Hitachi Carb Main Jets.

My bike is in the shop getting some carb work done and I was told I need to buy four main jets size #100 or #102. After looking all over the web, all I can find is sizes 110 - 134. Was this size ever used in a 82 maxim 650 or is 110 - 134 what came stock in these bikes.

Thanks-

 

Here you go.........#100 and 3102 fuel jets were never used on any Hitachi carb that went on these bikes. The stock size for your bike is #110 main fuel and #40 pilot fuel. I carry all sizes in stock.


Main & Pilot Fuel Jets:


ee) Aftermarket Hitachi brass MAIN FUEL JETS, sizes as follows, fits all XJ650 (except Turbo), all XJ750, and all XJ700 (exc. "X") models.

NOTE: stock Hitachi XJ series carbs used the following original sizes:

#106 (XJ 750 Seca, 1984 only)
#107 (XJ700 non-X)
#110 (650 models)
#120 (all 750 models except 1984 XJ750 Seca)

All the other sizes are for "tuning" or re-jetting purposes when changing intakes or exhaust systems.


HCP6316 aftermarket brass #106 MAIN FUEL JET (stock size for '84 XJ750 Seca)
HCP6317 aftermarket brass #107 MAIN FUEL JET (stock size for XJ700 non-X)
HCP6318 aftermarket brass #108 MAIN FUEL JET
HCP6319 aftermarket brass #109 MAIN FUEL JET

Any size jet from above, HCP6316 - HCP6319:

$ 6.00 each
or
$ 21.00 for a set of 4 (mix-and-match any of the above sizes okay)


HCP873 aftermarket brass #110 MAIN FUEL JET (stock size for XJ650)
HCP874 aftermarket brass #112 MAIN FUEL JET
HCP875 aftermarket brass #116 MAIN FUEL JET
HCP876 aftermarket brass #118 MAIN FUEL JET
HCP877 aftermarket brass #120 MAIN FUEL JET (stock size for XJ750)
HCP878 aftermarket brass #122 MAIN FUEL JET
HCP879 aftermarket brass #124 MAIN FUEL JET
HCP880 aftermarket brass #126 MAIN FUEL JET
HCP881 aftermarket brass #128 MAIN FUEL JET
HCP882 aftermarket brass #130 MAIN FUEL JET
HCP883 aftermarket brass #132 MAIN FUEL JET
HCP884 aftermarket brass #134 MAIN FUEL JET

Any size jet from above, HCP873 - HCP884:
$ 3.25 each
or
$ 11.00 for a set of 4 (mix-and-match any of the above sizes okay)



xx3) Reproduction Hitachi main fuel jet SPACER WASHER, round flat copper washer goes under the head of the main fuel jet. Perfectly replaces missing or bowed originals.

HCP887 Hitachi carbs main fuel jet spacer washer, each:
$ 4.50

HCP887SET4 Hitachi carbs main fuel jet spacer washer, set of 4:
$ 15.00



ff) Aftermarket Hitachi PILOT FUEL JET, sizes as follows, fits all XJ650 (except Turbo), all XJ750, and all XJ700 (exc. "X") models.

NOTE: stock Hitachi XJ series carbs used the following original sizes:

#36.5 all XJ700 non-X models.
#40 all XJ650 Maxim, Midnight Maxin, and Seca (RK) models, and all XJ750 models.
#43: all 1984 XJ750 Seca and Euro/UK XJ750 models.

The #41, #42, and #43 sizes are for "tuning" or re-jetting purposes when changing intakes or exhaust systems.

HCP885 aftermarket brass #40 PILOT FUEL JET
HCP886 aftermarket brass #41 PILOT FUEL JET

Either size jet above, HCP885 or HCP886:
$ 3.25 each
or
$ 11.00 for a set of 4 (mix-and-match #40 or #41 sizes okay)


HCP6326 aftermarket brass #42 PILOT FUEL JET
HCP6320 aftermarket brass #43 PILOT FUEL JET

Either size jet above, HCP6326 or HCP6320:
$ 5.25 each
or
$ 19.00 for a set of 4 (mix-and-match #42 or #43 sizes okay)

 

Hi, I'm rejetting my '83 Maxim and I bought some jets a wile ago because I was changing the exhaust and filter system. I got #41 pilot and when I finally got around to rejetting I found that my tuns out on my fuel screw is 4 turns.
Therefore I need to go up to a #42 but I cant find them anywhere! does anyone know who or where I can order some?

 

Hey mykl8...........if you read the post above yours, you'll find them there!!

 

hrm... I just cleaned my carb recently and my main jets were #120s. Will I lose fuel economy with that much fuel flowing through?

 

Curious, is a 750? What exhaust and intake mods? Mine is a 750 and i have 4 into 1 jardine exhaust. Very lean. I am trying to decide on my jetting. Im ordering 122 mains, and i thought a 41 would be ok, but maybe a 42...

