Logo
FULL SITE MENU

55 HP Mariner heavy on fuel.

D

dunesurfer

New member
I,ve got two 55 HP,Mariners on my boat.Both 3 cylinder,two strokes.(od-1129990 and od-1129992).I noticed for some time now,that the one motor seems to use more fuel then the other,on the same throttle settings.Then i changed the faulty throttle cable(old one was very sticky),and the problem is still there.The motors start very easy,no excessive smoking(normal for two stroke on idle),so,that indicates to me that the timing is more or less ok.

On a 15 mile trip,i use about 12 litres of fuel on the one motor,compare to about 20 litres on the other motor.A diffrence of about 8 litres for the trip,at the same revs.

So,my question,before we start on a goosehunt and change things that should have been left alone.Any advice and possble checks that i can do to help in finding out whats wrong.

Me,i have two possible problems.

a.Bad fuel pump diaphram.They have not been changed yet(motors is 1992 models)

b.leaking prime pump valve-this models have a little rubber ball you press to purge fuel before starting,next to the rope start handle.(this engines has,nt got electric starters)

So,what else.Any help is much appreciated,as i,m not close to a service centre.
 
Luderitz---the place for fast sailing.----------------------Look for a fuel pump diaphragm with a hole or a sticky float valve ( flooding ) in one of the carburetors.------------------Remove the covers in front of the carburetors and squeeze the primer bulb on the hose.--------Look for a carburetor that is leaking.----------------Run both motors full throttle with covers removed and shine a strong flashlight into the carburetor bores. Compare the amount of fuel coming up the main jet in ALL THE CARBURETORS . The motor using 8 litres may have blockage !
 
could the thermostat be faulty on the cooling system. If it were jammed openit wouldn't let the engine run at optimum temp. Just a thought.
 
I thought about the thermostat too,but motors seems to run at temp.Also,i do not think temp alone can bring about a 8 litre diffrence in fuel usage on the same trip.Me think something sucks fuel into the engine,thats not burned anyway.We will do also a compression test again,lats it was fine,and what is strange,motor fires up on first pull,all the time.Little bit rough idle,but i suspect air mix.
 
Why i would like to first hear what others say,is because i think,if the timing was that way out to bring about a diffrence of of about 8 litres at only moderate trhottle,then the motor would not start at first pull,even whenh cold.But ya,will do compression,timing,and then report back here.Reason why i do not want to strip and search,is i,m farrrrrrrrrrrrr away from suppliers of spares,and no service centre.
 
I would rebuild both fuel pumps and check the primer pump valve for a possible replacement. when were the carbs rebuilt last?
 
Quite recent,but something is bothering me,since i was there when the visiting mechanic opened the carbs,and i did,nt say the middle carbs,centre gasket on the high speed jet well,where it goes through the float chamber,dont know if it was stuck on the top casing maybe.I,m also not sure,he actually told me,all three was in place.Will strip first carbs and just confirm this.Then fuel pumps,and primer.

Will keep you guys up to date on this one.
 
Our fuel here is over 1U$ for one litre,thats besides two stroke oil,so,nearly 20 litres on 15 miles at not even WOT,is very very expensive.
 
Have you had a look at the bottom of the keel to the cavitation plate if its below the keel it will be fighting to keep it on the plane, have you tried using a cavitation plate I have a sports SE 300 as she jumps out of the water
 
Have you looked into all the carburetors with a flashlight while it is running or is that too much of a bother for you ?????
 
I,w work on the boat on friday,so,will follow all up thats been said and give feedback on said problem.What we wil do is as follows.
check compression again.
Check timing(this motors has got the .459 marks on them.
Remove resonator boxes from carbs and run motors to check with light the fuel thats been delivered
Then block off valve on primer bulb.
Before stripping fuel pumps,would just strip that motors carbs again,and check all seals inside.
Then strip fuel pumps

After that,i hope all is back to normal.Lets cross fingers.
 
Ok,feedback from what we found so far.Flywheels has got the .459 mark on,but no adjustment plate,as described in the manual.So,basicly,juts use normal timing marks.All is within 1 degree to what the manual states.Fuelpump,s one vacuum chamber was wet,so changed both diaphragms,and gaskets.Tested compression,ok,gauge not calibrated,but all reads the same,on both engines and about 5 bar.Due to this engines being manual start with rope,i would think that one can add at least one or two bars to it,if the motors was turned with a starter.Carbs pulled again,and all seems ok.Gaskets is ok,jets ok and spec to what the manaul states.Boat has not been tested yet,but ya,this is what we did so far.Now a intersting topic came up,while discussing more.This motors is not counter rotation engines.Thus,they turn same direction.On a setup as with this,one motor will use more then the other one.To some extend it make sense,but ya,any comment to this idea.

The boat will be tested this weekend,and i,m also gonna to block off the primer bulb,juts to see if under power,fuel is not pulled in through the valve in it.Lets cross fingers on this one.
 
Back
Top