Engine Trouble Pre ignition / detonation at WOT

[Vikingimike01]

it just seems every post you list more parts but still no cure.

Yeah. I haven't used my bike for 3 months almost. The piston broke. These parts have been planned, but not ordered all at once. Just as money came (I'm working a summer job)

such as... excessive vibration causing foaming, or the floar level being too low, or another great one... the tank breather isnt breathing. restricted fuel flow... simple test for that one is to pop the fuel line. a cup should fill in about 30 seconds.

I tested, fuel flows OK. Tank vents OK. I don't know about excessive vibration causing the fuel to foam in the bowl. It doesn't really vibrate all that much. Defenetly less than with my 50cc and that didn't have a problem like this.

take all bling off. even take the exhaust off. (get some earplugs) eliminate EVERY POSSIBLE CAUSE before progressing.

The mods are not yet fully installed. When I started having this problem, I was using stock everything. Only thing I know, that when I changed to the 75 size jet, it wasn't that noticable as with the 80 jet.
The only thing that wasn't stock, was the plug. It's a B7HS. I tried with the yingying or something plug the engine came with, it still had the problem.
If you mean take the whole exhaust off, and just have the port. Are you sure? Wouldn't that damage the engine by running waaay too lean? Can someone else confirm this is OK to do because I don't want to destroy my engine. I don't think i should do that (if you meant that)

I don't remember if I had the problem before sanding down the cylinder. I don't think I have gone over 40 before that.

I'm trying to provide as much information as I can. Should I try a different cylinder? I have one stock that has small ports.

 

[gary55]

No don't run with no exhaust. When adding a reed you generally need to go larger with your jet. Don't know if surging is due to vibration causing foaming in the bowl due to poor mounting or other means of fuel starvation, but a up and down surge is most likely fuel and not electrical. Heat is probably the need for a larger jet.

 

[Vikingimike01]

I currently have a size 80 jet and am gonna be running these mods. Do you think a 85 jet would be enough with a 20mm carb?
I had slight 4 stroking with the size 80 jet.

My altitude is 151m above sea level

 

[gary55]

Not a clue. I'm not a big reed valve guy, and the biggest carb I've ever used is a 16/16.

 

[Vikingimike01]

Alright, I'll just have to see. I hope the stock 80 jet will be still OK

By the way gary it doesn't do this at idle, or any other RPM. It does this from 40-50 and then over 50 it goes normally again.

 

[GreasyChris]

You won't really know until you get it set up and running. Then you will be able to tune and jet accordingly.

 

[Vikingimike01]

I have seen a ton of videos on how to jet. I still can't tell if it's running rich or lean. The fact that I'm using a 25:1 oil mix probably makes my plugs darker than they are.
Could I run a lower mix with mineral oil? They don't really sell synthetic oil anymore here. The 2 stroke is long considered dead in Europe. They want to pass laws against diesels as well now.

 

[GreasyChris]

I've never seen a pz20 carb so I'm not sure what's involved in tuning that carb. But start rich and lower the jet size until the 4 stroking stops.

 

[gary55]

Alright, I'll just have to see. I hope the stock 80 jet will be still OK

By the way gary it doesn't do this at idle, or any other RPM. It does this from 40-50 and then over 50 it goes normally again.

Are your motor mounts tight?

 

[Vikingimike01]

Well. I don't know, back then it wasn't too tight probably. But now it probably will be considering the jackshaft kit has an extra mount, and the front mount isn't installed yet just the 2 on the back and I can't even push the engine to move on the frame.

I had to use 2 of those connectors under the frame and one on the outside. It's kinda hard to explain.

So crankcase, 2 brackets as a spacer, bicycle frame, and a third bracket on the outside bolted on to secure it.

If it WAS from vibration, why did it not do it over 50 at all? like at all. I could go 60 with my banana pipe with stock 44 tooth.