pre detontaion

[backspacer90]

heys guys whats causes pre detonation on my 250r and what would the piston look like if it is happing like bad pits or like melting away layers of the piston ... just curious and how could i fix it if so

[Honda 250r 001]

pre detonation is caused by running too low of ocatane for the compression or timing advance...

Whats your compression at?
Have you advanced the timing?

What is your carb?
What jets are you running?

[backspacer90]

a can you tell if it is doing it while riding
210 compression with cool head
stock carb
main is 172 and pilot i belive is 52
timing advanced i have set on plus 3 it is adjustable

the r is bored 60 piped open box uni filter reed spacer ported jug .
it runs fine just making sure i wasent burnig the piston up.. i used race gas but it killed the bottem end so i went back to 97

[rsss396]

its not called "pre-detonation" just "detonation" you are mixing that up with "pre-ignition"

3 ways to know if your motor is detonating

- knocking or rattling noise from the cylinder
-spark plug loosens up
- small aluminum specs on the spark plug electrode/strap

[backspacer90]

thanks man good to no..
i never heard of the plug getting loose before i have to watch for that

[250r grave yard]

switch to c-12 or same octane as it

thats a high compression motor to be on pump gas

pump gas is more combustable than c-12 thus causing detonation on a high compression motor

a stock 250r compression is 110-130 psi . pump gas is good up to 180 but you have to know how to set the ignition timing for that . C -12 is good for 180 on up but if you want to run pump gas safely and still have power get your psi around 160-175

high compression is good for bottem end power but hurts the top end and is bad for your crank

you might be at 210 psi when kicking it over but when that bike is fired up your looking at over 400 psi