Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

[vi009dz]

I have a 2002 Mercury Bigfoot 25hp 4-stroke motor on my 21' pontoon boat. My first boat.

The boat ran okay last year, but was finicky at startup, and for some reason, would never rev past 3k rpm.

I put fuel stabilizer in the tank, ran it for a half hour or so in the fall and winterized it. This spring it will not start.

I pulled the carb off (Keihin, which I'm having a hard time finding info on), cleaned everything as best I could, and noticed that everything seemed fairly well in order; float moved freely, no gunk in the needle/seat, jet was clean, gaskets looked good.

I put it back together, reinstalled and still nothing (WILL fire off ether though). I pulled the plugs and they looked terrible; very black and sooty. I put in new plugs per OEM recommendation, and got a little bit of a sputter.

Where things stand right now.....on the carb, there is a vertical shaft that looks like it acts as an accelerator pump. When I move the likage, that shaft moves downward, I hear fluid squirt, and when I hit the key, it fires for a second then craps out, regardless of how I run the throttle to help it take off.

Also....fuel is coming out of the carb body around that shaft; there is no gasket or anything there, which I thought was weird. On the very outside lower edge of the carb, there is also a brass screw that goes down near the float bowl (screws in horizontally from the front of the carb). When I loosen that screw, I get fuel to leak out, which tells me the bowl is getting fuel.

Can anyone recommend where to go from here?? If you'd like pics, please let me know and I can provide them.

+ EDIT +

Fuel pump IS working. Removed carb and watched while cranking the motor; AMPLE fuel from the feed line.

-adam

 

[vi009dz]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

Just pulled the carb apart again....cleaned everything I possibly could with an ample amount of carb cleaner. All jets are open, float moves smoothly, needle & seat look clean. All passages I could spray out, I did so.....reassembled and have the EXACT same condition.

Part that is really getting me down is that I'm finding NO information on this carb. Its a Keihin, but only has stamped numbers of J68B and PJ23; neither of which show jack squat when googled.

I wrench on everything I own, and have yet to bring any kind of motorized vehicle to a true mechanic / garage for work. I've always done ANY repair myself, no matter how large.....but this is really frustrating the heck out of me and has me heading toward the Yellow Pages soon....

 

[hkeiner]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

There are lots of possibilities. I suggest that you check the spark with a spark tester to eliminate an ignition problem. Also, squeeze the fuel bulb while cranking the motor to see if the motor responds better to starting. Depending on the results of these two troubleshooting tests, the possibilities narrow down quite a bit and you may get better guesses to your problem.

 

[jbrown270]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

black plugs are usually a sign that the motor is running fairly rich, which would explain why you could only get to 3000 rpms and fuel is leaking around the carbs. the needle valve (float level) is most likely the cause. try adjusting it.

 

[CharlieB]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

No fuel should leak from the carb, anywhere.

Two common problems with that carb

Needle and seat
Invert the carb and blow into the fuel line to check for a seal. Carefully inspect the viton tip on the needle, ANY 'ring' type indentation showing where it seats then replace the needle

Itty bitty idle passages in the top of the carb throat under the top plate.
Three or four idle fuel passages that become exposed as the butterfly begins to open, very easily plugged and difficult to clean even with spray chemical cleaners. A very fine needle works well, followed by spray chemical.

 

[vi009dz]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

Thanks Charlie.....

Where that shaft drops down into the lower portion of the carb, should there be some kind of gasket, or grommet there? There is a brass portion with a C-shaped groove in it, that looks almost like a rubber gasket should slide down over and catch in that groove.

I noticed the small idle holes in the top, and sprayed them as best I could. I also stuck the red nozzle of the carb cleaner into every orfice I could in that top plate, and saw the spray on the other end of the hole where the passages go. I did not get after anything with a needle though; perhaps I should have. I just sprayed the snot out of everything and looked for holes in the jets by holding them up to the light...

The needle looked good with no indentation, or "ring" around the tip of it.

Sounds like you're familiar with this carb. Can you point me to ANY info on it? Keihin part number, Mercury part number??

