhere on the track . The corners are so quick that if you blink you are exiting the corner already .
Kinda like riding a skateboard in the bath .

I am sure you will find the cause of the det , rather sooner than later !

We have found the cause of detonation and its part throttle at high revs! The pistons destroyed from me holding the throttle part open more than proved this (yes we had tried jetting, timing, and everything in between)
If you ride from full throttle to no throttle and nothing in between then you're simply not going as fast as you could/should be.

[bucketracer]

Its not that clear from what TeeZee posted, but this is a rpm related deto problem that happens at full throttle and well past peak power, ie well into the over rev zone where the power is dropping off. From memory, when he shuts the throttle its worse briefly until the rev's drop, maybe as little as 500 - 750 rpm. It happens on the dyno and at the track, bigger jets and fiddling with the TPS 3D ignition map did not cure it.

[Frits Overmars]

Its not that clear from what TeeZee posted, but this is a rpm related deto problem that happens at full throttle and well past peak power, ie well into the over rev zone where the power is dropping off. From memory, when he shuts the throttle its worse briefly until the rev's drop, maybe as little as 500 - 750 rpm. It happens on the dyno and at the track, bigger jets and fiddling with the TPS 3D ignition map did not cure it.

Makes sense to me. 'past peak power, well into the over rev zone' it's not only the power that is dropping off; so is the blowdown time.area. That may result in a cylinder pressure above the scavenging pressure when the transfers open.
Nice affirmative detail: 'when he shuts the throttle its worse briefly until the revs drop'. That makes sense too: closing the throttle will lower the scavenging pressure, aggravating the problem of spent gases entering the transfer ducts, polluting and heating the fresh charge.
A simple cure might be to radius the timing edges of the auxiliary exhaust ports.

[TZ350]

I think we have the concept of the TPS and 3D ignition map nailed.

This over rev deto thing is another problem. Next time on the dyno I will try to get a video of the det sensor lights and dyno screen together so we can clearly see whats going on and if lowering the pipes internal pressure at high rpm helps.

Thanks Frits and Wob for your help, you have given me a bunch of ideas to work on.