Noise in top end
 

I have an 18 gp 300 with a lectron and rk tech billet head. Bike is new with 100 miles on it. I get a intermittent clank from the top end when holding at 1/4 throttle. plug looks fine ,and bike has the update for the ecu from Gasgas. Head was milled for my elevation ,but is cold here. Have not tried mixing race gas yet , back to 2 strokes after many years on four stroke so need a little advice. Is this an octane problem ping ? timing out? It is freaking me out !

Is it a ping might need race gas or 50/50 pump gas with race gas get 100 octane min

Possibly rich at that particular throttle position? If so the noise could be unburnt fuel igniting in the exhaust/expansion chamber.

Try moving the carb needle up/down a clip position and see if it's better or worse.

Do you know what compression ratio you have? As Frankinberg suggests you may need higher octane race fuel to enable you to run a higher than stock compression ratio safely. If it's pinging/detonation don't ignore it or you could end up with a hole in your piston.

I used to race a Honda RS125 GP roadracer, it ran really well with 50/50 mix of Avgas and 98 octane pump fuel. This was recommended by Frank Wrathall, one of the UK's top race tuners. I used to get the Avgas from a local air field.

All the best, Dave.

has a lectron and plug looks fine not a pipe bang it is in the chamber. don't know compression ratio but will call rk tech in the morning. head was made for pump gas.....

Oppps, sorry missed that!

Sounds like detonation then. Can you fit the stock cylinder head and try running it like that? Or try some High octane race fuel?

To get an accurate compression ratio measurement you'd have to give them your complete engine to measure, unless you're confident of measuring it yourself.

All the best, Dave.

BTW... There's a common misconception that High octane fuel gives more power which isn't true, it allows you to run higher compression ratio (which in turn gives more power) without premature ignition/detonation.

Thanks Dave I am getting some race gas this week to see if it solves it....

Great, let us know how you get on. :)

If race gas doesn't help and jetting is good maybe there's a mechanical issue. A single mechanical noise like a clunk could be a loose pinion nut on the crank.

Called RK Tech and when he returned my call I am sure I would never order another thing from them .Total asshole to me and talked to me like I was a little kid. Then Called Lectron and they were super cool and offered some suggestions on adjusting the metering rod to eliminate the possible lean condition . If you buy a RK Tech head don't expect any customer service for your three hundred bucks.

Real shame to hear that about RK Tek. So I guess they couldn't/didn't give you any indication of what your approximate compression ratio is.

Good to hear Lectron were more helpful. I assume adjusting the metering rod has the same effect as raising/lowering the needle in a conventional carb.

All the best, Dave.