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SERVICE
Paul Dean
A little whine, sir?
I recently bought a brand-new, ’99 Honda VFR Interceptor 800, and I’ve found it to be even more wonderful than all the motorcycle magazines have claimed. Except for one thing: the constant whine that comes from the engine. I’ve already taken the bike on a couple of weekend trips, and by the time I got home, I had Excedrin Headache No. 4 from listening to that whine for two or three days. According to some other riders I’ve talked to, all VFRs make this noise. Is there anything that can be done to eliminate or reduce the whine? It spoils what otherwise is a perfect motorcycle. Rafe Ochoa Stockton, California
All VFR engines, which date back to 1986, use straight-cut gears instead of chains to drive their dual overhead cams. The whine you hear is caused by the meshing of the gears in those drives. 1 use the plural, “drives,” because VFRs, which have V-Four engines, use tw’o of them, one for each bank of cylinders. So, not only do these bikes have a gear whine, they emit a double dose of it.
Flonda chose to use a geared cam drive to eliminate any chance of cam-drive failure or the gradual deterioration of cam timing that occurs with chain drives. The VFR 's predecessor, the original VF750F Interceptor that debuted in 1983, broke new ground for sportbike design and performance, but its reputation for reliability was sullied by a few mechanical problems, including some involving the camshafts.
When giving the bike a thorough redesign for 1986, Honda went to great lengths to ensure that the engine would be absolutely bulletproof and that involved the adaptation of noisy but dead-reliable gear-driven cams. Aside from entirely remanufacturing that part of the engine, there is nothing you can do about the noise.
More gas vs. less fuel
I own a ’98 Honda VTR 1000 that occasionally backfires through the carbs when I rev to downshift (usually from second to first gear). Since I’m also a little disappointed with the range of a tank of gas (the fuel light comes on at 100 miles), could this backfiring be a clue to an underlying problem that needs to be addressed before my warranty runs out? I run only premium gas and my bike otherwise performs flawlessly. Line Gurley Bigelow, Arkansas
Let us not confuse apples and oranges here: Your VTR 1000 s fuel mileage has nothing at all to do with its occasional backfires. Excessive fuel consumption is a symptom of a rich condition, while backfiring often occurs because of a lean condition.
Our experiences with the VTR have produced fuel mileages in the 32to 34mpg range, and the fuel tank holds 4.2 gallons with about a 1.1-gallon Reserve capacity. Do the math: 3.1 gallons on the main tank at about 33 mpg equals 102 miles. But Reserve will carry you about 36 miles beyond that, and even farther if you ride conservatively. So, as far as fuel mileage is concerned, your VTR is right about on-track.
The backfiring, on the other hand, is a by-product of huge carburetors and lean jetting. The VTR is fitted with the largest carbs (48mm) found on any production motorcycle; and to meet the EPA-mandated emissions standards for motorcycles, the jetting must be leaner than what would be ideal for optimum performance. When attempting a clean, smooth downshift, most riders tend to snap the throttle open from a fully closed position more quickly than they do at any other time. The sudden exposure of the carbs ’ huge venturis causes a drop in intake vacuum large enough to momentarily make the already-lean mixture even leaner. And since lean mixtures burn more quickly than rich ones, excessive leanness can cause some of the burning fuel charge to escape past the intake valve before the valve is fully closed. In other words, it backfires.
Dynojet, K&N and Factory all offer jet kits for the VTR1000 that should cure the backfiring condition—and allow the engine to enjoy better allaround performance, as well.
Retarded advancer
I just recently bought a 1996 Yamaha FZR600 and have a question about timing advancers. My brother also has an FZR600-his is three years older-and it has a timing advancer on it, but his bike doesn’t feel any different than mine. They both accelerate the same and both have the same top speed. So, I’m wondering what those advancers do and if putting one on my bike would be worthwhile.
Brian A. Hanson Wesf Fargo, North Dakota
/ think you 've already answered your own question, Brian. If your brother 's FZR runs and feels exactly as yours does, the timing advancer on his bike is not affecting performance one way or the other. There 's no reason to believe, then, that putting one on your FZR will have any other result.
On most modern solid-state ignitions, the spark is triggered by a small rotor spun by the crankshaft. Every time one of the little tabs or protrusions on the rotor passes an adjacent pickup coil, one or more of the sparkplugs is fired. Timing advancers simply are aftermarket rotors that change the indexing of the triggering tabs relative to Top Dead Center, thereby advancing the entire ignition spark curve.
Some have a fixed amount of added advance, while others offer a small amount of adjustability. A few examples of these advancers are pictured in the photo above.
Stock ignition curves are intended to accomplish several goals, one of which is to help the engine meet the EPA ’s requirements for exhaust emissions. The aftermarket advancers, however, usually are designed only with higher engine performance in mind, allowing them to provide more aggressive spark timing.
