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Old 16 May 2015, 15:14   #21
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OK, the golden rule

Stop, look, listen and retrace your steps.

Start with the easy bit.

Different tank, fresh fuel, vent open.

Connect line, does bulb prime hard?

If yes, fuel line to engine is OK. If not, with everything being new and it keeps priming fuel into the engine, it will be a burst fuel diapragm in the fuel pump or a stuck float needle in the carb and you will be able to tell which one as fuel will pour out the carb vent.

None of the above.

1) Check for spark on all 3 pots.

2) Change plugs anyway.

3) Start engine and run on 1 cylinder at a time. This will tell you which cylinder is the problem.

4) Once you know what cylinder it is, it is likely to be the carb requiring cleaned or a coil breaking down which is less likely.

5) If the bottom plug has a reddish tinge, the bottom crank seal has gone

6) The oil on the bottom carb is not necessarily a concern.

7) I'm assuming your mixture screws are set at 1.75 turns out from the lightly seated position.

8) You could run a compression test, but I'm sniffing a common fuel or spark issue.

9) lastly, when running press your finger on the thermostat housing. If you have to lift off after 5 seconds it is fine. If you can leave your finger on all day, it is stuck open. If it gets red hot, it's stuck closed and this may trigger a safety cut off on the engine which will reduce rpm.
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Old 16 May 2015, 15:52   #22
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Quote:
Originally Posted by RIB-Teccie View Post
OK, the golden rule

Stop, look, listen and retrace your steps.

Start with the easy bit.

Different tank, fresh fuel, vent open.

Connect line, does bulb prime hard?

If yes, fuel line to engine is OK. If not, with everything being new and it keeps priming fuel into the engine, it will be a burst fuel diapragm in the fuel pump or a stuck float needle in the carb and you will be able to tell which one as fuel will pour out the carb vent.

None of the above.

1) Check for spark on all 3 pots.

2) Change plugs anyway.

3) Start engine and run on 1 cylinder at a time. This will tell you which cylinder is the problem.

4) Once you know what cylinder it is, it is likely to be the carb requiring cleaned or a coil breaking down which is less likely.

5) If the bottom plug has a reddish tinge, the bottom crank seal has gone

6) The oil on the bottom carb is not necessarily a concern.

7) I'm assuming your mixture screws are set at 1.75 turns out from the lightly seated position.

8) You could run a compression test, but I'm sniffing a common fuel or spark issue.

9) lastly, when running press your finger on the thermostat housing. If you have to lift off after 5 seconds it is fine. If you can leave your finger on all day, it is stuck open. If it gets red hot, it's stuck closed and this may trigger a safety cut off on the engine which will reduce rpm.
Brilliant guide and troubleshooting steps! Thank you! I have tried the first piece of advice, different tank, line and fuel hence the new fuel line

I will continue with your troubleshooting steps and feedback, I'm assuming the engine will not be happy running on 1 cylinder at a time and would I disconnect the spark plug leads or remove the spark plugs fully?

With regards to the mixture screws, the carbs and timing were set up properly by NS Marine not to long ago, not something I wanted to touch! Also, I'm fairly sure (but not 100%) that this engine doesn't have a thermostat as its always pumped water continuously but again may be wrong!
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Old 16 May 2015, 16:07   #23
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Has the engine been laid up over winter with fuel in it?
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Old 16 May 2015, 16:24   #24
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I'd start engine with all plugs in place and then carefully disconnect a plug making sure you don't electrocute yourself. If engine doesn't notice then the plug lead wasn't doing anything. I'd it sounds rougher or dies it was. Process of elimination.

I may be wrong but thermostats sometimes redirect the water round the head rather than straight out, but the water keeps flowing no matter what...
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Old 16 May 2015, 16:25   #25
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In a bucket of water (once warmed up a bit) an engine will run fine on 1 cylinder at a time. Take the bottom two leads off and run the top only. Then it's the top and bottom lead off and the Middle only, etc. You leave the plugs in. Whichever pot doesn't run (or run well) that's where the problem lies.

It may be you have a blockage in your slow running jet in the carb.
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Old 16 May 2015, 16:29   #26
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Has the engine been laid up over winter with fuel in it?
It was drained as best as possible once it was fogged, though some probably was left in the system..

It may well be a blockage as the fuel filter wasn't 100% clean, but only had small particles in it. I will give all advice a go with regards to spark plug leads etc and go from there
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Old 17 May 2015, 04:26   #27
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Originally Posted by RIB-Teccie View Post
In a bucket of water (once warmed up a bit) an engine will run fine on 1 cylinder at a time. Take the bottom two leads off and run the top only. Then it's the top and bottom lead off and the Middle only, etc. You leave the plugs in. Whichever pot doesn't run (or run well) that's where the problem lies.

It may be you have a blockage in your slow running jet in the carb.
I suppose it would be worth mentioning that when I did run it yesterday it was fine when I revved it, but just not when left at a constant RPM.. how would I test for a bad fuel pump as well? Before it dies it will sound as though it's not firing on 3, it sounds like a constant stutter. Will be troubleshooting more today
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Old 17 May 2015, 09:13   #28
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A 3 cylinder 30 hp engine is just 3 10hp engines one on top of the other. You find out which cylinder is causing the problem and take it from there. If it seems like all cylinders, that's when you are looking at an air leak caused by a crank seal.
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Old 17 May 2015, 10:09   #29
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Run in a bucket remove air filters and let engine idle,spray carb cleaner or petrol in a spray bottle into each carb if engine starts to run better you have either a blocked carb or slow running jet on that carb.Follow rib techies advice as he is Mr Yamaha he talked me through repairing and old 55hp which now runs like new.
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