Engine Knock?

[denny crane]

2000 250 Beta

Knocking noise when letting off the throttle

will rev fine run fine just when letting off it will knock occasionaly ???

[bob]

Thats almost certainaly just engine knocking caused by pre ignition of the fuel. It is a common problem, i sorted it on mine I believe by running the pilot jet slightly richer (although someone else will be able to confirm that) and by using shell V-power or BP Ultimate petrol only. Nothing really to worry about, I don't think that the occasional pinking causes noticable engine damage and won't shrten its life, athough if it was doing it often it is possible it might strain the little end more.

Bob

[denny crane]

Thanks Bob

I sounds strange but the noise occurs most when riding a wheelie????????????????

If your on & off the throttle to balance when letting off it will knock intermittenly.

I'll try some fresh fuel before I panic

My experiance tells a physical problem of excessive clearance tends not to be intermitten ????

Denny

[paul w]

try a de-coke, piston ,head and exhaust, cures mine everytime. the knock is an ignition in the cylinder not caused by the spark, when you look at the piston it will have pin head holes in the carbon but not the metal, this is where its gone PING ! de-coke and it will be cured. use new base gasket and new o rings as well. hope this helps

[daggs888]

Had the exact same problem on a gasser once ... it turned out to be the jetting ! .. worth a try before a full strip down or new rings, rebore etc.

I'd describe the problem I had as 'heavy pinking'

Daggs

[amcq46]

Denny,

I am very interested to know if the de-coke or higher octain fuel fixed the original problem?

My 2003 Beta will also pink heavly when on a light load and 1/8th throttle opening.

The bike is new to me and I found the air screw was 1/4 turn out when I got it. I moved the air screw back to stock 1 1/2 turns, the rest of the jetting is stock, and I use super unleaded mixed at 70:1 with an NGK #5 plug.

I plan to try it next time with the air screw back in to 1/4 turn, but interested to hear if de-coke was needed on your bike.

[shercrazy]

I HAD THAT PROBLEM WITH MY 99 BETA, I WAS TOLD IT WAS PISTON SLAP, I ADJUSTED THE CARB A THOUSAND DIFFERENT WAYS, NO GO, I TALKED TO THE GUYS AT B.R.X. AND I BOUGHT A CAN OF V.P RED RACING FUEL AND MIXED IT HALF WITH 93 PUMP GAS AND POOF THE PROBLEM WAS GONE! MY BUDDIES 96 GAS GAS 250 DID THE SAME THING, HE WAS GONNA TEAR THE THING APART THEN I HOOKED HIM UP WITH A TANK FULL OF MY MAGIC POTION AND HIS RAN FINE, MAY NOT HELP YOU BUT IT SOUNDS LIKE A SIMILAR PROBLEM AND THAT'S WHAT I DID.......................