ESE's works engine tuner

[Condyn]

Thank you for taking the time.

[wobbly]

Pleased to help.

[90GTVert]

I've been spending a bunch of time testing and looking over things suggested to me related to tuning issues after swapping to a 34mm PWK.

Pretty sure I found why the 210 main jet acts totally different (richer) than the jets near it. These are Keihin jets, all ordered at the same time. The 210 has a large opening in the end. The orifice through was checked in the past and seems to be on par somewhere between 205 and 215. It's just the entrance that's bigger than every other jet I bought, Keihin or Stage6. Number stamp is on the side vs top like the others. Stamping size doesn't match on any of them.




I made up a little test rig for checking fuel flow through the carb. Drilled a 1/2" hole in the bottom of a bowl and did multiple tests. I checked the 28mm VHST that I used prior to the 34mm PWK and a 28mm PHBH just as another reference point.

Fuel through PWK : 410ml/min, ~2.8mm float needle seat hole
Fuel through VHST : 520ml/min, 3.1-3.2mm float needle seat hole
Fuel through PHBH : 420ml/min, ~1.9mm float needle seat hole

Fuel through 3/16" hoses and filter without a carburetor : 870ml/min


Someone that saw my posts here was kind enough to email me a French language vid showing PWK mods for better fueling (linked below). I drilled out the cap covering it and then drilled the fuel passage headed to the needle area to 4mm. The holes around the float were enlarged to 2.5mm and the vent holes were done with a 3/32" bit. The fuel passage was sealed back off to the outside by tapping to M5x0.8 and installing a set screw with a very small amount of JB Weld on the threads to be sure it seals. The float needle chamber was deburred from drilling and polished with a Q-tip and aluminum polish.

https://youtu.be/EFXFvepG59c?si=VlGWV0ExmHVGAEVd




I also removed the float stop in the bowl. It lets the float open just a tiny bit more.





I rechecked fuel flow and it went up to 560ml/min. That's almost a 37% increase!


F5 Dave asked about stinger size, so I checked the MHR 94cc pipe made for the RC-One and the Stage6 R/T 100 exhaust that I have. The MHR stinger is around 19mm. The S6 pipe is 22mm, but using a 20mm removable reducer. I have used the R/T 100 exhaust on this engine and it will allow more RPM, but 1/8 mile times are slower so I never actually use it.





Here are 20, 30 and 40 hole Polini atomizers. It's odd to me that the 20 and 40 have small holes and the 30 has large holes.




I searched for info about atomizers, but it was contradictory in some cases and left me uncertain overall. I thought about it and assume that holes open to fuel will richen the mixture some and holes open to air will lean it out a little. If that's the case, I wondered how many holes were bathed in fuel.

I marked the carb where holes should be, height-wise. All of the atomizers match up, having 5 holes per column, just different amounts of rows.




After more testing, I think 1 atomizer hole is in fuel. That's with the carb straight up. I would think if fuel drains at all, then the fuel bathed hole becomes another air entry and leans out to some degree. If that's the case, I still don't know if I want 20 small holes or 30 large ones. I didn't notice any obvious difference when I broke the original 30 hole and swapped in a 20. Some like to say no holes on a 2T atomizer, but I don't have a 0 hole atomizer and I don't know that trying to fill with solder would be wise.

The atomizers are different IDs. About 2.71mm for the 20 and 40 hole and 2.76mm for the 30 hole. I don't have a really precise way to measure those, but somewhere in the ballpark and the 30 hole is definitely larger inside.


That brings me to the needle tip and emulsion tube annulus that Wobbly mentioned. I've used JJK and HLJ needles.

20/40 Hole Atomizer with JJL leaves me at about 28% larger by the time I get up to a 220MJ. With the HLJ I'd have to stay around a 210MJ.
30 Hole Atomizer with JJL allows just above 220MJ to stay 30% larger annulus. With the HLJ, about a 215 would fall in the range.

