For those that know - cause I don't, what do you mean, "rev the engine until the valves float" - what feedback do you get from the engine that indicates floating valves? Thanks!

 

I believe valve float is where the engine is reving so fast the valve springs or valve train can't keep up an you lose power since the valve isn't sealed properly when the fuel mixture fires. I don't see you encountering it on a evo since it will require reving it up crazy high unless you have a high lift cam.

 

Any Evo will do it if you take the rev-limiter off...

 

Hey Spanners I hear some guys use sportster modules to get the slightly higher rev limiter an a little more aggressive spark curve. True or internet hearsay

 

True, I have done it many times and it works, although the curves don't make a massive difference it does seem to make the bike a bit crisper and less hurried on the cruise.....its a cheap-as upgrade.

 

Hydraulic lifters pump up at high RPM and effectively lengthen, stock valve springs can't close the valve fast enough for the RPM. Bottom line is the valves don't close and "float" a little bit, which stops the power. Happens to my bike around 6K or so. Who needs a rev limiter?

 

So what happens?
You just sit on the side of the road waiting for your lifters to bleed down?

 

No, after the RPM's drop 'cause ya shifted, the valves seal fine again and you try again in the next gear.

Back in Shovelhead Dazes, people would replace the hydraulic lifters in their bikes with solids so you could rev them higher. I dunno if anyone does that with Evos. Haven't heard of anyone doing it. Ironhead sportsters came with solid lifters for higher RPMs without floating the valves.

 

Maybe easier explained by saying that the lifter doesn't remain in contact with the camshaft in the higher RPM range?

 

The lifter remains in contact with the cam (that would be very bad if it didn't, lol). It's the valve that doesn't close fully and contact the valve seat when it should, allowing compression to escape through the partially opened valve, and effectively reducing power. It is just as it sounds, the valve is "floating" above the valve seat surface during this event, never fully closing until you back off the revs and the lifter bleeds off the excess pressure. Think of it as a "mechanical rev limiter" if you will.