A Carb Jet + Needle disaster

Hey Fam,

I'm finally (2 years in the making) onto the last part of my full motor rebuild. Everything has gone relatively smoothly up to this point. However, a couple of concurring issues are making the Carb rebuild exceptionally challenging.

XJ650 (82' I think)

1) I've never touched a carb engine before this one
2) The previous owner that I bought the non-running bike from decided this bike would be the one he learned on
3) I think he tried to rebuild the first carb as cylinder 1 was having issues - This is because some of one of the rebuild kits had some pieces used, but it must not have worked, so then...
4) He fully disassembled all the carbs, leaving me without the chance to see how they were a) running before I started the rebuild or b) exactly what pieces went to each carb c) Water got into the 1st cylinder when the carbs were off, then requiring a full rebuild. I also found one of the cam chain rubber guides completely in pieces in the oil sump, but aside from that the motor was in pretty decent shape for being 40 years old!
5) He bought what looks like two separate rebuild kits, with different jet and needle sizes, all of which are different than the stock sizes

So I've scoured this forum and all available youtube videos and I've been able to make it most of the way through the cam rebuilds, but now I need some help with Jet and Needle sizes from this knowledgable community.

QUESTION: I'm planning on using Pod Filters, but no other engine mods. I'm also in Denver (5,000' above sea level). From what I've read it is likely these factors will more or less cancel themselves out. If that is an incorrect assumption, please chime in. So, I think I'd like to just reuse the stock air jets, and maybe even the fuel jets?

Right now I plan to use:
stock Pilot Air: 205
stock Main Air: 50

stock Pilot Fuel: 43
Main Fuel: 110 (I have new 112's and 122's I don't think I'm going to use)

Starter Jet: 36 (8 count) (Stock spec is 40, but I only have (4) 40's)

QUESTION: The jet needles are a bit less straight forward. The two sets of needles I have do not match the numbers shown as the stock spec. Shown in the pics below are the new Y403S and Y262 Jet Needles, I don't have any other needles. Which of these Jet Needles should I use? ALSO - What kind of washers should I put on as a way to set them in the 'middle' like I've seen others mention as best practice?

The Needle Jets (Emulsion tubes? The cylinders with the holes in them) I have a used and new set, but all the exterior dimensions appear the same. The book says the spec is 3mm for these, but I don't know where that is measured, my tubes are like 5mm in diameter.

The two sizes of needles have different 'girths', shown in the photos below, it seems the larger needle bottoms out into the tube/jet making a friction seal (with no washer spacers on), the narrower jets do not seem to make a seal, Second photo shows the difference in needle interference depth). So which should I use? How many and what kind of washers do I need for spacers?

As a third question - When I put the new needles in with the spring and white plastic locking nut, the needle movement in the bottom of the vacuum piston does not feel smooth, it feels bound up, not sure if I have the wrong spring, or if there needs to be some silicone grease in there instead of it being dry? Or maybe this is because this is where the larger needles are binding in the stock hole in the bottom of the vacuum piston? Open to any advice or ideas.

Thanks for the help y'all.

 

What I think you are referring to is the "air compensator jets" which are fitted into the carb throat (both sides, 3-o'clock and 9-o'clock) facing into the airbox. The #36 size is the correct one. STARTER jets are in the tiny recessed well in the fuel bowl, and except for very early 1980 model bowls, are non-replaceable.

The Y262 needles are the equivalent of the stock Y-10 needles, correct for all XJ650 (except Turbo) USA carbs. Other countries could have used the Y-11, Y-12, orY-14 needles.

The Y403 needles are the equivalent of the stock Y-14 needles, non-USA market XJ750 (1981-84, except XJ750RL and XJ750E-II) models and XJ750 Police (24L and 37H) models.


Needle comparisons:

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 and XJ750E-II) 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-19: used on all XJ700 air-cooled models (Canada)

Y-20: used on all XJ700 air-cooled models (USA)

All of the following size needles are used on Hitachi HSC40 series carbs, and are much longer (and do not interchange with) the HSC32/33 series needles above.

Y-22: 1981-82 XV920 RH/RJ models and 1981-83 XV750 models

Y-23: 1981-83 XV750 models

Y-24: 1982 XV920 J models

Y-25: 1982 XV920 J models

Y-29: all 1984-85 XV700 models, 1986 XV700SS on the #1 cylinder, and 1988 XV750 California models

Y-31: 1983 XV920 K models and 1983 XV920 MK models

Y-32: all 1986-87 XV700 models on the #1 cylinder

Y-33: all 1986-87 XV700 models on the #2 cylinder, 1983 XV920 K models, all 1984-85 XV1000 models, and all 1986-87 XV1100 models

Y-34: all 1984-85 XV1000 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-19 needles (XJ700 models Canada) are "skinnier" at the bottom of their shaft than all of the other stock Hitachi needles, thus the Y-19 needles are the "richest" needles at higher rpm ranges than any of the other needles (including the Y-20 or the HCP20965 needles).

