ESE's works engine tuner

[90GTVert]

Hope it's OK for a FNG to ask a question here.

I was told that I should rough up both the air filter and engine sides of a PWK carburetor for better performance on my 2T. I've searched, but haven't found much. Most just seem to polish the filter side. I've always thought that pre-fuel areas would be best polished. Once fuel is introduced, then some texture. Maybe this doesn't apply to carburetors? The person that told me claims to be the builder of some fast bikes, but it's the internet so I wanted to see what the real pros have to say about it and I never got any clarification from this person as to why they think I would want a rougher finish on the filter side.

[F5 Dave]

Get an old carb and make a real mess of it with a bastard file, take a picture and post it on same forum, say thanks, gained you 2hp.

Then carve some power grooves in an old head claim another 2.

If that hasn't aroused derision , try one of those propeller tailpipe fittings from the 80s, claim 7hp. And better gas mileage, obviously.

[wobbly]

Gotta have some golf ball dimples somewhere as well, then add some " turbo" slots in the crank flywheels.
But obviously adding boundary layer turbulence on the dry intake side dramatically increases airflow , once its been proven send the results to AirBus so they can rough up the intakes of their jet engines.
Come to think about it , Boeing are in trouble as well , maybe this is the silver bullet for intake efficiency and decreasing fuel consumption in commercial jet liners.
Sorry , not very helpful but I can think of plenty more suggestions - this is the Interweb as you said.

[_____]

Gotta have some golf ball dimples somewhere as well, then add some " turbo" slots in the crank flywheels.
But obviously adding boundary layer turbulence on the dry intake side dramatically increases airflow , once its been proven send the results to AirBus so they can rough up the intakes of their jet engines.
Come to think about it , Boeing are in trouble as well , maybe this is the silver bullet for intake efficiency and decreasing fuel consumption in commercial jet liners.

Made my day!

Sorry , not very helpful but I can think of plenty more suggestions - this is the Interweb as you said.

Slide50 additive, Nology wires & anything that is CNC milled and blue anodized?

BR Chris

[Pursang]

Save all that trouble, just buy a heavier power band.....the Red ones are usually the fastest!

[Frits Overmars]

I was starting to get seriously worried that no one here bothered to stress the importance of the powerband. Fortunately, Pursang saved the day.

[90GTVert]

OK, got it. Thanks.

I've got an engine that refuses to stop killing pistons with even large amounts of fuel and some of the things the person said made a lot of sense so I was exploring the idea just in case I was missing something. It runs well, but by the end of 1/8 mile passes EGT is high and I have to basically drown it in fuel to finally cool it, but by then it's down on power. Piston shows detonation. Seems to be carb related, because it ran just fine with a 28mm VHST and now it's putting pistons on the wall of shame with a 34mm PWK. Simple answer is to go back to the VHST, but I've been trying to figure out why it's happening. Put a programmable ignition on it and put a 16* flat "curve" in it (what the manufacturer of the cylinder suggests at peak power) and it still did it, as it did with more traditional curves. I found that it was actually delivering less fuel with larger jets at one point, even though the bowl didn't appear to be draining (clear bowl & GoPro observation) so I used a larger bowl and made a main jet extender to put the jet near the bottom and then it was showing richer and richer on plug reads as it should, but still failed with high EGTs at the end of runs. It's to manufacturer spec on squish with no modifications to change compression or porting, aside from port matching at the base to the supplied gaskets. I have rode with 2 other people with the same engine (Malossi RC-One 94cc) with 34mm PWKs and neither had trouble with them. One is the exact same carb and I took his tune and it was 1400 EGT within 1/8 mile and even tried his entire carb and filter to make sure I didn't have a bad carb with no luck. I've ran a scope in the pipe (the pipe made for this engine) to make sure the stinger didn't have anything restricting it in case that was causing more heat. At this point it's quicker with the PWK, but even when I can match past best results for EGT observed at 60MPH during acceleration, it will heat up more than it should by the time I let off around 70MPH.

I just finished installing a detonation gauge (the one Wobbly has suggested to others in this thread). I've swapped atomizers, but some things I've read say they can cause fueling issues at sustained WOT if they aren't right. I'm going to dial timing back more at peak and probably go ruin more stuff once the new piston arrives.

Anyway, I wasn't trying to introduce stupid ideas and be a clown. I'm just grasping at straws because this has been going on for way too long now and every time I think I may have finally got it... it murders another piston. Thanks again for even bothering to read my posts.

[136kg136ps]

Okay, so seriously. Go to page 1 of this thread and also register at PitLane which is French forum and find the Aprilia threads.
Pay particular attention to Wob, Frits, Jan and Vannik but also to see all the mods which have worked or failed and WHY they faile or worked.


