Engine dies when going from idle, straight to full throttle

[GXPWeasel]

Thanks for the comments here guys, espeicallyl Chill'n the most, & belercous.
I do in fact have surface gap plugs, (which like I said, were totally new to me before this boat). I installed them mid-season last year, and ran the boat maybe 4 times after that, for a total of 5 hours. I purchased NGK's as that's a brand I'ave always had good luck with. I can however see how they could be fouled, I guess, since last last season, and early this season was a lot of trolling and going along below 4k rpm. I will probably just purchase new plugs, as they were only like $4 a piece. I think I will take my plugs to Auto zone or somewehre though, and try to find a plug that has the same threads and lenght, and see if I can get a traditional style plug. I would prefer this anyways, but don't want to worry about hitting the piston either.

While I"m there, I'll change the in-line engine fuel filter, as I have never changed it, in 3 years of ownership, and it appears to be original as it still has the zip ties holding the fuel lines tight, and not normal hose clamps.

Thanks again guys.

[chill'nthemost]

Let's us know that it fixed the problem (thinking positive ) If it isn't a pain try the plugs first and see how it runs. I hate doing a couple of things and wounding which was the fix, or sometimes it was a combination. I think NGK's are great. I've always ran Ford Auto lite in everything (my Harley too) for years just because a old tec I really respected ran them. Cool things about these forums, if this cures your issue, down the road it's going to help someone else too

[GXPWeasel]

Just got off the phone with my selling dealership/shop.
I called to ask about a part number for a traditional syle spark plug for the motor, instead of the rim-fire style. I actually was able to talk to a mechanic, and not the office clerk, and he told me they didn't show anything in their manual, and what they actually recommended was what I have anyways, NKG BUHW-2's. After explaining my situation for about 5 minutes, he said that it actually sounded like a fuel starvation issue, and not a spark issue. He said the obvious would be a cracked or bad fuel line, or soft ball, but that my symptoms didnt' match that. He suggested a free / easy test, that the next time my engine sounded like it was going to die when going from idle to full throttle, to give it a little bit of choke. If this fixed the problem, then I more than likely had a fuel starvation issue. He has seen a few this season already, and most often it is caused by ethanol in the fuel, and it jellies, or solidifies over time, in the carb, and causes flow issues in the carbs. This is exactly what I didn't want to hear, as I didn't want to have to re-build the carbs on the motor. I haven't done this before, but since I am mechanically inclined, I will tackle this myself, if I need to. Anyone know where I can find the proper procedures on how to re-build the carbs on an '05 Mercury 90hp 2 stroke?

[curtiscapk]

Greg piece of cake! Call me when you are ready and I will walk you through it.

REplace your lines too mine were full of shit.

[GregF]

I thought of that "choke" thing myself but I wasn't sure if the enricher worked when it was not cranking. It is not really a choke. They just open a solenoid valve that squirts a little extra gas in there.

I seem to remember there was a similar thing when you slam down the throttle but I don't remember how that worked and I gave my shop manual to the guy who bought my old 2 stroke 75 (pretty much the exact same engine you have).

[chill'nthemost]

I wouldn't disagree with the Merc tec, but before I did anything I'd still throw a set of new plugs, whatever style you want (personally I'd not run the non-gap able plugs, if they were so cool they would be the automotive industry standard) Remember when Split Fires were going to revolutionize the automotive industry? They're still making spark plugs but they discontinued the "v" design. Your Merc tec know way more than I do for sure, but if it isn't a fuel problem you'll foul your plugs for sure using the choke. Plugs are cheep and you need to start somewhere

[GregF]

The surface gap plugs are a 2 stroke thing. That does not apply to cars unless you have a Trebant.

[chill'nthemost]

Another article I found. This guy claims he has found burned pistions form motors using gap plugs with they were designed for surface gap Until today I didn't know there was such a thing


Bob: Once you understand the engineering behind sparkplugs, then it all becomes simple.

Sparkplugs are designed in Heat Ranges for different applications. The heat range indicates basically how hot the plug will run in the engine.

The center electrode and porcelain insulator of the sparkplug are exposed to combustion temperatures and with each cycle they heat and cool.

The amount of center electrode and porcelain exposed to combustion temperature determines how hot they will run. Surface gap plugs have almost no electrode and insulator exposed to temperature AND the steel shell of the plug body provides a short path for cooling through the cylinder head. These plugs run COLD. In a 2 cycle engine where there is one power pulse per revolution, (twice that of a 4 cycle) the plug is exposed to MORE heat and less cooling time, so frequently, these plugs are specified for outboard engines.

On the positive side, these plugs protect the engine from damage. Yes, I have seen engines designed for surface gap plugs with holes melted in the piston crowns as a result of using bent electrode plugs --Evinrude QL77 type--(which run much hotter). On the negative side, these surface gap plugs require the extremely high voltage of an electronic ignition. Most will not fire at low speeds with a magneto ignition or a regular points and battery ignition. The do tend to foul and misfire with prolonged trolling or low speed operation.

Many people say that there is no danger in substituting bent electrode plugs and the idle substantially improves, BUT: Do you think it was an accident that Mercury engineers specify the L76V surface gap plug for their engines?

As far as multiple electrode plugs like Splitfire or Bosch, all a bunch of marketing hype. B.S. and hogwash of the first degree.

