|
09 January 2010, 15:32
|
#1
|
Member
Country: UK - England
Town: Portland
Boat name: rekrab
Make: Avon
Length: 4m +
Engine: outboard 50 Mariner
Join Date: Apr 2007
Posts: 9
|
Outboard doesn't like the sea :-)
happy new year to you all.
Here is hoping someone can point out the error of my ways for me, please.
I have a Johnson 30 2 stroke, which seems to have taken a sudden dislike to going in the sea.
I can run it up on muffs, with or without prop engaged, at various speed settings and it runs just fine. As soon as I drop the outboard in the water, it will not run. If I up the fast idle, it will start in the water, but won't keep going. When I remove the outboard from the water and put it back on Muffs, it runs fine.
I have reseated the jetin the carb and cleaned it, but still no difference when it goes in the water.
Any ideas, suggestions will really be appreciated.
Many thanks
Paul
__________________
|
|
|
09 January 2010, 16:30
|
#2
|
Member
Country: UK - England
Town: yorkshire
Boat name: little vicky
Make: avon ex RNLI
Length: 3m +
Engine: tohatsu
Join Date: Mar 2008
Posts: 2,310
|
try setting it up in the water or in a barrell or a tank ,it could be that there is not enough back pressure on the exhaust ,i have seen it happen loads of times where people have set up the engine on the hose put it in the water and then the engine wont start or run right , especially with some older models ,have you checked the reed valves at the back of the carbs where it fits into the enigine,or any gaskets that may be passing /drawing air
__________________
|
|
|
09 January 2010, 16:46
|
#3
|
Member
Country: UK - England
Town: Essex/Vendee
Boat name: shockwave,Voluntry 2
Make: Pac 22/ searider5.4
Length: 6m +
Engine: 180hp turbo,yam 90
Join Date: Nov 2004
Posts: 1,022
|
Hi,I,m no engineer but a little more info would help.Does the difference in running happen imeadiately its in the water.Is the outboard at the same angle each in and out of water.Say the boat is on the sloping slipway on muffs the outlet for fuel is covered ,when in the water the boats level so the fuel levl is not picking up.Check for fuel line kink when in the water.It will be something simple unless its to do with backpressureor or dont know if theres any conection with crank oil seals.You need to determin what differences between in and out and list them .If the outboard is trimmed up on the bracket when out and runs fine lower it to the same position that it would be in the water and check it then.
__________________
|
|
|
09 January 2010, 16:46
|
#4
|
RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,069
|
Check the timing. Also compression test it and post the results.
__________________
Need spares,consoles,consumables,hire,training or even a new boat?
Please click HERE and HERE and support our Trade Members.
Join up as a Trade member or Supporter HERE
|
|
|
11 January 2010, 10:02
|
#5
|
Member
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,671
|
Two words - Back Pressure.
With a 2-0 stroke, you don't get the flywheel driven "piston pump" effect that you get on a 4- stroke to expel the exhaust, you are relying on the power form the other piston to keep it all going& loop charge / discharge the one that is exhausting.
The idle settings are somewhat delicate, and a small change in back pressure (i.e your exhaust being a foot or so below water level) will be enough to prevent quite as much exhaust escaping, therefore the cyl fills up with oxygen starved air, and so it stalls.
Or, simply, set your idle mix when in the water.
__________________
|
|
|
11 January 2010, 12:53
|
#6
|
Member
Country: UK - England
Town: Portland
Boat name: rekrab
Make: Avon
Length: 4m +
Engine: outboard 50 Mariner
Join Date: Apr 2007
Posts: 9
|
Thanks
Many thanks for the replies, it has given me something to look at next weekend.
The exhaust back pressure sounds a good one, so will have a go at adjusting the fuel mixture, but will probably do it whilst outboard is in a bin, froze my feet last weekend standing in the water.
Will also do a compression check and see what the results are.
To answer one of the questions, the outboard when ran on flush muffs, was at the same level and attitude as it would be in operation, also the boat was on a level ground.
Is adjusting the mixture the only was of changing back pressure, or are there any other actions that can be taken.
Cheers
Paul.
__________________
|
|
|
11 January 2010, 13:40
|
#7
|
Member
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,671
|
Maybe should have phrased that a bit clearer......
The back pressure is the result of the water above the exhaust port. You've seen the films where submarines go too deep & get crushed, and divers getting the Benz when they suface too quickly - that's because the deeper you go, the higher the pressure. Admittedly you have to go well deep to crush a sub, but you get the idea.
Now, imagine that on a microscopic scale - on muffs, the exhaust of your outboard is open to the air - absolutely no restriction. Zero pressure (simplistic view, before you lot all start picking holes in this explanation). Put the boat in the water, and there is a depth of water above the exhaust port. Not a lot of water, but that is your back pressure. Not a lot, but it's there.
Your idle setting as you have probably discovered will make the engine rev ridiculously easily when on muffs with not a lot of movement of the adjuster screw. That effect is heavily damped when in the water. All you are doing by adjusting the idle is upping the idle power slightly to allow it enough grunt on one cylinder to push the exhaust out against the water pressure on the other.
For completeness, a bit of info - on some engines, there is a pressure relief valve that means the idle exhaust comes out above the waterline. If you are on muffs, that never opens as the easiest way out for the exhaust fumes is via the unrestricted prop.
Hope that explained it a bit batter.
__________________
|
|
|
11 January 2010, 13:57
|
#8
|
RIBnet admin team
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: Tohatsu 30HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 11,632
|
Quote:
Originally Posted by Weydagger
but will probably do it whilst outboard is in a bin, froze my feet last weekend standing in the water.
|
if it is really cold don't leave the prop standing in a bin of water for hours... ...or end up with a giant ice cube on the leg
__________________
|
|
|
11 January 2010, 14:14
|
#9
|
Member
Country: UK - England
Town: Southport
Boat name: Qudos
Make: 5.4 Searider
Length: 5m +
Engine: Yam 115 V4
MMSI: 235068784
Join Date: Sep 2008
Posts: 3,930
|
Quote:
Originally Posted by Polwart
if it is really cold don't leave the prop standing in a bin of water for hours... ...or end up with a giant ice cube on the leg
|
What would you know about such things
__________________
|
|
|
12 January 2010, 09:55
|
#10
|
Member
Country: UK - Scotland
Town: Comrie
Boat name: Explorer 1
Make: Halmatic Pacific 22
Length: 6m +
Engine: Yanmar 4LHDTE 175hp
MMSI: 235075148
Join Date: May 2009
Posts: 33
|
Back Pressure
Yeh the back pressure will be about 0.5psi/foot of seawater.
__________________
|
|
|
14 January 2010, 12:28
|
#11
|
Member
Country: UK - England
Town: Portland
Boat name: rekrab
Make: Avon
Length: 4m +
Engine: outboard 50 Mariner
Join Date: Apr 2007
Posts: 9
|
All done
Hi
Thanks for all replies.
Adjusted idle a little and now runs ok in the water.
How simple was that :-)
Cheers
__________________
|
|
|
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
|
Recent Discussions |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|