There is more two stroke wisdom in their posts than the entire rest of the internet combined. You can eliminate a lot of early trial and error by learning from the honest mistakes some the home mechanics here have made and how they remedied them using advice freely given.

[Frits Overmars]

Okay, so seriously. Go to page 1 of this thread and also register at PitLane which is French forum and find the Aprilia threads.
Pay particular attention to Wob, Frits, Jan and Vannik but also to see all the mods which have worked or failed and WHY they faile or worked.
There is more two stroke wisdom in their posts than the entire rest of the internet combined. You can eliminate a lot of early trial and error by learning from the honest mistakes some the home mechanics here have made and how they remedied them using advice freely given.

The Pit-Lane forum in its entirety might be a rather large lump to swallow. And on top of that it's French. But no worries, if you go to
http://www.pit-lane.biz/t117p246-gp1...es-aprilia-rsa
you'll find that the Frogs allowed me and other two-stroke characters to write in English. And as I keep pointing out, all photos are in English anyway.

As for KiwiBiker, this is the thread to visit, as 136kg136ps already remarked. I have fond memories of my first encounter with Wobbly, which you will find here:
http://www.kiwibiker.co.nz/forums/sh...post1130172752

I also posted some stuff in "FOS tips & concepts":
https://onedrive.live.com/?authkey=%...D58EFB966FB3DC

[90GTVert]

Thanks for the links and advice. Believe it or not, I'm not a total noob to two-strokes. I'm a scooter guy that's been messing with them for roughly 20 years. Predominantly bolt-on and pretty mild porting and I do cut trenches in cases, which was how I was introduced to Wobbly's presence online. I've read Bell and Jennings long ago and got very little into Blair before realizing it was over my head, and I know of the legends like some of the present company. I have had this and Pit Lane bookmarked for quite some time now, but I run my own scooter forum and YouTube in addition to some locals that are looking for help and by the time I get done reading and replying to other people's problems I make excuses and don't want to spend more time reading daunting page counts worth of undoubtedly valuable info. I used to google search this thread and could find some answers easier that way, but that no longer seems to work.

Hopefully this gets posted soon, along with my previous reply. I've moderated and ran scooter forums for nearly 20 years now so it's really weird being the new guy awaiting approval.

[wobbly]

So you have confirmed that the bowl is not gradually lowering in level over the duration of your test time - yes.
The quick check would be simply to take off the bowl nut on both carbs , and using the fuel on/off valve on the tank , do a flow rate test on both carbs for a set length of time.
You might find that the smaller carb has bigger fuel passages and or a bigger float valve area when the floats are fully down.

If that isnt an issue then you need to do a needle tip/emulsion tube annulus area check at WOT.
This annulus should be at the very minimum about 30% larger than the main jet.
It can also be confirmed by taking out the main , or drilling out a huge sized one.
With no main installed it should carburate fine up to about 1/2 throttle, then go so rich that it dies up top - if not then the needle end is too big, and or is combined with a too small tube.
But PWK's dont have a replaceable tube from memory, so in that case it must be the needle.
I have seen this issue several times when people fit big PWK carbs on LC 250/350 and RZ racebikes , the needle tip annulus simply wont pass enough fuel at WOT.

The next area for investigation is the main air corrector jet or drilling.
If its too large the fuel curve goes progressively leaner with rpm.
The same can be said of the needle shroud height - the higher it is , the richer the carb will run , and thus obviously visa versa , with rising rpm.

Lastly , something you have also tested it seems is that if the ignition curve is overly retarded past peak power , trying to generate overev , then you can end up having to fit a huge main to cool the engine as the rpm goes past peak power.
This means you are using fuel as a coolant and to control the egt , not to make power.

Man 1400* is insanely lean on any fuel - so something is very , very wrong - just the mere fact it goes there sends alarm bells about lack of compression or ignition , as well as the obvious fuel restriction scenarios.

[Wos]

Maybe there is somewhere a leak in case, sealings, mainfold rubber that allows engine to breath fresh air!?

Especially check rubber, if its another one for the bigger carb ��

[90GTVert]

So you have confirmed that the bowl is not gradually lowering in level over the duration of your test time - yes.
The quick check would be simply to take off the bowl nut on both carbs , and using the fuel on/off valve on the tank , do a flow rate test on both carbs for a set length of time.
You might find that the smaller carb has bigger fuel passages and or a bigger float valve area when the floats are fully down.

