EU vs US carbs...

[ST1100Y]

So, any more known differences except the idle and main jets?
(US: slow #38, main #125; EU: slow #40, main #128)

Checking the fiche I not only found different P/N for the vacuum pistons
(US: 16111MT3610, EU: 16111MT3640)

I also spotted different P/N for the needles
(US: front & rear: 16131MT3730; EU: forward 16131MY3760, rear 16151MY3760)

OTOH do both versions use the identical needle jet holder 16165MT3610...

Have the needles a different curvature/shape?
Should I order/replace them as well just to be sure?

 

[SMSW]

You raise an interesting point. I've never heard of needles wearing out - they float inside the jet and don't (or should not) touch any metal. The needles I played with on my Guzzis all seemed to be straight tapers (I only ever checked one with a straight edge). Those were for dellorto carbs. On those, once you picked your jet, you fine tuned things with the needle position.

 

[Slydynbye]

I have seen wear on the Needles. They get damaged along the sides and can contribute to uneven fueling.

 

[raygks]

So, any more known differences except the idle and main jets?
(US: slow #38, main #125; EU: slow #40, main #128)

Checking the fiche I not only found different P/N for the vacuum pistons
(US: 16111MT3610, EU: 16111MT3640)

I also spotted different P/N for the needles
(US: front & rear: 16131MT3730; EU: forward 16131MY3760, rear 16151MY3760)

OTOH do both versions use the identical needle jet holder 16165MT3610...

Have the needles a different curvature/shape?
Should I order/replace them as well just to be sure?

I don’t know about the different pn, but my bike has 40/125(slow/main jets) from the factory, same as UK st1100 I believe. I’m based in south east Asia with a 2000 y model pan euro non abs.

There’s probably different carbs setup for different markets, hence some on differences of carb mode naming conventions.

Attached a picture from a post from UK member I downloaded some time ago

 

[ST1100Y]

There’s probably different carbs setup for different markets, hence some on differences of carb mode naming conventions.

Thus the question...
A different needle shape/cone/curvature might/will influence response and performance curve...

 

[raygks]

Thus the question...
A different needle shape/cone/curvature might/will influence response and performance curve...

Not sure about our st11 on the needles differences.

I rode a Yamaha rd350lc 2 strokes in 80s/90s, I was always fooling around with different main/pilot jets sizes, these seems to have more influence on the response/performance(pickup and back end power) but there’s always compromise with bogging/mileages/top end.

And yes the needles and holders do have some wear on that bike as I tend to get overflow and fuel leaking from carbs very often

 

[afrymoyer]

Here is the US rundown:
1991-1996 NON-ABS slow speed/pilot #38 --- main #128
1992-1996 ABS Emission camshafts-slow speed/pilot #38 --- main #125
1997-2002 ALL Models, emission camshafts - slow speed/pilot #38 --- main #125
All US models have the same needles, per-say. However, the left and right sides have different part numbers on all models. I've had quite a few ST1100 carb banks apart. Honda says that the needles are different between the left and right sides. I've kind of measured, but difficult to measure the taper. Visually, I see no difference and my micrometer really couldn't find a difference either. But, they do carry a different part number. If you determine the difference, let me know...Something is different... The old "Factory branded" aftermarket jet kits had all the needles at the same diameter and taper, for what it's worth. I will say this though... The VFR 750 needles will make an ST1100 scream above 5000 rpm's! The fueling is way off, but she'll rip! LOL

As mentioned, I've had a good number of these things apart. I did a set a couple of years ago that had 220,000 miles on it. The needles
were untouched, as was every other one I've done. I'm sure there's someone out there that MAY have some scratched up ST1100 needles. But if that's the case, there's something else going on in there.

I've helped a number of members from different countries. Some countries are standardized, but many individual countries have different emission standards. I seen some whacky factory jetting sizes and initial mixture screw turns, along with the different standard/emission camshafts and with different left/right needles. Seems like when the "European Union" formed, all of the settings were choked off, but yet more standardized.

The very early non-emission Canadian carb settings and tune are the best. This is how mine are set up, plus a little extra.

 

[ST1100Y]

left and right sides have different part numbers on all models...

Positive that this is left<>right and not front<>rear (which would IMHO make more sense for temperature differences...)
The fiche are a bit unclear on that...

 

[TerryS]

I have seen wear on the Needles. They get damaged along the sides and can contribute to uneven fueling.

I had terrible wear on the emulsion tubes on my RF900. the needles had vibrated and the orifice in the emulson tubes had worn oval, which meant the fuelling was terribly rich, fuel consumption awful and I could even get enough soot on the spark plugs to cause a misfire.

 

[afrymoyer]

Positive that this is left<>right and not front<>rear (which would IMHO make more sense for temperature differences...)
The fiche are a bit unclear on that...

Yes...
USA Numbers:
CYL #1 & #3 16151-MT3-670
CYL #2 & #4 16151-MT3-750

I'm almost certain that we had a discussion, either here, or over at ST-Riders, about the needles quite a few years ago. Nobody could definitively come up with anything. Just that Left / Right had a different part number.

I do have a freshly rebuilt USA '94 ABS carb bank on my bench, ready to go back in a bike. Maybe I could pop off the diaphragms and check yet again for differences between Left / Right...

 

[ST1100Y]

Well, it seems the point is mute anyway, since 16131MY3760 as well as 16151MY3760 have been discontinued thus are unavail... anywhere... (so is 16131MT3730 BTW...)

So whatever you do with your ST's carb needles, watch them precious thingies like your eyeballs...

What's special about the 16131* and the 16151' needles?
They're unique to Austrian and Swiss models...
So my guess this is related to the terrain; alpine roads, altitude... adaptions to character and throttle response on steep narrow hairpins...

Using aftermarket parts?
Questionable... doubt that they take different needle designs under consideration...
OEM Honda brass is far superior in any aspect, like precision, corrosion resistance and general durability... (ever worked on a SOHC from the 70ies... drop them jets into the ultrasonic and they turn out like new!)

So, I'm going to thoroughly overhaul that US/CN carb bank I have here, throw #40 & #128 jets into it, put EC spec idle screws in, bench sync, plant that on the bike and just see how that performs...
Giving me the chance to no less thoroughly overhaul my original carb bank, while not having to ground the '00 ST in the meantime...

 

[ST1100Y]

To bring this topic to an end...

#40 & #128 jets installed, nothing else altered, installed, fires, warmed up, sync done... smooth...

it does require a bit choke for a little longer then just firing it up...
the known 'omph' right out of idle, under "normal" acceleration strong pull and smooth till >7000rpm...
under "hard" acceleration it sounds a bit hard in the +/- 3000rpm range... IIRC the spot the overlap from idle to main jets takes place...
so, in combination with requiring a bit more choke, maybe just 'a tad' too lean... might give the screws another 1/8th turn during the next tuneup...

 

[ST1100Y]

BTW things you might find inside ST1100 carbs:

rotten, cracking diaphragms...





fortunately I had some spares up in the shelf...