First I visually inspect the machine, and I continue to do so as I work. Decades of familiarity with Honda's GL1000 has enabled me to visually make conclusions about the kind of care and attention the bike on my lift has received in the past, and this directs my thinking on the systems I'll be optimizing as I proceed.
A compression test is an important first. There is no point in investing time and money in a machine that has a seriously worn engine. Eighty percent of the GL1000s I see in my shop have at least reasonable compression, a certain minimum. The rest do not. I won't proceed on an engine that has low compression. So naturally this needs to be determined right away.
If the engine has good compression, the carburetors are removed for rebuilding. A signifacnt part of a GL1000 super tune takes place in the carburetors. They are invariably seriously neglected, suffer from rough handling, and exhibit signs of inexpert prior service (such as the use of rebuild kit parts), so they are always included. I don't even consider not fettling them. That's not an option. The carb work alone is worth at least $800, with the factory Honda float valves alone worth $300 of that.
Then the coolant pipes are examined. About half the time they are damaged or disturbed so need attention. So they get resealed and repainted. This is quite a lot of work as Honda glued the coolant elbows to the cylinder head.
Next I remove the seat and with a flashlight inspect the inside of the fuel tank and check the flowability and general condition of the petcock. Very frequently the tank needs rust removal. In every case I drain the fuel tank because the gas in it is unreliable.
Then I adjust the valve clearances. Two things make this special. One, I use a 0.006" clearance spec. I've done this as long as there have been GL1000s. The engine starts better, idles better, and has better throttle response at this spec. The second special thing is I adjust the valves in the engine's firing order. It makes a difference. Every experienced career mechanic knows the advantage this offers. I install new factory valve cover gaskets and bolt seals--the aftermarket ones are junk.
I remove the cam belt covers and do four things. One, obviously I inspect the belts. This is not as crucial as forums want to make it. But it needs to be done nontheless. Two, I check for correct cam timing. A third of the GL1000s I see have incorrect timing, presumably from belt replacement or cylinder head gasket replacement in the past. Three, I adjust the cam belt tension, and I use a special technique for this that involves rotating the crankshaft while feeling the belt by hand. This gets the tension, which is important for accurate ignition timing, exactly where it should be--neither too tight or too loose. I spend some considerable time on this. And four, I inspect the cam belt housing for oil leaks. I occasionally find them--most often at the cam seal--and I write this on the observations sheet so the customer can know about it.
About this time I get a good look at the battery. More often than not it is a $40 battery, not one of the better brands. Sometimes the terminals are so corroded I have to cut them off. The main fuse is often corroded also, and the wiring before and after the fuse noticeably melted, and of course the stator connector also. Electrical repairs such as this that affect engine running are part of a super tune.
Next is ignition timing. Between this and the the carb work, these are the two most important and most labor-intensive parts of the super tune. Timing the GL1000 ignition is the least intuitive tuning operation of any Honda. It takes a lot of knowledge, a lot of time, and a few special tools. I do it by hand--statically--as every GL1000 professional does and as Honda themselves encouraged, and I use only Honda factory points. If a Dyna ignition is fitted, I time that, though I recommend against aftermarket ignitions and have become familiar with many over the decades. They work when they work, but they are not as user-friendly or long-term reliable. Nor do they deliver any advantage in either engine performance or ignition system maintenance. No aspect of tuning a GL1000 is as impactive as ignition timing. Few want to believe this, but it is true. I have a how-to booklet on adjusting this ignition. Check it out.
After ignition timing I bypass the ignition ballast resistor. All Honda mechanics did this back in the day. No GL1000 ignition service is complete otherwise. It's as common and as needful as replacing the spark plugs. The factory ignition coils are hidden gems. They are as powerful as any high performance coil and removing the ballast resistor enables them do their job.
