Merc 90 2 stroke starts then stalls... over and over and over

[kmagnuss]

2007 Mercury 90 2 stroke carb'd.

Rebuilt the carbs, new plugs, new filter all around 100 hours or so ago. Maybe a little less. Been running great.
I changed the fuel line a couple weeks ago and I've had it out on the water probably 3x since then and it's been good. No different.

Today, started it up, pulled off the dock, everything is fine... then about 5 minutes into the no wake zone putting around it sounds like it ran out of fuel. It just sort of bogged down and died. I start it back up and it dies within 5-10 seconds each of the 10,000 times I get it started. I tried starting it and revving it up and it will do that for 5-10 seconds then it just sounds like it starves for fuel.

The primer bulb isn't sucking flat, if I press on the bulb while it's running it makes no difference.

I tried putting on a new fuel/water separator but it didn't help.

I'm going to mess around with it tomorrow... check the fuel for water, change the plugs... see what happens.

Any ideas to look for would be great.

Thanks.

-Mag

 

[oldman570]

Re: Merc 90 2 stroke starts then stalls... over and over and over

When you replaced the fuel lines do you get the check valve in correctly. Look at the link.
Mercury, Mercruiser, Force, etc. - Bleed System - 75/90 HP 65 JET (3 CYLINDER)
If it is not in in the right direction it could be your trouble, or the idle setting on the carbs is off if a link and sync of the carbs was not done after working on them. JMO
Oldman570

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Sorry I should have been more specific...I didn't replace those lines on the engine. I replaced the main line going from the tank to the fuel/water separator, from the separator to the primer bulb, and from the primer bulb to the engine.
The lines on the carbs all look brand new ("look" being the key word here, lol).
Link and sync was done after the rebuild.

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Is it possible that the diaphram on the fuel pump went bad and now it's only starting on the enrichener?

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

I just went out and messed with it again and realized that it absolutely will not run at all unless I hold the enrichener button in. Even after it's warmed up for a few minutes. I'm leaning towards a fuel pump rebuild, but after taking it apart I was expecting to see the rubber diaphrams all torn up or cracked... but they looked fine to me.

 

[oldman570]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Have you changed the fuel seperator filter and made sure that all the air is out of it? If there is air in the seperator the fuel pump will not suck the fuel as it should. You can disconect the fuel line from the pump and using another piece of hose in its place, pull the kill switch and spin the motor over to see if the fuel is being pumped to the carb in a steady even stream into a coffee can.
Being that it will run when you hold the enricher valve, it sounds as tho the trouble is in the carbs. The float level is probly set to low and not letting the fuel into the carbs. When working on them it is always best to hook a tank and primer bulb to the inlet on the carb and TesT The float levels to get them set correct. This willsave having to take them on and off all the time if things are not right. JMO
Oldman570

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Thanks. I just did some more searching and more people lean towards cleaning the carbs like you mentioned.
I have a big fishing trip coming up on Friday so I better go get some gaskets.
In the meantime I'm going to put the fuel pump back on and see if it's pumping fuel like you suggested.

Thanks.

 

[dpeslinger]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Not to hijack thread but will old gas cause engine to backfire, or sputter. carbs were rebuilt last year.

 

[CharlieB]

Re: Merc 90 2 stroke starts then stalls... over and over and over

rebuiltl carbs 100 hrs ago

They are gummed up from sitting, take them apart, soak, squirt carb spray thru EVERY passage, followed by blowing every passage clear with compressed air.

Reassemble with the new gaskets you have on order.

Follow the directions in the service manual TO THE LETTER in setting linkage and accelerator pump adjustment, timing.

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

That's the thing though... the boat doesn't sit. I use it 2-3x a week every week. 100 hours ago was 2 months. Ha ha.

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Well I took off the carbs, didn't notice anything out of the ordinary when I took them apart... no dirt or debris that I could see. One of the floats was a little off so I re-set it. Threw everything back together and it runs like a top. Weird. Something must have come loose during the cleaning process.

