Mercury 8HP difficult ot start at first.

[davidpbo]

When I return to the boat after say 2 weeks my (Y. of manufacture 1989) Mercury 8 Hp pull start is difficult to start. I usually discoonnect the fuel line at the end of a weekend's sailing and let the carb run dry.

When I come back I hand pump fuel using an in line bulb pull the idle knob (Which is also the choke) out and try and start it. It takes a lot of pulls.

Thereafter throughout the entire time on the boat it starts first pull, and I imediately push the idle knob back in.

I probably should treat it some new spark plugs but they look fine although I did give them a clean on Saturday.

Would Easy Start help on this first occasion?

Can anyone suggest anything else that might help.

 

[Lakesailor]

I think there will be a fuel pump on that motor. If so you may only be priming the fuel as far as the pump and having to fill the carb by handcranking to spin the pump (or actuate the diaphragm, more correctly).
Thererafter the fuel is ready for use in the carb.
I would not bother running it dry. I've never subscribed to that procedure.
I've not had any gelling problems in the carbs.

 

[VicS]

With a remote tank there will be a fuel pump!

The priming bulb should push fuel though the pump and fill the carb bowl. Are you sure you pumping the bulb until the bowl is full and it has become firm and cannot be squeezed any more.

Maybe it would be wise to check that fuel is getting through ... is the drain plug accessible so that can be removed to check?

Always wise to replace the plugs when having trouble.

have you checked for good sparks?

Have you checked the compressions?

have you checked that the choke is closing, assuming its flap type choke? I take it that it also opens the throttle a little, have you checked that is happening

Easy start is frowned upon because it contains no oil. It is better to put some 2 stroke mix in a spray bottle and spray a little directly into the carb. But give it a try just once to see what happens if you have some

 

[VicS]

Ah I think it has pump type primer rather than a flap type choke.

Prime the system first with the bulb then operate the "choke" several times. Progressively; twice, then try three times, etc.
See if that helps. Draining the carb probably means that the primer pump is also empty and it may take several operations of the "choke" to refill it.

 

[davidpbo]

Thank youu for the replies. Should the hand pump pump the fuel through to fill the float chamber or just to the diaphram pump?

Should I hear sloshing from the fuel tank when activating the hand pump?

I am thinking maybe I have a defective hand pump that isn't generating enough pressure to fill the float chamber.

Given the motor is 20 year old would replacing the diaphram pump (which not not appear to be faulty) be timely maintenance this winter.

Can you still get 10L metal fuel tanks? I feel the hole lot could need replacing. Alternatively are there any plastic tanks with internal bracing so they don't expand as much if the vent is shut? I had one that became decidedly spherical.

 

[VicS]

By hand pump You mean the fuel line bulb?
If so I would expect it to fill the bowl .... certainly does with Johny rudes! 'swat it's for!
Pressure at the inlet to any diaphragm pump that I have met would simply pass all the way through. Just a chamber, a diaphragm and a couple of NRVs, one on the inlet and one on the outlet.

No you'd not expect to hear any sloshing from the tank while pumping the bulb.
If you can it suggests a defective valve at the inlet end of the bulb.

After there or four squeezes the bulb should feel firm. Exactly how firm depends on how much air is trapped in it. If it does not become firm it is defective, but easily replaced. One squeeze, or less, and it should be firm when the fuel line is not connected to the engine

( I have come across fuel systems where there is a foot valve on the pick up from the tank.. dont know if that applies to the Merc. I will check.)**

If it runs OK once it is started the diaphragm pump must be OK otherwise as soon as the fuel in the bowl is used it will stop.

I'd expect to be able to get a 2 gallon or a 10litre metal tank but I have a 25 litre (6.6 US gallon) plastic tank. I leave the vent open when it is on deck or cover it with something light coloured to keep the sun off. ( some scrote nicked the original metal tank but at least the plastic tank does not leave rusty marks or affect the compass.

** no diags of the tank and fuel system so assume nothing unusual about them.


Check what I said about the "choke" operating the fast idle. Did operating the choke / primer pump several times not help?

 

[duncan]

'wot Vic says plue one small check - the valves on the primer bulb.

easy enough to check for any rubbish around them.

I would also try not running the engine dry and see how that affects your 'problem'