Pontoon Boat & Deck Boat Forum

Hey guys, the subject says it all.

I haven't had this problem in the past, but the last couple of times that we have gone out on the boat, this is the problem I'm getting. I can go from idle, to slow speed pretty easilly, then punch it, and it takes off. However if I am sitting there at idle, or even just in gear to tighten up the rope for kneeboarders or a tuber, and then punch it to get them up, it will die.

Any suggestions? I have good fuel, as I have filled the tank just before going out both times this has happened, and I know I'm using my 2 stroke oil like I should, as it's use rate is the same as it has always been sinve I've owned the boat. I had brand new spark plugs at the end of last season, and they maybe have 25 hours of running time on them now. I stored the boat last winter with them in it, and with stabil, but I didn't fog the motor, and again, she wasn't doing this at the beginning of the season. The only thing I haven't done is change on-motor fuel filter. This is something I'm going to do asap. Should I use the Mercury filter, or can I use an in-line car fuel filter that costs less because it isn't a boat part?

Let me hear it guys, what to you recommend?

Spark + Air + Fuel

I would double check your plugs again (they could be fouled, even after only 25 hours of use) then change the fuel filter. Sure sounds like it is starving for fuel.

Yep, how bout your bulb might have a slight leak you really don't notice till you want every ounce of fuel in .0005 a second? at least yours runs, so who am I to give advice?

Haven't checked the fuel bulb yet, thought it would be best to replace the fuel filter first. I have taken the plugs out to look see, and they're fine. I cleaned them just to be sure, and it made no difference.

Does anyone know if I can use a car's in-line fuel filter that I can get at an auto parts store, instead of paying $20 for something that is worth about $4???

I used the inline car store fuel filter with no ill effects.

schmir wrote:I used the inline car store fuel filter with no ill effects.

That's what I was thinking, but wanted to be sure. In my mind, it shouldn't make any difference, as gas is gas, and a filter is a filter, in this sense.

If this were on a vehicle, I'd be 100% confident in the direction to go, but I just don't know much about 2 strokes.

I had this same problem on my pontoon however my motor is a 90HP 4 stroke outboard. Going from idle to WOT killed the motor but if I went slow it worked fine.

The problem was on one of my spark plugs the gap on the plug was almost closed, I put in a new set of plugs and gapped them properly and it fixed the problem perfectly.

I'd pull your plugs out and verify the gaps are correct and make sure there are no cracks in the porcelain (as it would have the same effect) if it was grounding it out.

pontoon_mike wrote:I had this same problem on my pontoon however my motor is a 90HP 4 stroke outboard. Going from idle to WOT killed the motor but if I went slow it worked fine.

The problem was on one of my spark plugs the gap on the plug was almost closed, I put in a new set of plugs and gapped them properly and it fixed the problem perfectly.

I'd pull your plugs out and verify the gaps are correct and make sure there are no cracks in the porcelain (as it would have the same effect) if it was grounding it out.

There aren't any gaps on 2 stroke plugs, just an annode on the plug. THis was new news to me when I replaced them last year.

GXPWeasel wrote:

pontoon_mike wrote:I had this same problem on my pontoon however my motor is a 90HP 4 stroke outboard. Going from idle to WOT killed the motor but if I went slow it worked fine.

The problem was on one of my spark plugs the gap on the plug was almost closed, I put in a new set of plugs and gapped them properly and it fixed the problem perfectly.

I'd pull your plugs out and verify the gaps are correct and make sure there are no cracks in the porcelain (as it would have the same effect) if it was grounding it out.

There aren't any gaps on 2 stroke plugs, just an annode on the plug. THis was new news to me when I replaced them last year.

There are gaps on my 2 stroke plugs. What is the plug you are running?

