Service

SERVICE

JOE MINTON

Fork foibles

What is the expected mileage/life of a street-ridden telescopic front end, mainly the stanchion tubes and aluminum slider assemblies? I have read just about every bike publication for the last 15 or so years and can’t recall ever seeing an article dedicated to this issue. Could the front end of my 1980 GS750 (with 74,000 miles) be worn out already?

Bill Cushenbery Santa Maria, California

Your Suzuki's fork can last almost indefinitely. Considering your bike's mileage, however; it is possible that the fork needs an overhaul. Like most other Japanese bikes made after ¡979, your GS750 has replaceable, Iefionimpregnated fork bushings that wear very slowly. Unless the fork is crashdamaged, the sliders and fork tubes shouldn 7 need attention, but the bushings may need replacement.

An excessively worn fork can bind and give a rough ride. It can also be dangerous. Am looseness in the front end. whether it is in the fork. steering head. wheel bearings or spokes. will increase the chances of a high-speed wobble. I stronglr recommend that you thoroughly inspect your bike `sfront end at least every 10,000 miles.

To check the front end for wear, prop the bike with the front wheel off the ground. First, test for wheel-bearing and spoke looseness by trying to wiggle the wheel from side to side while holding the fork sliders steady.

I hen, to check for freeplay in the steering bearings, grab the bottoms of the sliders and try to move them back and forth; you should not be able to feel any movement. Finally, check for fork-bushing wear by removing the front wheel and separately trying to wiggle each slider leg on its stanchion tube. Again, you should not be able to detect any movement. If the front end fails any of these tests, it should be suitably repaired.

One of our Shadows is missing

I have a problem that I don’t think has been addressed by Cycle World. I know I am at wit’s end for a solution.

My 14,000-mile, 1986 Honda VT1 100 Shadow will not accelerate below 3000 rpm in fifth gear without bucking like it’s missing or being lugged excessively. My attempts to correct this condition include cleaning, adjusting and synchronizing the carbs; replacing the vacuum diaphragms; checking the timing; tightening the motor mounts; checking the air cut-ofif valve and emission controls; and making sure the engine compression is within specs.

The engine starts and runs perfectly in all other respects, but it takes a lot of enjoyment out of riding the bike when I have to downshift on every light grade unless I’m going over 50 miles per hour. I would appreciate any suggestions you might have.

Frank Moore Chula Vista, California

There are a couple of likely causes of the difficulty you are experiencing with your Shadow. One you can fix, the other you can 7 (at least not easily).

First the bad news: The /100 Shadow has rather light flywheels for such a large, twin-cylinder engine. The resistance each cylinder presents during its compression stroke slows the crankshaft considerably, especially when the rpm-level is fairly low, which it is in top gear at moderate road speeds. You can 7 fix this without major surgery (reduced compression ratio or heavier flywheels). The other possible cause is lean carburation. Federally mandated motorcycle-exhaustemissions requirements can, so far at least, be met with careful carburation. The nature of the testing procedures typically lead to lean mixtures at low throttle settings. When you attempt to moderately accelerate from within this throttle range, the engine may lean out so much that it cannot run smoothly.

This condition can often be corrected by richening the idle circuit.

This can be done in two ways: Adjust the idle-mixture screw and/or replace the idle jet with a larger one. Your first step should be to remove the stops on the idle-mixture screws and open them to riehen the idle circuit slightly. Typically, about one-half turn will be enough, but you should experiment for best results. You may have to install the next-size-larger idle jet, which you can buy from your Honda dealer.

Oil treatment queries

I am considering the use of a friction-reducing engine treatment (such as Slick 50) in my motorcycle engine as part of a long-term maintenance program. My question is, are there any proven benefits of such a treatment that would warrant its use?

Scott Rollison Tampa, Florida

Engine manufacturers and oil companies have conducted literally hundreds of millions oj miles of engine-oil tests. The motor oils we buy are the direct result of that testing.'

They contain additives to help resist wear, corrosion and deterioration. If additional additives were needed, chances are they would be included.

However, petroleum-based oils do wear out, and, in the majority of contemporary motorcycle engines, will do so at an accelerated rate compared to car engines. The relatively high operating temperatures of many aircooled engines increase the rate at which oil oxidizes. And, the shearing effect of transmission gears on petroleum-based motor oils can wear them out rapidly. My advice is to either change your oil more frequently than recommended to insure that it has its full film strength, or use a premium synthetic oil such as Motul. Red Line or Mobil 1. 7 he best oj the synthetics are not substantially affected by the extreme pressures of meshing gears, and are much more resistant to the effects of elevated operating temperatures. Their greater cost is somewhat offset by the fact that they don 7 need to be changed as often as conventional oils.