#3/#4 leaking carb after rebuild, XJ550 Maxim

Hi XJ Xperts,

My 1982 Maxim was running fine, but it was cutting out occasionally at very bad and dangerous times. The spark and compresson seem OK, so I figured it was a bad petcock, which was dumping fuel at ON (not just PRI), so the fuel petcock must have been bad. Therefore, I replaced it with a brand new fuel petcock.

Unfortunately, the engine stopped running strongly on cylinders #3,#4; the exhaust pipe was just warm on #3,#4, and burning hot on #1,#2. So I figured it was time to do a carb rebuild. The bike has 25,000 miles, and I have no records when a rebuild was done last.

So I carefully rebuilt my carbs and took my time and did it right. But when I filled them with gas from the tank (off the bike), either carb #3 and/or carb #4 leaked steadily originating between the two carbs, seemingly at the connecting tube which delivers the gas,( but it could be coming out of a dump port, if one exists; I don't know what I am looking for.)

No problem, I figured it was an overfilling float problem. To prove this, I swapped the float, new needle and seat from #3,#4 into #1,#2. I expected the leak to move to the other side but it did not, it remained in between #3,#4 (wow!) This strongly suggests that it has nothing to do with the float system, which makes sense, I just replaced the needle valve and seat assembly, and tested that the floats actually floated in gas, and did NOT bend any tangs.

So what else could it be? Could it be the tubing between the two carbs that deliver gasoline is leaking? Could I have cracked it when pushing/pulling on the carb assembly? ANY hints and ideas appreciated! Could it be as simple a gaskets?

Another strangitude is with the choke plungers. The spring is missing from choke plunger #4, due to a previous owner apparently losing it. Or is the spring missing in #4 by design? Since I did not have any problems running before, I figure I can just leave it off again. The choke cross bar moves all the other choke plungers synchronously and the other spring action are strong enough to return the unspringed choke plunger.

But this makes the choke system a suspect to me. I don't think that leaving the choke on can cause the #3,#4 leak described , but can a malfunction in a choke on #3 or #4 cause an overflow? I haven't seen a cutaway carb blueprint to be able to predict malfunctions in the choke that could cause a leak.

Thanks for any ideas, I don't want to disconnect the 4 carbs apart from each other as Clymer says, but may need to.

Joe

 

There is a tube that runs from #3 to #4 to carry the fuel. Sounds like your leak is there. More likely one of the seals at the end than the tube itself.

The choke plunger should be held closed by the spring rather than the fingers of the mechanism. I'd be real tempted to take one of the other springs to the hardware store to find a good match.

 

The springs are not that special. Mine were so rusted they were falling apart. I just went to the local hadware store and looked in the spring assortment box and found some very close the the originals. The springs can be alittle heavier spring to hold those plungers closed tight. I would think your #4 cylinder might be getting too much gas with no spring in that carb. As for the gas leak between the carbs. I would replace your o-rings on the transfer tubes. You will need to sync when you are done for sure. Also check to see if the tubes are clear and there is no debris just ahead of your needles and seats. Dress up your seats with a unpainted golf tee and your drill. Polish your seats so the needles will seal their best. Hope that helps.

 

Or you can buy the correct original springs!:


HCP25 OEM Hitachi Starter Enrichment Circuit brass jet needle PLUNGER SPRING. Each.
$ 6.00


I also have plenty of good used original plunger springs available, drop me a PM if you're interested.

 

You guys nailed it! Instead of messing around, I forged ahead and just separated the carbs and found that the #3/#4 transfer tube had split o-rings! And the #1/#2 did not! Halleluyah!

I will go out and get new O-rings, but now I am in territory which the Clymer does not cover. You said I needed to do a "sync"? What is the theory of syncing, why do I need to do it? I will search the forum for directions to implement a sync.

Is there anything else I need to do to reassemble properly? Is it really necessary to adjust the float levels again, especially since I did not touch the float tangs?

THANK YOU!!!THANK YOU!!!
THANK YOU!!!THANK YOU!!!

