Pwk ballpark jetting?

Anything related to Vespas... ask tech questions, post helpful info, or just read and learn.
tony172
registered user
Posts: 124
Joined: Sun Jan 13, 2013 10:50 pm
Main scooter: vespa t5
Contact:

Mon Dec 31, 2018 11:11 pm

Hi,
Built a motor with a mate recently, looking for a pointer on jetting.
Mainly as it's a b@5t@rd to start. Runs ok when going although I've only revved it up and had it ticking over for about half an hour.
Revved up fine, tickover is lumpy but it's got a 1kg flywheel. Starting its easy when warm but getting it going is fooken hard work when it's cold.

It's a
polini 177 with casings matched,
Sterling pipe,
Mazz cut crank,
Malossi inlet with casings matched,
Hp4 flywheel,
Ngk b8hs
Few other bits but nothing to affect the actual running.
BGM PWK 28MM unfiltered (says YSN on side)

So far it's got a 112 main, 38 pilot, needle on bottom clip and mix screw is about 3.5 turns out.
Plug gets very wet very quick
No real logic that's just what was in it.

Any help massively appreciated as it needs as much run time as possible before we send it to dynO and my foots killing me from kicking it over

tony172
registered user
Posts: 124
Joined: Sun Jan 13, 2013 10:50 pm
Main scooter: vespa t5
Contact:

Tue Jan 01, 2019 5:47 pm

After a bit more dicking around today it seems that the plug is fouling meaning it won't start. Clean it up and it starts first kick, but soon fouls again.
Not the whiskering I'm used to but fouling around the ceramic inner part causing small orange sparks around the inner part of the plug.
Change the plug and the same happens in a short space of time.
Anyone come across this?
Thanks
TONy

User avatar
johnd
registered user
Posts: 233
Joined: Wed Jan 07, 2009 7:53 pm
Main scooter: 1970 Dl125
Location: Belfast, Ireland
Contact:

Thu Jan 03, 2019 12:58 pm

When you say that needle is on the bottom clip, you mean richest setting( closest to the pointy end)? Or do you mean the lowest needle setting (top groove near the blunt end)

tony172
registered user
Posts: 124
Joined: Sun Jan 13, 2013 10:50 pm
Main scooter: vespa t5
Contact:

Thu Jan 03, 2019 3:02 pm

Hi,
Thanks for the reply,
The needle clip is at the rich/ pointy end. I can change this tonight, I'll go right to the leanest setting to see if this helps.
I've changed numerous stators, flywheels, cdi's and plug caps and leads off mine and mates bikes to no avail, so can pretty much rule out an ignition fault causing the fuel not to burn away efficiently (although never say never)
so I'm leaning towards jetting more and more.

Any help gratefully accepted as My mate doesnt want to sell the carb and buy a PHBH.

Many thanks again
Tony

User avatar
johnd
registered user
Posts: 233
Joined: Wed Jan 07, 2009 7:53 pm
Main scooter: 1970 Dl125
Location: Belfast, Ireland
Contact:

Thu Jan 03, 2019 3:32 pm

I'm not overly familiar with PWK jetting, but starting by dropping the needle to lean off the mix should help. Also check the choke plunger seats correctly when the lever is in the off position. Had that problem with a TMX before.

tony172
registered user
Posts: 124
Joined: Sun Jan 13, 2013 10:50 pm
Main scooter: vespa t5
Contact:

Thu Jan 03, 2019 7:46 pm

Thanks mate, I'll be out there after me roast 😊

tony172
registered user
Posts: 124
Joined: Sun Jan 13, 2013 10:50 pm
Main scooter: vespa t5
Contact:

Sat Jan 05, 2019 6:11 pm

So I've had no luck with this still, but have run out of decent plugs for now.
Leaned off the needle to the top clip, and changed the pilot to 35 (smallest i have)
I took the phbh off my 210 and my plug out of that and it seemed to run fine with that although it seems to run fine with the pwk till the plug suddenly fouls so that's not really definitive. Nobody jetted a similar setup before?
35 pilot seems small, as does the main.
I forgot to.mention its using a jjh needle

Thanks again
Tony

User avatar
johnd
registered user
Posts: 233
Joined: Wed Jan 07, 2009 7:53 pm
Main scooter: 1970 Dl125
Location: Belfast, Ireland
Contact:

Sun Jan 06, 2019 11:47 am

I've not jetted a PWK, but my mikuni TMX35 used a 17 idle jet on an RB22.
I'm pretty sure that the jet sizes on Japanese carbs have nothing in common with dellorto sizes, also the mixture screw was quite sensitive and was turned in to richen the mixture.
Have you tried posting on modern Vespa forum? There are a couple of people on there that may have more experience with that carb on a Vespa?

Andy_S
registered user
Posts: 3
Joined: Sat Jan 21, 2012 6:52 pm
Main scooter: SIL Lambretta GP200
Contact:

Mon Jan 07, 2019 10:13 am

A very handy web tool for jetting changes to Keihin PWK
http://www.kyajet.de/?lang=en

tony172
registered user
Posts: 124
Joined: Sun Jan 13, 2013 10:50 pm
Main scooter: vespa t5
Contact:

Thu Jan 10, 2019 8:51 pm

Both useful, particularly the modernvespa site.
A few threads on there detailing the tribulations of others trying to use the same carb.
Unfortunately I'm still not managing to get any closer. I've been through all the jets i have and still too rich.
I have gone down to a 32 pilot and a 102 main which is actually leaner than I can find anyone else using but can't find any leaner to buy.
Still I've got a couple of new plugs to try so I'll have a better idea this weekend.
Onwards!

Post Reply Previous topicNext topic
  • Information
  • Who is online

    Users browsing this forum: No registered users and 1 guest