Merc 115hp 6cyl Alluminium on plugs

[ril0]

i keep getting alluminium deposits on plugs engine runs fine for about 20 mins then loses power when plugs removed usually 3 and or 4 have alluminium deposits on them but ocasionally on others instead have checked compression and all at 120lb. max revs im getting when ok is 5200 running 17" pitch prop on 17ft dory equates to 40mph engine not been run for 18mth previous cannot find any blockage in carbs or fuel lines any ideas

 

[The Marine Doctor]

Re: Merc 115hp 6cyl Alluminium on plugs

This is a timing issue or really lean carb...Do not run the engine anymore until such time as it is corrected.<br /><br />Is this engine Distributor driven? If so the belt may have jumped a cog.<br /><br />TMD

 

[ril0]

Re: Merc 115hp 6cyl Alluminium on plugs

heers mate it is not distributor driven.Surely the timing could not be out on individual cylinders? Wouldnt all the pots have alloy on plugs if that were case.

 

[andrewkafp]

Re: Merc 115hp 6cyl Alluminium on plugs

TMD also mentioned, "Lean mixture", which can cause very high temperature in combustion chambers, leading to burnt pistons. You should also check for this too.

 

[ril0]

Re: Merc 115hp 6cyl Alluminium on plugs

Thanks have checked all usual fuel supply probs previously ie tank, pipes did find kinks, carbs(non adjustable mains) etc replaced kinked pipes and ran same problem again though but now have lost compression on no;4 ie 50lb. Tonight am starting strip down and re ring .Looking through plug of 4 shes picked up at the top of stroke am hopeing piston still serviceable.Trouble is dont want reacurance when put back together.Will retard the timeing though and hope will be ok.Could ther be anything else to check .Have fairly good experience with fourstroke motors ie. car engine but little experience of 2 stroke.

 

[ril0]

Re: Merc 115hp 6cyl Alluminium on plugs

Have now rebuilt engine with new rings luckily bores were ok but deglazed them anyway compression 130lb all round .Took awhile to fire up but sounds good.Have retarded ignition and cleaned all carbs again.As an afterthought have been useing a motorcycle come chainsaw two stroke oil could this have had any bearing on the problem. Will now change to marine oil just in case.

 

[andrewkafp]

Re: Merc 115hp 6cyl Alluminium on plugs

Use Marine grade 2 stroke. <br />Consensus on Iboats, I have found to be.<br />"Don't use ANY auto chemicals on Outboards" <br />This includes L/U oil, 2 Stroke oil, and Fuel additive (For gum removal and carb cleaning).<br />Marine shops sell the proper stuff and it is not noticably more expensive. (And always use fresh fuel)..

 

[ril0]

Re: Merc 115hp 6cyl Alluminium on plugs

Thanks Unicorn will definately do so in future .Hopeing to get on the water on Sat fingers crossed. BFN

 

[ril0]

Re: Merc 115hp 6cyl Alluminium on plugs

Whent out sat engine ran fine just slight misfire up until main jets come in then v smooth pulls about 5200 rpm I think this is about right do you ? I think misfire due to over rich on idle jet mixture or possibly to retarded on original pick up will set these next time out .Also ran a little rich on oil mix this time just to run it in a while ie; 30;1 mix . Many thanks Unicorn & T M D Cheers