YZ125 H 1981 Reed Valve Upgrade

[Ji Gantor]

I know this is not that technical but it still has to be done, especially if I am going to sell the bike.

This is the original OEM reed block with the S/S reed valves.

Ji

[Ji Gantor]

The curved steel with the holes in them are the rev plates. They stop the reed valves from over bending.
When the steel valves have been used for a while they tend to bend in the direction they open and stay that way. This means that there is a gap between them and the reed block. Most riders at this stage flip them over and hay preston they seal again. I believe you can only do this once as the metal work hardens and will snap off and go through the engine, NOT GOOD.

Ji

[Ji Gantor]

Okay, grab your phillips head screw driver and remove the three screws and release the rev plates and reed valves.

Ji

[Ji Gantor]

Clean the block with some carb cleaner and ready the new Boyesen or what ever brand you like reed valves. Also locate some loctite.

Ji

[Ji Gantor]

Test fit the valves and rev plates and make sure they seal against the reed block.
I had to flip the valves over to get them to seal so it is worth test fitting.
Now drop a dab of locktite on the screws and do them up.
Again check to see that the valves seal.

Ji

[oldfart]

I hope you didn't put your reeds in without the plate as pictured 

[Ji Gantor]

Hey Oldfart are you going to be at Rocksberg this weekend.

Ji

[Ji Gantor]

The reeds as pictured are in the engine and the plates are in a box, as per instructions and pit crew chief Mrs G.

Ji

[Ji Gantor]

No light so no gaps.

Ji

[Ji Gantor]

Ready to use.
When these fibreglass valves go wrong they rip and some times some of the pieces goes through the engine. So the valve makers say it does not harm the engine.

Ji

[Lozza]

The 'looking for light' and checking for gaps is a complete WOT. As a reed petal will go from rest to full deflection and back down again 100 times a second at 6000rpm and 200 times a second at 12,000.
Under dynamic conditions the petal is never really at rest.I have had petals break the rear skirt (as that's going up and down at a similar rate) chops the wayward petal into tiny pieces that dissappear out the exhaust.

[Ji Gantor]

Hi Lozza,
What brand of reed do you use?
Have you used the black carbon fibre reeds?
Are they that stiff that they only concentrate the power band at the very top of the rev range?
I have heard that Ex Pro racers used to cut them with a stanley knife to get them to work better, do you know about this method?

Ji

[jimg1au]

lozza makes his own i have a set in 1 of my 250 elsinors.only had 2 rides on it but it seams to go good
cheers
jim

[Lozza]

Ji,
Hmmm I get the petal material from the US, they are marketed under a brand name over there and unfortunately over here, so I can't say the name(or post it on the net) otherwise my supply will dry up.
Yep I only use carbon fibre and I have a range of thickness and construction, in an effort to tailor the petal to the rpm range.
I have yet to do a full evaluation on different petal thickness but from the feedback a mono petal of stiffer modulus works better off the bottom for 'snappy' acceleration(maybe ask Hoony) and a thinner petal doesn't make the engine 'run flat' at high rpm on a 125 road race engine.
I tend to find mono petals better than fingered petals, as I modify the cage to suit the mono petal

http://www.aktive.com/

[GMC]

Is the fitting of the backing plate on the reeds correct?
Seems to me you have the sharp edge against where the reeds hinge from which would eventually fatigue them.
The reed stoppers may not be necessary but I would have thought a shorter version would be of benefit to help the reeds bend in a radius rather than bending at the sharp edge of the mounting plate??