Mercury 5hp outboard woes

BlueChip

BlueChip

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My Mercury outboard is giving problems.
I've identified the problem as the fuel feed to the carburetor, specifically the square black assembly that feed the fuel bowl, no fuel is getting through this.
I've stripped it down and there are two diaphragms and what look like a couple of leaf valves, all seems to be in order yet there is still no fuel geting through this. It's possible I've reaasembled it in the wring order and the valves are the wrong way round yet it looks ok.
Is it some sort of demand valve that needs a vacuum to get fuel to flow, seems unlikely?
Does anyone have an exploded diagram or can offer assistance here?
thanks
 
this is the fuel pump and its driven by the vacume from the engine running. to test it try blow from the inlet and then the outlet, you shouldnt be able to pass any air. if its not pumping it could be the float valve needle stuck.
 
Thanks for both replies - very useful information.
I've cleaned thee carb and reassembled everything correctly and the engine now seems to be working ok, give it a high speed test in the water tomorrow.
 
steve28 said:
this is the fuel pump and its driven by the vacume from the engine running. to test it try blow from the inlet and then the outlet, you shouldnt be able to pass any air. if its not pumping it could be the float valve needle stuck.
Click to expand...

Still got problems, the motor starts ok and runs at full throttle for about a minute then cuts out, starts again after a few pulls and then will only run at idle or just above.
Obviously a fuel flow problem (I think) but as I've cleaned all the jets and filters I'm at a loss to know what to try next. Any suggestions. I checked the pump as above and all seems ok.
 
You not not give full details of the engine, so it is difficult to look up any particulars. Year and or preferably serial number should enable that to be done.

I agree it sounds like a fuel flow problem

The fuel pump has been identified but you should be able to blow through it in the normal direction of fuel flow ie from the inlet to the carb bowl. You should not be able to blow in the opposite direction but perhaps that's difficult to test!

Does your engine have a remote fuel tank, an integral tank or the provision to use either?

If you are running from an integral tank make sure the tap is opening properly, that the inline filter is not choked and that if you pull the pipe off the inlet to the pump that you get a good fuel flow.

If you are running from a remote tank then check in the fuel lines for blockages and possible in leakage of air ( esp at the connector).

If the fuel pump is not pumping or if there is an air leak into the fuel line you should be able to keep it running by gently pumping the bulb. (unless of course you have assembled it incorrectly)

In both cases check the tank venting ( take the cap off if in doubt)

Check the pulse connection between crankcase and fuel pump.

If you are using an integral tank and the motor has provision for a remote tank check that the remote tank connector is not allowing air to enter the system.

Any possibility that the carb is flooding?

Dont completely ignore the possibility of an ignition problem. Have you tried a new plug and checked that you can draw a good spark from the plug lead.

Exploded diagrams at the link given although I usually use Crowley marine

Got an owners manual or do you need a link to that?
 
VicS said:
You not not give full details of the engine, so it is difficult to look up any particulars. Year and or preferably serial number should enable that to be done.

I agree it sounds like a fuel flow problem

The fuel pump has been identified but you should be able to blow through it in the normal direction of fuel flow ie from the inlet to the carb bowl. You should not be able to blow in the opposite direction but perhaps that's difficult to test!

Does your engine have a remote fuel tank, an integral tank or the provision to use either?

If you are running from an integral tank make sure the tap is opening properly, that the inline filter is not choked and that if you pull the pipe off the inlet to the pump that you get a good fuel flow.

If you are running from a remote tank then check in the fuel lines for blockages and possible in leakage of air ( esp at the connector).

If the fuel pump is not pumping or if there is an air leak into the fuel line you should be able to keep it running by gently pumping the bulb. (unless of course you have assembled it incorrectly)

In both cases check the tank venting ( take the cap off if in doubt)

Check the pulse connection between crankcase and fuel pump.

If you are using an integral tank and the motor has provision for a remote tank check that the remote tank connector is not allowing air to enter the system.

Any possibility that the carb is flooding?

Dont completely ignore the possibility of an ignition problem. Have you tried a new plug and checked that you can draw a good spark from the plug lead.

Exploded diagrams at the link given although I usually use Crowley marine

Got an owners manual or do you need a link to that?
Click to expand...



Its a Mercury 5hp - s/n 09890219
Remote connector and built in tank, I'm using the inbuilt tank, vent is open ok.
Fuel is getting to the pump ok. Ive cleaned all filters and fuel tap, new spark plug fitted and shows a healthy spark. When I blow through the pump there is no flow, but the leaf valves look ok, the rubber diaphragms look ok and are the correct way round. The remote connector looks ok.

> Check the pulse connection between crankcase and fuel pump.<
How would I do that?

I dont have an owners manual, a link would be useful.

cheers
 
Last things first
You should be able to download an owners manual from the download center at http://www.brunswickmarineemea.com/ Not always easy to locate what you want though! You may have to look at different years to find it.

I make yours 1996 model and Belgium Made.

How to check the pulse connection. Thats a good question. I dont see a hose between crankcase and fuel pump so if there is not then there must be an internal connection. It's pressure/vacuum pulses from the crankcase that drive the pump.

It might be worth your while posting your problems on the Merc board of the
iBoats forums but I am wondering whether the model was marketed in the USA or was purely a European model.
 
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How old is the fuel? Your problemsa are very similar to what I was experiencing last year with my Mercury 8HP and this year with my Tohastsu 3.5. If you have cleaned the carb and jets might be worth doing it again in case any crud has been pushed through. Might also be worth draining the tank and rinsing it and trying again with some new fuel.
 
QUOTE]When I blow through the pump there is no flow[/QUOTE]I would have expected to be able to blow though the pump , but perhaps not easily. You should be able to blow through it with the dinghy pump though.
 
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