Carb Rebuild Question

I Know,I know there are tons of post on this but I cannot find what I'm looking for!!
I am doing a full tear down and rebuild of set of Hitachi carbs for my 83 XJ750K Maxim. I need a List of all the parts that I need to replace. "O" rings, seals, jets the works.
The carb that is on the bike has the standard jet set up. The only mod on the bike is MAC 4to1 exhaust. I had to turn the mixture screws way out to get the proper fuel/air mixture. Should I re-jet to a larger jet?
Any help would be appreciated.

 

Question #2: What Parts Will I Need?:

The parts you'll need depends on what is there, what is missing, what is worn out, what gets broken or damaged during the dis-assembly process, etc., but the "basic items" needed for the rebuild process (besides any special tools and tuning equipment) is as follows:

- throttle shaft seals (you'll have to split the carbs from the rack to replace these).

- fuel supply tube o-rings (you'll have to split the carbs from the rack to replace these) on the models that use them (some Mikuni carbs do not use these).

- float valve needle and seat rebuild kit (seat, needle, clip, seat washer. The float valve seat filter screens are also available separately). Mikuni owners will also want to replace the float valve seat o-rings.

- float bowl gaskets.

- idle mixture washers & o-rings for sure, and the idle mixture screw springs and mixture screws if they are damaged.

- jets, if damaged or incorrectly sized.

- carb bowl fuel drain screws, if damaged.

- new replacement carb hardware (screws, etc.)---now is the time to upgrade to stainless steel and/or allen-head fasteners if so desired!



From Our Experience:

Since the carburetors are THE most troublesome (and thus most expensive) aspect of these bikes, let me offer a few dozen words and insights about them, their service, and expense:

These carbs are quite simple, mechanically speaking.

The process of making DARNED SURE that you get them unbelievably, positively zestfully clean is a matter of stick-to-it-ness and resisting all attempts to take "shortcuts" or to brush off the tedious aspects of it. Many of the passages in these carbs are tiny, and it's that "tiny-ness" that bites most people, as they don't want to or don't realize the amount of effort that has to be undertaken to deal with such small passages.

If you read through these forums, you'll see many tales of woe of people who are now "cleaning" their carbs for the 2nd, 3rd, or 4th time BEFORE they get it right. The problem is, they never really "cleaned" them correctly the first, 2nd, and 3rd time. After all of the frustration and hassle involved, by the time they get around to the 4th go-around, then they understand that when people who have SUCCESSFULLY rebuilt carbs say things like "you'd better make SURE that you get clear flow through each and every passage, and you'd better polish that piston diaphram bore", etc. aren't just saying that to be over-the-top retentive about their own habits and style of working on these carbs, what they're really doing is issuing an experienced WARNING: do it right, or keep doing it again, and again, and again. And although they're kind of fun little critters to play with, taking them all apart and putting Humpty Carby all back together again, well, it's time better spent on other things.


Think we're kidding? The following thread is a "must read", because the title says it all:

http://xjbikes.com/Forums/viewtopic/t=17821.html


One last note: "cleaning" the carbs (internally, not just making them look pretty on the outside) is just one of the small subsets of tasks necessary to the proper REBUILDING of the carbs. I cannot stress this point enough. The use of the term "cleaning" is used as if it were the end goal of the process; in reality, the proper way to think about it would be this:

"A complete and exceptional level of carb CLEANING is a vital and necessary part of the process of properly REBUILDING the carbs."

And what are the other components of the rebuilding puzzle?

a) getting the darned things off the bike! This might help:

http://xjbikes.com/Forums/viewtopic/t=29695.html


b) replacing the worn, missing, or necessary "wear parts" on the carb.


c) Proper "service" work to the carb bodies, especially:

- polishing the piston bore for silky smoothness.
- repair or clean up of any stripped threads in the carb bodies.
- replacement of any damaged or worn parts. In fact, the ability the recognize what is damaged and worn (besides the parts above which are designed to wear out) is the most difficult part of the entire task, since it requires a level of experience: are my needle tips worn? What, exactly, does a worn needle tip look like? How "smooth" is smooth enough? Etc. This is where the advice and experience of the members of this forum are invaluable.


d) Proper "settings" of the various components during re-assembly:
- the fuel levels (float heights).
- the "basic or bench synch" of the throttle valves


e) On-bike "settings":

- first and foremost, the measurement and setting to specifications of the valve train (shim) clearances. Failure to do this "wastes" 90% of your efforts involved with the carbs.
- final synch (using some type of manometer and the YICS tool if your engine is YICS-equipped)
- idle mixture screw setting, preferably using a Colortune plug.



One last thought about these carbs, since they are THE most troublesome aspects of these bikes, and something to consider:

- the four carbs concept is really neat looking, and is certainly performance-oriented to the extreme.

- for many of us who had lots of experience with automotive carbs, just beware that while these Hitachi and Mikuni carbs are a bit different in operation (and thus parts), a carb is a carb, and they're pretty basic little devices. The main difference is that the fuel circuit passages on these carbs can get bizarrely tiny, especially if you're used to working on automotive carbs (which have canyon-sized fuel passages compared to these carbs).

- like I've said, the cleanliness part is really just tedious work, with a couple of "tricks" thrown into the mix, given the small sizes you're having to deal with. The "rebuild" part is basic mechanical knowledge and skills, knowing which way to turn a screwdriver to loosen vs. tighten, when and how much force to use or not, being organized, stuff like that.

- but the "tuning" part will require some special tools, but no type of any rocket-science knowledge or skills----once you master the rebuild and tuning process with these bikes, you are pretty much a Carb Tuning God, as these carbs are about as "complicated" as it gets with carburetors. I mean, VERY few vehicles have multi-carbs, not until you get to the really high-performance machines level in the automotive world.

- well, as "complicated as it gets" until you start adding pods, etc.----which if you do, I sure hope you've got every last one of the basics listed above down to a science, and you can do it all, properly, and blindfolded, too!

- finally, if you do not have a service manual(s) for your particular bike(s), and you're going to wrench on it and want to do things right, then the only thing I can surmise from such a course of action is:

a) you're already an expert, or.....

b) you aren't really serious about doing things right, and that's okay, too---just don't expect good, quick, or cheap results!



The following guide may save untold hours of frustration and grief:

http://xjbikes.com/Forums/viewtopic/t=14692.html

 

Thanks for the reply Len. I have the carb completely broken down. And I will be replacing throttle shaft seals, fuel supply tube o-rings, and everything you have listed including one jet that was stubborn and new drain screws and a few other parts.
My main concern is the jetting, I have a mac 4to1 exhaust, came on the bike. Now my carbs that are on the bike have the standard jets for the stock exhaust. And when I tuned the carbs I had to turn the fuel air mixture screws way out to get the bike to run right and obtain the proper color on the plugs. So should I go to a lager size jet? Or just stay the same.
This is going to be a complete rebuild done right, as this is a spare set of carbs.

 

The answer to your question is near the bottom of the page that chacal linked to: http://xjbikes.com/Forums/viewtopic/t=14692.html (The Church of Clean.)

"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"

Also included is an explanation of other things that may or may not need to be changed, like the pilots, etc.