Service

SERVICE

Paul Dean

What the DR ordered

I have a 1991 Suzuki DR350S that absolutely refuses to start when the engine is hot. When it's cold, two or three kicks (with choke, of course) are enough to get it running. And once it fires up, it runs perfectly and will idle indefinitely. But if I shut it off and then try to restart it right away, it just won't come to life.

I'm a mechanic on marine and small engines, and I’ve checked about everything. The spark will jump a -Vx-inch gap on a coil tester; there is plenty of fuel at the carbs; and the plug is dry after I kick the engine what seems like hundreds of times. It doesn't matter whether the choke is on or off, and squirting a shot of fuel into the mouth of the carb doesn't do anything.

The bike is completely stock except for a SuperTrapp muffler and a Dynojet carb-jetting kit (installed after the problem first surfaced). I’ve tried starting the engine with throttle open, throttle closed and throttle partially open, but I don't even get a backfire or a pop. Yet. if I let it sit and cool, it starts with just a few kicks. Do you have any idea what is going on here? Steve Thatcher Kapaa, Hawaii

Your DR may he suffering from any of several conditions that could lead to its hot-start problem (improper ignition timing, too-tea it id/e-mixture setting, insuffic ient valve clearanc e, to name a few); and while the eoil might throw a fat, healthy spark when it’s hooked up to a coil tester, in actual use on the motorcycle, its performance may be sufficiently impaired when it reaches full operating temperature to allow the engine to idle but not start. If you haven't already used your mechanical knowledge to check these possibilities, you should do so.

Understand, though, that singlecylinder four-strokes can be quite frustrating to kick-start, and that the DR250 and 350 both the dual-purpose “S" models and the off-roadonly versions -rank among the fussiest, especially when hot. So, if further troubleshooting fails to turn up any gremlins, the problem may be with your starting procedure.

The prescribed starting drill for the DR involves getting the piston positioned properly before beginning your kick stroke. And the compressionrelease mechanism is designed to help you find that sweet spot. First, hold the throttle wide-open, squeeze the compression release all the way in, and briskly kick the engine through a couple of times. This helps clear out a loaded-up engine or prime a dry one. Then, kick the engine through very slowly until you locate the point at which the compression-release lever remains in the full-on position. Continue kicking the engine slowly until the lever snaps back out to the off position. From that precise point, give the kick lever a firm prod all the way through its entire stroke, using no throttle whatsoever. IJ you do all of this properly, you 'll be amazed how easily the engine comes to life, usually with no more than two or three kicks.

Clunkers, part deux

I read with interest the letter in your August Service column from a guy who has a clunking noise in his Honda VF700 Sabre. I have a similar bike, a 1983 VF1 100 Magna, that also makes the same kind of noise when I take off from a stop. The instant the bike starts in motion, it gives off a loud, distinct clunk. It doesn't matter if 1 take off fast or slow, hard or easy, the noise is the same. It also clunks when I shift up or down.

From what I can tell, the noise is coming from the rear wheel. My guess is that it's the U-joint on the driveshaft. What's your diagnosis? Steven Dee Bryant Paragould, Arkansas

// the clunking noise truly is emanating from the rear-wheel area, the problem most likely is not with the universal joint, which is at the very front of the driveshaft, right on the centerline of the swingarm pivot. Rather, the clunk is probably being caused by the driveshaft damper assembly, located just ahead of the rear-end housing.

This damper unit is a cam-and-ramp device that cushions major shocks in the driveline. It involves two large, rounded protrusions (the “cams ") situated ISO degrees across from one another on the aft end of the driveshaft, and they fit into two deep, rounded notches (the “ramps ’’) attached to the front of the final-drive pinion gear. Although the cams are a rather loose fit into the ramps, a large, stiff spring pushes them down into the bottom of the ramps and holds them there with considerable force.

When the bike is running at steady speed, or is under very light acceleration or deceleration, the damper does nothing, effectively behaving as though it were one solid piece. But any time the driveline is subjected to a large or sudden increase or decrease in torque, the damper's earns are forced to climb the sides of the ramps and compress the spring. This momentary compression action absorbs enough of the impact of the torque variations to cushion the driveline components and help them survive the tremendous shock loads they must endure.

It 's my guess that the spring in your Magna's damper is either fatigued or broken. This would allow the damper to compress and bottom-out much too easily, causing the loud clunk that occurs every time the torque load changes significantly. If this condition has existed for long, the cams and ramps could have been damaged and may also need replacement.

Old smoky

My '86 Honda GL1200 Gold Wing often gives off a big cloud of white smoke when the engine is started, regardless of the ambient temperature or humidity. Any time the engine is started when warm, the smoking is not as noticeable. This has been a problem ever since 1 rolled the bike off the showroom floor, right up to the 52,000 miles it currently shows on the odometer. I use Pennzoil 10W740 oil year-round change the oil and the filter every 3000 miles, and drive the hike regularly. The engine docs not appear to be using any noticeable amount of oil between oil changes. So. why all the smoke? Is there anything 1 can do to avoid these billowing white clouds? C.B. Cranford Richmond, Virginia

/ 'm going to take an educated guess and assume that YOU usually park your Gold Wing on its sidestand. Most people do. since the considerable heft of a GL discourages the use of the centerstand, ff this is the case with your Honda, the smoking probably is caused by the burn-off of engine oil that seeps past the piston rings in one of the two left-side cylinders while the hike is parked.

On bikes with horizontal cylinders, engine assemblers usually are careful not to position any of the piston-ring end gaps on or near the bottom side of the pistons. They do this because any oil left on the crankcase side of the cylinder walls when the engine is turned off will run down and accumulate at the lowest part of the horizontal cylinder. And if the cylinder is angled slightly downward as is the case with the left-side cylinders on G is and BMW's when those bikes erne parked on their sidestands the oil will try to flow toward the combustion chandler, its journey arrested only by the sealing capabilities of the rings. If any of the ring ga/).s are on the bottom particularly the ga/) on the oilcontrol ring the oil can seep past and get into the combustion chamber. If it does, it gets burned o ff as smoke when the engine is started.

On rare occasion, one or more of the ring end gaps inadeertently get positioned on the bottom side of the piston during engine assembly, leading to the aforementioned smoking on start-up. The smoking isn 7 as pronounced when the engine is warm because this oil seepage takes time and the engine isn 7 shut down long enough to allow all the oil to gain entry to the combustion chamber, in any case, though, the amount of oil consumed during startup is downright miniscule (a few drops of oil can produce an enormous billow of smoke), as eeidenced by the lack of oil consumption between oil changes.

My adyiee is simple: Until you huye to worry about this problem, don 7. □