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gazza76
12-03-2006, 09:29 AM
Hi all,
I have a 50 hp mercury that Surges when under load in the water
It will run at about 5 knots and not have a problem same with idle and when it is out of the water there is no problem with it at all.

I have tried squeezing the fuel bulb when this happens but there is no difference.
Full power it will run at about 5 to 8 knots with a big surge like it is getting fuel or spark then it is not
it will run at about 25 to 30 knots with out the problem
any idea on what the problem is and can any one recommend a good mechanic around the bribie area or i dont mind if i have to travel to find a good mechanic.
All help will be much Appreciated Thankyou
Cheers
Gary

Angla
12-03-2006, 10:59 AM
Does it do this often or does it just happen once in a trip?

How long does the boat sit idle between trips?

Does it do this every trip?

What sort of fuel tank do you have?

Angla

Blackened
12-03-2006, 11:39 AM
G'day
Well, depending on the consistency of the problem... it sounds like ignition system to me.
Dave

Fishin_Dan
12-03-2006, 12:08 PM
There might possibly be an air leak somewhere in your fuel line... Check all the points from the fuel tank to the motor. Check the joints (tank - line, line - bulb, bulb - line, line - motor, etc) and check all of the fuel line as well.

gazza76
12-03-2006, 12:42 PM
Hi,

It was sitting for about 3 months before this trip and started every two weeks< i also filled it up with fresh fuel before the trip
It does it all the time now and getting worse
The fuel tank i have is one of those plastic ones 25L from the shops.

When it started we sat with the engine off for about an hour and fired it up again and it ran fine for about 2 minutes then played up again so we stoped again for about the same time and fired it up again and it went for about 1 minute so we stoped again for the same time and fired it up again and it goes fine for about 20 sec.
That was the last trip two days ago.

Tried it again today with some new spark plugs and new fuel lines but no go it surges straight away so it is worse now.
it will still idle fine and i left it idling for about 20 minutes with no probs.
It will run fine with a little acceleration to about 5 knots and when i give it a bit more it surges and loses power all the time now.

The engine starts first go every time and out of the water with the muffs on it will run fine.

Keep the help coming
Cheers
Gary

blaze
12-03-2006, 01:48 PM
Maybe a blockage in the high speed circuit in the carbie, water in the carbs.
Remove the drain screws out of the bottoms of the carbies and drain the fuel, catch the fuel in a glass bottle to check for water, to do this cut a plastic soft drink bottle in half (from top to bottom), sit this under the carb and direct fuel into a catch container. You can also flush a bit of fuel through the system like this using the primer bulb.
cheers
blaze

Angla
12-03-2006, 06:26 PM
Gary,

Is there a chance you could run it in water at night with the cowl off? Obviously it has to be under load to see the problem.
I'm thinking it could be the high tension leads or coils giving you problems.
If its electronic ignition then just the leads might be at fault. When in the dark you will see the sparks jumping to the frame but if it will not play up when the cowl is off then it may be shorting to the cowl material

Angla

gazza76
12-03-2006, 08:51 PM
Thanx i will have a look at that,
I will give it a try tonight as i have some time off and plan on doing a lot of fishing so i need it running asap.
if all else fails it will go to the shop tomorrow or tuesday.
Cheers
Gary

rajawolf
13-03-2006, 12:24 AM
Carbies need cleaning.

Oldyella
13-03-2006, 08:04 AM
I also think it's a carb restriction issue. It's hard to get at the bottom carb on those inlines, but try to drain the bowls at least and get clean fuel running through them. A "lean condition" on a multi-carb motor could cause detonation. Check the plugs for consistant colour. Very light means lean.

gazza76
13-03-2006, 08:59 AM
Hi all,

Tried it last night but could see no spark anywhere.
To clean the Carbies do i just run a cleaner through them or do they need to come off and be rekitted.

I have drained the bowl on the bottom of the Carbies and squeezed the primer bulb to flush some more fuel through them.

The sparkplugs are a dark colour and they all look like they are firing.

Cheers
Gary

unhappyseajaybuyer
13-03-2006, 02:24 PM
try disconnectig kill switches as this has happened to me sometimes killswitch wiring is worn because of engine movement and wire placement when disconnected if motor runs good one or both of the leads to switches will be be earthin some where .it has happened to me sometimes motor would run great other times it would stutter and fart i done the carbi and everythhing i could think of at a cost and it ended up being a dodgey wire on kill switch lead wich ran under carbie

Gotim
13-03-2006, 04:43 PM
Karma

Angla
13-03-2006, 05:14 PM
Beats me. One last thing though could be to make sure the main -ve and +ve connection on the motor is not loose or highly corroded

Angla

gazza76
13-03-2006, 06:05 PM
Thanx all for the help
Just got back and when i disconnect the kill switch all is good.
The darn kill switch
will go to the shop tomorrow and have new wires in replace of the old ones and a new kill switch.
Thank you to all that have helped Very Very much Appreciated
Yous have me some of my holiday pay.
Thanx again
Cheers
Gary