Cycle World Service

CYCLE WORLD SERVICE

Rusted CB750K mufflers

My Honda CB750K has a small rust hole through one of its four mufflers. I try to keep the bike clean, but trying to get into all the nooks and crannies around four mufflers is time-consuming at best.

The bike is covered and stored in an unheated garage during the winter months. How do I prevent rust holes in the mufflers?

Darrell E. Broten Eau Claire, Wisconsin

Rusted mufflers are a big problem with motorcycles that have 4-into-4 exhaust systems, and it has little to do with how clean you keep the bike. Each muffler in a four-muffler system has quite a large volume compared to the amount of exhaust gas that passes through it; and so it takes a long time for each muffler to get hot enough to burn off the condensation that forms inside when the engine is first started. So, since the average trip on the average motorcycle is far too short to allow the engine to reach full operating temperature, most of the condensation in a 4into-4 system’s mufflers is not burned off, and the mufflers eventually rust from the inside out. That’s why motorcycle manufacturers tried for years to discontinue the use of 4-into-4 systems, and Honda even did so at one time; but enough riders clamored for their return that four-pipe systems were brought back into the Honda line.

The solution? Either ride the bike until it is at full operating temperature every time you start it, or replace the 4-into-4 system with a 4into-2 or 4-into-l. Otherwise, your four-piper is destined have rusty mufflers.

Virago oil burner

I am stationed in Germany and ride my 1983 Yamaha TR1 (very similar to the U.S. Virago 920 but displac ing 981cc) on the high-speed Autobahns. Speeds vary fror 130 to 180 kph (80 to 112 mph). My problem is what I feel is abnormal oil usage. The bike has 9000 kilometer (5580 miles) on it and uses 400cc (almost ½ qt.) of oil ir 1400k (862 miles) and 800c (almost a quart) in 2876k (1783 miles). My dealer say~ this could be normal. Norms for a Vega, maybe, but not for a motorcycle, I hope.

Ray Lovinggoo West Germany

The oil usage you describ does sound normal for a BMW run at those speeds, and possibly could be normc for the Yamaha V-Twin as well. Continuous high-speec use can build very high crankcase pressures that force oil past piston rings, around seals and out breather hoses. You didn’t say whether the oil was blowing out of the engine, simply disappearing, or if the exhaust was smoking. If the oil is being blown out a breather hose, enlarge the diameter of the hose. If the exhaust is blowing black smoke, the piston rings could be worn or broken. If none of these things are happening, contact a Yamaha service representative about the problem.

Stalling Honda XL600

I’m having a problem with my XL600 stalling as it comes to a stop. The bike is also a bear to keep running when cold.

Is the jetting too lean?

Dan Delaney

Tacoma, Washington

These sorts of problems were common with the early XL600s. There is a dealer bulletin, R#2, that details a cure for the ailment. The fix is fairly extensive and involves the installation of an Easy Start Kit that consists of new carburetor jetting, a different ignition box and different timing. Your Honda dealer should install the kit free of charge under warranty.

Hot oil

I own a 1982 Honda CB750K equipped with a Windjammer fairing and VDO oil-temperature gauge. The oil temperature regularly runs at 230 to 240 degrees on summer days. Is this an abnormal temperature for a motorcycle’s oil? Will my engine be damaged? I use Castrol 20w-50 oil.

Mark Swanson

Downers Grove, Illinois

Motorcycle engine-oil temperatures in the range you describe will cause no problem. In fact, that’s a mild temperature for motorcycle oil. We have done considerable riding of a GS1100 Suzuki at a race track, for example, and the oil temperature consistently hit 320 degrees without damage to the engine. The oil you are using should be fine as long as regular change intervals are maintained.

Hushing the RM80

I’m tired of getting complaints every time I ride my ’82 Suzuki RM80. Is there a way to make the bike quieter without sacrificing performance?

Ronnie Cox Oxford, Mississippi

Your problem is that the stock silencer has blown out most of its soundabsorbing material and that it can’t be repacked. Replace it with one of the repackable silencers on the market such as the aluminum-bodied unit from An swer Products. Performance won't be affected and noise will be reduced. When the noise level of the aftermarket silencer starts increasing, remove the end cap and repack the interior with fiberglass.

Weak mid-range

I’m thinking of buying a Nighthawk 700S because it has most of the features I want in a bike. However, according to the tests I’ve read, the engine is very strong on the top end and a little weak in the mid-range area. What could be done to move some of that top-end power down into the mid-range, and would it be worth the time and expense to do so?

K. Retzlaff

Waukon, IOWL

It would be fairer to say the Nighthawk 700 is average in mid-range power, and spectacular on top-end power. In any case, the mid-range power could be enhanced. Slotting the sprocket on the intake cam so that intake opening and closing occurred about 5° earlier than stock would boost mid-range power at the expense of the top end. This might require some carburetor rejetting.

Another approach would be to increase displacement. A 3mm overbore would boost displacement to 760cc, and would boost power everyplace. Again, some carburetor recalibration may be needed afterwards.

As far as these modifications being worth the effort, that’s hard to say.

We’d suggest you buy the Nighthawk if you want it, and see if the mid-range is acceptable for you before making any changes.

Fast-idle takes a hike

I’m having a problem with my 1983 Honda 650 Nighthawk. When the bike was new it would start easily and idle at 3000 rpm with the choke on when cold. Now the bike has 4000 miles on it, and starting is hard and the fast idle no longer works. What happened? My local dealer is no help.

Thomas Moore Lakewood, New York

The CV carbs on the Nighthawk use enrichener circuits for cold-starting, not true chokes. A cable connects the “choke” lever on the handlebar to a carb-mounted bell-crank that links all four enrichener plungers together. If the cable has too much freeplay, the plungers won’t be lifted far enough to engage the enrichener circuits when the choke lever is rotated. That results in hard cold-starting and loss of fast idle. To adjust the cable, remove the gas tank and seat, then push the choke lever all the way open. The enrichener plungers should be lifted upward between 5mm and 7mm. If they aren’t, loosen the clamp that secures the cable’s outer housing to the bell-crank bracket, and shift the cable housing upward until the plungers are lifted the required amount.

This should remedy the condition. If it doesn’t, your Nighthawk probably has some sort of fuel-contamination problem best diagnosed by a dealer. If the dealer can’t find a fix, remind him that Honda offers a toll-free 800 number for dealers to call when they get stuck on such problems. If he refuses to try, report him to American Honda.

Interceptor start-up clatter

When cold-starting my ’84 Honda 750 Interceptor, there’s a lot of valve noise. The racket disappears after the engine warms up. I called Honda on the problem and they referred me to a dealership, but every dealer I talk to tells me something different. What should I do? My warranty expires pretty soon.

S. Cameron Toronto, Ontario, Canada

In all likelihood, what you are hearing is not coming from the valves, but is instead a noise caused by a looseness in the flange nuts that secure the exhaust pipes to the cylinder heads. The noise is a combination of a sharp “chirp” caused by exhaust gas briefly escaping past the head-pipe gasket during the exhaust stroke, plus a slight metallic rattle of the pipe inside each loose flange. The resultant noise sounds remarkably like some sort of valve clatter, but it is not. When the engine heats up, these components expand enough to snug everything together, thus both the leak and the rattle go away. According to the Honda tech spokesman who gave us this information, the two rear-cylinder exhaust flanges are probably the offenders, and the most likely culprit of those two is the left-rear flange. Have all four checked, however, and also have the dealer verify that there are no problems with the valve gear . . . just in case. S