Hitachi needle & jet size question

Can anyone tell me which setup would produce a richer mixture in my Hitachi 32s - Y10 or Y11 needles and 195 or 205 main jets
ie. which needle is fatter/slimmer and which jet is larger/smaller?

I have a mix'n match set on my carbs and although it runs superbly I would like to know if it could be worth putting them back to OEM specs

 

HITACHI MAIN FUEL JET NEEDLES:

Attached to the vacuum piston assembly is the MAIN JET NEEDLE, and as the vacuum piston is raised or lowered due to the vacuum signal through the carb throat, the main jet needle is raised or lowered into the brass emulsion tube (also described as the "main jet" or "power valve" in some technical literature). These jet needles control the overall fuel flow in the main jet circuit of each carb.

These precisely made aluminum replacement needles correctly replace worn, damaged, or incorrectly sized original needles in all Hitachi HSC32 or HSC33 series carbs. The needle "size" is inscribed on the shaft of the needle, just below the plastic head cap. Although all needles are interchangeable between any type Hitachi HSC32 or HSC33 series carb, their different "sizes" are designed to be used in specific applications as determined by factory design engineers.

However, as long as all four carbs on your bike are using the same size needle, you can swap needle sizes between different carbs. So, for instance, you can use the Y-20 size needle (XJ700 models using HSC33 series carbs) in an XJ750 engine (which normally used the Y-13 size needle in their HSC32 series carbs). This type of swapping of needles can be useful in situation where you may wish to fine-tune the fuel mixture in an engine, for instance when changing the air-flow through an engine using pod filters and/or aftermarket exhaust systems.

NOTE: original Hitachi main jet needles have a depression on the bottom of the plastic cap, and this should be oriented with the half-circle bump inside the diaphram.


Original main needle size configurations are as follows:

Y-10: used on all USA market XJ650 (except Turbo) models, 1982-84 XJ650 Canadian bikes, and 1982 XJ650 Euro (model 14R) carbs.

Y-11: used on all 1980-81 XJ650 Euro (model 4K0 and 4K1) and XJ650 Police (37G) carbs.

Y-12: used on all Canadian 1980-81 XJ650 Maxim, Midnight Maxim, and Canadian 1982 XJ650RJC Seca (non-yics) models.

Y-13: used on all USA market XJ750 (1981-83) models.

Y-14: used on all non-USA market XJ750 (1981-84, except XJ750RL) models and XJ750 Police (24L and 37H) models.

Y-17: used on all XJ750E-II models.

Y-18: used on all XJ750RL Seca models (1984) only.

Y-20: used on all XJ700 air-cooled models.

others: all other Y-xx size needles are used on other model Hitachi HSC series carbs, such as XV750, XV920, etc. models.


Original main needle size characteristics:

As noted previously, as long as all four needles are the same between all the carbs on your engine, you can swap around different sizes for "tuning" purposes. Although we have no guidelines nor experience available to assist you in your tuning exercises, we can offer these needle shape characteristics to help you in analyzing your needs. Be aware that the thickness of the needle at any position along its length determines the fuel flow through the main fuel circuit, and the rate of change of the needle thickness (the "taper" amount) determines when and how much the needle allows the fuel mixture to become leaner or richer.

- the Y-20 needles (XJ700 models) are "skinnier" at the bottom of their shaft than either the Y-13 (XJ750) or the Y-10 needles (XJ650). Thus the Y-20 needles are "richer" at higher rpm ranges than either the Y-10 or Y-13 needles.

- the Y-10 needles (XJ650 models) are "skinnier" at the bottom of their shaft than either the XJ750 Y-13 or Y-14 needles. Thus the Y-10 needles are "richer" than either the Y-13 or Y-14 needles, although the Y-20 (XJ700) needles are even richer, but only at wide-open throttle positions.

- the Y-11 needles (XJ650 Euro) are a bit leaner than Y-10 all the way through the rpm (needle position) range, especially at wide-open-throttle position. They are a bit richer than Y-13 needles, except at the wide-open-throttle position.

- the Y-13 needles (USA XJ750) are "richer" than the Y-20 needles (XJ700) throughout the rest of their overall length.

- the Y-14 needles (non-USA XJ750) are "richer" than the Y-13 needles (USA market XJ750) at 3/4-throttle positions and beyond; otherwise, almost identical to the Y-13 needle.

- the HCP20965 needles (custom) are the "richest" at all throttle positions except for the wide-open-throttle position characteristics of the Y-20 needles (XJ700).

- Summary: of all the stock needles, the Y-10 (XJ650) needles are, except for their lowest section, the "richest" stock needles available. The Y-20 (XJ700) needles are the "richest" needles available for their lowest section, but then quickly become the "leanest" needles past their lowest 1/3 range of length. The HCP20965 needles are the richest needles available at all throttle positions overall, and people who are running pods and other modifications on XJ700 and XJ750 engines may wish to keep this thought in mind when trying to tune their engines.


One last thought: remember than fuel system tuning is mostly an art, rather than a science. The different size needles can produce very differing characteristics on any given engine, not only due to their relative "richness" or "leaness" characteristics, but also their rate of richness or leaness at any given needle position, along with the differences in main fuel jet sizing.



The #205 jets are larger in the size of the opening, which means they will produce a slightly leaner fuel mixture, but it's more a a very-fine-tuning type of change (but, all fours carbs should be set up the same).

 

Perfect, my needles are richer and my jets are leaner than standard, exactly what I wanted to hear
thanks Chacal

 

I've been trying to understand chacal's explanation of the differences and the similarities of the needles...
It almost seems circular for some reason by the time you read from Y-20 to Y-14 but I know it will make sense somehow if I just read it over and over again!
I would LOVE to see these needles, side-by-side, in order in a MACRO picture. Then I could see the tapering and the skinnieness differences.

Please someone get the camera out!

and yes I have gone mad attempting to tune my carbs after replacing the exhaust with a 4into1 and a HUGE kawasaki muffler

So close...

 

That is most informative and helpful, Chacal. Can you or anyone else tell me, is there any difference between the carb bodies on the different models? I do not refer to the jets and needle, just the shape of the airway through the carb.

I have been told that there is, but I'm not convinced since the people involved wanted to sell me a set of carbs. :roll:

 

There is no difference in "the shape of the airway", however, the HSC32 series has a smaller throat diameter vs. the HSC33 series carbs (a difference of about 1mm difference).....the "32" and "33" refer to the throat diameters.

Within each series, there are minor structural/mounting/fuel passageway differences between different carbs (#1, 2, 3, and 4).

Also, the HSC32 series vent the bowls thru the carb throat (airbox side), whereas the HSC33's vent thru separate a separate passage outfitted with a t-fitting (connecting adjacent carb bodies together).

Some HSC33 models also have emissions ports, which HSC32 versions do not.

 

That was quick! I should have asked, "is there any difference between the carb bodies on the different models of XJ650 and 750" but you have answered the question anyway. Thank you.

So I was being told a tale so they could make a sale. What a surprise.... :roll:

 

The XJ650 (except Turbo) and the XJ750 (air-cooled 1981-83) use the same HSC32 series carbs (but with differing internal jets and main needles).....additionally, the earlier XJ650 carbs would use a coarse-thread pilot (idle) mixture screw; the later XJ650 carbs used the same fine-threaded mixture screw as did all of the XJ750 carbs.

The 1984 XJ750RL uses the Hitachi HSC33 series.

The 1985-86 XJ750-X uses Mikuni carbs, which are completely different animals.

 

I'd forgotten about the XJ750RL, and I've never heard of the XJ750-X, which was never officially imported to the UK.