Service

SERVICE

Paul Dean

Vulcan under fire

My '93 Kawasaki Vulcan 750 backfires out of the exhaust when I use the engine for braking. It has 15,000 miles on it but has been doing this since new. The harder the engine braking, the louder the backfire, which seems to happen right around 2800 rpm. Other than this, the bike runs fine and I've had no problems with it. Is this something peculiar to the Vulcan or are my carburetors out of adjustment? Also, will this backfiring harm the engine? Steve Berto

Annandale, Virginia

In order to meet federal emissions standards, l arger-d is placement fourstroke Twins and Singles generally require very lean carburation, especially in the low-speed (idle) circuits. Those same lean mixtures, however, also can lead to backfiring during deceleration. Usually, the backfires are either so weak or so well-controlled that the rider isn't aware of their occurrence. The curbs on most of these engines including your Vulcan 's are equipped with little vacuum-operated valves that enriehen the fuel mixture on trailing throttle, thereby either reducing the intensity of the backfires or eliminating them altogether

On Vulcans, these valves are called coasting enriehers, and each carburetor has one. When you 're cruising down the road and close the throttle, the change in intake vacuum causes the coasting-enricher valves to open and allow more fuel to enter the intake stream. The slightly richer fuel mixture promotes quicker combustión, which, m turn, defers backfiring.

If everything else in your Vulcan 's ignition, carburation and valve-train systems is properly tuned and adjusted, it s likely that one of the coastingenricher valves is malfunctioning. They 're easy to access, so you should be able to remove the valves voursclf and give them a thorough inspection and cleaning.

Each valve is located on the outer flank of its respective curb body, behind a little round cap secured by two small Phillips-head screws. Undo the screws and remove the cap, which will then allow you to pull out a small spring and the coasting-enricher valve itself. Clean the valve, the valve housing and the valve seat with a good solvent, and blow everything dry with compressed air before reassembly. If you suspect that either valve is damaged or defective in any way, replace it.

hi all likelihood, the backfiring you describe will not harm your engine— unless, of course, it is very severe. But that 's not the point: loud backfiring is an abnormal condition and should be remedied as quickly as possible.

Fill 'er up?

In response to David Basore’s problem with those goofy vapor-recovery gas-pump nozzles (November ’94 Service) that are showing up in more places around the country, I have the solution. I’ve found two little devices that capitalize on the fact that all of these nozzles have either a raised ring or a pin on the nozzle shaft about a third of the way up the shaft.

One of these devices is called the Trick Fill, and it’s a flat, octagonally shaped piece of aluminum with a large, V-shaped cutout in the center. The other is called the Gas Hog, and it, too, is a flat piece of aluminum (cut in the shape of a pig, thus its name), but with a large cutout on its bottom edge.

Both devices work on the same principle: Once the bellows that surrounds the nozzle shaft is compressed, you just slip either of these devices behind the ring/pin on the shaft to keep the bellows in place. You then can go about the business of pumping the gas into your tank with one hand, much as you do with a conventional nozzle.

Both of these devices sell for about $5 and can easily be carried in a jacket pocket, a tank bag or even in the smallest on-bike storage compartment. The Trick Fill is available from Southern Motorcycle Supply (3670 Ruffin Rd., San Diego, CA 92123; 619/560-5005), while the Gas Hog is sold by Quality Tool & Manufacturing (1756 Timothy Dr., San Leandro, CA 94577; 510/3521222). These little gadgets are simple, clever and, best of all, really work. 1 never leave home without one.

Carleton Sypolt Fullerton, California

Buick 1, Sporty 0

When my ’89 1200 Sportster and I lost an argument with a Buick, both fork tubes got bent. I had a local repair shop fix the crash damage, which included replacement of the tubes, but now the front end is out of line. When I'm going straight ahead, the handlebar is angled slightly to the left. The shop that repaired the bike claims the frame is bent and that straightening or replacing it will be a very expensive job.

I didn’t think I hit the car that hard. Could the frame actually be bent, or is this shop just trying to generate a big, fat repair bill? Kevin Kelley

Ashtabula, Ohio

From this distance, / have no way of knowing whether your frame or your shop is crooked. Bnicks can be very solid objects if you hit one in the right place, so your mechanic may be correct.

On the other hand, many front-end collisions that bend the fork tubes will distort the triple-clamps before twisting the frame out of alignment. Consequently, checking the triple-clamps for damage is a worthwhile endeavor.

To do this, loosen the bolts that pinch the tubes in the triple-clamps, and slide each fork leg down until it slips out of the upper clamp. Then stand off to the side of the bike and sight along both fork legs to see if they’re perfectly parallel to one another. If they’re not, the lower triple-clamp (and possibly the upper one, too) is bent.

Then try to push the fork legs back up into the upper clamp. If either clamp is bent, the tubes will tend not to align with or easily slide into the holes in the top clamps. If the front end fails either test, you 'll have to replace the triple-clamps which is considerably less expensive than replacing or straightening the frame.