Detonation on a 115 Mercury (Australian Made)

[Denismcf]

I have just bought my first boat and have pulled the motor down to find detonation on the third cylinder ...can anyone let me know if replacing the trigger will eliminate this prob and whether there is truth in jetting the middle carby higher to compensate for the leanness? We still have super fuel over here so I dont think octane is a problem? Any suggestions welcome...

 

[Denismcf]

Re: Detonation on a 115 Mercury (Australian Made)

Sorry its a 76-77 mercury inline six..

 

[sony2001]

Re: Detonation on a 115 Mercury (Australian Made)

To keep detonation at bay, remove the carbon from piston heads except for an outer ring, close the engine up, run on high octane, and decarb 1-2 times a year with the spray. Trigger and rejetting won't have an antidetonation effect.

 

[sharkcat]

Re: Detonation on a 115 Mercury (Australian Made)

Hey Denismcf,what part of Oz are you in?Im in WA & we havent had super here for a few years.You can get LRP which is sh-t & unleaded premium which is higher octane than regular...To stop detonation you need higher octane/less compression/more fuel or retard the timing 1 or 2 degrees will do it you may lose 1-200 rpm at WOT but your pistons/wallet will thank you.Decarbing will reduce compression so will help.We used to put tolulene in fuel as an octane booster in offroad buggies(Yes I cheated but I didnt get caught so it doesnt count ) way back when...Cant remember the ratios sorry someone else may be able to help.

 

[Denismcf]

Re: Detonation on a 115 Mercury (Australian Made)

Thanks for the responses...I did make a mistake by saying Super ..I meant LRP .thanks again!

 

[andrewkafp]

Re: Detonation on a 115 Mercury (Australian Made)

G'day Dennis<br />Whats the serial no of ur Merc ?

 

[sharkcat]

Re: Detonation on a 115 Mercury (Australian Made)

Denis have you done anything to fix your problem? Has the information given helped?Give us some feed back so we can learn from your probs & help others...

 

[Denismcf]

Re: Detonation on a 115 Mercury (Australian Made)

Sorry for the late reply...I am putting the motor back together in two weeks and hopefully will have the boat in the water in three will keep you posted... A mechanic at Independent Outboards told me they usually remove the idle jets from the carbies and this makes them run a little richer, (not the main jets) I am not too sure about doing this at this stage!??

 

[Denismcf]

Re: Detonation on a 115 Mercury (Australian Made)

sorry again My SERIAL NUMBER IS 8029568