Speaking of the spark plugs, no matter what the bike has in it, I fit Champion A-8Y plugs properly gapped. The stock NGKs are great plugs, and Champion's motorcycle plugs don't have the greatest reputation among the mechanics of any brand or model. But in the case of the GL1000 and this particular plug, it is a very happy marriage that I have been taking advantage of a long time. Just one of those unique instances, tricks of the trade as they say.
The spark plug caps are next. Virtually every GL1000 I see has bad caps. They are always loose on their wires--indicating a lack of maintenance--and they are almost always degraded from their original 5K ohms to 10K or more. I nip the plug wires and install new caps. The original NGK caps are getting rare and quite expensive.
If I find resistive spark plug wires on the bike I change them out for actual metal wires. This is another thing that is not negotiable. I refuse to leave them. There are three reasons. One, non-metal plug wires reduce ignition performance. Two, that performance degrades further over time. And three and most important, such wires can never be made to connect electrically as securely as metal wires. Suppressive plug wires do not belong on your Honda.
The carburetors are completely disassembled down to unracked, individual bare bodies (castings). The throttle shafts sometimes are removed, but not very often as that is necessary only when they or the throttle plates are damaged. The carbs have often been molested with rebuild kits, so all of that is put back to stock. Oddly, the air cutoff valve diaphragm I often find installed upside-down. The various size air bleeds are put in the right places, and stock type fiber-reinforced bowl gaskets are fitted. Invariably, at least half of the threads on the carb bodies have to be repaired using steel thread inserts, due to these carbs weak zinc based alloy. The float levels are adjusted using the factory tool and method, the correct--and hard to find--o-rings go onto the primary and secondary main jets, the carbs are bench-synced and leak tested, and the pilot screws are set to three turns out. This unofficial setting makes up for the GL1000's too-large carburetors and consequent poor throttle response. I also slightly richen the idle circuit by the well-known expedient of reducing the size of the air bleed. And I slightly richen the midrange by stretching the slide springs. The slide spring trick I have been employing as long as I have been tuning GL1000s.
Then the carbs are reinstalled. There is a special way to do this because tightening the manifold clamps before installing the carbs results in vacuum leaks. I put in new intake manifold o-rings and take special care when fitting the air cutoff valve body. The chrome beauty covers are left off until after the super tune so as to make proper manifold installation easier and to allow better access to the pilot screws.
When the engine is started a careful check for oil and coolant leaks is made. Once warmed up, the carburetors are painstakingly synchronized to a standard that is three times as precise as the factory specification.
An exhaust gas analyzer is used to confirm the pilot screw setting and if indicated, the pilot screws are adjusted to a reading of 3.0 percent CO.
With a hot engine the temp gauge and fan operation is noted for the observations document. The fan should come on no later than three-quarters into the gauge's white zone.
Finally, I adjust the clutch, which does not mean at the lever. Correct clutch adjustment is done at the pressure plate at the back of the engine. This requires a bit more work and some special tools. I usually also tighten the steering bearings--they are always loose. I don't charge any more for these things. They take only a few minutes. And every bike needs them.
On a GL1000 this super tune service costs $2500. When brakes and electrical are added the ticket can reach $3500. I have done GL1000 super tunes, in this fashion, since the early 1980s. I also do super tunes on the Honda SOHC four and the 70s Honda CB450/500 twin.
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One of my favorite tasks as a lifelong Honda mechanic is a service I call a "super tune". It consists of all the things that through long experience I have found a particular model needs at any given time. This is not a simple "tuneup", a phrase that is obsolete in the industry and wholly insufficient for what I am talking about. Nor would the 1980s term "tune and service"--which used to mean eassentially a factory-scheduled axle-to-axle maintenance service--be accurate. Little of a super tune involves things outside of the engine and its support systems, though I always create an observations document for the customer in which I list observed issues. These things are brake system overhaul and the inevitable electrical repairs. They're always needed, even on so-called "restored" bikes. They are not included in the super tune. Following is a brief outline of what I do in a GL1000 super tune, which takes about fifteen to twenty hours.