Mercuiser not starting. Please help

[Alex57]

Hello everyone,

I am a begginer with boats but have some experiance with cars...


Motor is a Mercruiser 5.7 litter
2 barrel carb Thunderbolt 5 Ignition
The thing ran fine for a while, then wouldnt start when hot and kept getting worse, until eventually now doesnt start AT ALL.


It cranks, turns over but no signs of life. I am getting gas for sure, can see plenty of gas in the carb. I already changed the spark plugs, wires, cap, rotor. No change.

There is voltage going to the coil and continuity throught the coil.

There is spark comming from the main ignition wire (visible if you touch ground) There is also spark comming off the ignition wires (when you touch ground)

When it did run, it ran just fine and I didnt't touch anything, so I doubt it's the timing..

SO I get gas, I get spark and nothing.... I am aware of the ignition
module/sensor and some kind of a changable ignition pick up sensor in
the distributor, but I have no idea how they work and wether they are
the problem. Me and my buddies are totally stuck. Anyone have any
ideas?


Any help would be greatly appreciate it....


Thank you,


Alex.

[marshmat]

You've already tested everything I would think of. This is a tricky one.
I know you're getting sparks from the ignition system, but that doesn't necessarily mean it's A-OK. Even a lame ignition will spark pretty well across double or triple the standard plug gap, when at ambient air pressure. To properly test the ignition you'd have to do an air-gap plug check using an air-gap tester suitable for your engine. A dealer might be able to advise you on this.
Since the carb seems fine, fuel's probably not your problem. And had anything gone wrong with the internals, I'd think you'd have noticed pretty quickly. Another long-shot guess might be that a head gasket has blown and is letting cooling water into the cylinders?
The trip to a Merc dealer might in the end prove worthwhile, much as I hate spending $$$ on things I should be able to fix....

[Alex57]

Thanks Mat,

I don't think it's the head gaslet as the plugs are dry. I bought the spark testing tool which sort of makes it a closed end spark test nad it seems a little weak even though it's there. The mercruiser book says to do a specific test where you unplug the coil from the distributor and try to turn it over... according to the test i need a new pick up/sensor in the distributor. If that doesn help then it's time to go to the dealer like you said... Thanks again.

Alex.

[Alex57]

Hey Guys,

changed the sensor... no change. Got spark, but then again I had spark before.

After cranking it for a bit, I looked into the carb and maaaaan there is alot of gas in there..

COuld it be the carb? flooding the motor?

Funny thing, it's still dripping long after i stop cranking..

THis has been a frustrating 2 weeks and no progress what so ever...

Well looks like i will need a pro after all, but i will let you guys know what it was after I figure it our so this nonesense does not happen to you.

[drewpster]

alex has a carb problem

[Alex57]

Hi Drew,

Thanks for your reply, can you please be a little more specific? Is flooding common? what can I do?

Should I just rebuild it?

How can I eliminate other non carb issues?

thanks again,

Alex

[drewpster]

Alex,
If the carb is dripping fuel something is wrong with it. Especially if it continues after you have stopped cranking the engine. What has most likely happened is the float inside the float bowl of the carb is failing to close as fuel pressure is brought to it by the turning engine. Unfortunatly there is no easy fix for this. I would remove the carb and take it to a professional unless you have some experience with this or, like me, you are crazy enough to tackle the job yourself. The truth is, carbs are not very complicated. But they are picky about mechanical settings and have little teeny parts. It is also very important they are very, very clean inside and out before putting them back together.

[Alex57]

Thanks everyone,
it was a stuck choke, which was to tight to operate properly. The mechanic at the marina got it to run in ohhhh about 10 minutes flat. I think he may not have adjusted the carb perfectly casue my max rpms are a little lower then before but aside from she is good to go. FINALLY!

Thanks again to everyone for replying.

If it happens to you, check the choke operation in detail first!

Alex

[drewpster]

Just goes to show~ Check to most obvious things first. It simply did not occur to me to check the choke. Great ! glad to hear your up and running with a simple fix.
Duh Drew

[Alex57]

Thanks Drew,

now if this rain in NY ever stops, I am going fishing!!!!

[kach22i]

This person seems to have a similar problem, can anyone help them? They might of posted in the wrong section.

Link:
http://boatdesign.net/forums/showthread.php?t=12290