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TALKIN' TECH: Various Thoughts on Various Issues


Below you'll find some of my thoughts on various technical, tuning, or maintenance issues that I hope will be of interest and of some assistance to you as you navigate the various trials-and-tribulations of being an XJ-owner!


"Do I really need to adjust my valves before I do my carb tuning? I just want my bike to run better than it is now."


Yes, what some commentators say is true, you certainly CAN "synch" and Colortune without first checking/setting your valves, but if your synch-and-tune results in a much better running bike (likely) AND IF THAT MAKES YOU LESS MOTIVATED TO CHECK/ADJUST THE VALVES-----well, that's where your troubles really begin (you've won the battle-lost the war type of thing.....).

The key to understanding this whole issue begins with understanding that you DON'T "synch" THE CARBS.........this poor use of words leads to a mountain of mis-understanding of what it is that you're actually trying to accomplish.

The word "synchronization" means "getting things equalized" between various component pieces. Are you setting each individual carb to the exact same specs?----the same idle mixture screw setting, the same throttle valve (butterfly) opening during this procedure?

NO, YOU'RE NOT. You will have different settings on all four carbs when you're done with the procedure.



You're "synching" the engine, or, to be more precise, you're SYNCHRONIZING THE POWER OUTPUT OF EACH CYLINDER TO EACH OTHER.

So that each cylinder provides the SAME (and not necessarily the maximum) POWER OUTPUT.

You measure the "sameness" of power output via how much vacuum pull each cylinder develops. This is why the synch procedure measures cylinder vacuum rather than a carb-specific issue (such as rate of fuel flow, air flow through the carb, etc. Notice how the vacuum draw is measured DOWNSTREAM of the carbs...........).

You can ADJUST how much power each cylinder outputs (and thus how much vacuum each cylinder draws) via a number of methods, here's a few that come to mind:

- you can bore out a single cylinder, giving it a bigger displacement, thus more power output.

- you could re-ring an individual cylinder to give it a better seal and thus more compression.

- you could ADJUST THE VALVE OPENINGS (or timing, and the two are related, as pointed out by a previous poster) on an individual cylinder to be more or less than on others, thus affecting how much air/fuel is drawn into that cylinder, and how much compression that cylinder builds.


Note the very important issue in the last statement above: you can adjust the carb settings to "starve" the best cylinders down to the performance of the lowest-performing cylinder......and thus can "equalize" (synch) the output of each cylinder DOWN TO THAT LOWEST-COMMON-DENOMINATOR cylinder.

You know, you COULD actually set all the carbs to be exactly equal in their mixture screw settings and throttle blade openings, and then mess around with the individual intake and exhaust valve opening settings (re-shimming) until all cylinders matched each other in power output (vacuum draw), too......

That would be silly, not to mention quite time consuming.

And THAT'S WHY the factory (or any engine builder/tuner) says to get all the valve clearances set to spec, first, and then do the "fine-tuning" adjustments via the carb adjustments.

Also, on these engines, over time, as wear occurs in the valvetrain, the valves LOSE clearance, and thus become "tighter" and spend more time in contact with the actual cam lobe.

On the intake side, a tighter (less clearance) cam-to-shim clearance gives you more lift, and more valve "open time" duration.

On the exhaust side, it results in exactly the same things.

AND SINCE THE EXHAUST VALVE DEPENDS ON A PROPER AMOUNT OF "ON-THE-VALVE-SEAT TIME" FOR COOLING, having a "too tight" exhaust valve means the exhaust valve doesn't get enough seat (fully closed) time on the valve seat in the cylinder head, and thus runs much hotter than designed.

And that slowly burns the exhaust valve.

And that results in a much more expensive fix in the future, or, if it's just a wee bit burned, much less performance from that/those cylinders, which means then next time you "synch", you're going to be bringing all the other cylinders DOWN in performance to the one with the slightly burned exhaust valve.......

Yamaha motors are pretty bullet-proof little devices. Best to keep them that way through following proper maintenance procedures.

To review:

Although many people will disagree with the above, and feel that I'm just an enthusiastic salesman, there are reasons why I say to do things in the way the factory manual instructs the user to perform such tasks.

Trust me, the factory engineers had both the theoretical and the practical knowledge at hand when they wrote their instructions, and such types of people INTENTIONALLY attempt to provide the bare minimum amount of steps necessary to do the job right---contrary to popular belief, there are no "stand on your head and juggle BB's with your toes while you adjust this screw" type of extraneous steps are included.

I think what puts people off is that in order to do a proper engine synch, you must go through (or have gone through) ALL of the following steps BEFORE you get to the stage where you are ready to "synch" and/or colortune:

a) valve adjustment.

b) compression test.

c) carbs cleaned (internally) and functioning absolutely properly (slide drop "clunk" test passed, correct air and fuel jets, diaphragms good, no vacuum leaks at the throttle seals, idle mixture o-rings replaced, intake manifolds checked for leaks and repaired or replaced, same for airbox boots).

d) coils, plug wires, plug caps, and plugs are checked and are performing properly.

Only once all of the above steps are taken, and any problems identified AND CORRECTED, are you ready to synch THE ENGINE.

And the use of the proper tools to do the above is just part of the game!

