detonating early

[kwickez]

i just got a new banshee and the pipes/engine pings alittle i know this is usually because of carbon buildup or early detonation.hes been running premium gas but his advanced timing plate is set at 4.5 would knocking it down to 4 help???

[Bansh-eman]

carbon buildup has nothing to do with detonating (assuming you dont have a hotspot from it). if you have alot of carbon its because your running too rich. the differance in .5 degrees will make almost no differance. what compression does your motor have? also list all your mods. and jetting

[mopar1rules]

carbon buildup has nothing to do with detonating (assuming you dont have a hotspot from it). if you have alot of carbon its because your running too rich. the differance in .5 degrees will make almost no differance. what compression does your motor have? also list all your mods. and jetting

 

 

actually no carbon to little carbon on the piston crown, means it running rich. the extra fuel that's being passed through the cylinders, is washing the oil off the top of the pistons. there is no extra fuel being passed through to cool the piston, so the piston crown gets hot, thus creating it to burn and create the carbon on the piston top. if you have lots of carbon on the piston crown, with no wash to very little wash (like 1/8" diameter clean spots by the piston crowns edge, where it lines up with the transfers)...then you are lean. here's a link...read on:

 

http://www.cpcracing.com/site/256083/page/196309

 

....the pic to look at is halfway down.

[sheefreak]

actually no carbon to little carbon on the piston crown, means it running rich. the extra fuel that's being passed through the cylinders, is washing the oil off the top of the pistons. there is no extra fuel being passed through to cool the piston, so the piston crown gets hot, thus creating it to burn and create the carbon on the piston top. if you have lots of carbon on the piston crown, with no wash to very little wash (like 1/8" diameter clean spots by the piston crowns edge, where it lines up with the transfers)...then you are lean. here's a link...read on:

 

http://www.cpcracing.com/site/256083/page/196309

 

....the pic to look at is halfway down.

 

Good info!

[87bansheeguy]

Good info!

wurd

[Bansh-eman]

actually no carbon to little carbon on the piston crown, means it running rich. the extra fuel that's being passed through the cylinders, is washing the oil off the top of the pistons. there is no extra fuel being passed through to cool the piston, so the piston crown gets hot, thus creating it to burn and create the carbon on the piston top. if you have lots of carbon on the piston crown, with no wash to very little wash (like 1/8" diameter clean spots by the piston crowns edge, where it lines up with the transfers)...then you are lean. here's a link...read on:

 

http://www.cpcracing.com/site/256083/page/196309

 

....the pic to look at is halfway down.

hum that is interesting, i have always heard backwards of that, thatbecause you had too much fule it almost acted like it would pool on the piston crown and cause the buildup. and running lean will casue the motor to run hotter which inturn burns off carbon deposits. that ste has alot of good info. I still wonder which is correct, i am by no means a mechanical engineer. just going off of being around and racing small motors for years.

[mopar1rules]

I meant to say: "there is no extra fuel being passed through to cool the piston, so the piston crown gets hot, thus creating it to burn THE OIL and create the carbon on the piston top."

 

INSTEAD OF:

 

"there is no extra fuel being passed through to cool the piston, so the piston crown gets hot, thus creating it to burn and create the carbon on the piston top."

[kwickez]

it also takes awhile to start would that mean something?unless its jump started or i drop alittle gas into the carbs then it starts right off

[Bansh-eman]

Whats your jetting? and What temps are you in?

[kwickez]

the jets are stock setup except the main which is 250 and the temp is 60-95 and the elevation is always under 1500

[2bzy2p]

whats your compression,what domes and any port work? detonation alot of the times is due to advanced timing!

[kwickez]

whats your compression,what domes and any port work? detonation alot of the times is due to advanced timing!

 

not sure what the compression is.stock domes and no port work.the timing is advanced to 4. i run premium gas.only mods are pro circuit pipes and silencers,k&n filter and pods without snorkel, and its bored 50 over.i run a 40:1 ratio

[deckheight]

With stock head and compression... 4 or 5 deg. ignition advance in an of itself will not cause deto., especially with 91+octane fuel. Hard starting without primeing the carbs would probably indicate a carb problem. Low speed adjustment, float level, etc. or an air leak. The "pinging" your hearing could just be the exhaust resonating in the pipes??? Or not, who knows...

The piston wash pics in the link from earlier in the thread are basically correct. To expand on good, solid info... The color and density of the carbon build-up on top of the piston are also an indicator of fuel/air ratios and combustion chamber temps. Black, dense, burnt on carbon = Bad. Tan to chocolate brown, soft (scrape it with fingernail) type carbon = Good. Also, build-up on the underside, center of the piston, directly beneath the piston crown is a very good indicator of combustion chamber temps. Hard, black cooked on oil and fuel residue indicates excessively high combustion chamber temps. No build-up or only light brownish build-up would indicate a good running recreation type engine that is off the "edge", combustion chamber temperature wise anyway. Unfortunately, the cylinders have to come off the to get a look at the underside of the piston...