How well an advancer works depends upon several factors-the year and model of bike it is on, whether the engine is stock or modified, condition of the engine and so forth. What’s more, while some stock engines respond rather well to the installation of an advancer, others barely react at all. I’ve never tested an advancer on an FZR600, so I have no first-hand knowledge of their effectiveness on that model of bike. You also gave me no information about the brand of advancer on your brother’s FZR or whether the rest of his engine is stock or modified. But based on your very own comparisons between your bike and your brother ’s, a stock FZR600 apparently is one of those bikes on which an advancer effects little or no improvement.
In my opinion, advancers are best suited for use on modified engines. When a bike has more radical camshafts, higher compression and improved breathing capacity, it can make much better use of more aggressive spark curves.
Cutting no slack
I read with great enthusiasm Brian Catterson’s story about the MV Agusta F4 (“Return to Monza”) in your August issue. What a fabulous bike! All that stands between me and ownership of one is the $37,000 needed to buy it. But I was puzzled at Catterson’s explanation of why the camchain tensioner is located at the front of the engine instead of the rear.
I fully comprehend that the cams turn backwards compared to most others, but why does direction of rotation on any engine impact the location of its camchain tensioner? Steven Shifflett McKeesport, Pennsylvania
In theory, the tensioner could be positioned in just about any convenient spot along the run of the camchain. But in reality, the location has a significant effect on valvetrain friction, chain-tensioner life and accuracy of cam timing.
As the crankshaft (or in the case of the MV Agusta, the secondary cam-drive gear) turns, it rotates the camshaft by effectively “pulling” on the camchain; on multi-cylinder engines in particular, that pull is almost constant. If the crankshaft rotates in the conventional direction (clockwise, as seen from the right side of the engine), that pull is on the front run of the camchain, so any slack in the chain will, naturally, be on its rear run. If the crank rotates backwards (counterclockwise), that pull will be on the rear of the chain and the greatest amount of slack in the front. Either way, it makes the most sense to locate the tensioner on the side of the chain where the greatest slack occurs.
If the tensioner were located at the part of the chain that is constantly being pulled against the resistance of the valve springs, several things would happen. For one, the tensioner would be under much greater strain, rendering it less durable for any given size. There also would be more frictional losses due to the heavier loads imposed beleen tensioner and chain. Last but not least, the cam timing would vary more dramatically as the chain wore.
In the end, the latter reason may be the most important of all. Chain wear is, essentially, the stretching of the chain, the net effect of an increase in the pinto-bushing clearance of each individual link. The more links involved, the more the total stretch. No matter where the tensioner is located, it pokes the chain inward toward the interior of the cylinder as it takes up the slack, forming kind of a shallow Vee in the chain; so, if the tensioner were on the run of the chain that pulls the cam, there would be more links between the crank and the cam. This would cause the cam timing to be slightly more retarded with a worn chain than if the chain were allowed to pull in a straight line between crank and cam. And this is why the tensioner is always put on the slack side of the chain.
And it feels so fresh, too
1 just put a new tire and tube on my bike. The instructions that came with the tube said to sprinkle some talcum powder inside the tire before installing the tube. We had no talc in the house, so I used some Vagisil instead. Can I expect any problems down the road?
Walter T. Scott River Forest, Illinois
Using talcum powder greatly lowers the coefficient of friction between the tube and the inside walls of the tire, reducing the likelihood of a fold in the tube developing into a pinch as the tire is inflated. Since the original Vagisil is a cream, I can only assume that you used Vagisil-brand powder, which will work just as well for these purposes as talcum. If you’ve had no flat-tire problems so far as a result of using Vagisil, you probably won 't have any in the future. And as a bonus, you’re not likely to get a yeast infection, either.
Pipe dreams
Recently, I bought a brand-new, redand-white Yamaha YZF-Rl. The bike is awesomely fast, of course, but I noticed that in your long-term update of the Rl (April, 1999 issue), you got excellent results with an aftermarket exhaust pipe without the need to do any rejetting. I have a Yoshimura RS3 full system in the garage just waiting to be installed. I spoke to a mechanic at the local Yamaha shop and he recommended I use a Factory jet kit. What do you suggest? Jet kit or not? Do you have any preferences for jet kits? Dave Gayaldo Fort Worth, Texas
The exhaust we tried on our long-term Rl test bike was a complete, ultra-lightweight system made by Akrapovic (pronounced Ah-CROP-o-vitch), a company in Slovenia. Despite the high, $1325 cost of this system-which uses a stainlesssteel header and a titanium canister-we were quite impressed with it because simply bolting it on netted the Rl nearly 9 additional rear-wheel horsepower (140, as opposed to 131 stock) with no jetting changes whatsoever. That’s not the case with the vast majority of aftermarket exhaust systems, which usually require at least minimal rejetting.
I can’t tell you to what degree any rejetting will be needed when you slip the Yosh exhaust on your Rl; I have no experience with that system on that bike. But I can tell you that although the jet kits from Factory, Dy nojet and K&N are top-quality products, you always need to do more than just screw in different jets and needles after installing a new exhaust system, because every engine is a little different, even on the very same model of motorcycle. You should also take sparkplug readings at various throttle settings to confirm that the carburetion changes you have made are producing combustion properties that are as close to ideal as possible.
