Engine seems to have given up on me...

[tue]

Originally Posted by Mr-d

It's only a 20HP.
The carb has a float in it which regulates the ammount of fuel taken in. As soon as the 2nd stroke is done, a small one way valve will open to the crankshalft, Sucking fuel into it, and therefor drawing fuel up through the hose to. The fuel line is about 2metres (6 feet) long.

it has been running without a fuel pump all its life, and i believe that it is still the stock tank, but the hoses have been replaced (1997 is what they say)

The float is there to work in the same way as a toilet systern. It stops the float bowl from over filling a leaking fuel into the engine cowlings.

The one way valves called Reed valves serve the the same purpose as a valve does ona 4/ engine allowing the fuel/air mix to enter the crankcase at the particular moment in the engines stroke for it to pass into the intake port and into the combustion chamber.

I may be wrong but I do not think there would be sufficient vacum for the carb to draw the fuel in by itself.

Are you saying the fuel line enters the engine through the fuel fitting and then goes straight to the carb?

[tue]

not sure exactly what model yours is (if you post your serialnumber I will get a better idea). But this is off and old 2cyl 20hp merc. (Its the fuel pump!!)

[Mr-d]

Tue, yes that's what i think, i have not seen any pump on it, its a manual start so has no electrics on it (it has got a navigation light socket on it, 12V 60W max) so i dont see how a pump would actually be able to be ran.

The fact that it backfires through the exhaust should indicate plenty of fuel and a bang at the wrong time/ hot gasses igniting the excess fuel.


It only has one carb, and its getting enough fuel (it just does not fire it)

However, today, after snapping 3 bolts and getting shouted at, and me getting P***ed off at the "Marvelous" American design of the machine (it would not take my big ratchet, To fit it on you need to undo the spark plug lead clamps, which can only be undone if you remove the bracket, and to undo the bracket, you need to stick your ratchet with socket on the bolt, but it does not fit because the spark plug lead clamp is in the way...

Ended up removing the ratchet out of the car set, it was narrower and DID fit.
So, coils removed... and im shocked...



As you can see, the left one has a crack, and arc-ing marks on it. it also has a bit of sticky tape to hold a wire (which is also half burnt through) down.

The right one is TOTALLY cracked, and the magnet bit is shattered into tiny pieces, but yet again somebody has used some clear tape (Not the stock tape that is already there) and taped it all back together, on the right hand side of the right one you can see a black mark, this is also due to arcing...

New coils, Anyone?
(and new bolts....)

*Edit* Tue, its a 1978 Twin cilinder 20HP/14KW Mercury Blue Band with Thunderbolt Ignition IV
S/N 9205082 (It's a "Belgium" model, has a different flywheel for some reason)

[tue]

Originally Posted by Mr-d

Tue, yes that's what i think, i have not seen any pump on it, its a manual start so has no electrics on it (it has got a navigation light socket on it, 12V 60W max) so i dont see how a pump would actually be able to be ran.

The fuel pump is manual. It is worked by using crankcase pressure/vacum.

Those coils look very knackerd!!

[Mr-d]

Any idea where to find some new ones, UK based?
I believe these are special coils, rather than earthing the negative pole to the bracket/engine housing it feeds it back to the switchbox. All the technical drawings of mercs just earth them to the engine housing.

[tue]

OK think this is it. The fuel pump is mounted on the side of the carb

and this is these are the ignition parts

[tue]

Originally Posted by Mr-d

Any idea where to find some new ones, UK based?
I believe these are special coils, rather than earthing the negative pole to the bracket/engine housing it feeds it back to the switchbox. All the technical drawings of mercs just earth them to the engine housing.

Go to your local merc/mariner dealer armed with your serial number and they should be able to source some. They may even have some knocking around. I will lookat work for you. i think we may have some somewhere .

[Mr-d]

Now, that's the problem... "Local" does not work for me, Closest store is probably in Inverness or Glasgow, both 2 hours + away from me.

339 - 5748 - 358 is what they say on them.

Google UK comes up blank

on the parts list it is called 339 - 5748A 2

Anything that resembles it and could possibly work, yes please... I've heard they are quite expensive though...

If you can find some for me, i'd be ever greatfull!
(And it's probably cheaper than going out to collect them in inverness at ~200 miles.)

[nickjaxe]

Bill higham manchester has lots of bits for old and new engines also second hand bits he will post to you.

0161 790 7678

this was his number last time I called about 3 years ago.

Nick.

[Matt]

American Marine Imports have an extensive stock of sierra brand parts, cheaper than I've ever found anywhere else, including coils. Also, he's pretty reliable on the mail order at getting them out the door ASAP. 01675 442647