Gy6 72cc valve float

[KSR Moto]

What can I do to make my engine revv higher, I can push it to 45mph but valve float starts to kick in and cant go any faster

[jackrides]

Valve float is the engineers way of telling you 'This is max RPM before one or several things fly apart'. The valve springs, retainers, keepers, valves all have stronger aftermarket parts, but after that other reciprocating parts (the highest stressed ones) are pistons (at the wrist pin area), conrod rod bearings, and the list goes on and on. What kind of scoot & engine?

[KSR Moto]

Nov 19, 2018 16:32:47 GMT -5 jackrides said:

Valve float is the engineers way of telling you 'This is max RPM before one or several things fly apart'. The valve springs, retainers, keepers, valves all have stronger aftermarket parts, but after that other reciprocating parts (the highest stressed ones) are pistons (at the wrist pin area), conrod rod bearings, and the list goes on and on. What kind of scoot & engine?

Taotao atm50

[90GTVert]

Some changes to the CVT (rollers/sliders, aftermarket variator) or a different gear set may let you go faster at the same or lower RPM. Could even be as simple as something like a worn belt causing higher RPM.

[GrumpyUnk]

I think the most important tool to have when trying to figure out what is going on is a tachometer. Seat of the pants is good, but a tach will tell you if you are reaching rpm levels that are too high for engine life, or are stuck in the slow lane... That will indicate whether to investigate the CVT, adjust the variator weights, or consider using different final drive ratios. Tach readings will also indicate when the clutch starts to engage, and how much the spring is 'fighting' the force of the variator which is trying to move to a higher effective ratio as engine rpms increase. It really is a necessary tool, even if only temporarily mounted, as far as I'm concerned. One last thing that I have noticed is that the overall friction of the wheel bearings, and the final drive geartrain can differ significantly from machine to machine. Those that you can wheel around with little effort seem to have a lot more performance than those that feel as if there is syrup in the gearbox or thick grease on the wheel bearings. Some of that feeling is likely due to different clearance in the gearbox. The one machine that I felt really flew with a 44mm BBK had suffered a bearing failure in the gearbox. The bearings were all replaced, and I put it back together. The gear teeth had some wear, but were not scored. That little monster was one quick machine. When I opened the throttle, I could actually feel it respond. I did nothing else except fix the box, and install a 44mm kit. I even left the well-broken-in belt and variator and clutch totally alone. When it had the gearbox failure, the input shaft(which carries the clutch assembly & bell) was flopping around inside the CVT chamber. That bearing was hard to remove as the shaft was totally free, and there was no edge to tap on for the outer race. But it was fast when I got done.
tom

[ratdog]

First, if you are gettingvalve float and max speed, you are already doing damage to your engine.

As already mentioned, the first thing we need to know is what RPM are you getting float at. In other words, you need a tachometer. The reason this is so important is that if you are getting valve float at 9000 rpm, then we can work with new ( after market ) vale springs to move that point up the RPM range. On the other hand, if your getting valve float at 12,500 rpm, there is really nothing wrong with the valve train, we have to change the final gear ratio to reduce your RPM at top speed

I have built a number of engines with stock size valves and stock springs that will rev past 12,500 rpm with out float. Of course if you have an aftermarket head with oversized valves but stock springs, you may have a much lower RPM peak ( bigger valves are heavier, and therefore harder to stop at max lift)

[jdl357]

How can you recognize valve float?

[jeff84]

typically you will get some backfiring at high rpm under load. or loud bag of nickles sound fronm the top end. worst case a valve will impact the piston and bend or break.