I've observed it on a couple of different test days with a GoPro. Here's one before the main jet extender when it died and lost compression as I slowed from the 2nd pass (stuck ring), but the bowl wasn't really draining. This was with a 200MJ.
https://youtu.be/52bbQkNldqc?si=oZItL-sxVKKcaNVB


These are plug chops before the main jet extender, where you can see the mix ring disappearing as I went larger. Note : these are not test pass and immediate plug removal. I don't have a track or great spot to use regularly, so these all include a few miles to/from the spot at low throttle, but they seem to tell the story regardless.


These were after the main jet extender. I think the 220 has less of a mix ring due to washing. The other guys with my setup are 175-195MJ so that's getting to be a lot of fuel. What's odd is that it ran the best time on one pass with the 220. For some reason the 210 acted very rich, with lower RPM and EGT.
L to R : Break-in ride (new ring), 205, 210, 215, 220, 210 redo.


I should test the flow through the carb. I have tested supply flow and that was around 450ml/min using 3/16" hose from tank to carb. I found once that fuel supply flow was low some time ago and why surprised me. I had 1/4" hose up to the filter and then 3/16" to match the carb's barb and that mismatch caused flow to drop. I would have thought that the 3/16" would dictate max flow, but not that it would flow less than all 3/16". Did multiple tests and it was always better for me to use equal size hose on both sides of the filter. I haven't put the GoPro on to look at the carb with the bigger jets and main jet extender, but I saw the fueling and figured it was fine. Plus, by the time I realize I need to try something else, it dies again.

If that isnt an issue then you need to do a needle tip/emulsion tube annulus area check at WOT.
This annulus should be at the very minimum about 30% larger than the main jet.
It can also be confirmed by taking out the main , or drilling out a huge sized one.
With no main installed it should carburate fine up to about 1/2 throttle, then go so rich that it dies up top - if not then the needle end is too big, and or is combined with a too small tube.
But PWK's dont have a replaceable tube from memory, so in that case it must be the needle.
I have seen this issue several times when people fit big PWK carbs on LC 250/350 and RZ racebikes , the needle tip annulus simply wont pass enough fuel at WOT.

I haven't done any annulus test, and TBH I'll look up what that is. LOL
I have tried a needle first tuning method, where I ran it on the stand and made sure it broke up from richness with no main jet. That process is shown in the video below if anyone's interested.
https://youtu.be/UUzZfZHvsAU?si=1e5lTn0UYQv0shAP

The next area for investigation is the main air corrector jet or drilling.
If its too large the fuel curve goes progressively leaner with rpm.
The same can be said of the needle shroud height - the higher it is , the richer the carb will run , and thus obviously visa versa , with rising rpm.

I've never had to fiddle with either of these in all the years of tuning scoots, so if it comes to that I'll be looking up more info as well.

Lastly , something you have also tested it seems is that if the ignition curve is overly retarded past peak power , trying to generate overev , then you can end up having to fit a huge main to cool the engine as the rpm goes past peak power.
This means you are using fuel as a coolant and to control the egt , not to make power.

The last tests that I did were with 16* flat and a sort of clone of the curve that the engine maker's ignition provides with slightly less timing between low and high rev because I was pretty sure I heard detonation on my way back from test runs at about 12,000RPM and low throttle. Here's that curve. I did notice that it looks like less fuel on the plug with the more standard curve vs the 16* flat. Also, it wants to foul plugs with 16* at low RPM.

Man 1400* is insanely lean on any fuel - so something is very , very wrong - just the mere fact it goes there sends alarm bells about lack of compression or ignition , as well as the obvious fuel restriction scenarios.

Yeah, it was quite scary. I actually tested my EGT sensor and setup because I thought it had to be wrong if it didn't fail immediately, but I got away with it a few times and the EGT appears to be working roughly as it should as near as I can tell.


Thanks very much for the info/suggestions!!!

[90GTVert]

Maybe there is somewhere a leak in case, sealings, mainfold rubber that allows engine to breath fresh air!?

Especially check rubber, if its another one for the bigger carb ��

Good thought, but I leak test regularly. I had one that refused to stay in tune probably 10 years ago and found a crack in the case and that taught me to check whenever I make a change that affects sealing. Thanks.

EDIT : I posted a long reply to Wobbly with pics and video before this post, but I don't know where that went. Hope it's just still waiting for approval.

[F5 Dave]

I've used a main jet extender in desperation on long tracks before I realised that my carbs internal drilling feeding the float needle was actually the restriction.

But let's start at the beginning, or rather the end. What size was your stinger? As you raise in power it needs to increase. The perfect size to 20hp may kill a 25hp bike.

Oh and sorry for the ribbing at the start, but to be fair we did have a marvelous time.