3.0 Mercruiser stalls out after a few minutes of throttle....

[Coryb]

Hello all!! I have a 90 sea ray with a 3.0 mercruiser which uses the mercarb carb. I did a tune up, changed all filters, and put fresh gas in the tank and it has an almost new fuel pump. I also rebuilt the carb because of dead/bog spot issues, which I still have. I did some research and made some small adjustments to the float. That seemed to make the dead/bog spot smaller, but it's still there. It won't idle right unless I have the idle mixture screw turned almost 4 turns out (which doesn't seem right to me) and now the engine dies out and stalls after just a few minutes of being at 3/4 to full throttle. It's actually stalled twice at almost the exact same spot on the lake that we use after running for almost the same amount of time. Maybe something to do with temperature? I'm not a mechanic and I am stumped as to what is causing the engine to stall out after a few minutes of being on plane and why I still have the dead spot in the throttle after a rebuild. After the engine stalls out it's hard to get it started again if it starts back up at all. It seems to be starving for fuel but I feel I have it set to run very rich. I'm sure could be a few different things but I'm not sure what else to check. Any direction would be great!

 

[Bt Doctur]

try running it on a remote tank and report the results. could be a clogged vent line/vent fitting or a sticky anti-syphon valve

 

[Rick Stephens]

As stated, probably a filter or other fuel supply component is plugged. I would probably start by replacing filters. Then pull the fuel line off the carb, disable the ignition and slip a clear container over the end of the fuel line and crank the engine. See if you are getting good fuel flow. If insufficient, you are then checking through Bt Doc's list.

Ricl

 

[CaptDuck]

I had about the same problem with the same engine this year. I rebuilt carb more than once, i changed all filters including filter in the fuel pump. I disconnected my air vent hose for fuel tank to make sure it wasn't plugged up and changed my anti-syphon valve. And all is well now. I think between the carb rebuild and the anti-syphon valve being changed, that my problem was the anti-syphon valve.

 

[airshot]

Just a suggestion here....are ya sure you got all those tiny passages cleaned out on the carb rebuild? When you have to turn the idle out almost 4 turns it sounds like a passage may be clogged. Then I would consider running from a portable tank and see what happens. Having read many posts on carb rebuilding on this forum, it is not unusual to have to go back thru the carb again being extra carefull to clean it thoroughly.

 

[CaptDuck]

Yeah i suggest rebuilding the carb. I rebuilt mine about 3 times before i finally got everything right. My last resort was going to have it done by a boat shop and pay an arm and a leg! i just bought a cheap harbor freight ultra sonic cleaner and let it soak in there. The last time did the trick. Boat sat for a few years and had water in the tank and carb all varnished. Runs good now.
Just take your time and clean all passages real good. And make sure your float is set right!!!

 

[Coryb]

Thanks for all of the good advice! I believe I found the culprit that is making my engine stall out. I checked the anti-siphon valve first and low and behold it probably wasn't opening all the way because it was being blocked off by a bunch of crap! You wouldn't believe what it was so ill leave it at that. As far as the dead spot goes I feel like I cleaned the carb pretty good. I will probably go ahead and tear it back down and clean it with an ultrasonic. What product is best for cleaning in an ultrasonic? I've heard simple green but I've also read that it's not good to use. I think it's an accelerator pump issue, but it seems to be working properly. My carb's ap linkage is the older style that only has one hole so I may need to upgrade it to the one with 3 settings which might fix the problem. Any ideas on that?

 

[Fleetwin]

I had the same issue with a Volvo 3.0 (same engine).

After I had added an external fuel filter, it was sucking air. I had to double clamp every rubber to metal connection.

 

[Rick Stephens]

Accelerator pump shouldn't effect you at constant throttle. Sounds like fuel supply problem. Work your way through the system and you'll get it.

 

[Coryb]

Accelerator pump shouldn't effect you at constant throttle. Sounds like fuel supply problem. Work your way through the system and you'll get it.

I think I found the problem with the fuel supply once I start to enter into WOT. I just can't seem to figure out the dead/bog spot that is in the first quarter of throttling up. All advice seems to point to the accel. pump but I changed it out during rebuild And still have problem

 

[Bondo]

but I changed it out during rebuild And still have problem

Ayuh,.... Durin' the rebuild, did ya make sure the passages feedin' the acc. pump were good, 'n Clean,..??

Blown out with compressed air, 'n all that,..??

Check-balls all in place,..??

 

[Rick Stephens]

Plus you can visually check to see two streams of fuel squirting into the venturis when you work the throttle. Should be strong and equal on both sides.

 

[Coryb]

Ayuh,.... Durin' the rebuild, did ya make sure the passages feedin' the acc. pump were good, 'n Clean,..??

Blown out with compressed air, 'n all that,..??

Check-balls all in place,..??

I feel like I cleaned all passages out pretty good, I blew everything out, and I filled the bowl with cleaner and manually worked the accel. pump which was squirting equal amounts to both sides. My mercarb only has one check ball which isn't in the bottom of the pump well but under the retainer and spring which feeds the ven. cluster. I'm going to take it apart again re-clean it and double check everything.

 

[thumpar]

If you are getting the squirt of fuel it is not the accelerator pump. Did you try running it on a remote tank?