Yam 50 hp 4s falters on acceleration

[lffoar]

Hi all,
just purchased my boat with a 2000 Yamaha 4 stroke carby model with 90 hours on it, (Australian delivered 62Y - L451546T - 50AEHT).
I changed the oils, fuel filter and had the impeller done at the workshop (due to a small leak in a seal). Took it out and find that it starts OK but when accelerating away it will falter and stop "going" around 1500-2000rpm. If the throttle is pushed hard down it will stall. All I can do is move the throttle gently forward and when it starts to miss, let it sort of stabilise after a cough/splutter before pushing the stick further. Once over that it runs fine and responds OK to the throttle. It may or not be relevant, but I did notice if left to idle for too long it seems to miss a bit and start to die so have to lift the manual throttle to just above idle speed to keep it running smoothly. This happens cold or warm. Any ideas on where to start would be appreciated thanks.

 

[Ldavidgrover]

Re: Yam 50 hp 4s falters on acceleration

Compression test 1st. Then pull carbs and clean them

 

[lffoar]

Re: Yam 50 hp 4s falters on acceleration

Thanks Ldavidgrover,
Tested compressions, all 4 pots within 2psi of 145psi so as I was going past a marine workshop, called in and spoke to a mechanic who was recommended as knowing his stuff! He suggested due to the motor having been laid up for a lot of its life, it could be as simple as "varnishing" so suggested running a strong solution of a carb cleaner through the fuel and giving it a squirt through the intakes as well. I'm not too optimistic but will give that a shot later in the week and post back.

 

[lffoar]

Re: Yam 50 hp 4s falters on acceleration

FYI,
just to follow up: I'm amazed, put two bottles of Wynns Spitfire carby and fuel system cleaner in about 20litres of fuel, (recommended dose is one bottle to 60 litres), took her out and gave her a solid one hour run around 3000-4000rpm with an intermittent gutful of revs, stopping now and then to let things settle. It's idling much better....I mean lots better. Also I can give it more acceleration now when moving off without the "dead zone" and sometimes cough and splutter to a stop. It's still not perfect, by that I mean there is still a little hesitance at the 1000-1500 rpm mark when giving it some "go" but nowhere near as bad as it was. It's inevitable I'm going to have to get the carbies off and cleaned at some point but I'll give it another dose of carby clean next trip and see if it's better still. $20 is better than $400 aye??

 

[99yam40]

Re: Yam 50 hp 4s falters on acceleration

only problem with doing it that way is you may end up hurting the motor, cleaning the carbs properly makes sure the motor is run the way manufacture designed it. Lean running cylinders will cause hotter parts and may melt piston or other problem

 

[lffoar]

Re: Yam 50 hp 4s falters on acceleration

Are you saying that the additive will actually "lean" the mixture? I would have thought having mixed with fuel and being a type of hydrocarbon itself, being designed for its intended use, it would have a similar ignition point and so not cause harm. Hey, I'm not disputing what you say, I will always bow to greater knowledge. If that is the case, I won't try the "gunk" again!

 

[99yam40]

Re: Yam 50 hp 4s falters on acceleration

Just saying if plugging of passages or jets are a problem then adding snake oil to fuel will take time if it will work at all and in the mean time your motor is running lean

 

[lffoar]

Re: Yam 50 hp 4s falters on acceleration

Got it 99Yam40! Misunderstood you first up, now I see what you mean. Thinking about your comments, I reckon carbs should come off so that's what's gonna be the go. Thanks mate!
Oh well, a boat's just a hole in the water you pour money into, aye??