Intake boots

Just got my new 1981 xj650 and has a strange idle. will idle fine but once reved comes down very slow and when left si will rev up on its own. Also wondering the two intake boots on the right side have the rubber caps pointed down. Wondering if that is right since most pics show them pointed up.

 

the boots are installed wrong. the caps are always up.

it's possible that the boots are shaped so that they only work one way. if mounted wrong. they might not seal. i never paid attention to the shape as i've always mounted in the proper way. others might chime in for better insight.

 

Someone either installed the correct boots upside down, or more than likly, is trying to fit 1982-83 style intake manifolds to the 1980-81 model head.........and the only way to get them to "fit" is to install them upside down:

NOTE: all intake manifolds differ between the left side and the right side versions in two critical manners:

* intake manifolds, when installed on the engines, "curve" inwards towards the centerline of the bike.

* they also curve "upwards" (as well as inwards).

This combination of both upward and inward curvatures of the intake manifolds is why it is not possible to simple swap left side (cylinders #1 and #2) and right side (cylinders #3 and #4) intake manifolds.....some people think that you can just "flip upside down" a right side manifold and it will become a left side manifold (or vice-versa). This would be true is there were only the "inward" curvature to the manifolds; however, the "upward" curvature prevents such swapping from occurring (as the swapped-side manifold would be curving "inwards and downward")...........and you'll never get the carbs to fit correctly into such mis-aligned manifolds, and on the slim chance that you do get them to fit, you'll end up with major vacuum leaks at that joint.


XJ650, XJ700, and XJ750 engines:

NOTE: the non-YICS (1980-81 and 1982 XJ650RJ Seca) left side (cylinders #1 and #2) manifolds differ from the YICS (1982-84) manifolds in the orientation of their mounting:

* non-YICS engines have the intake manifold mounting bolt holes in the cylinder head aligned in this manner:

<#1 \ \ \ \ #4>

* YICS engines have the intake manifold mounting bolt holes in the cylinder head aligned in this manner:

<#1 / / \ \ #4>

This is why the left side (cylinders #1 and #2) intakes differ between the YICS and non-YICS engines, and why they are the same for the right side (cylinders #3 and #4) on all XJ650 non-Turbo engines!

 

That makes sence. I though they were wrong. Thanks a million. I am sure that is why i am having idle issues. When i get all that fixed up i was wondering what kind of jetting changes you would have to do if went to pod filters the stock air box is in rough shap.

 

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 main or pilot air jets, the main needle or main needle jet size, and thus are additional variables and opportunities for tuning excellence. These are areas which are largely unexplored by most tuners, but logically should allow for additional fine tuning or additional rage and frustration.........


Normally, changing to an aftermarket exhaust does NOT require re-jetting, (or minimal re-jetting) as almost ALL of the airflow restriction in the airflow path thru the engine (meaning: ATMOSPHERE > AIRBOX > FILTER > AIRBOX BOOTS > CARBS > INTAKE MANIFOLDS > CYLINDER HEAD PASSAGES > EXHAUST SYSTEM > BACK OUT INTO THE ATMOSPHERE) is within the intake side of this air flow path, and primarily within the stock airbox/air filter. Your stock EXHAUST system can already flow more air volume than the stock INTAKE system allows.

Thus changing only the stock EXHAUST system, with no changes to the intake side of the heads, normally makes NO DIFFERENCE IN TOTAL AIRFLOW, and "no difference in total airflow" means "no difference in TOTAL FUEL FLOW" either, and thus bigger jets are not needed.


But once you start freeing up the INTAKE side of the entire system, you will produce more system airflow, even with a stock exhaust system (because, the stock exhaust system has the capability to flow more air through it than what the stock intake system allows).

This is why re-jetting is usually needed even if you keep the stock airbox and the stock exhaust, but use a K&N low-restriction filter, or even if you drill holes in the stock airbox, or leave the filter lid off.

All such actions free up the intake side airflow restrictions; the stock exhaust will move this additional airflow, and without providing addition FUEL flow to match the increased airflow (within limits, an engine will gobble up the maximum amount of airflow that it can; an internal combustion engine is actually just a self-powered AIR PUMP) then the engine will run "lean"---meaning not enough fuel to match the amount of airflow that the engine can (and now will) gulp.

Most pod type filters allow for vastly increased airflow, and thus require fuel re-jetting, and although no one really talks much about it, probably also require AIR JET changes to match the additional fuel flow, but since no one likes to deal with two parameters at once, it becomes a "tuning nightmare".


BUT, when you read all of the common symptoms of people who use pods, you quickly come to the conclusion that it's not possible to reproduce the stock "smooth in all rpm ranges" engine response. The reality is that you SHOULD be able to match it pretty darn closely, even with the increased airflow through the system, but ONLY changing the fuel jets isn't going to accomplish that. There are also air jets in the system, and they are there for a reason, as well as needle tapers and vacuum piston responsiveness issues.


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.

As one of our favorite experts says about pod filters: "Get a Rubik's Cube instead.....it's less trouble and actually has an eventual solution!"

 

If you look at the air box on your bike from the side you will notice that the front face is sloped. The rubber intake boots for this bike are also sloped on their ends that plug into the holes in the front of the air box.
Also, above each of the four holes in the front face of the air box are a pair of small projections that stick out about 1/8". The rubber intake boots should have a small tab molded into their ends that engage the airbox. This tab should be positioned such that it sits between the pair of projections molded into the front face of the air box. I own a 1981 XJ650H and have have removed the carbs many times to clean them. I swab a little silicone oil around the ends of the intake boots whenever I go to re-install them. It makes assembly go much easier. The ones on my bike right now are replacements as the the OEM were hard and fit poorly. Also, the front face of my airbox was warped (concave) and I could not bring it forward enough so that all the intake boots met their respective carbs. I had to remove the airbox and fasten an aluminum bar across the front face to pull the warp out. The bar sits about 3/8" below the four boots. Now the fit-up is perfect. I replaced all the OEM boot clamps with 3/8" wide Stainless gear clamps that I bought through McMaster Carr.