Lastly...what is the little electronically-operated needle that screws to the top of the carb?? A choke of some kind??

 

[jrgunner]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

check this:
when you turn the carb upside down, with the float bowl off, the floats shoud be level. if they are not level they need adjusting. adjust by bending the tang (the tang is the thin metal piece between the float and the pin)
hope this helps

 

[jrgunner]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

A picture would help, I don't think I've seen one.

 

[vi009dz]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

Here are 3 pictures of the carb.....the vertical shaft that at times leaks fuel is the one covered in crud, directly below the idle set screw. If you move the throttle linkage by hand, but hold that shaft in place, THEN quickly drop that shaft, you get a shot of fuel squirting into the intake; kind of like an accelerator pump does. I have NO clue what the electrical thing on top of the carb is. There is a needle that sits into a tube, and that needle is spring loaded; apparently powering that thing makes the needle suck upward or move back downward??

KILLS me that I cannot find squat for info on this carb. The KEIHIN casting is on the motor-side of the carb where you have to remove it to see it.

 

[hkeiner]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

KILLS me that I cannot find squat for info on this carb.

When you say you can not find any info on your carb, have you checked the Mercury OEM shop manual for your motor? It should have all the info you are looking for. Purchasing an OEM shop manual is one of the first things to do when buying a motor. if one expects to work on it at all.

Pending your purchase of an OEM manual, the below linked thread has a link to a 25 Bigfoot manual. I took a quick look at the manual and the carb described in the manual seems to match the carb in your pictures.



http://forums.iboats.com/showthread.php?t=309079&highlight=manuals

 

[vi009dz]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

When you say you can not find any info on your carb, have you checked the Mercury OEM shop manual for your motor? It should have all the info you are looking for. Purchasing an OEM shop manual is one of the first things to do when buying a motor. if one expects to work on it at all.

Pending your purchase of an OEM manual, the below linked thread has a link to a 25 Bigfoot manual. I took a quick look at the manual and the carb described in the manual seems to match the carb in your pictures.

http://forums.iboats.com/showthread.php?t=309079&highlight=manuals

Thank you kindly for the link.....a hardcopy manual is pending delivery, but I'll definitely keep this one and look through it until the paper version arrives. That carb does indeed look like the correct one. I'll pull it AGAIN and check the float to make sure it looks correct when the carb is inverted.

 

[CharlieB]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

Merc used different carbs, depending on engine displacement and serial #'s.

Have your #'s ready and go here.

http://www.mercruiserparts.com/SelectProductLine.asp

You will find the complete parts diagrams and #'s for your motor.

The electric solenoid on yours is a temperature controlled enrichener that provides a small amount of additional fuel during warm up.

There is a bellows that should be on the accelerator pump shaft to keep dirt from causing any wear to the pump, it is not intended to seal fuel, the float level should keep the fuel level below this point.

I see that you have NOT removed the plug covering the idle jet, first picture, side view of the carb, above the throttle shaft.

This plug must be removed to properly clean/adj idle fuel.

EPA Regs, blah, blah, certified shops must reinstall a new plug.

 

[vi009dz]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

How do I remove that plug? We're talking the steel-colored one that's flush into the body of the carb, just above the butterfly shaft, correct???

 

[vi009dz]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

I pulled it apart yet again, and ran a needle through the small idle passages. It was tough to tell if they were clogged, but I slid a needle through and hosed everything sufficiently with carb cleaner.

I also inspected the tip of the needle for deformation; none found.

The float sits flat, and there is no adjustment to that 'tang' part; the entire float is plastic, including the tab where the needle attaches.

...........headed to the dealer to let them figure it out. ** bend over **

Disappointment is at an all time low, but thank you all very much for your pointers so far. I'll report back with what the issue was.

-adam

 

[kyle345]

Re: Mercury 25 Bigfoot 4S - Won't start; I'm not dumb...just new to boats

Any update on what this was I am havign a similar problem withthe same motor and am fearing the cost.