View Full Version : Motor Question

11-20-2005, 07:39 AM
I have a 25 hp Merc. Big Foot. I put new plugs in it and changed the oil about six trips ago. That's all I've done to it in the two years I've had it, and it's always run great. Now it's starting to run pretty rough when I first take off, and it actually stalled out on me twice last Friday. I use the boat year round at least once a month, somtimes up to four times a month, so I don't think it could be bad gas. The fuel filter looks good too. Can any of you mechanics out there give me some advice? Is there somthing I could check, or should I take it to a shop? Thanks for any info. DF30 ???

11-20-2005, 08:47 AM
Couple things to consider; when you end up back at the dock are you leaving the gas in the carb, or running the motor dry? Fuel left in the carb can gum the works up pretty fast.

If fuel injected, never mind.

Other thing, is the gas. I always run StaBil in my tanks, even if I know I'm gonn run the tank dry, keeps it fresher.

Pull the plugs and check them out, they should look similar to each other, the right look is kinda brownish-black, not real oily. If one it a lot different than the other, might be electrical of a fouled plug.

You mention the fuel filter looking good, might still have issues and look ok, they are cheap to replace.

11-20-2005, 10:02 AM
Thanks Mr. T, It's a 98, and I'm not sure it's fuel injected, but I do run the fuel out while I go get the truck. Can I get StaBil at Kragen's? You mentioned electrical. The two times it did stall, the depth finder went out. Could that be an indication on an electrical problem? Thanks again,DF30

11-20-2005, 11:47 AM
sounds like a bad ground or positive lead

11-20-2005, 01:01 PM
Yea, At first I thought it was electrical too, but it was running so rough like a fuel problem.

11-22-2005, 10:48 PM
Definately check all electrical connections. If the fish finder went out at the same time it sounds likely that this is the problem. If this is not the problem there is a possibility that you may have some water in the carburetor. There may be a drain on the bowl. If so you may want to open it up and let some fuel flow to flush the contamintion. Another thing to consider is if you used a different brand of spark plugs the engine may not work properly with them. Change them out for the factory brand and part number. It's cheap and easy and can at least eliminate one possibility.

Good luck

11-23-2005, 12:21 AM
Just to narrow down the possibilities a compression test is quick and easy and wouldn’t hurt. If you don’t know the correct compression at least make sure all cylinders are the same.

11-23-2005, 07:46 AM
Thanks for the input folks. I took the plugs out and they still look good. I am thinking more and more that it's electrical. This past summer my depth finder went out and Lowrance sent me a new one. They also sent me a new transducer. Well, I replaced both of them and there was a ton of wires down there. There possibly could be a short. The only thing is, it didn't start running so rough for a few months after. I might have to take her in to the shop. If I do take her in, can anybody recommend a shop in the general Modesto area? ??? Thanks, DF30

11-23-2005, 07:12 PM
You should at least check both connections at the battery. Take them off, clean and reinstall with some anti-corosion grease (available at Kragens). Especially in a marine environment corrosion can build up quickly. If the problem is affecting more than one system it is likely to be a main connection. It's worth a look and may save you money and fishing time.

Good luck.

11-24-2005, 10:29 AM
DF30 - Not to say this is your problem but thought it best to inform you.
I also have a Bigfoot 25. I faced a problem within the first year of owning the new motor. It would run great and then lose power and stutter and then pick up and run fine again. It did emit white smoke when this happened. It would use a quart of oil and I found oil had been sucked into the carb. I took it back to the dealer twice with no good results. I finally did a Web search and found another case identical to mine.
It seems that the factory installed the wrong power head gaskets in some of these motors. Most repair shops had no information on this subject.
I took the motor back to the shop and informed them of the info I had found. They called the factory and sure enough, mine needed the replacement gaskets and the repair was totally covered under the warrantee. Now all is fine.

11-24-2005, 10:46 AM
Well, I'm not a mechanic, but I checked everything I could. I finally broke down and took it in yesterday and sure enough the carb needs to have a "kit" put in it. I'm guessing that means it needs to be rebuilt. I'm having that a a few other things done to her all for under $200.00. I sure hope that takes care of the problem. Thanks to all for your input. Tight lines, and Happy Thanksgiving. DF30

11-24-2005, 01:17 PM
Do you have an internal fuel tank?

The reason I'm asking is I had a problem with a new motor this year and it was caused by the ethanol/gasoline which absorbs water and trashes the carbs.

The fix was a "Kit" which is larger and longer jets and an inline water fuel seperating filter (Raycor)and make sure it's ten micron and always treating your fuel with a stabalizer like Stabul.

There are all sorts of problems starting to surface with the chaneover to ethanol based fuel here in California.

A lot of people are going to be pissed come next spring when they attempt to use their boats and they won't run worth beans beacause of this fuel.

11-24-2005, 06:29 PM
Should I use stabul or bil what ever it's called in every tank of gas? And I think one of you said I could get it at Kragen's? Also, I use my boat all year. Is there anything I need to do like the folks that put theirs up for the winter do? DF30

11-24-2005, 06:31 PM
Yep. Use it all the time in boat fuel. It's available most anywhere including Walmart. And run the fuel out of your carb after every trip.

11-24-2005, 06:58 PM
the way i was told besides sta-bil and running the carb dry spray a little marine fogging oil in the intake till it start to smoke. this puts oil on the valve stems and on the insides to retard rust from condensation. ??