Service

SERVICE

Paul Dean

Out to launch

I own a ’91 Yamaha V-Max, and I’ve recently noticed a problem that worries me. During the, ahem, “occasional” launch from stoplight to stoplight, the oil-level light illuminates. As soon as I roll off the throttle, the light goes out. As I said, this only happens during really hard launches. I’ve asked my dealer’s service department about this, but I can’t get a straight answer. Please tell me if I’m worrying too much about this problem, or if not, what I can do to solve it. Chip Monie

Vienna, Virginia

No need whatsoever to worry, Chip. The oil-level light illuminates during hard acceleration simply because the sensor for the light is located at the very front of the oil sump. During a super-hard launch, the rate of acceleration is so severe that it causes the oil in the sump to be slung toward the rear, away from the sensor, thereby making the warning light illuminate. As soon as you roll off the throttle, or when the rate of acceleration slows sufficiently, enough oil sloshes back to the front of the sump to make contact with the sensor and turn out the warning light.

Besides, the really critical part of the oiling system is the oil pressure, and it is unaffected by even the fiercest of drag-race launches. The oil pickup for the engine’s entire lubrication system is located at the very rear of the sump, which is where all the oil tends to accumulate under heavy acceleration. So, even during the most violent of dragstrip-style launches, there’s no chance of engine damage due to oil starvation.

No diving, please

I have a 1995 BMW Kl 100LT, and it has excessive front-end dive and rebound-so much so that applying the front brake even at parking-lot speeds can be anything between embarrassing and downright dangerous. I’m fully aware that using the front brake while turning is risky, but trying to manhandle and control the LT while my only braking method is to drag my feet on the ground isn’t very practical. Some expert BMW riders I know also have experienced this phenomenon and agree that it truly is a problem. The stock fork doesn’t have any provisions for compression or rebound adjustment, and the local Beemer dealer tells me that upping the viscosity of the fork oil is the only practical remedy. What’s your recommendation?

Thomas 0. Gray Gretna, Louisiana

Your BMW dealer is partially correct. Heavier fork oil slows down the rate of damping, but it doesn't necessarily reduce the amount of suspension compression; the front end still can compress just as far, but takes a slightly longer time to do so. Thus, increasing the oil viscosity will help the rebound-damping condition, but it will harshen the compression, as well. As a result, you may then find that the fork still compresses too far and that the ride quality up front has deteriorated, especially over little ripples and choppy bumps in the pavement.

Instead, increase the amount of fork oil, not the viscosity. This will raise the fork’s overall spring rate and reduce the amount of dive.

See, when the front-end dives, the aitcaptured inside the fork tubes (above the oil level) is squeezed into an eversmaller space. Because compressed air essentially is a spring, the air that gets squeezed inside the tubes contributes to the fork’s overall spring rate. Increasing the oil level not only makes the air-space smaller when the fork is at full extension, it also makes it proportionately smaller at full compression. Forcing the air into that smaller space raises the fork’s overall spring rate and reduces front-end dive.

So, simply drain the oil out of both legs and replace it with the recommended amount of the same viscosity you ’re now using, then add another 20cc and reinstall the fork caps. If the fork still compresses too far, add another lOcc and try it again. Continue in lOcc increments until the fork dive is reduced to a level you deem acceptable. Then, if you think that either the rebound or compression damping still is too quick, go up to the next heavier grade of fork oil, filling each tube with precisely the same amount as you did with the lighter oil.

Talking trash

Just recently, I bought an ’86 Yamaha FJ1200 with 28,000 miles. While coming off an exit for a lunch break after riding about 60 miles, the engine began to run rough, but cleared up after a few minutes. The bike had done this same thing previously, and I figured there was trash in the carbs. So, prior to this ride, I had drained the carbs and installed an in-line fuel filter. After the lunch break, during our ride home, the bike began to run really bad again and finally shut off altogether. I let it sit for a few minutes, and it started up and made it home without another occurrence-although it did run poorly one time but quickly cleared up.

My dealer says the carbs need work, but I think it sounds more like a fueldelivery problem, maybe a bad vacuum petcock or a plugged vent cap. There’s a tiny bit of rust in the gas tank, and the fuel-reserve once quit working, but I don’t think the two are related. What do you think? Walker Nelms

Roanoke, Virginia

I think the rust in the gas tank is the culprit. The ’86 FJ1200 has a fuel-filter screen on the end of the petcock s stand pipe, inside the gas tank, and it sounds as though the screen has gotten clogged with particles of rust that have fallen to the bottom of the tank. This is why you don’t see any contamination in your in-line fuel filter: The rust can 't get past the screen inside the tank.

This is an easy fix. Drain the tank, remove the entire pectcock, take off the screen and clean it. And while the tank is off and empty, take the opportunity to remove the rust and coat the interior with a good sealer, such as the three-step clean/prepare/seal process sold by Kreem.