Electricity takes the shortest path OR the path of least resistance. With multiple electrode plugs like the 4 electrode Bosch, the spark will preferentially jump to only one electrode until that electrode has higher resistance than another one. There will NOT be multiple sparks at one time. (Note that MSD ignition modules DO generate multiple sparks at the same ignition cycle but I do not have an opinion on any benefits outside of racing)

Hotter spark? Phooey! Blue-white is blue-white. What is a couple of hundred degrees difference (if any at all) in a couple of thousand when there is more than sufficient temperature to ignite the air/fuel mixture? Again, marketing hype! Why use a propane torch to ignite a cigarette when a match will do it just as well?

For your engine, use the BRAND of sparkplug that you like in the STYLE specified by the manufacturer.

[GXPWeasel]

Thanks again Chill'n themost & Greg.
I am taking the boat out tomorrow, and will try replacing the plugs before I go out to see if that's it. You're right, as they are a chep fix, and even if they don't fix, I can always use spares. IF that don't work, I'll try the choke thing just once or twice to see if that fixes it. If so, I'll rebuild the carbs at the end of the season. This really doesn't affect how we use the boat much at all. Since I know it will normally bog down, I don't punch the throttle right away, I let it get to about 1,000 rpm first, then punch it. This doesn't reallymatter on a tube or knee board, but would drive me nuts on a ski boat.

The Merc mecanic also did say he wouldn't run the traditional style plugs, as the surface gap is what is was designed for.

Thanks again guys.

[belercous]

If the plugs & plug wires aren't the problem and you're going to wait until the end of the season, try running Sea-Foam in the gas. Enough of it in fresh gas will dissolve the deposits. When there are deposits in the jets an engine tends to run rough if they're in the idle systems, and won't develop full power at W.O.T. or the power comes on slower if the main jets are clogged.

A spot you might want to check on a Merc. O.B. is the fuel line that runs from the engine's fuel inlet to the fuel pump. I had to replace that line last year. It's kinda hidden, it runs under the air intake manifold. Take the cover off and pump the primer bulb. Look for fuel in the bottom of the cowling.
Now that I think of it, this sounds like it could very well be your problem. As the line is on the inlet side of the fuel pump, a sudden decrease in fuel on the outlet side (as when going W.O.T. suddenly) will cause the pump to have a higher pressure differential as the pump needs to draw more fuel in to fill the carbs. If the line is cracked it will allow air to be sucked in to the fuel system, causing the engine to stumble. Once the pressures equalize the problem will go away. The line is a factory part and is not real expensive (I think it was about $25.00-30.00 last year).

I took the carbs on my boat last year and cleaned them out (before I owned half of it. That bought me some free boat time.) in the water. Replace the rubber fuel lines. if you do it. It took me about 2 hours to remove, clean & reinstall all 4 and I've never had a boat engine apart in my life.

[GXPWeasel]

Well, the new plugs didn't help it. We took her out Saturday for the entire day, and ran a 1/2 tank ( 8 gallons ) of fresh gas through her, and still the same problem. Also, the choke thing the mechanic told me to do didn't help either, it may have actually made it worse the 2 times I tried it. So, maybe it is a fuel starvation issue. I will have the boat out at the lake the entire weekend coming up, and the thing still runs fine, and now that I know how to accelerate, I can even predict when it will cut out, so pulling the knee boards and tube still work out great. Still no problems at all when going from 1200 or so rpm, up to full throttle, and she runs excellent once there.

I did notice too that she is harder to start though once warm. There are times when I can just flip the key, and she starts right up. But if we have sat for about 10 minutes, wating to for the next person to get ready to knee board or something, then I have to give it throttle for the motor to start. Maybe there is a issue with the fuel bulb or line that is letting the gas go back to the tank. ? . ?

Once the weekends over, I will go over it with a fine tooth comb on the fuel lines, or maybe even while I'm at the lake, since it will be a guys camping trip, and I should have some slack time without the wife and little girl.

Thanks again for the help guys. Keep the suggestions comming, and I'll keep trying them. If it comes to rebuilding the carbs, I'll waint until the season is over for us to dig into that.

[Tmore]

Next time you are out, check the bulb to make sure it is staying hard the whole time. You may need to re-pump it throughout the day, and it may need replacing.

[belercous]

This doesn't seem like a fuel starvation issue, it sounds like the engine is running rich. I'm pretty new to boat motors, but I've seen the same problem on other 2 cycle engines with a vacuum or pressure operated fuel pump.

Check what kind of fuel pump your motor has, but if it's a vacuum or pressure operated unit (run off of crankcase pressure or intake vacuum) I'd check the diaphram seperating the pump from the crank/intake. One small hole is all it takes to introduce extra fuel in the engine.

How did the plugs look? Black soot on them is carbon from running rich. Light gray is a proper mixture.

[GregF]

It just sounds like a 2 stroke to me. That is why I bought a 4 stroke. I was tired of all of that "is it too lean, is it too rich, too hot, too cold etc etc"?

[HandymanHerb]

Boo who, them 2 strokes are just to hard to figure,i think I get one I have to change the oil in weather I get to use it or not and I don't care about the extra 400 pounds it adds to the back of the toon.

Four strokes mean extra maintance,oil changes, mine changes the oil itself every time I use it, so I stick with 2 strokes and still want a E-Tec in the future as soon as we can get obama out of office and the get money started flowing again.