Restored Rocket: Yutaka Hoshi’s Yamaha TZ 250 Factory Racer

[The Spin Doctor]

Love those old TZ’s they are my idea of ‘proper’ racers. Just my era I suppose.

Mate of mine raced 250’s and 350’s and my abiding memory is him constantly changing jets depending on the weather.

A dilema known to anyone who jetted a two stroke for the 'Mountain Course'

Or Spa-Francorchamps... always reputed to be a course which was oxygen-rich under the trees. I was never convinced about that, but it would usually have been several degrees cooler on a sunny day.

[The Spin Doctor]

The 125's were even more tricky, you were either very fast or shit slow.
The old air-cooled MT125s (pre RS125) were knife edge power, but by crikey they went well in the very small power band they had.

My brother raced one of the MkIII water-cooled MTs for a few races... considering his lack of experience on the track he did surprisingly well, particularly at the Plum Pudding at Mallory. He was running in 4th when they black flagged him... somehow he'd got confused in the paddock holding area and escaped out on track in the unlimited 4 stroke race. He was supposed to be in the next race

[Screwdriver]

Or Spa-Francorchamps... always reputed to be a course which was oxygen-rich under the trees. I was never convinced about that, but it would usually have been several degrees cooler on a sunny day.

I distinctly remember the effect of atmospheric variation on my road bikes, a succession of RD350LCs. Riding along on a spring morning out in the countryside, you might suddenly come across a patch of cold dense air. The bike would suddenly perk up and become noticeably more zingy.

[Le_Fromage_Grande]

LCs went better in cold sense air, I think late RGV250s had solenoids in the carbs to try and get over the effect of atmospheric conditions. I do know every race RGV I've known has been an arse to her right, I remember one bloke at Cadwell could get it to run right on the open part of the circuit, and not the woodland section, he changed the jets and it then ran right on the woodland section, but not on the rest of the track, in the end he gave up and got a 4 stroke out of his van.