Here's where it is confusing and odd to me. Maybe this is normal, but I had to look up annulus so clearly I've never done this sort of analysis before. The nozzle/needle bushing/needle jet ID is 2.6-2.65mm. They make both of those sizes and I can't tell which, but I believe it's in that range. If the needle is going through there still at WOT, shouldn't that be a restriction? I need to check where the needle is for sure. If it's not in the nozzle, then I suppose the area is just fine and not a restriction so it's a false alarm. If it is in there, then at 2.6mm I'd need to stay 200-205MJ to keep that 30% margin. EDIT : The needle is out of that orifice and only behind the shrouded section at full throttle.


Regarding the pic that looked like a water droplet in the bottom of the bowl; that's just a water spot on the outside.

I've never had it on a dyno. I have had others suggest a wideband, which I have, but I haven't wanted to put a big bung in the exhaust so I haven't done it here at home.

To koenich; this is a Polini PWK. The only other PWK I have tried is my friend's identical PWK. Both of us got them from the same source and everything and they seemed to check out side by side. I actually chose it because he had it and the same engine so I thought it would be a matter of using the tune he came up with as the baseline and a little fine tuning and I'd be ready to roll. Did not expect to be 8 months in (carpal tunnel surgery in that time and waiting on pistons multiple times now) and still tearing up parts.


Thanks again to all that have read and replied.

[Tim Ey]

Regarding the aftermarket PWKs:
I fiddled a lot with the aftermarket stuff.

Stage6 anno 2006 gave my bike seizures.
OKO was fine.
Polini on an Aprilia RS125 did funny stuff in fast lefthand corners - it leaned out badly.

Apart from overflooding due do even the most microscopic debris, I never had an issue with original Keihin carbs.

Today, I would check every hole in the aftermarket carbs before mounting them. You'll never know what hits you.

[wobbly]

First off the main jet issue.
Having totally different entry geometry means that the actual flow rates will bear no relationship to each other.
You will have to make a simple flow rig using a bottle with a hose connected to the jet, and flow a set amount of liquid over a time base to find out what is going on. But having differing venturi setups is a huge spanner in the works.
I have never seen that in any other carb main jets, ever.

Re the emulsion tubes.
Again that is super wierd as I have seen dozens of Keihin 2T - 34/35/38 PWK carbs and none of them even have an emulsion tube.
The transition/ mid jetting is changed by the needle parallel diameter , then the taper.
This is a Keihin design " thing ". As all other carbs have screw in tubes of incremental size variation.
All the other 2T carbs with a variable diameter emulsion tube have no side holes, and the shroud height changes the fuel curve flow rate with rpm/ air flow

The only two stroke carbs I know of that have holes in the emulsion tubes are only a couple of years of Mikuni - RD Yamaha I think.
That system of emulsion tube air correction is for 4 strokes - but having said that I have no previous experience with carbs designed for " scooters ".
But anyway , those holes admit air from a main air corrector jet/drilling that comes in thru the front of the floor of the bellmouth.
The tube is in a " well " with fuel entering at the bottom and air at the top, and the holes change the fuel curve, more/bigger holes = increasing leaness with rpm/air flow.

Then you say the tubes are differing inside diameter and have differing hole configurations.
So in my opinion what you have is a bunch of jet parts that make it impossible to apply any logic whatever to get the carb tuned , as everything has more than one variable changing at a time.
An absolute complete nightmare when not all the parts being changed are from the same " series " of jet type, they should be all exactly the same apart from one variable.

[90GTVert]

Thanks once again guys. It's at least sort of nice to hear than I'm not totally crazy and inept. It drives me nuts that everyone else just throws these things on and goes. One guy uses coolant temp as his only indicator for the engine, which I explained is a terrible idea, and I'm recording RPM, EGT, ET, in a spreadsheet with practically a book now of each change made and it's just eating pistons that now I can't even find. I bought the last AA piston that the manufacturer has and they tried to offer me a BB or D as the others they had around. Awesome. That's why I went ahead and added the detonation gauge to it. I can use whatever info I can get. It sounds like I should just put a 28mm VHST that worked before back, but it kills me not to figure it out and I learn best through experience so I'm going through the wringer for no good reason probably... but at least the experience and you guys and others have taught me a few things. I think that's why all of us do this crap. We wanna be fast, but you gotta like to learn and experiment too.

[F5 Dave]

I'd try running the bigger stinger pipe and see if that brings your temp down as an experiment.

