Service

SERVICE

Paul Dean

Summer of discontent

I bought a ’91 Suzuki GSX1100G (preBandit) that had been sitting for two years. I gave it a tune-up and had the carbs cleaned out. At first, it ran very strong (crazy pull!), but then it began surging, puffing black smoke, stalling at intersections and fouling plugs. So I took it to a mechanic and had the carbs really worked over—new jets, float-bowl gaskets, airbox and choke plungers, plus the tank was drained and checked, and a test of the compression showed it was just fine. But the bike still has the same damn problem. The whole summer has gone by and I’m unable to ride my bike due to its bucking, snorting and smoking. The mechanic felt real bad that he couldn’t find out what was wrong with it, and he suggested trying an exhaust analyzer. Despite my lack of $$$ and my annoyance at losing a summer of riding, I really like this bike. It’s got mega-power with lady-like seating (don’t tell all the guys I said that). So, please, can you tell me what's going on? Sasha Nellie Shapiro New Paltz, New York

You won 7 learn anything from an exhaust-gas analysis that your eyes and in-the-saddle experiences haven ? already told you. An engine that emits black smoke, runs poorly and fouls plugs does so because it is not completely burning all of the fuel in its cylinders. This means that either too much fuel is being drawn into the engine (i.e., the carburetion is too rich) or that the mixture is correct but something else is preventing the fuel from fully burning.

I must assume, for two reasons, that the problem is not with the mixture delivered by the carbs. First, the chances of all four carburetors developing the very same too-rich condition at the very same time are astronomical; it ain 7 gonna happen. Second, the complete overhaul of the carbs seemed to have absolutely no effect on the symptoms. Even if that repair had not been done properly, the mechanic changed or serviced enough pieces that the symptoms should have been affected in some discernible way.

Something else, then, is hindering the engine’s ability to completely burn all the fuel, and that something probably is in the timing of the cams or the ignition. It’s my guess, from 3000 miles away, that of those two possibilities, the ignition is the most likely cause. If something has gone haywire in the ignition control unit (the “black box ”), the spark could be erratic enough to prevent the fuel from burning completely.

I appreciate your financial situation, but if you possess neither the skills nor the tools needed to check the ignition and cam timing, you have little choice but to take the bike to someone who does. I don 't know if the mechanic you have been using is competent, but he at least seems sincere. So, explain to him what I’ve told you here and give him a shot at the repair. If he s even a halfdecent wrench, he should then be able to track down the cause of the problem and get you back on the road.

More power, commander?

I have a ’99 Harley-Davidson Road King that has electronic fuel injection. My dealer is going to install Harley’s Screamin’ Eagle Stage II kit, but with a Thunder Header exhaust. My question is, do I have to use a K&N Power Commander? I’ve asked everyone I can think of and they’ve all given me different answers. Some told me that I will need a Power Commander and others said that I’d just be wasting my money. I don’t care about the cost, I just want to do what is right. I love your mag and trust your answer. jimihd Posted on America Online

Without having made those very same modifications myself, I can 7 say for sure whether or not you will need a Power Commander, but there ’s a fair chance that you will. The Screamin' Eagle Stage II kit includes hotter cams, a freer-breathing air cleaner, a set of slip-on mufflers and a cartridge that remaps the fuel-injection and ignition curves in the engine control module (ECM). The remap was calibrated by Harley-Davidson to work with that specific state of engine tune, including the slip-on mufflers; but if a dijferent exhaust system is bolted on, the tuning requirements could vary enough to call for a dijj'erent set of curves. Just as a change in exhaust systems on a carbureted engine often requires different jets, so too can an exhaust change on a fuelinjection system require an adjustment in the parameters that affect the fuel mixture. The remap cartridges for both the Stage I and Stage II kits each contain just one set of revised curves, and each can only be downloaded into the ECM one time.

But the Power Commander, which plugs into the EC M’s circuitry, allows a number of fuel-mixture and ignitioncurve changes in and of itself; plus, the manufacturer of the Power Commander, Dynojet, also offers a wide variety of other maps that can be downloaded from its website (www.powercommander.com) and then uploaded into the Power Commander. This procedure requires a laptop computer, as well as the knowledge to use it; but with the ever-increasing use of electronic engine-management systems, being computer-literate is becoming just as important as knowing how to use a torque wrench.

Die hard with a stoppie

I have a 1999 Kawasaki KLR650 that occasionally will die after hard braking. When I get off the throttle and brake abruptly with the clutch pulled in, there is a short period where the rpm drops off and the engine almost quits, and ! have to rev it to keep it from stalling. The bike is a California model, but all of that state’s required emissions equipment has been removed, since it’s not mandated here in Oregon. I would appreciate any gems of wisdom you might share on the subject. " Cheloveyk Posted on America Online

If you indeed have removed all of the California-only emissions gear, such a problem would most likely result either from a too-high carburetor float or a small leak in the cold-start enrichener system. You said this condition only happens occasionally, so I'll rule out the float; if it were too high, it would always be too high, not just every once in a while. So while I suggest that you also check the float level, the enrichener seems the most probable culprit.

When the enrichener (commonly but incorrectly referred to the “choke ") is on, intake-manifold vacuum draws raw fuel from the float bowl, past the open enrichener plunger, and up into the intake stream through an orifice in the carburetor bore, just ahead of the throttle plate. That raw fuel combines with the normal mixture entering the intake port, creating the rich mixture needed to let a cold engine start and run. When the enrichener plunger is closed, the supply of raw fuel is cut off and the air-fuel mixture returns to normal. But if the plunger does not seal properly when closed, or if a hangup in the linkage prevents it from reaching its fully seated position, intake manifold vacuum could still draw enough fuel through the system to make the engine run excessively rich.

