Had a thought that the issue might be carb orientation, when its tipped over the float level may be changing due to the lever arm
facing across the bike instead of front to rear as its designed to.
The Dellortos usually have the floats on rods.
But I did use a pair of TMX carbs on a Rotax twin in a kart that did exactly the same thing, even with the float rods.
It would not blip to change gears, and would die after the overun into corners.
I set it up to idle,and played with the air screw, eventually found that the idle jet and slide were a big mismatch.
The idle jet was way big and the slide was way lean, so the rich idle was masked by horrible lean on the transition onto the needle4 circuit..
Changed them a couple of sizes each way, and for the first time I could snap the throttle off idle, and it would spin up faster than my hand and hit the limiter.
Suddenly it would blip on the down change correctly, and spun up the tyres off slow corners.
So my guess is to ditch the emulsion tube holes and get the snap response correct off idle.
Re Frits comment about reinventing the Lectron - its been done already..
I have been working with APT in USA and that is exactly what they have done, developing small carbs for generators etc to meet CARB regulations.
The first Billet big set was used at Pikes Peak on a 500 version of my 400, same pipes and ports etc, was easily the fastest,with perfect jetting over a 4000 ft elevation rise.
I have the first pair of die cast 40mm on the way now to test on the next F3 bike.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Had a thought that the issue might be carb orientation, when its tipped over the float level may be changing due to the lever arm facing across the bike instead of front to rear as its designed to.
It happens on the dyno to, same symptoms but depends on how far it is revved out.
Originally Posted by wobbly
It would not blip to change gears, and would die after the overun into corners. I set it up to idle,and played with the air screw, eventually found that the idle jet and slide were a big mismatch.
The idle jet was way big and the slide was way lean, so the rich idle was masked by horrible lean on the transition onto the needle4 circuit..
Changed them a couple of sizes each way, and for the first time I could snap the throttle off idle, and it would spin up faster than my hand and hit the limiter.
Suddenly it would blip on the down change correctly, and spun up the tyres off slow corners.
So my guess is to ditch the emulsion tube holes and get the snap response correct off idle.
Yes the pilot jet is big #50, air screw 1/2 turn out, slide a number #3, needle diameter rich.
Also I have shortened the needle jet so it doesn’t protrude into the throttle bore so much and cut the back away like a regular primary jet thinking that would richen up the transition.
The air correction orifice was to small and had to be drilled out, so it could be the orifices in the pilot jet circuit are to small too and masking the pilot jet.
Anyway its handy it does it on the dyno, I will get some spare bits and bobs and have a play.
re Frits comment about reinventing the Lectron - its been done already.. I have been working with APT in USA and that is exactly what they have done, developing small carbs for generators etc to meet CARB regulations. The first Billet big set was used at Pikes Peak on a 500 version of my 400, same pipes and ports etc, was easily the fastest,with perfect jetting over a 4000 ft elevation rise.
I have the first pair of die cast 40mm on the way now to test on the next F3 bike.
OK........ As i said earlier the PWK28 has a removable needle jet and holder.
It also (err maybe i should'nt mention it hasa dedicated foul stroke version.)
If you look at the pics below you will see why i think the OKO carb TZ uses, is based on the PWK 28.
Why, because it is the only 2 stroke std Keihin that seems to have this feature removable needle jet and holder.(Not counting the FCR and CR and PE)
It happens on the dyno to, same symptoms but depends on how far it is revved out.
Yes the pilot jet is big #50, air screw 1/2 turn out, slide a number #3, needle diameter rich.
I reckon Wob's called it on this one...that is a VERY lean slide IMO. Every 2 stroke I've ever tuned has at some point needed the slides machined to reduce the cutaway hence go richer at that point.
With this done the ide jet comes back to something reasonable.
As an aside I remember Dick Hurdeman complaining to me that the idle jets he was using in the BMS Ducai on nitro were so big that raw fuel was running into the motor on braking.
OK........ As i said earlier the PWK28 has a removable needle jet and holder.It also (err maybe i should'nt mention it hasa dedicated foul stroke version.)
If you look at the pics below you will see why i think the OKO carb TZ uses, is based on the PWK 28.
Why, because it is the only 2 stroke std Keihin that seems to have this feature removable needle jet and holder.(Not counting the FCR and CR and PE)
Definatly based on the PWK28 but is it 4 or 2 stroke? is it the 4-stroke version, how do you tell.
Originally Posted by Grumph
I reckon Wob's called it on this one...that is a VERY lean slide IMO. Every 2 stroke I've ever tuned has at some point needed the slides machined to reduce the cutaway hence go richer at that point.
Agreed, also I think I may have cut the protruding part of the needle jet away to much and left to much area exposed to the air stream at idle. I will fit a new one and modify some slides.
Originally Posted by speedpro
I've devconned the bottom of a slide with good results. Reduced the cutaway by probably 50% and it made the transition from off - 1/4 throttle work
Good idea Thanks ........
Will get a chance to look at this when I get back to work next week (been away for a few days). Kel has offered to help and Thomas is putting an electronic det sensor stethoscope thing together so hopefully we can setup the IgniTechs detsensor properly and develop the ignition curve some more and sort this hesitation.
With any luck it will be sorted for Kel to ride at the next meeting.
Definatly based on the PWK28 but is it 4 or 2 stroke? is it the 4-stroke version, how do you tell.
The foul stroke version i posted were for a Scerco trials bike
the Normal Keihin PWK28 sold were for a two stroke (Cr85 and so on)
My thoughts are your OKO is a carb made to work on 2 strokes and four Strokes.
So there is a compromise try getting a needle holder for a PWK28 from a 2 stroke have a go. What can it hurt.(Make sure it flows enough of course)
But didn't the symptoms only first appear when you set the rev limiter up?
The other parts i linked may be an option for Wallace (Marsheng) with is Diesel
Originally Posted by Katman
I reminder distinctly .
Kinky is using a feather. Perverted is using the whole chicken
My thoughts are your OKO is a carb made to work on 2 strokes and four Strokes. So there is a compromise try getting a needle holder for a PWK28 from a 2 stroke have a go.
I have a genuine PWK28 Keihin that I was told was from a 2-Stroke, RM125??? is that possible? and the internal parts look the same as the OKO's.
Originally Posted by husaberg
But didn't the symptoms only first appear when you set the rev limiter up?
No no ... by using the rev limiter we found that if the engine was prevented from being reved right out it didn’t hesitate so much coming back on the throttle but if it was maxed out it was a dog to get going again. We need to fix this as we want the widest rev range possible.
I have a genuine PWK28 Keihin that I was told was from a 2-Stroke, RM125??? is that possible? and the internal parts look the same as the OKO's.
No no ... by using the rev limiter we found that if the engine was prevented from being reved right out it didn’t hesitate so much coming back on the throttle but if it was maxed out it was a dog to get going again. We need to fix this as we want the widest rev range possible.
Def not a 125 but could be a KR1s or cr85 Rm85 etc.
I see:- Tuning data: Jetting specs and tuning results will be posted as the bike is set up.
Baseline will be what the KX85 comes stock with ie. 45/#3 NAPE/140 which should be close. (Keihin jetting is different than Mikuni's) Based on what people run on the KR1(125)/KX100, it will prob be around 42/#2 NAPF/135 but we'll see.
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Originally Posted by wobbly
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