[koenich]

Agreed with Dave. 19 mm stinger (plus added dp of the 180° pipe to the silencer) sounds quite critical for an engine that should easily produce 40 HP on the crank...

[Frits Overmars]

Agreed with Dave. 19 mm stinger (plus added dp of the 180° pipe to the silencer) sounds quite critical for an engine that should easily produce 40 HP on the crank...

It is. 40 crankshaft-HP requires a restrictor diameter (D5 in the drawing below) of at least 19,6 mm Ø.
And that's just the restrictor; the stinger diameter D6 must be clearly larger than that.

[90GTVert]

Agreed with Dave. 19 mm stinger (plus added dp of the 180° pipe to the silencer) sounds quite critical for an engine that should easily produce 40 HP on the crank...

The manufacturer claims 31HP @ 13,800RPM and 14LB-FT @ 13,500RPM. I have seen one person on YouTube dyno one at 33HP, but his dyno also said it was at 10,500RPM. This thing is just waking up at that point so I don't know if something is up with his calibration or what. The same guy did his own scoot with the same Malossi engine and it was 29.75HP again at the odd 10,500RPM. Most say 25-30HP on a dyno from what I've seen.

52mm bore on 44mm stroke (93.4cc), 90mm conrod. 130* transfer, 195.5* exhaust durations. 14.6:1 UCCR. The engine kit comes with a 28mm VHST, but I swapped to a 34mm PWK as some say you can get a little more out of it that way. I have seen some improvement, but not much... of course I don't think it has ever been right either. For anyone unfamiliar, it's a whole kit. You buy an engine, but it's unassembled and the cases don't come anywhere near matching the cylinder base (cases are smaller). Some don't seem to touch it and some (including me) port match it. I'm sure that accounts for some variation.

Mine's not making 40HP. I've had it up to 85MPH. I don't really care about top speed though and I'm sure it could go a little faster. My best 0-60s and 1/8 miles are 6.9 and 9.6X @ 67-68MPH. I'm also not a jockey at 6'2 and 300lb (scoot and I are about 550lb) and the scoot is tall so I can't get into the throttle all the way quickly off the line. My smaller friend with the same setup and the same Polini PWK in a long low scoot does IIRC 5.7 0-60 and 9.1 @ 70-71 in the 1/8 and he can go over 90MPH. I'm not built for scooter racing, but I love the experimenting and trying to get quicker/faster... even if it isn't that fast. It's a street scoot that I actually ride. I've hit a deer on it that busted me up but the scoot came back to life, I've been hit by a hay bale lost from a truck ahead of me and wrecked it and it's still going. Used to ride 50-100 miles almost every night (not with this engine, but 90-110cc Minarelli clone strokers).





I got the piston and put it mostly back together. Just put the Malossi exhaust on last night. I think I'm going to start with it, because I already have multiple other variables from it's last runs and the exhaust changes the CVT tune, the RPM that it works at, and slows it down, and I think that's a lot for the first try. I typically do sets of 4 dragy passes when I test each change, back and forth, that way data stays pretty reliable when averaged. I may start doing 2 runs each time just to lessen risk slightly as I try to figure it out. If EGT still isn't looking good I will swap the pipe out. I'll be backing timing down slightly at power and more at lower RPM. Just trying to avoid detonation that is seen on the piston, but fingers are crossed that the knock sensor will help me see where it happens if it still does.

[Wos]

Bore 52... stroke 44...and engine is realy doing its max at 13500?...i am afraid it isnt..

[wobbly]

Usual story of an oversquare engine.

[wobbly]

I was going to edit the above and say " severely oversquare " that is always going to be limited in STA at high rpm.
But anyway the 3XV TZ250 mufflers are done , I am looking for a supplier here in NZ that used to have a huge bag of Silent Sport muffler packing and would sell any amount.
Anyone know who that was ?

[F5 Dave]

Silent Sport was the loose pack strand stuff. Local shop used to sell big bags. Went back to using Daytona matting as it was measurably quieter on the racebije.

[Flettner]

Wobbly, what pipe restrictor dia would you imagine a 65cc (say a KX65) would have?

Edit, I see Frits has a calculation, D5, but I need to know the HP first. Off to the dyno I guess.