ET4 CARB Expertise, Please
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Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Fri Aug 14, 2020 7:06 am quote
Greetings:

The pics show my open 2003 ET4 carb, bottomless. I don't recognize the float valve hardware, and have read that the early ETs had Walbro(?) carbs.

The stock ET4 pilot is a #34, and is different from any jet in my collection- Keihin. Polini, OKO, Mikuni - shorter although similar to the PWK and CV jets from Keihin and clones. Wise Greasy125 suggested I need a 38.

Since the much longer #38 I had did physically fit, and the "business end" dimensions were very similar, I decided to try it out. Turns out it works considerably better than the stock 34 - smoother idle, not as many turns out on the mixture screw, less of a flat-spot on initial throttle application.

Still, I'd like to find the CORRECT #38 if possible. I'd appreciate any info on sources.

Thanks in advance for any advice.

ISOCarbOpen.jpg
This is the stock ET4 carb, bowl removed. The pilot has been removed. It sat recessed a few mm from flush with the tower.

ISOCarbStkJet34.jpg
Here's the approximate length of the stock 34 pilot.

ISOCarbPWK38.jpg
Here's the PWK Keihin 38 Pilot jet I happened to have. It sits a mm or 2 proud of flush with the tower screwed in fully.

Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Fri Aug 14, 2020 7:32 am quote
ET4 Walbro 24
Greetings:

Pulled out the Manual! I generally skip the front part but carb is described in section 3-7 as a Walbro WVF6 24mm. It seems 3 or 3.5 turns out from seated is normal for the idle fuel mixture adjustment screw. I'm now wondering if it's worth increasing the main as well as the Pilot from 82 to 84, or at least raising the needle in the clip?

BTW, the carb and bowl were both remarkably clean! , considering this 17 year old scooter had only 500-something miles when purchased last April.

ISOCarbManl.jpg
Section 3, page 7. gives the nitty-gritty. Only lacks a current source for these jets...

Addicted
GTS 250ie Super, Italjet Velocifero, Scarabeo 150, S50,ET4
Joined: 22 Nov 2016
Posts: 507
Location: Winston-Salem, NC
Fri Aug 14, 2020 1:18 pm quote
If the one you have works why replace it. If you start having idle problems then go searching. But I decided to check my fall back company Jets R Us and found a listing for Walbro jets. I clicked it and found that it went to their Keihin jets. They do look close. Note that they have genuine jets and the after market may be where your difference is. Look for yourself https://www.jetsrus.com/a_jets_by_carburetor_type/a_jet_kits_walbro_selection.html You can also go here to identify my jet where they have dimensions: https://www.jetsrus.com/FAQs/FAQ_identify_that_jet.htm#KEIHIN scroll down to keihin.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Fri Aug 14, 2020 9:53 pm quote
Not Seamlessly Linear
Greetings:

I really appreciate the links, Pink.
The reason I'd like to try the Genuine Walbro Article is that the scooter does not start and run quite as perfectly as it did pre-Malossi. Idle can get erratic, and a bit upredictably so. I can't seem to find a good setting for the idle mixture screw that satisfies cold on-enrichener idle and warm engine idle. There's a trail of chuffing backfires off throttle still. Also the PWK jet installed, but only got 2 or 3 turns on the jet before it bottomed out. I could live with it as it is, but would like to see if the Walbro jet corrects some of this.

ISOCarbStkJet34.jpg

Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Sat Aug 15, 2020 1:39 pm quote
Lean Pilot?
Greetings:

I spent an hour fiddling with the idle mixture screw, landing somewhere between 4 turns out and outright removal as the ideal setting. Now someone please correct me if I am mistaken, but a well-respected Member stated that "out is rich". Completely opposite the Keihin PA, PWK, POLINI, etc. Non-CV carbs with which I'm more familiar.

