Mariner 75hp Carb help

[Scousedeli]

Originally Posted by clydeoutboards

Hi

you could always post them an outboard dealer to have a look at them for you to see if they can do anything. Not saying us as we get a fair few in but we would have a look if you are stuck.

Dave

Cheers Dave,

The float valves are solid not budging, the shield around the main jet on one of them snapped as it was stuck solid in the float bowl during disassembly, I don't think the main jet is replaceable, I maybe wrong.

[Davie]

I have a set of 3 carbs for you. £70 inc vat inc delivery to Liverpool.

[Scousedeli]

I have PM'd you Davie, Cheers

[Davie]

no pm here!

[Scousedeli]

Any idea if the wme 103 will work instead of wme 46s, I could do with getting this up and running for the season.

Cheers

Lee

[Festinghouse]

probably not as i discovered to my cost that the last of these engines were a larger capacity - with a 3.5inch bore instead of 3.375, and 8mm(ish) longer stroke. i had to buy a set of later carbs, and so i too have an old set of earlier carbs sat in my workshop. i also have various size jets if you need to do some playing around.

[Scousedeli]

Hi Davie

Your mail box is full so my PM won't get thru.

Cheers

Lee

[Scousedeli]

Hi all

Thanks for the help, the 103 carbs are working ok. The main starting issue was a knackered battery cable as well as gummed up carbs.

Does anyone know how to adjust the idle jet up properly?

Cheers

Lee

[steve-ribnet]

Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years!
click Mariner manuals, find your year and range, possibly this one?
Boatinfo - Mercury Service Manual for 70-75-80-90-100-115 hp

After service or replacement of carburetor, turn low
speed mixture screw adjustment in (CLOCKWISE)
until it seats LIGHTLY – then back off (each
carburetor) the number of turns per model as
indicated, following:
70 H.P. --- 1-1/4
75 H.P. --- 1-1/2
80 H.P. --- 1-1/2
90 H.P. --- 1-1/2
100 H.P. --- 1-3/4
115 H.P. --- 1-1/2
[some posts go 1/4 turn richer for startup]
This adjustment will permit engine startup.
LOW SPEED MIXTURE ADJUSTMENT
NOTE: Only the top two carburetors on four cylinder
models have adjustable idle mixture screws.
1. Start engine and allow to warm-up (run for several
minutes). Throttle back engine to idle for about
one minute to allow RPMs to stabilize.
2. With engine running at idle speed -- in water -- IN
FORWARD GEAR (prop on) -- turn low speed
mixture screw IN (clockwise) until engine starts to
“bog” down and misfire. Back out 1/4 turn or more.

3. Check for too lean mixture on acceleration.

[interpret as hesitation or bogging down on acceleration, and also a slow reduction in revs back to idle from WOT to neutral]
4. DO NOT adjust leaner than necessary to attain
reasonably smooth idling. When in doubt, stay on
the slightly rich side of the adjustment.

[uncle al]

The service manuals you should go by the serial number of your obm,
Set all three carbs at one and a half out from lightly seated,I found that was a better setting than the service manual,
when you have set everything up the rev range differance should be approx two hundred rpm, from fwd to nutreal,
as Steve_Ribnet says do notnot set the carbs to lean ,thats why I set the carbs at one and a half out ,
also when you are setting your carbs have the obm staight up and down,if its tucked under it is running in an over rich condition,
I have found after the dozens I have set up that the information I have written on this subject is the optimum settings for good performance,
dont forget the ign timming has to be correct and the oil pump set in the correct position thats the notch on the oil pump aperating arm as well.

[Scousedeli]

Cheers fellas. It starts fine now and idles well, however at high revs it's stuttering a bit and seems it has less power than before, any ideas anyone.

Cheers

Lee

[steve-ribnet]

I believe The high end jets are fixed for these (check) so assuming these are correct for your engine and the carbs are clean, I would look at the fuel pump, and fuel lines for restriction.

I would first try a spare fuel can set up -fuel lines, portable tank, bulb etc and check the lines on the engine for kinking or restriction- check fuel runs freely all the way up to the fuel pump - should gush out when pumped by hand.

Fuel pump diaphragms might look ok but not be 100% - throw in a service kit including diaphragms, gaskets and one-way valves to be on the safe side. I had exactly the same symptoms and the fuel pump all looked hunky dory on the inside, but gave it a service kit and it ran full throttle once again without hesitation.

