Skeltonsc wrote:
Hi Guys I have an old Johnson 60hp 2 cylinder 2 stroke outboard motor, the motor runs and starts great however it has developed a small missfire at around 3/4 throttle and after long runs I find that the one plug is damp where the other is nice and dry.
what could possibly be the issue here? what do I need to check.
Thanx guys
your initial statement was above:
normally we tend to run away with treads and all sorts of explanations are given.
however it has developed a small missfire at around 3/4 throttle and after long runs I find that the one plug is damp where the other is nice and dry.
does the damp refer to water? or over fuelling?
again, just coming to one of your last posts.
running the engine in a tank full of water will most likely not show the problem as the motor is not under strain.
I do agree that the 2 x carbs floats needs to be the same height.
also notice...... running away here again but it is interesting.....
2 stroke engine needs to run a certain rpm at which the best scavenging occurs.
thus, allowing the most combusted solution out the exhaust ports and getting fresh mixture in to burn again.
it is noted that 2 stroke outboards do this at around 4000 rpm.
so, the miss fire you had, was it below this golden rpm number?
another aspect to keep notice of:
2 stroke carbs are normally jetted for sea level conditions.
thus down there the same motor will run much better then up here in the reef.
if a motor stays here then it should actually be jetted for 1600 meters above sea level.
it is to get the mixture at about 14:1.
1 last aspect, changing float level height will have 3 results.
1. float level too low, will cause a lean run on top end, wot. regardless of jets
2. float level too high, will result in a rich mixture on top end wot, regardless of jets.
3. float level right, will cause a 14:1 air to fuel ratio which will be the best combustion mixture which will create the best power.
cheers