79cc predator 18lb valve spring issue

[G.W]

My buddy has been building a bike with a 79cc predator I sold him and he's recently started on upgrading the performance. He recently upgraded the valve springs to 18lb predator 212 springs. This upgrade was supposed to work just fine with the 79cc also. The issue he ran into is the springs are a bit longer than the 79cc stock springs, but went in fine. But when running they have a distinct pinging sound. When he pulled the valve cover off to inspect it, the springs were fully compressed causing the pinging. He was wondering if anyone else has tried this upgrade and could give some insight on it, and if anyone knows of any heavier valve springs that would fit the 79cc.

Before anyone suggests, he can't fit a bigger engine in his bike. It will not clear the frame and he doesn't want to modify the frame, so do bot suggest a bigger engine. I'm not here asking for suggestions on a bigger engine.

 

[Denny]

Get a bigger bike then get a bigger engine for it.

 

[Darren]

lower the spring seats with a suitable holesaw, the springs will sit lower preventing coil bind. Be careful when drilling, you only need a couple of mm.

 

[G.W]

Get a bigger bike then get a bigger engine for it.

They don't make this particular bike bigger, and where's the fun in that?

 

[Denny]

Big engine=Big fun!

 

[G.W]

Big engine=Big fun!

=Big$

 

[G.W]

Here's the bike. The 79cc is squeezed in it. A bigger motor is not an option.

 

[Whitetrashrocker]

Hot rodding tips.
Real carburetor, open headers, mill the head, remove govenor, advance timing, leave the stock valves. They'll float and act like a Rev limiter.

 

[G.W]

Hot rodding tips.
Real carburetor, open headers, mill the head, remove govenor, advance timing, leave the stock valves. They'll float and act like a Rev limiter.

All has been done. That picture was from when he first put the bike together. He has since installed a flywheel, shaved the head, removed the governor and upgraded the carb, and built a header. He just wants a little more rpm than the stock springs offer

 

[Darren]

Don't go too far with spring pressure, the valve train will suffer, because of excessive loading.

 

[panchothedog]

Stock pot metal valves ( what comes in all predator engines ) like to snap off the heads when you add too much spring pressure. That's why they make stainless steel valves. Don't know if they're available for the little engine.