Is it possible this is what you're running for plugs? (from another forum)

Dave: Go to a NAPA or auto parts or marine dealer and have them show you a surface gap plug. Surface gap plugs have a center electrode but no conventional side electrode. The spark plug shell forms the side electrode. There is a ring gap between the center and side of the plug that the spark must jump. Surface gap plugs are basically by design VERY cold plugs and are prone to fouling at low speed. Surface gap plugs are NOTHING BUT AN EXPENSIVE GIMMICK and violate basic principles of electron flow; i.e. spark jumps better between sharp points, NOT round or smooth surfaces like surface gap plugs have. That is why lightening rods have sharp points, NOT round spheres. Surface gap plugs are a MARKETING GIMMICK developed by the Mercury Marine and Champion Spark Plug Company's about 20 years ago. They did this so they could charge $5.00 for a plug that previouly sold for $1.00. I have replaced all the surface gap plugs in my 1990, 150 hp, 5 cylinder Force engine and the engine actually starts and idels MUCH better. It also seems to have better throttle response; but I have no scienific way of measuring this. If you go with standard J-gap plugs, you will need to carefully check piston clearance BEFORE cranking engine. Do this by removing all plugs and install a J-gap plug and rotate the crankshaft several revolutions by hand. Do this for each cylinder, one at a time. Set gap at 0.030". Be sure to read the plug after running the engine for a short time under full load to make sure the heat range is correct. I have had excellent service with NGK plugs and run them in everything I own with a two stroke engine including chain saw



I see where Merc recommends this style plug for some motors, but conventional plugs have been used and are still used in 2 strokes for years. I think I'd try a set of gap-able plugs and see what happens. Keep in mind what I pasted here is just one mans opinion too.

There are gaps in 2 cycle plugs, they wouldn't work if there wasn't. The gap will get bigger as the plug is used. The spark needs to be blue, not yellow. Even then a plug could be bad as it will be under pressure in the engine, but not in free air. One cannot always see a crack in the porcelain or carbon tracking (which a crack will cause, but carbon tracking is not limited to cracked plugs).

Chill'n is correct, most of the new spark-plug technology is marketing hype. The standard style plugs have worked fine for over 100 years and they still do. Just make sure the plugs are the correct heat range (manufacturer's specs).

You can trouble-shoot the plugs by replacing one at a time, when the problem goes away or lessens, that's a bad plug (if it lessens, you have more than one bad plug). Or you could replace all of them; it depends if you have more time than money, or vice-versa.

Make sure the air intake is not obstructed.

If this was a 4 cycle engine, I'd say look at the accelerator pump(s), but 2 cycle engines don't usually have them.

An automotive fuel filter will work just fine, there's no difference unless the boat has a screw-on type fuel filter (looks like an oil filter) which will capture water. I doubt this would be the problem as the engine would not run for more than a few seconds at W.O.T. if it was dirty or the fuel line was kinked. If the bulb had a leak the engine would rev-up but then drop as there is fuel in the float bowls (presuming this is a carburated engine).

I'm not a big fan of mechanic-in-a-can, but if there are deposits left from last year in the fuel system try running Sea-Foam. It make take a few cans. I'm syre everyone knows this, but it can't be stressed enough: before an engine (any engine) is put up for the season, disconnect the fuel line and run the engine till it dies. Then choke/prime it and crank it some more.

If the engine runs rough (at any speed), idling lower, or not giving the same rpms at W.O.T. as it used to, there is a problem. Rarely is it compression. As engines since the 70's don't have points, its not the timing (unless plug wires are crossed). To check if the plug wires are bad (and they do go bad), remove the cover and run the engine at night. If there is any arcing it will show up then and one can hear a slight ticking noise. If one wire is bad, replace them all unless it went bad due to chafing. If changing the plugs doesn't help, the problem is likely in the fuel delivery system, most often in one of the carbs, or a partially clogged injector.

Sorry to prattle on so. If none of these thing fix the problem, please say so, there are a couple of other things, but they're not as likely to fail.

They use surface gap plugs on most if not all old technology 2 strokes. There is nothing to adjust It is just the electrode and the base of the plug. The spark goes sideways.

Greg; I've seen them, they're marketing hype, what do they offer? The gap will keep getting smaller as the electrode wears. No way to adjust the gap on them, but on the standard plugs the gap can be adjusted. Standard plugs are a lot cheaper and work just as good. There may be a slight bit of difference in a tricked-out hi-performnace engine, but not in a stock engine.

