Service

SERVICE

Paul Dean

Don’t toast the Coast

I own a 1995 Honda PC800 Pacific Coast. I really like the bike and plan to keep it for many years. A friend and I are planning a trip out West this summer, and part of our route will take us across states that have higher speed limits than we are used to observing. The trouble is, my friend will be riding an ST1100, and he intends to cruise some areas at 90-100 mph. At these speeds, the PC800 runs between 6000 and 7000 rpm, and the redline is only at 7700 rpm. Will these speeds put any undue strain on the engine? The PC feels very comfortable at 85-90 mph, but I intend to rack up at least 100,000 miles on this bike and I don’t want to do anything that will shorten its lifespan. Any advice you can offer will be much appreciated. Russell E. Vernon Lebanon, Tennessee

In keeping with their desire to build extremely reliable motorcycles, most manufacturers-particularly the Japanese-tend to establish somewhat conservative redlines. With very rare exception, an engine ’s redline rpm is quite a bit lower than its maximum operating rpm, which is the engine speed above which structural or material failures will start to occur. And even after the engineers have established a tentative redline rpm, they run the engines at that speed for extended periods, sometimes as long as 24 straight hours, to determine if any weaknesses have slipped through the previous development stages. Consequently, riding your Pacific Coast at steady speeds that amount to just 80 or 90 percent of redline rpm shouldn’t worry you in the least-particularly since you won’t be able to run uninterrupted at those speeds for hours on end. If I were you, Id worry less about redlines and more about red lights— the ones on the police cars that are likely to be following you.

Mr. Mitch’s wild ride

When my Kawasaki ZX-10 was stolen, putting me in need of a street machine, I bought a 1986 Yamaha Radian, with just 2600 miles on its odometer, for only $100. The bike had been sitting outside with no cover on it for six years, but after many hours of work refurbishing the carbs, the gas tank, the shocks, the pipes, the swingarm, etc., I had it looking good and running great-except that I’ve never ridden a more ill-handling machine. In low-speed corners (especially on trailing throttle), it feels as though the front end is trying to climb a banked wall. Apply the throttle (no matter how smoothly) and it feels like the road camber has changed. At higher speeds it’s only marginally better. Going over uneven road surfaces or paving transitions is unsettling enough to make me want to drive a car instead. And the bike also rides like a truck. The suspension and the tires are stock, air pressures have been checked, and so have the steering-head and swingarm bearings. Is there any hope for this bike, or should I just buy fenders and a new DieHard for the Dodge Dart? Mitchell Rhine Long Beach, New York

The Radian was a stable, decenthandling bike when new, so something has gone seriously haywire on yours. Based on the symptoms, the tires seem the most likely cause. You didn’t mention replacing them, which implies that you re still riding on the originals. If so, they will have deteriorated badly enough to completely bollix the handling and ruin the ride.

If the tires aren’t the bad guys, the steering-head bearings may well be. You say you “checked ” them, but did you examine them for detenting of the balls and races? And if you adjusted the steering-head and swingarm bearings, are you absolutely sure that you didn’t get them too tight? Many things could be wrong with your Radian, but I strongly suspect the problem lies in one of these two or three areas.

Lead is dead

Washington state has finally gone the way of California: Leaded gas is no longer available. I own several older bikes, and the newest one I ride is a Honda CB750K2. I’m worried about damage to the valves, valve seats and valve guides caused by running unleaded gas. Do my worries have any merit? W.A. Fisher Port Angeles, Washington

There are some older bikes that will indeed suffer adverse effects if fed a steady diet of unleaded gas, but the CB750-including your 1972 model-is not one of them. I’ve talked to many owners of these ’69-to'78 single-cammers, including quite a few members of CB750 clubs, and no one reports any incidence of burned valves, damaged seats or worn guides resulting from the use of unleaded.

Two cautions, however: Only premium unleaded should ever be used in a CB750; and if the bike is raced, using unleaded fuel of any octane is much more likely to cause valve problems.

Because CB750s have proven not to need valve-seat or valve-guide conversions for compatibility with unleaded gas, no one makes them. So if, despite these assurances, you ’re still concerned about your K2 s ability to survive on unleaded, your only alternative is to use one of the several lead additives on the market.

That synching feeling

I have a Honda 650 Four Nighthawk, and I can’t seem to synchronize the carburetors. According to my mercury instrument, if I set the carbs at 20002500 rpm, they will not synchronize at idle. If I synchronize them at idle (1100 rpm), they don’t synchronize at 2000-2500 rpm. Is this normal? What rpm should be used for synchronizing carburetors? Don Martel Burbank, California

As with all multi-carb motorcycles, the synchronization procedure for the 650 Nighthawk should be performed at the bike s prescribed idle speed, which is between 1000 and 1100 rpm. But you also need to know that inconsistencies in synchronization between idle and any other rpm are not uncommon.

At any given rpm, the amount of fuel-air mixture an engine takes in depends upon two primary factors: intake-manifold vacuum, which is an insatiable monster that always tries to suck in as much mixture as it can; and the degree of throttle opening, which controls how much mixture the engine actually gets. On a multi-cylinder engine, any variations in intake-manifold vacuum from one cylinder to another will have subsequent effects on carb balance; so, too, will any variations in certain carburetor components have an effect on synchronization.

A 20or 25-psi deviation in compression, for example, is likely to affect carburetor balance differently at idle than at 2500 rpm. And remember that idle rpm is governed only by the carburetors’ pilot circuits, whereas running the engine at 2500 rpm brings other metering systems into play, including the vacuum-operated slides on the Nighthawk’s CV carbs. This introduces yet another set of variables that were not compensated for when the carbs were synchronized at idle. These variables can be in the form of differences in the pressure of the coil spring atop each of the four carb-slide diaphragms, in the fit between each slide and its carb body, or in several other carburetor components.

My advice, then, is that unless this carb-synch discrepancy is quite large, don’t lose any sleep over it.

Knocker stopper

In response to Mike Rigsby’s letter in your February Service, the knocking problem with his 1994 Magna is most likely due to side-thrust movement of the cam. The cam holders on some ’94 VF750C Magnas did not have their thrust-surface holes drilled at the factory, thus preventing the cam from riding on a thin film of oil as it should. Dealer Service Bulletin #1 VF750C, September, 1994, describes the correct fix. This should have been done prior to delivery and the frame punched right at the end of the VIN to show that this repair had been completed. Mark Sipin, Service Manager Pittsburgh Cycle Center Pittsburgh, Pennsylvania

Thanks for the input, Mark. The two Honda dealers 1 contacted before writing my response to Mr. Rigsby never said a word about any such Service Bulletin.