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Old 13 August 2011, 03:25   #1
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throttle Problems

Having read through hundred of posts on this and other sites i need to post a fresh thread as i am having real trouble locating a problem

I am running a 60hp mercury outboard from 1991/2

starts and runs fine, regularly serviced and it keeps coming back from the garage with "there is nothing wrong we can find"

problem is, on opening throttle, as you push forward past 3\4 on th way to WOT the engine bogs down. it is like the engine is starved of fuel. the revs drop off and the boat falls almost of the plane. now that is similar to may issues i have read on here.

the issue is that if i keep pushing the trottle the engine comes back to life and will run at max\optimum revs and sits comfortably on th plane at full speed.

any ideas what this "trough" in the throttle curve may be and how i might rectify it.
thanks in advance


glenn
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Old 13 August 2011, 03:51   #2
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Hi Glen
sorry if I state the obvious as I know you will have checked your filters but have you checked your diaphram on the fuel pump? It sounds a little like a problem I was having two years ago and that little bit was the cause yuou can get the kit from Barrus easy fit not expensive.Just a thought hope it helps.
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Old 13 August 2011, 03:59   #3
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Ill be honest, its been out of the water four times to be looked at and i would have assumed that they would have gone through those things before deciding that they could not find anything wrong.

I am now have second thoughts on that as on other threads people keep saying to look at the fuel pump diaphragm.

would this still apply though as it will get up there only after it drops off and comes back up again. ??

for the cost of a diaphragm kit i will give it a go though.

thanks
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Old 13 August 2011, 04:00   #4
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Fuel primer bulb and lines in good condition? Would be worth changing if in any doubt. Plenty threads on here about primer bulb diaphragm disintegrating. Also check and clean the fuel filter (if one fitted) and the fuel bowl on the engine itself. Try that for starters and see what happens under load.
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Old 13 August 2011, 04:04   #5
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new fuel lines and bulbs fitted. fuel filter changed. water separator changed. new plugs and leads fitted. carbs stripped and cleaned twice by Power Products in Rochester. ???

will go to full throttle but only after this dip in the power cure. Its not just a little dip though, its as though i pull the throttle leaver back fully and then pump it forward again.

very strange.
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Old 13 August 2011, 04:14   #6
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Glen,

Does this happen every time you do it? But the mechanic can't replicate in his workshop? Is the engine on the boat in his workshop (so he is using your fuel tank / lines etc?) if it is then he's presumably not testing it in "real" circumstances - i.e. with a load on the engine. To be honest, if you've been back 4 times with the same fault and he's not pointed this out / suggested he needs to test it in the water then I would be finding a new mechanic.
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Old 13 August 2011, 04:31   #7
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Quote:
Originally Posted by Polwart View Post
Glen,

Does this happen every time you do it? But the mechanic can't replicate in his workshop? Is the engine on the boat in his workshop (so he is using your fuel tank / lines etc?) if it is then he's presumably not testing it in "real" circumstances - i.e. with a load on the engine. To be honest, if you've been back 4 times with the same fault and he's not pointed this out / suggested he needs to test it in the water then I would be finding a new mechanic.
Seconded.


Has he balanced the carbs? (I'd hope so).

Have you tried looking at the coils,HT leads and caps? It could be that a coil is partially down or there's an HT leak somewhere.
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Old 13 August 2011, 04:49   #8
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Like has already been said, I had similar problems on my tohatsu 50 and was the fuel pump diaphragm but also had the similar thing with one of my coils on the 150hpdi
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Old 13 August 2011, 13:02   #9
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does it run ok if you keep pressure on the primer bulb? if so its probaly the fuel pump diaphrams the , does one spark plug when removed look differant to the others if so how differant blacker / white?
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