Anyway... gonna do a water test tonight. I won't stray too far from the dock though.

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

PS... am I the only one who wants to choke the sh*t out of the person who designed the carb layout on this motor? It takes me longer to get the bottom carb in than it does to take them all off and clean them. What a joke.

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Well that was short lived. Did the exact same thing tonight on the water. Ran great for about 10-15 minutes. Then at almost the same spot it died again. This time it was a 'little bit' different as I could putter back about half way to the dock. Also it would start without the enricher every time. So I'm just going to rebuild the fuel pump when the parts come in and take it from there. I'll check the compression while I'm at it also... hot and cold. Because whatever is happening it isn't doing it until it warms up... and it SEEMS to be fuel related.

 

[CharlieB]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Do you have a water separating fuel filter?

Drain each carb but hold a small bowl or something under as you remove the float bowl drain plug so you can catch the fuel.

Look for any 'beads' of water in any of the caught fuel.

You might pump the primer bulb once per carb to flush anything out of there.

Your next step is to DVA test the stator to see if the high speed windings are failing once the motor is fully up to temp. You may have to take the DVA along next time out as you'll never get the stator to full operating temp running on the hose with NO load.

Do NOT assume a bad stator, there is NO RETURN on electrical parts.

 

[oldman570]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Could be as Charlie states. Take a timming light with you next time out and use it to see if you are losseing spark to any of the cylinders when it happens. This will deffenatly tell if the trouble is electrial as it very well could be. Then start testing the coils on the plugs that were not fireing and then the stator with the DVA and that will only leave the switchbox. JMO
Oldman570

 

[quicktach]

Re: Merc 90 2 stroke starts then stalls... over and over and over

It does seem like a fuel starvation problem BUT... can you prove it ? Is there fuel in the on-engine fuel filter when it stops? Can you open carb bowl drains to see if you have fuel in the carbs? At that stop time, are the spark plugs wet with fuel? If so, you're likely into the electrical system - follow others advices. And how is the rectifier?

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

I checked compression today for fun and it was 130 across the board.
Started it up and it pretty much immediately died... I couldn't get it to warm up. It was acting just like it did last night on the water. So... I'm going back to fuel problem again for now. Fuel pump diaphragm kit comes on Thursday so I'll slap it on and see what happens.

However... you guys are smarter than me so tomorrow after work I'll check the spark out. Should have done that today but decided to play with the kiddo instead... more fun than swearing at my boat all night.

Thanks again for the help guys.

-Mag

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Oh, forgot to say I'll also pull the fuel line after the pump and see if it's got any pressure (again). Last time I did it, it was after I put everything back together and the motor ran for a good 20 minutes after that. Maybe something has changed since then.

(see how I keep avoiding the electrical stuff here... I know jackcrap nothing about boat electricals so I'm putting that off til last while crossing my fingers)

 

[CharlieB]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Temporarily install a clear hose between the fuel pump and carbs, start the motor and watch for any air bubbles which would show air sucking in somewhere BEFORE the fuel pump.

Remember to remove the clear hose once finished with repairs, clear hose is NOT RATED and is NOT APPROVED for fuel use, we only use it to test for air leaks then remove it.

 

[kmagnuss]

Re: Merc 90 2 stroke starts then stalls... over and over and over

Fuel pump kit came in today. (early... yay!) Tried to start the boat before I changed anything and it was doing the same nonsense. Changed the kit out and it ran good for about 20 minutes on the muffs. Gonna go down to the ramp tomorrow (maybe tonight) and let it sit there and idle on the trailer for 30 minutes or so to see if it dies... then take it off and run it like a scalded dog for a bit.

I did notice one thing weird when I was done today though... the idle was much higher than usual. It was running around 2100 rpms... before it would usually sit around 7-800. Think that's due to the new fuel pump?