If one feels better by spending more, go for it. But there are certain things which are pure marketing hype that offer nothing but psychological "feel-good." Higher octane gasoline is one. Fuel injector clening additives are another (unless you have problems there is no need for such), the latest hi-tech spark plugs are another, and expensive oil is a sham, especially on 2 stroke engines.

I've seen what synthetic oil does for a (4 cycle) engine that's been used to running regular oil; it makes a lot of new leaks. (Ptfe resin [Slick 50] additives do work however, but not in a 2 cycle) We run the $11.00/gal Wal-mart oil in our Mercury engine and have for years. We could spend $30.00/for the same result, but why?

Lemme clue ya'll in on 2 cycle engines; oil is oil. I've ran Wesson thru my dirt bikes when I had nothing else, worked fine. I've even heated up bacon grease and ran it thru 2 cycle engines when I had nothing else, worked fine but made me hungry. As long as the oil is evenly dispersed (and it took a bit of shaking to get the bacon grease dissolved) a 2 cycle engine is very forgiving. I wouldn't recommend using diesel as it's pretty thin, but it would work in a pinch, just don't run the engine W.O.T. and use a bit more.

And those gas/oil ratios, b.s., they're flexible (except on break-in). I've seen 2 cycles that said they required 24:1 up to 128:1 (golf cart). Used to be hi-performace dirt bikes ran 50:1, and those machines were run W.O.T. all day long. As a good rule, one can never go wrong using 1 oz. oil to 1 quart gas. that will not hurt any 2 cycle engine, and if you're a bit short on oil, it still won't hurt the engine to run 1 oz oil to 2 quarts gas.

belercous wrote:Greg; I've seen them, they're marketing hype, what do they offer? The gap will keep getting smaller as the electrode wears. No way to adjust the gap on them, but on the standard plugs the gap can be adjusted. Standard plugs are a lot cheaper and work just as good. There may be a slight bit of difference in a tricked-out hi-performnace engine, but not in a stock engine.

If one feels better by spending more, go for it. But there are certain things which are pure marketing hype that offer nothing but psychological "feel-good." Higher octane gasoline is one. Fuel injector clening additives are another (unless you have problems there is no need for such), the latest hi-tech spark plugs are another, and expensive oil is a sham, especially on 2 stroke engines.

I've seen what synthetic oil does for a (4 cycle) engine that's been used to running regular oil; it makes a lot of new leaks. (Ptfe resin [Slick 50] additives do work however, but not in a 2 cycle) We run the $11.00/gal Wal-mart oil in our Mercury engine and have for years. We could spend $30.00/for the same result, but why?

Lemme clue ya'll in on 2 cycle engines; oil is oil. I've ran Wesson thru my dirt bikes when I had nothing else, worked fine. I've even heated up bacon grease and ran it thru 2 cycle engines when I had nothing else, worked fine but made me hungry. As long as the oil is evenly dispersed (and it took a bit of shaking to get the bacon grease dissolved) a 2 cycle engine is very forgiving. I wouldn't recommend using diesel as it's pretty thin, but it would work in a pinch, just don't run the engine W.O.T. and use a bit more.

And those gas/oil ratios, b.s., they're flexible (except on break-in). I've seen 2 cycles that said they required 24:1 up to 128:1 (golf cart). Used to be hi-performace dirt bikes ran 50:1, and those machines were run W.O.T. all day long. As a good rule, one can never go wrong using 1 oz. oil to 1 quart gas. that will not hurt any 2 cycle engine, and if you're a bit short on oil, it still won't hurt the engine to run 1 oz oil to 2 quarts gas.

belercous I spent years calling on tecs in my tool truck. I think I'm a pretty good judge of guy's who know their trade and I'm going to say you've been around the block a time or two.

Mercury fell for the scam because they shipped new motors with surface gap plugs in the early 90s. I ran them for years until my motor was getting tired and I was willing to try anything to get it to run better so I went with a regular plug. It didn't fix anything.

BTW the theory is they are a lot harder to foul than a regular plug.