What elevation are you? I'm 4300.

Thanks ,

Rich

 

i have a maxim 700 with stock pipes and intake...i am putting on some bolt on aftermarket mufflers right now...how big should i go with my main jets...i am at 107 stock :?

 

WHAT ABOUT RE-JETTING FOR PODS, ETC?:

It's a question we get asked often and unfortunately, one that we cannot answer honestly about your specific bike besides with "it depends".

Which is a nice way of saying "you're about to enter the seventh circle of hell......."!

Carb jet tuning required by aftermarket modifications is somewhat of a black art, part science, part skill, part luck. It depends on the current state of tune of your engine, your altitude, the mix of aftermarket parts on your bike, etc........a lot of variables.

The best advice we can offer is: Just Say No. Don't do it! Leave everything stock!

But, since most people---with good reason, I might add---don't always listen to our well-intentioned advice, then the next best recommendation we can offer is: "if you want more power get a bigger bike!".

And since that doesn't cut it with many owners, either, for the remaining stalwarts out there who insist on "experimenting" with aftermarket intake and exhaust systems, here's the best information that we've come across to give you some GUIDANCE, which you should take as just that, and not as ANSWERS, because it isn't!



MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:


Typical Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

or

+4 main fuel jet sizes for 4-into-1 exhaust

or

+4 main jet sizes for no muffler (open headers)


Typical Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

or

+2 main fuel jet size for drilling holes in the airbox with stock filter

or

+4 main fuel jet sizes for individual pod filters (no airbox)


Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.



PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.



PRECAUTIONS:

- Make sure your carbs are in perfect working order before making ANY jet changes....meaning fully cleaned internally and rebuilt, operating properly in their stock configuration, proper sized air jets and needles, etc. Otherwise, you'll like find that all of your efforts are going to be a HUGE waste of time.

- Check plug color often and adjust as needed, 2 main fuel jet sizes at a time and 1 pilot fuel jet size at a time. Bright white plug insulators are a sign of an overly lean fuel mixture condition and WILL cause damage to your engine over time, up to and including engine seizure!

- Synch the carbs after each jet change.

- Make sure the floats are set correctly

- Seriously consider purchasing a Colortune Plug Tuning kit.

- You may find it necessary to make changes to the size or shimming of the main jet needle. There are no guidelines on what or how to do these changes, this is true trial-and-error tuning!



EXAMPLE:

A 1982 XJ750RJ Seca using an aftermarket Supertrapp 4-into-1 exhaust and a single K&N air filter in the stock, unmodified airbox. Bike is primarily operated at an altitude of 2600 feet above sea level.

XJ750 Seca Stock Hitachi HSC32 Carb Jetting:

#120 Main Fuel Jet
#40 Pilot Fuel Jet
#50 Main Air Jet
#225 Pilot Air Jet
Y-13 Needle


MAIN FUEL JET SIZE CALCULATIONS:

Changes made:

Exhaust:
4 into 1 with Supertrapp = +4 Sizes Main Fuel Jet

Intake:
K&N Pod Filters = +4 sizes Main Fuel Jet
----------------------------
Equals: +8 main fuel jet sizes above baseline
Subtract: -2 main fuel jet size per formula above
----------------------------
Equals: +6 main fuel jet sizes due to modifications, thus:

Stock main fuel jet size is: #120
+ 6 additional sizes
= a #126 main fuel jet size
---------------------------
Subtract: -2 main fuel jet sizes for Altitude of 2500' Average

= #126 calculated from above
-2 jet sizes for altitude adjustment

= a #124 main fuel jet size.


PILOT FUEL JET SIZE CALCULATIONS:

The formula is: +1 pilot jet size increase for every +3 main jet sizes increased.

Stock pilot fuel jet size is: #40
+ 2 additional jet sizes (since we went up +6 main fuel jet sizes before the altitude compensation was factored in):

= a #42 pilot fuel jet size.

Note that no altitude compensation is needed on the pilot fuel jet since our elevation is less than 6000' a-s-l.


------------------------------

RESULT:

A #124 Main and #42 Pilot is A GOOD STARTING POINT.

******************************************************

Note that the above calculations do NOT take into account any possible changes in the sizes of the air jets nor the main needle size, which are additional variables and opportunities for tuning excellence (or frustration!).

