ESE's works engine tuner

**F5 Dave** · 19th July 2024, 12:53

Strange, I've had little to do with PWM as PWK so ubiquitous esp in dirt circles where we feed a lot of parts from.

Attack of the Clones: I see Aliexpress etc offer PWM things too. Buyer beware in my opinion.

**wobbly** · 19th July 2024, 13:42

Yea , I just check on Ebay , PWM 38 from China $90 NZD , from Germany $ 900 NZD.
You decide who is taking the piss.

**Jonny snatchsniffer** · 19th July 2024, 14:21

I got that pwm for £26 of ebay brand new in box
Found out more about the polini pwk carbs
You cant adjust the float height as they ha a light float and a heavy one, use the heavy one if you have vibrations lol
There is also something called the air brake jet on the back of the carb at around 6 o'clock at the bottom of bellmouth, this should be closed for 2 strokes and open for the foul strokes, apparently this stops air entering the atomiser as there should be no holes in 2 stroke atomiser, the more holes in the atomiser with the open air brake jet the leaner it will run, this is for emissions crap
So for the 2 stroke you need to blank off or close the air brake jet, fucking mental, no wonder everyone has trouble with them as you may have been given an open one as to a m8s closed one
Still prefer the proper keihin, shame it goes from 28mm and then straight to 33 for the pwk, but don't waste money on the air striker as its just another gimmick and for me done nothing to performance.

Quick question, ive put a 54.5/105 crank in my vespa instead of standard 51/97 increasing the stroke, this means that with my particular barrel the piston ends up around 1.3 mm below exhaust and transfers at bdc, the scooter fraternity here say this isn't a problem but would it be beneficial to lower the bottom of the transfer ports to top of piston at bdc or not?

**Jonny snatchsniffer** · 19th July 2024, 14:24

Originally Posted by F5 Dave

Strange, I've had little to do with PWM as PWK so ubiquitous esp in dirt circles where we feed a lot of parts from.

Attack of the Clones: I see Aliexpress etc offer PWM things too. Buyer beware in my opinion.

The pwm was make for road racing, but then they made short body pwk's for the mx bikes, pwm is for outright power

**wobbly** · 19th July 2024, 15:04

I would say leave the bottom of the Exhaust port above BDC to help with short circuiting , but as the bulk of flow exiting the transfers is around BDC then having a big negative step there
will absolutely ruin the flow stream regime , but you still need the duct to be reducing somewhat linearly in area as it approaches the port , so how you drop the floor needs some thought.

And if you have done a port STA calculation , it will of course assume the port area goes from the timing height , down to BDC.

It has also been suggested having the transfer bottom flush will help the mixture adhere to and cool the dome.

**Vannik** · 19th July 2024, 17:09

Originally Posted by wobbly

And if you have done a port STA calculation , it will of course assume the port area goes from the timing height , down to BDC.

Not the calculation in Dat2T, it uses the actual port shape and timings.

**husaberg** · 19th July 2024, 17:39

Originally Posted by Frits Overmars

Having .PDF allowed would be fine too. I'm testing it now. So if I succeed, you can forget about this post.
Attachment 354834

I have had a few occasions when pdfs failed. I assume it was due to size. I will ask about that as well.
I had a feeling there used to be something like 2mb.
when this is the case you can save say first x pages as separate files by printing as a PDF using the the printing range to say 10 pages, so it will be 4 files instead of one big ones..

Valid file extensions: doc dxf gif jpeg jpg kmz mp3 pdf png pps ppt psd swf torrent xls zip

**F5 Dave** · 19th July 2024, 20:09

Originally Posted by Jonny snatchsniffer

The pwm was make for road racing, but then they made short body pwk's for the mx bikes, pwm is for outright power

I changed the long pwk for a short one on my GG 300 Enduro with an extender on the bellmouth. Best improvement was probably it being virtually new.

Bear in mind the Enduro an MX bikes have different needs from roadrace. As a long time 50cc racer I appreciated both.

Bigish 2 stroke dirtbikes are absolutely awesome. Different mindset in single-track forest.

**90GTVert** · 20th July 2024, 11:28

Originally Posted by Jonny snatchsniffer

Found out more about the polini pwk carbs
You cant adjust the float height as they ha a light float and a heavy one, use the heavy one if you have vibrations lol
There is also something called the air brake jet on the back of the carb at around 6 o'clock at the bottom of bellmouth, this should be closed for 2 strokes and open for the foul strokes, apparently this stops air entering the atomiser as there should be no holes in 2 stroke atomiser, the more holes in the atomiser with the open air brake jet the leaner it will run, this is for emissions crap
So for the 2 stroke you need to blank off or close the air brake jet, fucking mental, no wonder everyone has trouble with them as you may have been given an open one as to a m8s closed one
Still prefer the proper keihin, shame it goes from 28mm and then straight to 33 for the pwk, but don't waste money on the air striker as its just another gimmick and for me done nothing to performance.

Thanks for the info on the Polini PWKs.

In case this is useful for anyone, I bought a few more main jets for my PWK and spent some time testing jets that overlapped each other in size to see how it turned out. I got some real Keihin jets this time. Turns out the ones that I thought were Keihin (with the oddly ultra rich 210 jet that I showed) were Niche Cycle.

2L bottle with bottom cutout, upside down. Cap tapped for hose barb, epoxied in because the caps today are so thin that it won't seal otherwise. 3/16" hose > shutoff > 3/16" hose. Main jets fit well in the hose. 24" from end of hose to top of water level. Water level marked on bottle so I could make sure it stayed the same for all tests.

