Mercruiser 3.0 Cutting out at any rpm

[vroom ZOOM]

Hello. Recently I figured out the thumping noise in my engine, but that did not fix it from stalling. At first I thought it did, it ran good on the trailer so I decided to take it out for a spin. In the water it smelled like gas and wouldn't fire so I thought it was flooded, and rightfully so! After that it fired up and the problems began. It barely ran, and kept cutting in and out. The engine shook like crazy and stalled shortly afterwards. I turned the key and it fired up again, this time I revved it up to 2000 to keep it from dying, but it would cut out every second, as if someone was hitting the shift interrupt. I doubt its the carb, the thing reeked of gas. Running at 2000 it then had one big blip and went down to 500 and died with a couple of big sneezes in the carb. Any ideas on what this maybe be are appreciated! The coil, cap, rotor and plugs are new. The fuel filter had clean fresh gas last time I checked it. I will go check it again because after I put more gas in it it ran much worse, it wouldn't even start at all, I crank and there is no sign of firing whatsoever. I am really thinking this might be an electrical problem? While the engine ran the tachometer was bouncing up and down between 500 and 2000 like crazy, and it did not seem to match the blips of the engine.

 

[Scott Danforth]

first, stop throwing parts at the motor

second, if you smell fuel, stop. you are leaking fuel somewhere

check the clear tube from the fuel pump to the carb. if you see any fuel in there, you have a ruptured fuel pump. the extra fuel down your carb would make your motor run like crap and cut out (this is for safety reasons so you dont blow up.)

big sneezes in the carb are either running really lean or running really rich

so your issue is in your fuel system and not your electrical system

 

[vroom ZOOM]

Thank you for your help. I HATE throwing parts at it, it makes things expensive. The reason all those parts where replaced is because I was chasing down a weak spark issue last year and I thought it was the cap and rotor, but it turned out to be the coil and after replacing that it worked properly. New plugs... well that was the first thing I tried when this misfiring started this year. Anyways, I checked the yellow tube and it is dry. The nipple where it connects to the fuel pump was plugged with crap, so there was no possibility of stuff being there. It started smelling like gas after it stalled and when it wouldn't start. I looked for fuel leaks right away of course but I found none. I could see a little bit of gas on the water though behind the boat. Would you suggest a carb rebuild at this point? It never gave me trouble and ran well all last year. First time out below 3600 and above 4000 it ran well also. Maybe crap moved in the carb? Things got much worse when I put the new plugs in it, but maybe that's a coincidence.

 

[vroom ZOOM]

Ok so I took the fuel pump out and didn't find anything wrong with it, diaphragm is ok, but I cleaned out the yellow tube fitting anyways. Next I thought it must be the carb since that is the only other thing left in the fuel system. I took it apart and its clean as a whistle. I will still take it to my friend who has an ultrasonic cleaner. While I was taking the carb off I noticed a big white streak coming from the base of the carb and running down the manifold and block. I SWEAR that was not there a couple of weeks ago. Also to clarify the engine has a wheeze when it stalls and turns back half a turn probably due to high compression but I might be mistaken. I don't know what to think at this point, maybe a leaking manifold would cause this? Thank you, any help appreciated!

 

[vroom ZOOM]

Alright, I got a carb kit, I am about to put the carb together (after cleaning). Any recommendations or possible screwup areas that I should look out for?

 

[vroom ZOOM]

Okie.... I put the carb together, and slapped it on the boat. Half a bump and it started right up. no flooding so I guess I did the float right lol. Let it warm up and it seems to be running great. Idled down, almost stalled, so I tweaked that idle screw. Now it's idling perfect or near perfect in my opinion out of gear at 800 (so should be 750 in gear ezzz). Initially i turned the idle mixture out 3 turns, but I had to go leaner half a turn for it to run perfect. Now I will try take it out on the lake. Last time I tried it though it ran good on the trailer as well, but when I got to the lake it acted up!
One thing I am REALLY SCARED of is pinging. The carb is clean but what if??? How does the pinging sound? I want to be able to recognize it right away if it starts. Yes the carb is just rebuilt but I have been trying to sell the boat for a few months now while chasing this issue and I don't want to wreck the motor.

Second thing, just a word of advice. I will say that I made a mistake buying a carb kit from the merc dealer. It is way overpriced and comes with very few parts. No replacement jets, power valve and float, but costs $130! The only reason I got it is I needed it QUICK so I can sell the boat while the season is not over yet! pretty much only had a new gasket, needle, and seat with a couple of washers, spring, and check ball. Ugh!

 

[Rick Stephens]

The one thing could do every problem you had would be improper float height. If you kitted the carb, then that should have been a primary responsibility.

Pinging is a high pitched rattle when under higher power settings. Open your doghouse engine cover and run for just a bit if the motor is well insulated.

 

[vroom ZOOM]

ok, I think I found the problem. After running a little at idle, it's cutting out again. I pulled off the flame arrestor, and fuel was just pouring in out the venturis! So that was my problem all along! How do I fix this? It's clearly getting too much fuel! I used the spring loaded needle and seat.

 

[vroom ZOOM]

so now I found the cause of the problem. Th float has a hole in it. Not easily noticeable, but I put the float in boiling water and I could see small bubbles. Which also explains why the engine ran ok then slowly flooded, the float slowly sank and at some point it just flooded. Will get a new float and hope it will fix my problem!