Service

SERVICE

Curbing inflation

Paul Dean

I just bought a really cherry `68 Triumph Tiger 500 that's all original and in great shape except for a dent in the left side of the gas tank. There are no creases in the metal and the paint's not cracked, but there's a large, rounded indent right below the Triumph badge. A friend says I can pop the dent out by blowing compressed air into the tank, but I thought I'd better check with someone else first. Paul Durbin West Liberty, Pennsylvania

You can remove some dents by this method, but you have to be very care ful not to use too much pressure, lest you distort the tank. Your Triumph s' tank has a high center arch that al lows the sides of the tank to hang down over the frame `s~ single back bone tube. If you apply too much air pressure when trying to remove the dent, the sides of the tank will spread apart, not only changing the appear ance of the tank but making it impos

sible to mount on the existing brack ets. And with the tanks on some other bikes, too much pressure can cause the sides of the tank to be pushed to gether, preventing the tank from fit ting down over the frame backbone.

Because of this potential for dam age, I suggest using no more than 2025 psi when attempting to pop the dent back out. If this technique fails, you `ii have to resort to more conven tional means of removing the dent.

A Primer on starting

I've got a `98 Suzuki Intruder, and when it sits for a couple of days, it's hard to start. It will crank over just fine, but the engine won't catch. After a few minutes it fires up, but then it stalls right away. If I keep trying, it fi nally starts. Is this a common prob lem? If so, do I have to take the bike back to the dealership? I don't want to do that, because I'd have to leave it there a while, since the problem only occurs after the bike has been sitting a few days. Tinatina3 Posted on America Online

There is no "problem" with your In truder; the behavior you describe is fairly common on motorcycles-such as yours-that have vacuum-operated fuel petcocks. These petcocks use an inter nal on/off valve connected to the intake manifold, and the valve allows fuel to flow from tank to float bowls only when intake-man~fold vacuum holds it open. But any time the engine is not running, there is no intake vacuum and so the valve is closed.

When you shut off your Intruder's engine, the location of the carburetors between the Vee of the cylinders sub jects the carbs to considerable engine heat that evaporates some of the fuel in the float bowls. And when the bike sits unused for a few days, even more fuel evaporates from the bowls.

With a conventional petcock, either of two things occurs when fuel evapo rates from the float bowls. If the petcock is left on while the bike is not used, evaporated fuel is immediately replenished; f the petcock is left off evaporated fuel is quickly replaced once the petcock is turned back on. But with a vacuum petcock, fuel can enter the float bowls only when the valve is held open by intake-manifold vacuum; and when the engine is being cranked over on the starter motor the intake pulses are so small and brief that only a trickle of fuel passes with each intake cycle. Thus, it takes a lot of cranking before the float bowls are sufficiently full to allow the engine to start and run.

This is why vacuum petcocks have a "Prime" position, which bypasses the vacuum valve and allows fuel to flow even when the engine is off If the petcock is turned to Prime a few seconds before you attempt to start your In truder, the float bowls will fill quickly and the engine should start right up.