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Old 14 August 2007, 12:19   #11
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Id say it is a fuel problem under load, but you could try also changing the plugs. They can break down under load but still give a good spark when tested on the casing. For that matter so can the HT leads.........
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Old 14 August 2007, 12:58   #12
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I'd put money on it being one or more of what's been said. Doesn't sound like anything major.
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Old 15 August 2007, 06:34   #13
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OldSR,

Yeah, the primer bulb has two small ball valves - one at each end- the one on the tank end shuts as you squeze it, forcing the fuel out the engine end, and when you let go the rubber returning to it's original shape creates a vacuum, pulls the engine end one shut, and sucks the fuel through the other from the tank to fill the vaccum. When the engine is running both sit open (or closed, if it's the wrong way round!). I never could figure out why they put the same type connector on each end of the hose, especially when most connectors you can buy "Inline" versions of both M & F versions..... But that's another discussion entirely!

My thoughts with the hull were just that as I was talking about engine load, the water ballast will increase the load until it empties. (think of the difference between solo and having 4 people on board).

As for launching, there's a Slip at Largs marina, which is around the 7 each way mark to use - but has the advantage of a handy pontoon to tie to while you fiddle with things, and all the usual facilities you would expect with a marina. Alternatively if you cross the Erskine bridge there's a nice wide concrete one at Helensburgh Peir, if you don't mind all the shopping trolleys getting tangled round your prop, but I think is free. Parking might involve a pay & display? Failing that there is another by the Blairvadach Outdoor centre, (carry on along the seafront past the marina and Rhu, however you'll need to be good at reversing a trailer as it is narrow. Also gets a bit slippy for my liking below about half tide. (I also have an estate car & launched there without issue a few weeks ago). That one is absolutely free to use.

With the choke trick, don't leave it out for long or you'll flood it whether it's running lean or not. If you're on tiller steer /mech choke put it back almost as soon as you pull it. (and be prepared for a kick - be careful it doesn't get puilled out your other hand- and make sure you got your kill cord attatched for obvious reasons - tho' you should be attatched to it anyway! )

Still not sure of the weekend plans yet, other than it will involve the RIB!
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Old 15 August 2007, 16:11   #14
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cheers for that mate - I might give largs a go but I think I'll need to get this engine problem sorted first before I head out for the next trip.

Got it up and running again today in a barrel at home - first thing I done was change the fuel line round the other way - it was definately round the wrong way as I felt the priming bulb go firm whereas it kind of stayed squashed in before! It reved highly in neutral and then I tried to rev it in gear but couldnt rev it high as almost all the water was thrown out by the prop. Decided to take the prop off and try again - it seemed to rev high in gear but as there was no prop there would have been little load.

Anyway I then took the hood off and moved the throttle on the carb by hand gradually and it seemed to work fine - But then I moved the throttle quickly and it started doing the same it did on the water - carb started spluttering and then cut out - I then tried pulling out the choke as you said and yes it did take off like a scalded cat and I could rev it quickly without it cutting out but as you say I didnt have the choke out for long as it started dieing again - probably getting flooded.

So basically when you rev it hard in gear it splutters and cuts out but then when you open the choke it revs high but only for a short period. Does this help shed any light on the problem?
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Old 16 August 2007, 05:17   #15
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Yeah, props are quite good at emptying buckets!

Sounds like exactly the same as I had - somewhere on the carb will be an idle mix adjuster. Unfortunately I have never seen inside the engine you have, so can't help other than i would guess it will be the screw with a spring behind it to keep it from vibrating out of adjustment. (anyone else out there know these engines?) You just need to fiddle with that until the mix is right. I would guess 1/4 - 1/2 turn anticlockwise, but that is a complete guess! There may be two screws with springs (well, my Suz has two) - one will probably be the idle stop on the throttle shaft, it's the other one you want to adjust.

One word of warning - if you're adjusting your idle in a bucket, remember when it's afloat the prop exhaust will probably be a little further under the water, creating a small but significant increase in back pressure. If you adjust it perfectly in the bucket, there's a chance it may just cough & die (if it even starts) when you launch, unless you have a big wheelie bin & can get the water surface roughly where it would be when afloat. Probably not so bad for you if the water ballast is sealed up, coz you'll float a bit higher than me at idle!

I suppose the good thing about Largs for this is that you can do the adjustments in the relative safety of the marina.
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Old 16 August 2007, 08:50   #16
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Its a long time since i worked on outboards so i may be wrong, but depending on the age of the engine, if you rev it up on the carb linkage....no ignition advance so it may well splutter anyway? if i recall correctly you get a fair bit of throttle opening only advances the timing, usually 1/8-1/4 before the cam plate touches the carby linkage.
i may be wrong...... clamshells had only just come out when i last worked on them!! but one thing is for sure, unless the engine is under load with a prop on a boat or a proper test prop in a tank/dyno you wont really know if its fixed.
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Old 17 August 2007, 08:48   #17
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D'oh! If I'd read your last post properly then I'd suggest just going & testing it - no engine runs particularly well with a reversed bulb...... I'll bet it now runs OK!

If not then yeah, doggypaddle does have a good call, it's pointless testing in "no load" conditions. Nobody has a dyno, (this is probably where i'll end up eating my words!) and I suspect a test prop isn't something you have lying around, so I would suggest a trip to Largs for this one (even if you never launch there again), because if it dies as soon as you leave the marina & open up, you can then pootle back in at idle (which is the sort of speed that the marina speed limit would want you at anyway!), tie onto a pontoon, tweak the adjuster in relative shelter and calm water, then head back out to try again. That's exactly how I spent an afternoon trying to balance three carbs & make mine run sweet.

I tried to get a pic of your carbs from the Yam website to figure out where the idle adjust is, but there's something in there killing my browser after the "welcome" page, so no help as to which screw to turn yet, but hopefully you won't need to!

Still not sure when I'll be available this weekend, but if all goes to plan I should be around for the Lifeboat trip on the 25th, and might leave the Lamlash leg out & go straight to Tighnabruach (otherwise it's going to be a stupidly early start for us) so might see you then? As I said, now you've turned the bulb round it will most probably run OK.
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Old 17 August 2007, 18:13   #18
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Yip think you are right mate - only way to test is to get it back in the water! upon reflection I think you are spot on doggypaddle - when I reved it straight on the carb it did splutter and die but when I used the linkage on the outside of the engine it sounded fine.

Weather is supposed to be very poor this weekend but hopefully either get it down to largs one night through the week or have been looking at boatlaunch.co.uk and have found what appears to be 2 public slips which might be ok for a quick test trip - one at newark castle and one at inverkip - anyone got any experience of them and any idea at what times would be best to launch?
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Old 17 August 2007, 19:53   #19
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DONT rev the nuts off it in neutral or without load-there's no rev limiter on them and you'll damage it.
Without load is no test anyway-it'll rev out even if it's running like a bag of crap.

Take it out and try it.

From memory I think they are Mikunis. 1.25 to 1.5 turns out is the idle screw setting if they are.
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Old 12 September 2007, 07:20   #20
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Finally working;-)

Thanks to all for the help and advice and am pleased to say I got out at the weekend there and the engine ran without fault.

After my last post I took it out again with the fuel line round the correct way and it ran a little better but was still dieing when I increased the revs - I tried adjusting the carb but didnt make any difference so finally spat the dummy and took it into an outboard shop. The guys at the shop cleaned out the carb,fitted new spark plugs and ht caps - all very reasonably at just an hours labour plus parts - better still told me it had good compression and showed me it running with a test prop in the tank.

Have just got another couple of questions regarding prop and electrics but will start another thread as its not really relative to this problem.
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