Service

SERVICE

We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because of the volume of mail received, we cannot return any personal replies. Please limit your “Service” letters to technical subjects only, and keep them as brief as possible. Send them to: “Service,” CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.

SLUGGISH GS550

I own a 1977 Suzuki GS550, which seems to run fine, but lacks the top end I think it should have. In sixth gear it won’t rev past 8000 rpm, nowhere close to the 9500 rpm redline.

I’ve reduced the airbox restriction by removing the airbox cover, and enrichened the mixture by going three sizes larger on the main jet. Neither seemed to help.

Do you have any idea what the problem could be?

Andrew Gerlach, Jr. Mt. Holly, N.J.

It’s doubtful that a serious problem existed originally, and the modifications you’ve made probably didn ’t help at all. For starters, return to stock main jets, or at most use jets one size over stock. Three sizes up is too big a jump for a stock engine, and will not allow clean carburetion on the big end.

Next, give the carbs and ignition a thorough going-over. Set the float levels, make sure all jet needles are in the stock position, and synchronize the carbs. Clean and adjust the points, set the timing, check the centrifugal advance, and replace the plugs, if necessary.

At this point you should have a clean running stocker. We don’t advocate topspeed testing on the street, but from our dragstrip tests, your GS should do much better than 8000 rpm in top gear. Shift technique, and not a lack of power, is a potential limiting factor. At 8000 rpm in 6th gear, the GS is running at 93 mph. If you had been shifting at the 9500 rpm redline, which would be appropriate for maximum safe (for the engine) performance, you would barely have gotten into 5th, as redline in 4th is 91 mph. By shifting early—it’s called short-shifting—the advantage of the 6-speed, close ratio gearbox is negated, and the relatively small 550 engine just doesn’t have the power to overcome the drag.

Try shifting at redline in the upper gears: 3-4 shift at 77 mph, 4-5 shift at 91 mph, 5-6 shift at 102 mph. By shifting at these speeds, our test GS550 was able to attain 104 mph with a I/2-mile run—yours should perjorm comparably.

If the performance is still way off, you should have the engine checked, starting with compression readings. Most likely, however, that shouldn’t be necessary.

SMOKING SUZUKI

I have a 1976 Suzuki GT550 and it’s of concern to me to find out why, after 70 mph and up cruising, there is always a little smoke coming from my exhaust system. It’s not a terrible lot of smoke but enough to worry me. I had a ’73 GT550 and do not remember that one doing this. Otherwise the bike runs fine and is thoroughly satisfying. Maybe a change of brands of oil would cure this?

Paul Phénix Fall River, Mass.

Some smoke will be emitted from your two-stroke Suzuki any time the engine is running. The amount of smoke usually is> small enough not to be noticeable when cruising, though. Oil flow on the GT550 is controlled by a plunger-t ype oil pump. Both engine speed and plunger travel vary the amount of oil supplied to the engine. To adjust the oil pump, first adjust the throttle cable. Then remove the setscrew from the alignment hole of the righthand carburetor, open the throttle until the alignment mark on the carb slide is at the top of the alignment hole and, while holding the throttle in the same position, check that the alignment mark on the oil pump adjusting arm meets with the mark on the oil pump housing. The oil pump is located at the rear of the engine, on top of the transmission case and is accessible after removing a chrome plate.

An oil injection recycling system fitted to all Suzuki Triples beginning in 1974 is another reason why your 1976 GT550 will smoke more at highway speeds than the earlier Suzuki did. The earlier bike would load up with excess oil in the crankcase during low speed running and product excessive amounts of smoke whenever large throttle openings were used. The recycling system allows the cylinders to suck excess oil out of the crankcase at normal highway speeds w hich reduces full throttle smoking. A check valve at the bottom of each cylinder can also contribute to excessive smoking if the valve is stuck. A syringe can be used to check the check valve. If the syringe can suck in air but can't push it into the cylinders, the check valve is working.

LEGAL ENDURO

For about a year now, 1 have been competing in enduros in the East Coast Enduro Association. However, most enduros require the bikes to be street legal. This means that Japanese enduro bikes like the IT and PE and soon-to-be XR models cannot technically be used for what they are intended. So rather than continue to fasten my street bike license plate to my IT175E, I am trying to get it legal for the state of Maryland. I have bought a street legal taillight to replace the stock running light. My problem is finding or making a hot wire to run the brakelight and horn. And will this draw on the magneto’s output too much?

Bruce Goad

Gaithersburg. Maryland

A brake light and horn shouldn't overtax the electrical system on the IT. While just about any hot lead from the magneto will power a light and horn, the easiest lead is probably the hot lead to the light switch. In most jurisdictions a squeeze-bulb horn will qualify and eliminate having to wire a horn and switch onto the bike. Check with a local motor vehicle department office to make sure the bulb horn will qualify, however.

A lthough you don V say, we assume your street legal taillight includes provisions for a dual filament taillight-stoplight bulb. If it doesn’t, try to find one.

Besides the lighting equipment, many estates require that motorcycle lights operate independently of the engine and that requires a battery. Signal lights often are required by states as well.

** The toughest problem you face, if the IT is a 1978 or ’79 model, is meeting emission standards. Federal regulations establish ¿standards for any street legal motorcycle made after January 1, 1978. Most pure yenduro bikes such as the IT, PE or soon-tobe XR Hondas will have engines not certified to meet federal regulations. The cost of certifying an engine is clearly beyond the resources of any individual.

Technically, it is probably impossible to legally register a 1978 or later IT for the Kstreet. It’s not easy to register an earlier version in many states. But it can be done.

► The first place to start is at your local motor vehicle registration office. Not all states will enforce federal law in the same manner and not all motor vehicle offices Enforce state registration laws in the same manner.

FILTER CHANGES

I recently purchased a set of K and N filters for my 1978 550K Honda. Since I installed them, the bike has been running poorly at high rpm. I imagine the problem is too much air, not enough gas. I find that it is possible my main jets are unremovable so rejetting is a problem. Could you give rue more details? Is it possible to tune around the problem?

Keith Mathison

Grand Forks, N.D.

Main jets on the 550 can be changed and going to a larger, richer jet may help alleviate your problem but isn’t necessarily the Best solution. For one, the jetting on the carbs is part of the emissions control package and can’t legally be changed by a dealer <$r mechanic without violating federal law. You may be able to change the jets, going to Hhe next larger size, without violating the anti-tampering law. The problem, however, it more involved. Honda spent hundreds of hours testing airbox shapes until the airbox used on the 550 was devised. The shape of fite airbox forms velocity stacks for each carb and is designed to help the carbs work. vWithout the velocity stacks, the jetting isn’t correct.. 13