Well if so, even the 38 is too small if it needs that many turns out. Plus it carb-farts and slows down with a sudden throttle blip, another tell-tale of too lean. I ordered the correct shorter 38 plus a 40 and a 42 from Pinkscooter 's link. Thanks again for that Pink.
Hooked
lml 2t 150 with sidecar, Vespa ET4 150cc
Joined: 21 Jan 2018
Posts: 276
Location: Wales
Sat Aug 15, 2020 2:09 pm quote
Maybe of some use to you. I had carb issues on a ET4 recently. Eventually cured it with a new plug. Mine was giving me jip going up hills went through carb no difference. Had been meaning to change plug as no idea how long in there before I got it. Garage only had one of those iridium jobbies so I slapped that in and Bob's your uncle no problem since.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Sat Aug 15, 2020 2:19 pm quote
Greetings:

Yes thanks, I installed the same Iridium plug yesterday. Sutures from squeezing my hands into the tight space are healing nicely. Anyway this 2003 ET4 has only 855 miles, and the old Champion plug was doing fine. Still like the idea of the Iridium, although there's no clear evidence of performance improvement.

Have you met my Uncle Bob?!
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Wed Aug 19, 2020 6:28 pm quote
38 Ain't All That
Greetings:

Jets R Us had the shorter Keihin "equivalent look-alike jets. Listing was SKu K36 SHORT. I purchased a 38, 40 and 42 sizes. Screwed in the 40 because even with the Keihin Long 38, I needed to turn the Idle Mixture Screw out a whopping 4.5 turns out to get a smooth idle. I tried the 40 first. Starts and runs beautifully with the screw now a reasonable 2.75 turns out. I'll have a few spare 38s if anyone wants one.

Now need to find the round Main jets, 6mm head diameter and 9mm length. Looking to get an 84 and 86.
Enthusiast
Derbi Boulevard 125 4t
Joined: 05 Feb 2020
Posts: 70
Location: Lithuania
Wed Aug 19, 2020 11:54 pm quote
I doubt jet length in this case is important. I see only one difference: longer jet is easier to remove. But what i have experienced with these longer jets is that they are not accurate. #42 jet behaves like #35 and #40 behaves like #38. Please note my jet kit came from china, but i think big part of these jets are coming from there...
What i have eventually did is slightly and carefully enlarged stock short jet till i got desired idle screw adjustment.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Thu Aug 20, 2020 11:21 am quote
Isdeekelis Rocks!
Greetings:

And sincere thanks for sharing your experience. I agree, clone jets usually do not behave like originals. Trouble is i was unable to source Genuine Walbro components. WVF Carb evidently came in a dozen variations, unable to locate what model this one is on the casting.

Length of the Keihin did make it easy to remove; it sticks out. That makes me think float level will not be perfect and idle wasn't steady. Better with the 40 clone.

Where to source fine drills? My smallest #65 measures 0.88mm. Too big for Pilot hole - even the #42 jet.
Molto Verboso
Primavera ET3 & PX150 & GTS 300
Joined: 05 Apr 2009
Posts: 1464
Location: Berlin
Thu Aug 20, 2020 12:34 pm quote
I've had a look at a couple of carbs for sale. On one side it says „Walbro WVF Japan.“ On the opposite side under the black plastic lever it says 6B or 7C.1 or 7A7.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Thu Aug 20, 2020 3:54 pm quote
Greetings:

Thanks very much for the location of the carb model DB! I'll have a look next time I can.
Enthusiast
Derbi Boulevard 125 4t
Joined: 05 Feb 2020
Posts: 70
Location: Lithuania
Thu Aug 20, 2020 11:49 pm quote
Re: Isdeekelis Rocks!
Wheelman-111 wrote:
Greetings:

And sincere thanks for sharing your experience. I agree, clone jets usually do not behave like originals. Trouble is i was unable to source Genuine Walbro components. WVF Carb evidently came in a dozen variations, unable to locate what model this one is on the casting.

Length of the Keihin did make it easy to remove; it sticks out. That makes me think float level will not be perfect and idle wasn't steady. Better with the 40 clone.