 

HITACHI IDLE SPEED SCREW PARTS:

Not to be confused with the idle MIXTURE screw listed above, the IDLE SPEED SCREW is the large knurled-head screw that lives dead center, at the bottom of the carb rack, in-between the #2 and #3 cars, and pointing straight back. This screw is used to adjust the idle speed of the engine, and has no effect on the idle mixture nor the carb (engine) "synch" settings! Fits all XJ650 (except Turbo), XJ700 non-X, and XJ750 models using Hitachi carbs.

HCP4024 Aftermarket Hitachi carb idle speed screw WASHER, not an original part, but if you use a set of these thin flat plastic shimming washers in-between the spring and the screw, and between the spring and the bracket (in other words, on either end of the spring), it greatly reduces the friction between the two and makes the idle screw silky-smooth to adjust!. Each:
$ 0.75



FUEL PIPE O-RINGS:


mmm1) OEM and Aftermarket Hitachi fuel rail Connector Pipe O-RING.....all fours carbs share a common fuel supply, and this fuel supply is distributed to each carb via a brass or aluminum tube that connects one carb to another. These tubes fits into a machined bores in the carb base, and the tubes are sealed in their bores with these rubber o-rings. NOTE: original seals were "D-rings" rather than "O-rings", but are now serviced only as o-rings (both OEM and replacements), but are the correct shape and firmness to provide a leak-proof fit. You will only be able to access these seals if you break the carbs out of their rack! (and if you do break the rack, you need to replace these seals). Aftermarket seals comes in your choice of either a lower-cost Buna-N material, or a longer-life Viton material. Either one will work just fine and last until the next time you take your carbs apart!

The viton material is much harder than the Buna-N material and the use of the viton seals requires quite a bit of effort to install the connector tube into the carb fuel port bores!

- Use 2 seals per tube, or a total of 6 seals per entire carb rack, for HSC32 series carbs (XJ650 except Turbo, XJ750 all).

- Use 2 seals per tube, or a total of 10 seals per entire carb rack, for HSC33 series carbs (all XJ700 non-X models).


HCP92 OEM Hitachi fuel line Tube O-Ring, each:
$ 1.50

HCP92SET6 OEM Hitachi fuel line Tube O-Ring, set of 6:
$ 7.50

HCP92SET10 OEM Hitachi fuel line Tube O-Ring, set of 10:
$ 9.00


HCP2421SET2 Aftermarket Hitachi Buna-N material fuel line Tube O-Ring, pair:
$ 2.00

HCP2421SET6 Aftermarket Hitachi Buna-N material fuel line Tube O-Ring, set of 6:
$ 4.00

HCP2421SET10 Aftermarket Hitachi Buna-N material fuel line Tube O-Ring, set of 10:
$ 6.50


HCP2420SET2 Aftermarket Hitachi Viton material fuel line Tube O-Ring, pair:
$ 2.50

HCP2420SET6 Aftermarket Hitachi Viton material fuel line Tube O-Ring, set of 6:
$ 6.00

HCP2420SET10 Aftermarket Hitachi Viton material fuel line Tube O-Ring, set of 10:
$ 8.50

 

And here's a little bit about the theory and practice of engine synchronization:


"CARB" SYNCHING AND OTHER FANCIFUL MYTHS:


Q: I know that you adjust the valves first (valve cover gasket also on the next order) but what is the sequence for the Colortune and Carbtune?

A: Well, it depends on whether you've "rebuilt" the carbs or not....kinda depends. If you've had the carbs off the bike, then the first step is to "bench synch" them, which means getting the butterflies "pretty close" to being all equal in terms of how much they are open at their fully closed (idle) position (the butterflies never actually "fully, completely" close, they always remain open a tiny amount, otherwise the bike wouldn't get any fuel-air mixture in, and thus wouldn't run). "Synching" on a bench means adjusting the synch screws (there's only three of them, the #3 carb doesn't have one because all of the other carbs are synched in relation to #3) while eyeballing the other throttle butterflies, and getting them "close enough" to allow the engine to start and run.

