Outboard motor

Submitted: Sunday, Mar 10, 2013 at 16:53
ThreadID: 101012 Views:1478 Replies:4 FollowUps:4
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Hi all I have a 40hp Toshatsu outboard and it has a miss fire in the in the number one piston, it keeps fowling the spark plug ( they are brand new plugs and has fresh fuel ) so if anyone my be able to help me out that would be great thanks
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Reply By: Roughasguts - Sunday, Mar 10, 2013 at 17:47

Sunday, Mar 10, 2013 at 17:47
By Number 1 plug do you mean the Top plug or bottom ? Just cause it seems unlikely to be the Top plug as that Cylinder always runs hottest compared to the bottom.

Anyway probably needs a damn good 20 minute flat out run to burn the oil out the crank case that has been building up.

Clearly using Out board two stroke Oil arent you? as that burns colder than lawn mower two stroke oil.....

Cheers.
AnswerID: 506507

Follow Up By: Shaun T - Sunday, Mar 10, 2013 at 19:01

Sunday, Mar 10, 2013 at 19:01
Yes it's the top plug, I took it out for spin to clear its out it came good for a bit but as I backed it off then took it back up to full power it would start to miss a just over half throttle and yes I am running outboard oil
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FollowupID: 783465

Reply By: Roughasguts - Sunday, Mar 10, 2013 at 19:17

Sunday, Mar 10, 2013 at 19:17
Hmmmmm might be starving fuel! is that motor oil injected? might be getting the oil but no fuel that equals bad!!!! could lean out and melt a piston.

Is top cylinder hot to touch EG: cant hold your finger on it? 7 seconds before you have to lift your finger is rule of thumb so to speak if engine to Hot.

Thinking it may be a clogged main jet E10 will do that to a needle and seat and maybe even a main jet.

Drop the drain plug from the top carby and pump the fuel bulb see how much fuel comes out. Should flow out easy when you pump but if it doesnt say have 30-40 ml of fuel in it to start with say the float bowl could be the problem not letting enough fuel in.

Cheers
AnswerID: 506513

Follow Up By: Ross M - Monday, Mar 11, 2013 at 22:44

Monday, Mar 11, 2013 at 22:44
More likely a blocked emulsion tube which causes the richness and fouling and therefore a misfire.
The fact it runs up on full accelerating throttle which uses richness to produce the power but it is no good when backed off.

So main jet can't be at fault, but the fine holes in the emulsion tube can be blocked.
Petrol gumming.

No good using E10 in an outboard as it lowers the energy density of the fuel and effectively will run leaner. Less power needs more throttle to turn the screw, so no gain there.
The float bowl must be allowing enough fuel in as it runs high revs and it can't do that if staved by not letting enough. Exact opposite.

Ross M
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FollowupID: 783617

Reply By: Aussi Traveller - Tuesday, Mar 12, 2013 at 00:18

Tuesday, Mar 12, 2013 at 00:18
This would be my guess, I had a problem with my outboard a few years ago, I finally found the problem the CDI unit.

Phil
AnswerID: 506607

Reply By: happytravelers - Tuesday, Mar 12, 2013 at 21:54

Tuesday, Mar 12, 2013 at 21:54
I wonder if the HT lead is starting to break down
AnswerID: 506679

Follow Up By: Shaun T - Tuesday, Mar 12, 2013 at 22:37

Tuesday, Mar 12, 2013 at 22:37
Hey thanks all for all your help I have put it down to the coil breaking down as I have covered all other aspects, as in fuel lines, pumps and clean fuel. When I get a new coil I will post if that fixes the problem
Thank you
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FollowupID: 783722

Follow Up By: landseka - Wednesday, Mar 13, 2013 at 10:15

Wednesday, Mar 13, 2013 at 10:15
Can you swap the coils to see if the problem moves to another cylinder?
I assume each cylinder has its own coil otherwise a single coil wouldn't give a fault to one cylinder.

Cheers Neil
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FollowupID: 783743

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