Tims Yamaha YZ490

Post date: Jul 30, 2011 11:47:52 AM

This is a 1983 YZ490. 1983 was a big year for Yamaha, with Hakan Carlquist winning the world championship and, perhaps more importantly (from a sales perspective), Broc Glover winning the US National Championship, on a largely stock YZ490. Best of all for sales in the US, the pair ran 1 and 2 at the USGP, winning a heat each.

This means that Yamaha sold a truck load of these bikes, making rebuilding one very easy, as parts (both new and used) are widely and quite cheaply available. They weren't the best bike that year, I had an '83 RM 500 way back and it was probably a better bike, as was the KX. I never rode an '83 CR480 but they weren't that great from memory. The YZ490 has a fairly bad reputation, partly for "interesting" suspension, but mainly for impossible to jet for carburation issues. Run it on ordinary petrol and it will detonate all day long, be close to impossible to start and not stop running just because you've hit the kill switch. US Webpages are full of fixes, that mostly involve reducing the compression ratio and reshaping the combustion chamber. Here in NZ we have much easier access to high octane race or av gas, which is a far easierway of managing the problem.

I bought this bike for VMX, although it has only beenused that way a small amount. It looks pretty stock, but I made a few improvements when I rebuilt it. The forks have had RaceTech fork emulators fitted, when they were rebuilt, but there was not much done to the shock (other than have Robert Taylor rebuild it). The difference the fork mods make to a day at a MX track is the difference between numb forearms and blistered hands and a fun day of racing.

The engine is fairly stock, but has a new flat slide carb. The reeds are dual stage boysen. The transmission is the five speed (stock was four) that both earlier and latter models had. It has a DG exhaust. I also use an ignition "amplifier" called an i-cat, lots of claims are made for it, most of which I struggle to believe, but it definitely makes it easy to start.

This is a NZ new bike, that had a very hard life. Although bought as a runner, in the course of rebuilding and running it for a few years, I've replaced the frame, shock, plastics (other than the tank), crank, barrel, a few pistons and a couple of rods, all suspension bearings and seals, ignition system and fuel tap. The carb and pipe were performance enhancements, but are new too.

Despite the high maintainence, money spent and a few disappointing mechanical failures at important races, riding this bike is so much fun it makes me smile thinking about it. VMX would be fun on a pushbike, but is brilliant on this bike. Likewise, in three decades of road racing, I can't think of many better days than racing this at Whanganui (when it runs).

Tim Kendall