If you haven't had the carbs off the bike and apart, then you go directly to:

Then, you do a "real" synch, using the Carbtune or other such device. Again, what you're doing is manipulating the synch screws (3) in order to adjust each cylinder's output to be equal. On the "bench synch", all you're trying to do is get each butterfly valve to be equal with all others----like I said, close enough to allow the bike to start and run.

"Real" synching means you are going to be adjusting the positions of the butterflies (via those synch screws) so that EACH CYLINDER PULLS AN EQUAL AMOUNT OF VACUUM----if each cylinder pulls the same amount of vacuum (which is all a manometer is....a fancy, 4-in-1 calibrated vacuum gauge), then each cylinder is "pulling an equal load" as far as it's torque/horsepower output----hence each cylinder is "in synch" with each other cylinder, which results in a much smoother idle and better overall performance (less wear and tear).

Quite a number of factors affect how much power each INDIVIDUAL cylinder is producing......the valve adjustment of that cylinder. The piston ring seal of that one cylinder. The carb adjustment of that one cylinder. Etc. Etc. So the "real" synch that you perform with the Carbtune takes all of the those factors into account, and allows you to "compensate" for all those factors by opening or closing throttle butterflies valves enough to get each INDIVIDUAL cylinder producing the same power output---with the "power output" actually being measured by the amount of vacuum that the cylinder draws. Once each cylinder is adjusted so that it produces the same amount of vacuum draw as all the other cylinders, then your carbs are "in synch" (actually, your entire engine is "in synch", but since you do it via an adjustment to the throttle valves, it became know as a "carb synch", which is really incorrect terminology!).

Note that what you're really doing is bringing all the cylinders DOWN to the performance/power output level of the worst cylinder. Although this may seem like a dumb thing to do, it's the only way to synch the power output of each cylinder, and is a "lesser evil" type of thing as it relates to the overall performance of the engine.

Now, in regards to the "idle mixture screws", people throw around many terms that all refer to the same thing: idle screws, idle mixture screws, pilot mixture screws----all the same. The idle mixture setting is the ONLY adjustable setting on these carbs (besides the idle SPEED, which you do with the big knurled-knob screw that is dead center, on the bottom of the carb rack), and since this idle mixture setting goes through the PILOT FUEL CIRCUIT (which really means the "idle and low speed fuel-air mixture circuit"), well, there's why they call it a "pilot mixture screw" as well as an "idle screw" or an "idle mixture screw".

Words---they really get in the way sometimes!


NOW, SORTA WRAPPING THIS ALL UP:

Since the synchronization of each cylinder's output to a level of equality is the crucial goal, and since the synch is done at idle speeds (or, at least, at engine speeds in which the pilot fuel circuit is primarily the one that is active), and since the only fuel/air adjustment that can be done is via the idle mixture screw, then adjusting this screw WILL result in a difference in the fuel-air mixture in that cylinder, and thus will change the power output of that cylinder, and thus will change the synch of the entire engine (see where I'm heading?).

So here's what you do:

a) adjust the valves first. An out-of-adjustment valve---intake or exhaust---will reduce the power output of the cylinder that it is associated with, AND RECALL, "synching" means running ALL the cylinders DOWN in performance to the "lowest performing cylinder" in order to get them all producing equal power. This is why you adjust the valve clearnaces first, to get any performance issues associated with too tight or too loose valves "out of the equation".

b) Synch the carbs on the bike. This will be a "rough synch".

c) Adjust one idle mixture screw at a time to get that "bunsen blue" coloration. Once obtained on a cylinder, remove the colortune, put a sparkplug back in, and re-synch.

d) Go to the next cylinder, colortune it. Then replace the colortune plug with a real plug, re-synch the bike. (by the way, you leave the Carbtune Synch Gauge hooked up all during this procedure----as well as leaving the petcock on PRIME, since the petcock's vacuum source is now hooked up to the Carbtune).

e) Do this for all the cylinders, one at a time.

f) If you're aggressive and excited about the whole procedure, then go back and do the colortune #1/synch/colortune #2/synch/etc. routine again. By now you'll have that puppy purring.

g) If your fiddling with the idle mixture screws doesn't get the color of the flame in the colortune window to change AT ALL, then you're carbs are dirty internally, and, like or not, they need to be cleaned. Completely. Thoroughly. Zestfully cleaned.