[Scousedeli]

Cheers steve, I'll give it a go.

[Scousedeli]

Hi All

After a busy summer I have managed to start looking at the engine again, this is where I'm at.

I dismantled the carbs and carb three was full of gunk, with the air inlets that enters at the base brass shield was blocked solid. After 2 hours of cleaning, scrapping ets is now clear.

1. Engine starts with choke, runs for a while then cuts out.
2. Seem to be getting bcak pressure on the inline filter with occasional spurts coming coming out from the carb end.

Any help would be great,

Cheers

Lee

[matt h]

Sounds like its still blocked,Main Jet sounds suspect. carb needs to be ultrasonically cleaned if was that bad.

[billnorfolk]

Seem to be having the same issues with my 1988 mariner 75hp .Bought boat and engine a few months back ,serviced engine plugs ,impeller, gear oil .Ran fine in a tub so didn't pull carbs or fuel pump about at all ,i did bypass the oil injection system by taking drive out of oil pump ,blanking oil imput port on fuel pump ,engine still ran fine in tub on 50-1 mixture.Took boat out Sunday for first time got up on plain and ran well for about 5 mins then died ,bulb on fuel line felt soft so pumped up again and off we went this time for about 3 mins engine died again ,pumped up again and engine would only run on half revs and only for a few minutes .There is a new fuel line and pump on tank ,fuel is fresh .Engine had stood for a few years so looking at fuel pump and carb clean .Took fuel pump off and found fuel in what i assume is the vacuum pipe ,fuel pump has 3 pipes ,inlet ,outlet and another must be for vacuum to work diaphragms which by the way looked ok but will be changing them ,there was a tear in the gasket between the redundant oil chamber and the fuel inlet ,wether this would cause the problem or not .Any advice or suggestions gratefully received .Thanks Bill

[steve-ribnet]

Originally Posted by billnorfolk

,there was a tear in the gasket between the redundant oil chamber and the fuel inlet ,wether this would cause the problem or not .Any advice or suggestions gratefully received .Thanks Bill

Sounds like a fuel pump issue. Tears in the gasket/diaphragm would certainly do this. There shouldn't be fuel on the pulse line to the crank case unless these are torn. I have had a pump with no visible damage to diaphragms etc cause running issues, which were cured by a full rebuild of the pump with new parts.

I would get a rebuild kit for the fuel pump, which contains the diaphragms, gaskets and also the small non-return flap valves and plastic stems inside the pump. As with all fuel related service, keep meticulously clean on assembly, carefully removing all traces of old gasket, and cleaning any fuel residue with carb cleaner before re-assembly.

It's a straightforward job. A genuine Quicksilver rebuild kit will come with instructions and diagram on how the gaskets and diaphragms all line up, and how to install the small nonreturn valve stems inside the pump.

Remove the '3rd' hose from pump and block and blow through with compressed air (the pressure variations inside the crank case create pressure 'pulses' which move the diaphragms and pump the fuel) so you know it is clear for next time.

If you have bypassed the oil injection circuit, ensure that no air can enter the fuel pump oil port. I would put a short length of hose onto the fuel pump's oil inlet, then block the other end with a short fat machine screw and jubilee clip.
good luck

[billnorfolk]

Thanks Steve will be doing that this weekend, thought it strange for fuel to be in that pipe .Although diaphragms look ok no visible holes over time must perish .Do you mean leave one end of the 3rd hose connected to engine and blow through with compressed air?. I have blocked the oil inlet off with a proper tapered plug so should be nicely air tight .Will probably do the carbs as well ,any issues i should look for .Thanks Bill

[steve-ribnet]

Hi
I would just make sure that 3rd hose was clear - remove pipe from engine and pump first and blow through to remove fuel or oil residue from the pipe
Turning the engine over will clear excess fuel from crankcase if it has leaked in from this pulse line.
If you have the option to test the motor after rebuilding just the pump, it will give you an indication whether the problems did really arise due to pump problem, and what condition the carbs are in
Rebuilding carbs is quite straightforward- lots of posts on here about doing it. Just be thorough and meticulously clean - carb cleaner, compressed air and ideally ultrasonic cleaner too.

[office888]

Just a heads up :

Debris can wear out your jets...high velocity fragments will slowly erode the needles and jets, effectively stepping up your jet sizes, causing running problems.

Few people realize how important a good 10 micron filter / separator really is. Better too much filtration than too little!

(I'm running a 2 micron + vac gauge on my ETEC)