I know that many people will find it surprising (and then frustrating) that you bought a bike for $500 and then realize that oh-my-gosh, I'm going to have to spend another $500 or more JUST TO DO A TUNE UP! and thus get really discouraged.....well, that's one reason the bike was "only $500" and the cold, stark reality is that 20+ years of previous owner's (and perhaps dealership service department's) neglect, incompetence, and inexperience is now your problem to deal with.

And the only legitimate question and issue is: are you going to follow in the same footsteps as that previous owner, or are you going to do things correctly?

Well, are you punk? :D

Remember, you are now working on a high-performance, multi-carbed engine....if you can successfully work on these, everything else is a walk in the park.....so ask yourself, how many other multi-carbed engines do you know of? Ferrari's? Maserati's? Old Triumph TR-models? Mopar "six-pack" engines with Holley 3x2-barrels? Race engines? I mean, you're kind of in a small, rarefied area with these bikes and their multi-carb systems, and with that rarity and complexity comes a cost!

If all of the above sounds tough, please also take a moment to reflect that on the bright side, at least you can get the parts you need, and you can get the tools you need, and of course these forums are available to get the advice---no matter how discouraging the reality of such advice may be---to allow you to do a proper job. And once you invest the time and money to acquire the right parts and tools to do the job properly, you most likely won't ever have to spend much more on those items ever again.

Welcome to the world of working on classic vehicles! It's not always easy, it's rarely inexpensive, but you'll not only take great joy and pride from doing what other mere mortals are not able to do, but you'll also have a beautiful classic bike that will outperform most other bikes of any vintage.

One final caution: beware of people who "advise" you on taking shortcuts, or downplay the need to do a job properly or thoroughly. Their techniques may work for them, but of course they may only be planning to hold onto their bikes for a few months or so.

Just my 2-cents. Like the old Fram oil filter commercials said:

"You can pay me now, or you can pay me (a lot more) later....."

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

To get even more aggressive in your tuning efforts (beyond mere colortuning and synching), you'll need to do what people call a "plug chop"---and you do it carefully!

When you remove your 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 the procedure 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.


"I just purchased a 1981 XJ650 which is pretty much box stock.

From what I've read, there's a few things that should be checked immediately and could help me keep the bike more trouble-free. I know bikes in general pretty well, but Yamahas not much at all.

What are the key things to check and do, to avoid future problems?

Not shooting for a concourse bike, just a smooth, reliable rider."


These old Yamaha bikes are pretty darn reliable, almost bulletproof in the engine/drivetrain areas if they are maintained properly......which means that ALL of the maintenance schedules are followed. So if you do not have one, I would strongly suggest that you purchase either a factory service manual or aftermarket Haynes or Clymer service workbooks, and make sure that you do the following:

- change the oil and filter RELIGIOUSLY. Consider adding the aftermarket spin-on ("can") oil filter conversion........it not only makes oil changes incredibly easier, but a can filter provides much better filtration ability than the stock filter system.

- check your valve clearances and adjust as necessary. It's a pain in the butt type of job, but mechanically easy.

- replace the stock fusebox with a late-model style enclosed fusebox that uses the push-in "blade" style (ATC) fuses. A little "wire extending" is necessary on most bikes, but again, not technically difficult.

- check the condition of the electrical system, specifically the alternator stator and rotor electrical resistances, the condition of the battery, and measure the length of the alternator brushes----and replace if needed.

- clean and lube all of the electrical connectors on the bike. Corrosion is a factor with any electrical connector, but is especially true with bikes as they are exposed to the elements, and the length of time. Technically simple, tedious but boring to do, absolutely essential. Here, read this when you get the chance and print it out for future reference:


- flush the brake fluid. Put "replacement of the original brake lines" on your to-do list, as the factory brake lines are rated for only 4 years life from the factory----and it's a good bet that they've never been replaced, even after 25+ years! THIS IS A MAJOR SAFETY ISSUE THAT YOU DO NOT WANT TO NEGLECT!

- inspect the entire brake system, including pad thickness and rotor condition. If you don't know for sure as to when the last time (if ever!) that the calipers or master cylinder have been rebuilt, add those tasks to you to-do list, also.

- eventually, you're going to have to clean and tune the carbs. My advice, is to do it once, to it right, do it COMPLETELY, and do it thoroughly. Anything else is just a "penny-wise, pound foolish" type of effort.

- you'll have to invest in a couple of specialty tools: valve shim bucket tool, synch gauges a/k/a synch sticks, and a colortune spark plug for maximum tuning ability.

- add an in-line fuel line filter. And consider replacing the filter unit inside the tank (sits on top of the petcock) and perhaps rebuild the petcock in advance of it failing (they all do, eventually!).

- check the condition of the air filter element and replace if necessary. There are a variety of upgrades you can do that "flow more air", but flowing more air almost ALWAYS means you'll have to make plans to "pass more gas", also, which means a somewhat tedious job of trial-and-error carb re-jetting, etc.

Once your bike if properly tuned (valves set properly, carbs cleaned and functioning properly and the fuel mixture color-tuned, engine synched), if you still feel the need for more power, only then would I start considering air flow/exhaust flow changes.

Okay, that's about it. Again, let me stress that you do all the "basic, recommended" tasks TO PERFECTION, rather than try to cheap your way (or just ignore) through individual tasks. Just because the bike was inexpensive to purchase does not mean that it is "cheap" to maintain properly. It costs just about as much to tune up a 1993 Dodge Astro-Van as it does a Dodge Viper----if you get my drift!

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