Okay, all of that sounds like a lot, but once the gauges are set up on the carbs then it doesn't take long. Plus going from one cylinder to the other allows the little colortune plug some "downtime" in between cylinders to cool down.....and I'll also add, that during this downtime, you should also remove the YICS blanking tool from the passage, and allow it to cool down too (if the rubber seals get too hot they'll melt in there---and then you have a huge mess on your hands!) Wear gloves, trust me!!!

Oh, I forgot to add, that before you start the whole procedure you insert the YICS passage block-off tool into the chamber, and leave it in the entire time. At then end of the entire procedure, of course, you remove the tool, and then if you want to go one more round of COLORTUNE ONLY of each cylinder, go ahead, it shouldn't change things enough but may get you a final little bit of tuning accomplished.....but not enough to throw off the synch that you've just accomplished. And remember...a little rich on the mixture is much better than a little lean!

Then you go out and ride, and inspect your plugs after 50 miles or so. They should be a nice, very light tan color. Bright white = too lean....and that's a Very Bad Thing, especially on air cooled engine. It's also a shame and a devil's temptation, as engines produce more power when they run just a hair lean....such is the trade-offs of life, right? And dark brown or black = too rich or oil burning problems.


ABOUT VALVE SHIMS:

I carry all sizes of new shims, both aftermarket and OEM, in stock at all times, and given that you'll only find that two or three need replacing during a typical service, it really is rather inexpensive to do.

With used shims, you take the risk that the indicated size on the shim is still the actual size........although shims are "hardened steel", the hardening process only extend a few microns down into the surface of the shim, and once that hardened surface is breached, the shims wear rather significantly.

Thus each used shim must be miked (measured with an accurate, verified micrometer or other such precision measuring device) to determine it's "real" thickness as opposed to its indicated thickness, or otherwise you risk installing a used shim, thinking it will give you the proper clearance, and finding out (assuming you re-measure the clearances after replacement, as the service manual and common sense dictate!) that the (for example) 270 shim that your original calulations said you needed, and the 270 used shim that you installed, STILL doesn't give you the specified proper clearance............

Now, suppose you just throw the used 270 shim in, and don't bother to re-measure the clearance? Well, it might be right on the money. Or it just might not, in which case you'll STILL be operating with out-of-spec clearances, and even more important, without all of your valves being in spec---and here's the key point which you should ignore only if you wish to have continual, ongoing-forever performance problems--- ALL of your carb work (rebuilding/cleaning/adjustment, synchornization and tuning) is mostly for naught, because you can't "synch" an engine when it is out of adjustment......and while we're on that subject, let me add that the terminology used is fully incorrect: you don't "synch" carbs, you "synch" the entire engine, one cylinder at a a time, VIA THE ADJUSTMENT OF THE CARB BUTTERFLY POSTIONING. Understanding that concept is vital to understanding why it is so important to maintain proper valve clearances.


TO RE-CAP:

- you want to be able to have the power output of each cylinder to be equal in order to get the maximum performance, smoothness, and life expectancy from your engine.

- power output of each cylinder is strongly affected by a number of factors, with one of the main user-adjustable features and service parameters being the valve clearances.

- power output from each individual cylinder is measured via the vacuum draw of each cylinder on a mamometer, also known as a vacuum guage. The stronger the vacuum draw, the stronger the power output.

- in order to bring each cylinder's power output into equality---AND HERE"S THE IMPORTANT POINT TO PONDER----you have to DECREASE the power output of the best cylinder(s) to that of the weakest cylinder in order to get all cylinder's power output equal (meaning in "synch" with each other).