If the leak past the plunger is rather small, the mixture might not be significantly affected during most normal running, since there usually isn 't enough intake manifold vacuum to draw much fuel past a tiny opening. But when you brake hard, two things occur that can change those conditions: intake manifold vacuum is at its highest when the engine is on trailing throttle (as it is during braking); and inertia causes the fuel in the float bowl to slosh toward the front of the bowl, which is where the pickup for the enrichening system is located. That combination of high intake vacuum and a momentarily higher fuel level right at the enrichener pickup point allows fuel to get drawn into the carburetor bore-not a lot of it, but enough to make the engine stumble and stall. The cure is to remove the plunger, check its neoprene seal and ensure that it is fully seated when the enrichener is off.

Cash value

Regarding your “Adjust in time” (September, 2000, issue) response to Dennis Clark, who was concerned about valveadjustment intervals for his 1200 Bandit: Having done dozens of 600-mile services on Bandit 1200s (one just today, as a matter of fact), as well as 600-milers on many other models and brands, I can say that virtually all have had at least one tight valve and never any loose ones. After a few adjustment intervals, they seem to hold their clearances longer. Curtis Cash, Shop Foreman Orange County Suzuki Costa Mesa, California

Thanks, Curtis, for your first-hand input on a subject you obviously know well.

A matter of mileage

In two of the comparisons in your July, 2000, issue (“The Power of Two,” and “Imbalance of Power,” the fuel mileage varied hugely between very equivalent bikes. In particular, the Honda RC51 got 33 mpg vs. the Ducati 996 at 45 And the Honda CBR929RR got 33.1 mpg vs. the Kawasaki ZX-9R at 41.7 mpg. Can you provide an explanationor these differences? Stephen Pomerance Boulder, Colorado

I think so. Even though the bikes in each category were carefully and equitably compared to one another; they weren ’t always ridden together on the same days on the same roads at the same rates by the same riders. We did set aside quite a few specific on-track and on-road testing days that involved riding all the bikes together under the vety same conditions; but much of the rest of the time, they were ridden individually by different editors under varying circumstances, ranging from weekday commutes to weekend assaults on favorite backroads. Those variations were big enough to skew the overall fuel-mileage numbers.

Actually, when conducting some comparisons, we might not even have all the bikes in our possession for the same length of time. Depending upon availability from their manufacturers, some may arrive early in the test cycle, others later. This in fact is what happened with the 996 Ducati and Honda RC51. We had already racked up considerable road miles on the 996 when the RC5I arrived, just before a two-day racetrack session was scheduled. The Honda did get quite a few road miles logged on it before the test was concluded, but it also ended up with proportionately more track miles on it than did the Ducati. That alone helps explain why its fuel mileage numbers were so much lower.

Gixxer mixer

I took a set of wheels from a 1987 GSXR1100 and installed them on my 1986 GSX-R750, hoping to have rims wide enough that I could upgrade to radial tires. The 1100 came stock with bias-ply tires, a 110/80-18 up front on a 2.75-inch rim, and a 140/80-18 on the rear on a 4inch rim. I put a Dunlop D207 110/80-18 on the front, which works well, but I’m unhappy with the 160/60-18 D207 (the narrowest rear D207 Dunlop makes) on the rear. The handling is twitchy when leaned over because the tire apparently is too wide for the rim, creating a narrower contact patch on the outer edges of the tire, right where you need traction most. After searching the Internet, I found that Metzeler has a 150/60-18 MEZ1 radial for the rear. Will this also be too wide for the rim to offer a good contact patch at cornering angles? I like the ride and stability of radiais, so 1 don’t want to go back to bias-ply tires unless I have to.

I’m no racer, but I do enjoy attacking the twisty backroads on a Sunday morning, but I have no confidence right now in my rear tire’s ability to keep a good grip on the road. Brett Becker Altamonte Springs, Florida

According to most tire-company fitment charts, a 150/60VR18 radial needs to be mounted on either a 4or 4.5-inch-wide rim. In most instances, the 4-inch rim is the preferred width, so the Metzelers you have located should create no handling problems on the GSX-RJ100 rear rim.

You might also be interested to know that it 's not just the reduced contact patch caused by a too-narrow rim that makes your bike a little squirrelly at the rear. To perform as designed, radial motorcycle tires are extremely dependent upon maintaining a veiy high degree of sidewall stiffness; that’s the main reason the sidewalls on radiais are so short compared to those on bias-ply tires. Pinching the sidewalls together, as a toonarrow rim does, changes the angularity of the sidewalls relative to the direction of the cornering forces, and that allows the sidewalls to flex where they otherwise would not. So, some of the squirming you feel is the result of the sidewalls allowing the wheel to move around inside the tire, even when the contact patch is firmly stuck to the road.

Got a mechanical or technical problem with your favorite ride? Can’t seem to find workable solutions in your area? Maybe we can help. If you think we can, either: 1) Mail your inquiry, along with your full name, address and phone number, to Cycle World Service, 1499 Monrovia Ave., Newport Beach, CA 92663; 2) fax it to Paul Dean at 949/631-0651; or 3) e-mail it to CW1Dean@aol.com. Don’t write a 10-page essay, but do include enough information about the problem to permit a reasonable diagnosis. And please understand that due to the volume of inquiries we receive, we can’t guarantee a reply to every question.