rd350lc, 350ypvs

[superglym02]

can any body tell me the diference between an rd 350lc and an 350ypvs cheers, born again dont know a great deal about the ypvs.

[Guest JMW]

Quite a bit is the answer.

Mainly, engine and swingarm + wheels.

They look very different as well.

The YPVS is an alloy Power Valve that is fitted into a casting directly in front of the exhaust port. The valve has a flat section in it which, by turning the valve allows the height of the exhaust port to be effectively altered.

2 types of YPVS engine - both very similar with very slight differences.

31K - early YPVS up to N2 but not the F, F2 or R models.

1WT - later engine code for the late F, F2 and R models.

The earlier engines had a 27.5mm exhaust port height and a lower quality barrel material. These models do have a more agressive ignition advance so although the port timing was not as eventful as later models, they went better.

The later bikes have a 27mm exhaust port height but had poor ignition advance plots, they are almost 3 degrees behind at full advance when compared to the earlier bikes. What this means is that the later bikes were slightly slower and didn't respond to pipe changes as well as the older bikes.

Carbs on the YPVS models are Mikuni VM26ss, easily changed for Keihin 28mm PWK's, all bikes benefit from manual ignition advances, boost bottles, dual stage reeds and reed spacers plus loss of weight from the flywheel, rods, crank and so on. Porting can be excessive - I'm testing an engine with a 4mm raise in exhaust port height at the moment and matching the crank cases to the barrel lowers reaps big rewards.

Good F2's can be had for around £800 - £1000 and provide almost endless fun.... and expense if you get hooked..

Check out http://www.yamaha-rd.com/forum/index.php but be ready, there are come class tossers there.

J