- you reduce a cylinders output in a one of two ways: adjust the valves on a cylinder to not open as much as on other cylinders, or open much more than other cylinders (those two methods are obtained by allowing the valve shim clearances to be out of spec), or you crank the butterfly closed on a cylinder. A third method would involve messing sufficiently with the fuel mixtures, via the idle mixture screw, to choke a good cylinder(s) output down to the lowest output cylinder, although that has significant other ramifications of doing so.

In theory and practice, you could actually "synch" an engine simply by adjusting valve clearances on individual cylinders (while leaving the butterfly shaft openings all the same) until each cylinder's vacuum draw, and thus power output, were equal. NOTICE: leave the throttle shaft opening THE SAME, and adjust the valve clearances. OR, you can do it the way the factory recommends: FIX the valve shim cleaances to proper specifications---in essence, thus leaving the valve clearance "the same"----and ADJUST the butterfly openings to compensate.

Valve shim clearance checks and adjustments are probably THE most overlooked aspect of maintenance on these engines, mainly because it's thought of being such a pain in the butt to do, and if your clearances are out of spec, you then have to wait for replacement shims to be delivered to you. That's why I carry all sizes in stock, and can normally ship the same day, via priority mail or express mail or whatever service level you desire and wish to pay for.

In reality, CHECKING the clearances isn't technically or mechanically difficult, and changing shims isn't rocket science either, and the biggest hassle with the entire experience is getting the rubber valve gasket back in place during re-assembly---an exercise in frustration without having the proper adhesive. Of course, those owners that use a paper valve cover gasket don't even have to suffer that trial.

Also, when removing the valve cover, you should always check and probably replace the valve cover hold-down bolt washers, as that will go a long way to preventing oil leaks in the valvecover area.


PLUGS CHOPS, a/k/a the Zen(ith) of Engine Tuning:

To get even more aggressive, you do what people call a "plug chop"---and you do it carefully! When you remove the plugs after that 50 mile ride, what you're seeing is the color of the plugs due to the last few moments of combustion inside the cylinder......and those last few moments are usually at idle or just off-idle. So your plugs are telling you what things are like with a warm engine, at idle conditions....a very limited (and not-so-useful) insight.

Plug chops are where you run the engine (under load, meaning real-life riding conditions) and then if you want to read the engine conditions at, say, normal cruise speed, you get up to a normal cruise speed for a minute or two, keep it there, and then push the kill button (killing the engine), coast safely to a stop, and remove and read the plugs.....in this way, you get to see what the fuel mixture conditions are (determined via reading the color of the spark plug insulators) is at normal cruise conditions. You can do the same thing at full acceleration, or wide-open throttle (CAREFULLY killing it, lets say, at 5000 rpms in 3rd gear).

This is a much more accurate way of determining what the fuel mixture conditions are inside a real engine, under real conditions. Much more of a pain in the butt, too, which is why most people don't do it. But if you REALLY want to get things right, that's how it's done. NOTE: depending at what load conditions and throttle position you do the "chop" at (meaning "push the kill button") tells you where you might need to adjust things. The pilot fuel circuit is active from idle up to about 2500-3500 rpms, and at about 3000 rpms the main fuel circuit starts becoming involved, and by 4000+ rpms the main fuel circuit is responsible for about 80%+ of the engine's fuel supply conditions. So where you do the "chops" tell you not only what the fuel mixture and combustion conditions are like, but also, which circuits are responsible for those conditions.

This is what is meant by "tuning" a bike via changing fuel and air jets, needle shimming, etc......like when you change the exhaust system or air cleaners to those little "pod" filters.

Finally, here's a little video showing a colortune plug "in action"---kinda grainy, audio not academy-award quality, but better than nothing:

http://www.gadgetjq.com/ctune.htm

Hope you aren't bored to tears yet.....but, at least now you know more than 99% of the other people do!