Where to source fine drills? My smallest #65 measures 0.88mm. Too big for Pilot hole - even the #42 jet.
Float level will not be affected by jet length.
You can use sewing needle to enlarge jet, just grind it to be bit smaller than jet and use it as file.
Some jets are measured in mm, so #42 would be 0.42mm, thus making it possible to grind needle to 0.42 mm and use it as drill. But some jets are in some_volume_units/time. This depends on manufacturer and i don't know which numbering option Keihin and Walbro uses.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Wed Sep 09, 2020 10:15 am quote
Walbro vs. Keihin CV24
Greetings:

After several weeks of decent cold-start performance, ISO has begun to misbehave. Cracking open the throttle before the engine is thoroughly warmed results in a stumble, and having to "fan" the throttle go get the engine to rev and go. This is with an aftermarket Keihin SHORT 40 pilot and the stock 82 Main in situ. It seems the "handoff" between running off the pilot and main is compromised, at least until the enrichener circuit is fully closed. Once fully warmed, it Rips.

The problem would appear to have 2 possible causes; 1. The Pilot circuit is getting clogged or 2. The accelerator pump.
Either way I'm looking at dismantling and cleaning, a process I have previously done with other CV carbs, but hesitating because if the diaphragm rips or some other snag occurs, I'd be without motorway-capable Scootage.

The other alternative is outright carb replacement. A Keihin would have more easily obtained jet options. I saw that ScooterPartsCo has a genuine 2006-later Keihin replacement for the Walbro, for around $230. If anyone has experience with this (or perhaps a less pricey equivalent?), I'd be grateful.
Enthusiast
Derbi Boulevard 125 4t
Joined: 05 Feb 2020
Posts: 70
Location: Lithuania
Wed Sep 09, 2020 9:15 pm quote
Hi,

I have bought this one from ebay and i am happy with it. Seller is reliable, have bought number of parts from him. You can check if he has got what you need and if he can ship it to you.

https://www.ebay.co.uk/itm/CM156010-Carburator-Keihin-Piaggio-Genuine-Piaggio-FLY-125-LBMM57100-2006-On/263375482699?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Thu Sep 10, 2020 11:19 am quote
CVK24
Greetings:

Sincere thanks Isdeekelis! I have had some issues in the past ordering from overseas, and I will use the information to see if I can locate a North American source.
Hooked
lml 2t 150 with sidecar, Vespa ET4 150cc
Joined: 21 Jan 2018
Posts: 276
Location: Wales
Thu Sep 10, 2020 11:33 am quote
Wheelman-111 wrote:
Greetings:

Sincere thanks Isdeekelis! I have had some issues in the past ordering from overseas, and I will use the information to see if I can locate a North American source.
I have ordered many parts from this seller from Greece over the last few years with no problem always emails to say what's going on and when posted. No problems with him over covid lockdown.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Sat Sep 12, 2020 1:22 pm quote
Intermittent Reluctance to take Throttle
Greetings:

Misbehavior continues. From Idle, giving throttle causes revs to rise a little, then drop abruptly, almost stalling. In fact today it did stall once. "Fanning" the throttle occasionally brings up the power, but it remains balky. The behavior is inconsistent, however. It works fine most of the time.

Believing this 17 year-old Walbro to have possible internal problems probably resin in the slow circuit, I broke down and ordered an LX 150 Keihin replacement from Scooter PartsCo for about the same price as the Greek vendor you so kindly provided. The Keihin jets are easier to procure and the diaphragm won't be 17 years brittle. I'll report performance improvement, if any, when installed.

The Walbro I will dismantle and evaluate and clean thoroughly once the Keihin is on and working.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Thu Sep 17, 2020 5:33 pm quote
Keihin Kommonality
Greetings:

From ScooterPartsCo arrived this today: Will install the standard Keihin 38 jet and perhaps a larger-than-82 main to see if the "handoff" issue at midrange is corrected. Fuel and vacuum lines to be replaced and petcock filter inspected as well.

