Triumph Bonneville Revisited

TRIUMPH BONNEVILLE REVISITED

SOME MONTHS AGO, when we published a road test on the Triumph T 120 “Bonneville”, we reported a performance level that we considered very good. However, Triumph owners everywhere began sending us letters that ranged from mild admonitions to outright invective and personal abuse. We endure this, because it is inevitable that our reports will make someone, somewhere, unhappy. The shouts of rage are natural, and we expect them.

Even so, in the case of the Triumph, the clamor was so loud, and so prolonged, that we began to think that something had indeed gone amiss. Therefore, it was decided that we should get the Bonneville back from the distributors, Johnson Motors, in Pasadena, California, and do a complete re-test. Don Brown, Johnson Motors’ sales manager was agreeable to the scheme and took charge of preparing the Bonneville as well. We were not present at the “tuning” session that preceded the test, but we understand that it included a look into the engine to make certain that everything was right. Also, a mechanic and a van were dispatched to us along with the Bonneville, so one might say that “things” were very right indeed. The test was performed at Riverside Raceway, using their long straightaway and measured 1/4-mile (which we checked). The day was cool and there wás only a light breeze; even the weather was cooperating.

Sotpe initial runs were made with the stock mufflers in plape, but this setup made the engine feel “fluffy,” rather than crisp, and Triumph’s optional “straightthrough” system was substituted — after which the speed increased appreciably. During this period, there was a considerable amount of jet and spark-plug juggling, and the top speed kept edging up with each adjustment. Finally, the point was reached where the Bonneville was crackling along sounding extremely healthy and the color of the plugs told us that it was finally and 100 percent “go.”

At that time, we made a series of top-speed and acceleration runs and the results are enlightening — if not altogether pleasing for the Triumph boosters. Two consecutive best runs were made at exactly 112.5 miles per hour; further flogging did not improve this speed. We would like to mention that the Riverside straightaway is a bit short for this kind of work, and that the Bonneville gained slightly through the timed distance. Accordingly, to give it the benefit of the doubt, we have credited the Bonneville with a top of 115 mph — which, with some “get-rolling” room, it would no doubt do. The optional remote-float fuel bowl would have helped, too, as the bike showed symptoms of fuel starvation due to frothing in the carburetors. Anyway, the Bonneville was faster on this second test — at the top end.

Acceleration suffered; apparently the jet changes that boosted the top speed hurt the acceleration, because our standing 1 /4-mile time increased from 14.5 seconds to 14.9.

At the end of the test, everyone went home satisfied that this Bonneville, at least, would go no faster. The figures presented here show the difference between the two tests. We think that, between them, they represent a close picture of the performance that can be expected from a “showroom” Bonneville. Enough said? •