(re) Learning the Basics

Start with the basics instead of the most complicated when working on your classic motorcycle to find a simple problem.

Reader Contribution by Richard Backus
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by Richard Backus

On a sunny Saturday morning this February, I busied myself getting the 1974 Laverda 750SF ready for the first Wheelsport Vintage Motorcycle Club ride of the new year. Championed by Tech Editor Keith Fellenstein, the club meets on the third Saturday of the month at Gaslight Gardens, a bar housed in an impossibly tiny, cottage-like structure at the north end of the bridge over the Kansas River to downtown Lawrence, Kansas. Along with regular “club” members (it’s an open question if we’re really a club; there are no rules for membership and we don’t do much besides our regular meetup — but we do have T-shirts), we’re regularly joined by members of the local Moped Army, who buzz in on little scoots that sound like chain saws and are capable of some serious speed. Well, for a moped.

The weather was perfect, and while I typically ride the ’73 BMW R75/5 to these gigs, I thought the SF could use some exercise. Rolling it out in the sun it looked fantastic, its red paint gleaming, what little good surviving chrome reflecting the bright sun. I spun it over a few times to get the oil moving, opened the fuel taps, waited a few breaths, turned the ignition on, pulled the choke, and thumbed the starter — and it caught immediately. Awesome. It’d been too long since I’d ridden the SF, and I was stoked. That “too long” bit would become important.

Warming it up, it ran beautifully — as long as the choke was half on. But as soon as I parked the choke lever on its stop it sputtered and died out, like it wasn’t getting enough gas. Pull the choke on at idle and it ran OK, if maybe a bit fast. Roll the revs up and shut off the choke and it fell on its face, sputtering and gasping. Crap. I really wanted to ride the SF. A few minutes tampering with the fuel/air mixture screws didn’t return any positive results, and if anything it seemed like it was getting worse, so I rolled the SF back in the garage and fired up the trusty /5, which while slower to catch, ran perfectly once it did.

A few days later I set myself to sorting out the SF, checking the usual suspects: fuel and ignition. And you know what they say about fuel and ignition: Ninety percent of all fuel problems are ignition related, and 90 percent of all ignition problems are fuel related. The spark plugs weren’t fouled, but looked odd, dirty, like there wasn’t complete combustion. I dropped the float bowls and checked the float, main and low-speed jets; clean as a whistle. I pulled the fuel/air mixture screws and blew out the circuits, then buttoned it up to see if it ran any better. It didn’t.

The ignition is a new Sachse electronic setup, so I was hard-pressed to think there was an issue there, but I checked just the same. And then I started thinking; when was the last time I’d ridden the SF? I realized it’d easily been 18 months. Really? That seemed impossible, but checking the date stamps on a few pics proved me right. Was it a simple case of bad gasoline? Taking a long, hard draw of the odor of the gas in the tank, it was clear the fuel had gone sour. I’d been running down the wrong path trying to suss out the SF’s issue, when the answer was literally a sniff away.

In my defense, I’ll note that I’d been congested and my olfactory senses were not particularly acute, but once I caught that unmistakable stench of bad gasoline there was no question what was wrong. The fix was simple. Drain the tank and carb float bowls, refill with alcohol-free 91 octane fuel, and start her up. It took a few moments before the SF cleared its throat, and with a little fine-tuning of the fuel/air screws it was soon running as I remembered, settling into a solid idle and emitting a healthy bark when I snapped the throttle.

Frankly, it was an interesting exercise and a reminder of how easy it is to head down a path to nowhere. Although I know better, when a bike starts running poorly I too often find myself looking for the most complicated answer to what is often a simple problem. It’s a reminder of something I know too well, but too often forget: Start with the basics and work from there. Ride safe.

-Richard Backus/Founding Editor

Motorcycle Classics Magazine
Motorcycle Classics Magazine
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