- the Y-20 needles (XJ700 models USA) 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-19 (XJ700 air-cooled Canada) needles are the "richest" needles available for their lowest section, but then quickly become "leaner" needles past their lowest 1/3 range of length. The HCP20965 needles are the 2nd richest needles available at all throttle positions overall, and people who are running pods and other modifications on XJ700 and XJ750 air-cooled 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 change of their richness or lean-ness at any given needle position (vacuum piston height), along with the differences in main fuel jet sizing.

The thicker the needle shaft at any given position along the shaft, the "leaner" that needle will be (less fuel can get thru the emulsion tube). For the HSC32 and HSC33 series carbs, the different needle "sizes" differ in their shaft diameters along the shaft, meaning some are leaner (or richer) than others AT DIFFERENT POSITIONS (the "at different positions" is really the critical actor). Yamaha, for a variety of reasons, used different "strength" (richness or leanness) in different engines IN CONJUNCTION WITH different fuel and air jet sizes to get the performance they desired (or, to meet emissions requirements of the country the bike was being exported to, or, other reasons).

Emulsion tubes for the HSC32 XJ650/750 engines are all the same, while the HSC33-series carbs used a different size emulsion tube (and don't ask me what the difference is..........).

Shimming needles: basically, don't..........or at least, not until you get the carb/engine tuning sorted out using stock needles, jets, etc. Playing around with needle sizes and shimming is a sure way to get very frustrated, very quickly. Once things are running properly in stock form, then making a single change at a time (to all 4 carbs, of course) can produce good results, but it's very time consuming (and, a particular change may give you better low-end response, but kill the top end power, or vice-versa, so your driving requirements also come into play).

The stock carb set-ups by Yamaha were designed to give the best overall performance for a typical user's operation of a motorcycle across a broad range of conditions. As with everything else, it was a compromise setting between performance and drivability. USA model bikes tended to be jetted-and-needled pretty lean from the factory, reflecting the more stringent (at the time) emissions requirements in the USA (and in California)......like many manufacturers, their first reaction to tighter emissions standards of that era was to simply lean-out the carbs, as that will reduce both overall emissions and especially CO at at idle/just-off-idle throttle positions, which is where the emissions test were conducted.

Using pods makes the whole tuning process that much more difficult.....it can be done, but to get things "just right" takes the patience of Job.........

 

Beautiful description of the relationships of the jets and needles Len! I am a stock carb guy, mostly because I don't have the patience to mess with methodical changes. Partly because I am satisfied with the way a good running XJ performs.

 

And because you are a wise old bird, and possibly have better things to do with your time.

If you really want an idea of how to properly tune CV carbs ("constant velocity", or "constant vacuum", depending on what continent you live on) you should review the Factory Pro guidelines, which aren't easy to get to since the website design is very '90's-ish, so there is no direct link, but do this:

a) go to www.factorypro.com
b) select the "Product Support" link at the top of the page.
c) select the "Motorcycle Tuning Tools" link
d) select the "CV Carb Tuning" link
e) read that intro page, and then click the "High RPM Engines" link
f) enjoy

 

Looking at these things from the way they were designed, that is the constant vacuum side of things, anything that changes the upstream (filter side) pressure - actually it will be a vacuum, will drastically change the parameters the slide will be working at. So if the upstream pressure on the bottom of the diaphragm goes up, the slide runs higher. Up to you what you think this does to fuelling, but I'm of the opinion it reduces the vacuum at the jet, which will make it run weak.
Added to this, the slide hits the top before max rpm and load is reached, I believe (but have never tested this), that once this happens the vacuum at the jet will then start to rise (since the balancing of pressures under the slide has failed), and any more rpm at wide open throttle will make it run rich..
A lot of this is theory, but one day I will verify all this (or bin it)...
Long and short of it, changing jets does not fix this.

 

Thanks Len, this is exactly what I needed to understand. (You are correct Air-compensator jets is what I meant not 'starter' jets.)

The last question I have is about the spacers/washers that I saw in the Mezzmo Engineering Carb Rebuild video? He puts two washers around the base of the needle jet before placing it into the base of the vacuum cylinder. Is this something specific to the engine mods he had, or are these necessary pieces I'm missing?

Like I mentioned in the OP, those needles (or the spring behind them) tend to bind and jump instead of moving up and down smoothly like I would expect. Is some silicone grease the key or might there be something else I'm missing?

 

Can you post a link to the video you are referring to? It's been quite a while since I watched his videos which are great). On Hitachi carbs for your bike, all there is to install in the vac piston is: needle, then the spring, then the plastic nut. No washer(s) or grease needed. The needles should not be binding.

 

This is the video I'm referring to, time stamp 9:30 :

I think you answered my question though, I'll go back through all 4 and check I have the narrower needles in and see if that changes any thing.

Thanks as always for the help, I would have no shot at figuring all this out without this forum and the community in general