Service

SERVICE

Two-stroke fire works

I'm in the process of building a quarter-mile bottle rocket based on a 1972 Kawasaki H1 500 Triple. I need to know what I can do to make it go quick.

I had in mind adding expansion chambers, fiberglass reeds, an aluminum gas tank to lighten the bike, and larger carburetors. What do you think of my selection, and do you know where I can find these parts? Thomas R. Fair, Jr. Los Angeles, California

You shouldn `t have too much trouble building a rocket out of a Mach III; they were fast in their day, and knowledge on how to make them faster yet is still floating around. Your list of changes is reasonable, but we'd recom iiiend modifying the bike one step at a time. We'd start with expansion chambers as the easiest and largest power boost, and a good source would be Fast by Gast (1930 Baseline Road, Grand Island, New York 14072; phone 716-773-/536).

As far asfittingfi/'erglass reeds, the Hi engine is a piston-port engine and doesn `t use reed valves. Extensive work on the cylinders would be required to adapt reed valves, and this modifica lion might make the engine more trac table without necessarily paying a big peiformnance benefit. We'd save it for last.

The larger carburetors you men tioned could help the Kawasaki go fasrer~ and the Mikuni VM carburetors that would be the obvious choice can be ordered by your dealer through distributors such as Rocky or Sudco. And while niaking the motorcycle lighter would also improve perfor mamice, we're not sure ([[there are still any aftermarket sources left for light weight Hi chassis parts.

Nighthawk tappet tap

I own a Honda 650 Nighthawk that runs great, except that after my 600-mile service it started making a tappet noise on the righthand side of the engine only. It's a noise that comes and goes, but it always comes back. I took it to my dealer and he says it sounds normal and that maybe I should use heavier oil. The bike has 3000 miles on it and the noise is still there. I've worked on many auto engines and I know when I hear tappet noise. Has there been any problems with Honda's valve lash adjusters, and what can I do about this problem? Richard Zak Santa Cruz, California

There have been afew problems with Honda's hydraulic lash adjusters, mostly occurring on 1983 model Nighthawks. We'd suggest you contact Honda's customer service number (213-327-8280, ext. 2430), and see if Honda can put you in contact with one of its service representatives or suggest some other means of correcting your Nighthawk's valve clatter.

Turnout blues

I own a 1982 V45 Magna. After replacing the stock pipes on my Magna with Cycle Shack turnouts, the bike will only run on full throttle until it hits 6000 rpm. It won't run above 6500 rpm with full throttle. Do I need bigger jets to work with these pipes, or is there a different answer to the problem? R. Leonard Mt. Vernon, Ohio

You do need d~fferent jetting, but it ma be more complicated than simply installing bigger main jets. From your description it seems possible the jetting is lean in the range where the needles and needle jets are controlling the mixture, which would indicate you need larger needle jets or needles with a different taper. But because neither of these items is readily available for the Honda `s Keihin carburetors, it would probably be advisable to see if the problem could be fixed by going to bigger main jets.

ven then1 you mavfind it easier to drill the standard jets oversize than to find larger jets from Honda. Ifyou do have to resort to drilling, buy a spare set of main jets, and then enlarge them afew thousandths of an inch at a time using a number drill set. After that, it's trial and error to see fyour Magna responds to the richer carburetion. If all else fails, you can always reinstall the original exhausts.

Wobble-fix for CB900 and 1100F

I owned a Honda CB900F two years ago, and it had the same wob ble problem as discussed in some of your Service columns. At the time I was racing it and I had mentioned the wobbling to another racer who was also on a 900. He suggested moving the fork tubes down further into the triple clamps, but more important than that, he stressed that one's choice of tires was of the great est importance.

He told me his bike had wobbled too, but with the right tires it had completely stopped. So I replaced the Dunlops with a Metzeler ME99 on the rear and up front I put on a Pirelli Gordon. That tire change stopped the wobble altogether.

I now own two CB1 lOOFs (one for racing, one for the Street), and I keep Metzelers on the rear and Pirellis on the front of both bikes, with no wobbling or handling prob lems of any kind. So, anybody out there with a wobbly CB, give those tires a chance, and save wear and tear on the steering head bearings. Chris Collins Kensington, California

Your tire selection definitely sounds worth trying for the big Hondas, but we would like to point out that tires and chassis characteristics are closely related, and that the Metzeler/Pirelli combination may not be a cure-all for every motorcycle `s wobble problems.

XS-ive rattling

I recently purchased a new left over Yamaha XS 1100 Special. After a couple of thousand miles the bike developed a clattering sound from the engine. To me the noise sounds like piston slap. To my dealer, it sounds like detonation. He says that most XS 11 OOs make the noise, that it won't damage the engine, and that it can't be eliminated. He gave me a different vacuum advance which I installed but it only "rearranged" the noise without eliminating it. It sounds like popcorn popping in a large steel pot or marbles in a jar. Is the noise detonation? Will it damage the engine? Is there a cure for it? If there isn't a cure should I sell the bike or just wear earplugs? Brent Williams Boardman, Oregon

The noise that you describe is the sound of detonation, the premature, too-rapid explosion of the air/fuel mix ture in the engine's combustion cham ber. You probably hear it most often when your engine is running low speed at a large throttle opening, the kind of operating condition that the torquey XSJ 100 encourages. While it's not good for your engine, fairly light, low speed detonation will probably cause little damage. and you can probably expect a good long life from your Yamaha XSJIOO.

Still, it would be better to eliminate the problem. Higher-octane gasoline is more detonation-resistant, and switch ing to the best gasoline you can find and even adding an octane booster will help. Also, avoiding certain operating conditions can eliminate some of the racket; that basically involves shifting to a lower gear when an increased throttle application has started the noise. Finally, either dropping the compression ratiO (difficult,) or retard ing the spark wi//reduce detonation.

Even / after all that, you some times still hear light detonation, there's no real need to worry; ifyou can stand the noise occasionally, there's no reason to sell the bike.