ISONewKeihin.jpg

Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Mon Sep 21, 2020 9:07 am quote
Old ET4, New LX Keihin Carb
Greetings:

Replaced the fuel, vac, and evap lines from the carb. Discovered my vacuum-operated fuel valve doesn't stop fuel flow unless you Blow into vacuum line. The Filter Screen looked fine - no sludge or resin. Anyway I'm ordering a new one today. The line from the float vent was cracked at the carb AND at the "T" junction of the Evap system. Replaced that too. The "Handoff Hiccup" still happens while the engine is cold, but clears up when warm, throttle response is now linear. Jets are 38/82.5 from Jets R Us. Power is Awesome, but Tropical Storm Beta is 30 miles up the road and will postpone final testing.

ISOKeihinInstal.jpg

Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Mon Sep 21, 2020 4:22 pm quote
Between Beta Showers
Greetings:

Streets in Deepinaharta dried up for exactly 15 minutes, permitting a ride around the block. Hot Dang!! Keihin rocks. Can't get to top speed for a few days but will post outcome.
Addicted
GTS 250ie Super, Italjet Velocifero, Scarabeo 150, S50,ET4
Joined: 22 Nov 2016
Posts: 507
Location: Winston-Salem, NC
Tue Sep 22, 2020 3:41 pm quote
That mid range hiccup may be solved by raising the needle a little. I don't know if these have notched needles with clips. If they don't I've slipped small washer on the needle then slipped it in the hole to rase the needle. It helps that mid range when it's cold.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Tue Sep 22, 2020 5:45 pm quote
Helpful Pink
Greetings:

Thanks PS! Did a bit of Inspectin' tonight. More to come. Sticky slide seems most likely issue. [EDIT] This documents dismantling of the weirdo Walbro 2003 carb that came with the ET4 of this era. The Keihin is on the scooter and working well.

ISOWalbroNeedle.jpg



Last edited by Wheelman-111 on Wed Sep 23, 2020 6:21 am; edited 1 time in total
Molto Verboso
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 1076
Location: Toronto
Tue Sep 22, 2020 7:00 pm quote
Isn't this a brand new carb? I'm confused why the slide would not be smooth and the needle gritty?
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Tue Sep 22, 2020 7:10 pm quote
Greetings:

Sorry this is the surprisingly clean 2003 Walbro. More to come.
Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Wed Sep 23, 2020 9:53 am quote
Where's Walbro?
Greetings:

So here's the rest of the story of the Walbro inspection;
The pilot jet (a 40?) was brand new, and of course quite clean.
The 82 main was likewise in good shape.
The bowl was surprisingly clean. I suspect someone went through this carb before my April purchase, at 541 miles. Perhaps to get it running?
The Bystarter was working fine, although it closed pretty quickly after startup, with the engine not Quite ready to run off the pilot and main alone.
The Float Chamber was a real mystery. Some weird brown dust - like powdered cinnamon? - was contained 'neath the dome. Brushed it out. Float stickiness might be explained by this stuff.

ISOWalBowl.jpg
Very light yellow resin in the bilge of the bowl.

ISOWalBystrt.jpg
There might have been a light leak at some point,but the bystarter o-ring appeared undamaged and fit snugly.

ISOWalFloatChmbr.jpg
Here's something I had never seen. Powdered cinnamon in the chamber. I could see this causing stickiness on the float cylinder.

Hooked
2010 S50 Modified "Punkin"; 2003 ET4 150 "ISO"
Joined: 18 Feb 2017
Posts: 463
Location: Deepinnaharta, Texas
Fri Sep 25, 2020 7:07 pm quote
Draining Tank, Swapping Valves
Greetings:

In the course of replacing carb and lines, I discovered my vacuum-operated fuel valve wasn't functioning correctly. I fuel flow wasn't completely blocked without vacuum on the smaller line. Evidently both the Walbro carb and the new Keihin have good functioning float valves, or there'd be a lake in my garage. Also now I know exactly how much fuel is in the tank when the Low Fuel light starts to flicker.

ISOLowFuel.jpg

IsoOldFuelVlv.jpg

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