For further insights and understanding, the Holy Grail (meaning: the whole miserable, un-varnished truth of what a real chore carb tuning is going to be, written by people who actually know what they're talking about, rather than by people who are trying to sell you something) can be found at:

www.factorypro.com

and then click on the "Product Support/Technical Support" link at the top of the page, then on the "Motorcycle Tuning Tech" link, and then the "CV Carb Tuning" link........and then read, weep, study, and do....if you still dare to! HINT: if reading through it makes you think to yourself "sheesh, this sounds like an incredible amount of effort!", well, you're right! That's just some of the joys (and pitfalls) of getting to play "tuning engineer", which is what you're going to be doing. Yamaha probably has 10 of those types of guys on staff, and millions of dollars of test equipment, both physical and computer-aided, that allowed them to get the mixture settings just right---from an overall drivability AND power output standpoint----and now, since you're changing the airflow parameters thru the engine, you'll have to figure it all out "from scratch", but WITHOUT the benefit of 10 trained engineers and all that test equipment and experience.

That's why we warn you that setting up a bike for pods can be quite a bit of trial-and-error procedure. You can make the calculations according to what is shown in that guideline and then order the jets that the "formula" recommends, and that should serve as a good STARTING POINT............you may (or may not!) have to do more tuning and trial-and-erroring substitution of different jet sizes, etc. to get it performing to you satisfaction, with the recognition that you may ALWAYS end up with a situation that has some kinds of trade-offs.....lazy at the lower end but runs well at mid/upper-ranges, or runs well at the lower end but a "flat-spot" at some other rpm range, etc. Unfortunately there is no magic formula........you might want to read through the factorypro.com article that I list at the end of that section, and you will get a better understanding of what is involved to get the carbs set-up properly in a non-stock configuration.

 

thanks for the advice chacal, i will buy some jets from you soon. i am not changing the exhaust because i want more power, i just cant stand the look of the huge megaphone mufflers. its an old bike but i looks pretty good for its age but those HUGE mufflers on both sides really age the looks of it and i wouldnt mind a little more noise either

 

Hey Wesbaker293, what did they say was wrong with your old jets?

Just curious.

 

Hello All, I recently purchased an 85 xj 700 non x and need to replace all the main and secondary jets. Cant find these anywhere, I need #107 main and #36.5 secondary, are these still available? Thanks for all your help

 

Hey Shorts, we carry them in stock, just drop us an e-mail or PM and we'll provide you with prices and ordering info!

 

Hello, I have purchased a MAC 4-1 exhaust to my Maxim X (because its near impossible to find a stock exhaust in good condition) I have not installed it yet, but if the exhaust doesnt "pop" do I have to change the jets? I also have K&N Airbox filter.
I Have a dynojet stage 3 kit at home, it says:

1. Remove the vacuum slides from the carbs. Remove the stock needles and spacers, noting the
order of assembly (Fig. A). Locate the slide lift holes (Fig. A). Using the slide drill (DD #37) provided,
enlarge the slide lift holes. Do not drill the needle hole.

2. Install the Dynojet needles on groove #3 from the top. Use all stock spacers (Fig. A). Install the
small Dynojet washers above the E-clip. After installing the slides in the carbs be sure to check slide
movement manually.

3. Remove the stock main jets and replace with the Dynojet main jets provided. Install the DJ116
main jets when using a stock exhaust. Install the DJ112 main jets when using an aftermarket slip-on
or full exhaust with a high flow baffle. Be sure that the jet you are changing is the main jet.

4. Locate the fuel mixture plug (Fig. B). If you see a screw head at Fig. B proceed to adjusting
procedure. With the DD #5/32 drill bit provided carefully drill through the plugs. NOTE: The mixture
screw is directly underneath this plug, be ready to pull back on the drill the instant you break through.
Use screw provided to secure and remove this plug. Carefully turn mixture screws clockwise until
lightly seated, then back out 3 turns.

"Locate the slide lift holes (Fig. A). Using the slide drill (DD #37) provided,
enlarge the slide lift holes." Is this a permanent alteration? Can I put the main jets and needles back after I have done this?

After reading this post, the size of the dynojet kit jets seems a bit big, the stock on the Maxim X is JET,MAIN #105 .
The stock JET,PILOT #35, but the kit doesnt have a pilot jet replacement. Should I be worried?
And should I install the 116 or 112 jets? (this kit seems like its for both the X and the non-X altho they have different stock main jets)

Thank You

 

I would strongly urge you to NOT install a Dynojet kit, especially on the Maxim-X models, most owner's experience shows that these engines do not repsond well, at all, to intake, carb, or exhaust modifications!

 

I have to install the new exhaust from MAC, because the old exhaust is in a terrible condition. But I dont want to install the dynojet, I will wait and see if the new exhaust "pops". I see on ebay that 6SigmaRacing sells jet kits made after the mods you have on the bike.
But is it better to have the bike run lean, rather than installing new jets?

 

hi i am rebuilding a set of xj700 non x carbs and need a complete set of jets . main and pilot , can u help . thanks john

 

hi i am rebuilding a set of xj700 non x carbs and need a complete set of jets . main and pilot , can u help . thanks john

 

I was wondering that too. You know they don't wear out. I suppose the could have somehow gotten damaged.