This is what I came up with. I think the flow numbers are probably somewhat arbitrary. I've got 24" of water above the jet, not sure on volume. If you tested with more or less water you'd get different results. I just wanted to be able to compare what I have rather than worry about some standard. I almost got wrapped up in a project to build a rig that would keep a set height of water above the jet at all times and horizontal exit flow at the jet after reading about Ford Zenith main jet testing and then I thought... you're still waiting to order a cylinder kit (circlip came out and trashed the current one with a brand new piston)... why spend money testing these things and turn it into a whole thing? I assume flow would be greater with water level always constant instead of draining, possibly changing results with larger jets more than smaller... but I think this comparatively simple method still tells a story.

I don't have full sets of all jets, so that's why data points are missing. GZYF are the amazon jets. Flow numbers are ml/min. All tests were 20 seconds. 3 tests gives a 60 second flow figure. Better to do 2-3 tests to watch for inconsistency than to do 1 60 second test for each IMO... and I'm transferring out of a beaker and into a graduated cylinder for more accurate measurement... which takes a lot of time so doing 3x the volume multiple times would greatly increase time/effort. I assure you, it's not just pour in and look. I'm tapping and smacking stuff trying to get air bubbles out and it's a whole process.

Niche Cycle jets are to be avoided! They are the leanest of all of the jets, but even worse than that is that they have a huge spike at 210 and otherwise there's only minimal change from 205 to 215.

The amazon jets aren't awful... but then 235 and 240 flowed less than the 230. Not by a lot, but it's dangerous to think you're adding fuel while reducing it any.

Both Keihin and Stage6 jets seem to go up at a good rate without anything that alarms me. Stage6 jets flow slightly more than their Keihin counterparts and their flow rate change doesn't look as steady. I think both are just fine choices though.

What I think I learned is what I've known for years... go with big name brand jets and buy as many as you can from one manufacturer. Also, orifice size is what we usually think about, but entry design/size matter quite a bit.

Example 1) The 210 in the Niche jets that flows way more than the jets around it. Orifice size falls in line, but the entry on the 210 is huge compared to the others.

Example 2) My drilled main jet, 2.5mm (250) flows less than the amazon 250 jet. The smaller GZYF jets flow as much as it does. The drilled jet is one diameter all the way through. The others have a larger area at entry.

**wobbly** · 20th July 2024, 13:17

You are right off course Neels , but I was alluding to the fact that if a cylinder is lifted and is set to a specific timing, that timing will not
have the " correct " area and a port, with its floor above BDC, extra timing would be needed to generate the required STA
But yes EngMod can have that higher floor timing incorporated , and thus the STA created will be with the actual reduced area generated by the roof and floor heights from TDC.
But as we spend alot of time trying to center as big a depression at the Exhaust port as possible around BDC , it seems counter intuitive to me to firstly have to lift the transfers higher
than otherwise would be the case , and have to do this as the transfer floor is above the piston . What possible advantage could this approach accrue.

**Jonny snatchsniffer** · 21st July 2024, 23:59

I originally went for the 54/105 crank as the bgm one twisted on the dyno, at the time my budget was was pretty much limited as the bgm so called race crank was only £160 and only needed the sealing pad removed from cases to fit, the polini crank was a 52.8 stroke with a 102mm rod to make the cc 135 to comply with the Italian polini cup race series, standard is 51/97 and at the time the polini was about £650, 3 times my budget.
Wish I'd gone with that in the first place as the bgm twisted so much, about 1.2mm runout it also made the flywheel magnets smash into the stator laminates, rendering it useless, it also ruined the cases with the drive side bearing spin in the case wearing the lip that stopes it coming into the main case, so in effect was now floating instead of being fixed.
Replacement cases and macining £300, a fabric crank with primatist rod with vat was around £600 then all new bearings another 100
I've learnt my lesson for sure.
Polini spec for timings were 131 transfers all the same height for A B and boost port and 190 for exhaust wich ended up at 192 to suit the pipe, the head is spigoted into the barrel
I've not done the sta as im inherently lazy
My porting the barrel to get the bridged exhaust to get the port ends in a non linear path so the port edge went into the barrel with the sort of scoop that's better for flow was very limited bt barrel studs which also make the transfers narrower than they should be
I'm not equipped to do anything inside the bore either and don't have the knowhow so I think I'll leave that alone, plus my polini kit is no longer made as they are now 60mm bore and are now allowed in 152cc form for racing.

The plug in my lambretta head is shit too with it being too short for the b9egv plug, usually on all my othe heads the non thread part of the plug sits flush with the combustion chamber but on this on its like a mm short, it's also an offset plug and has a chamfer on the combustion side, seems OK with no plug washer a bpr9es is better to get the spark further in, ive never tried to use a plug without a washer so don't know the outcome of what would happen if I did, why the offset plug with a center squish I have no idea, original lambretta heads have an offset plug too but also a side squish

**wobbly** · 22nd July 2024, 14:55

We won 4 SKUSA titles with no plug washer, and as a by product I could index the plug much easier.

**lohring** · 23rd July 2024, 02:30

Model boat racers have used flow meters for years to set needle valves. They should work equally well for carb jets. Below is a diagram and picture. The flow rate of propane through a regulator is measured. We used 40 inches of water as the propane pressure.

Lohring Miller