Can I Run A Hotter Plug

[Salmonseeker]

Hey guys,

I am having a problem with my motor not burning all the fuel/oil mix. I am thinking about possibly trying a hotter burning plug.

I use the boat mostly for trolling. Here is a link to my original thread about the problem. http://forums.iboats.com/showthread.php?t=194563

The Motor is a 2004 Johnson 50HP 2-stroke. The plugs Johnson recommends are Champion QL78YC gapped at .030"

Is there a hotter plug available for this motor? Perhaps another brand other than Champion?

 

[iwombat]

Re: Can I Run A Hotter Plug

You need to look at the plugs to determine if a hotter/colder plug is appropriate. What's the colour of the ceramic insulator, and overall condition?

 

[Salmonseeker]

Re: Can I Run A Hotter Plug

The insulator is a white with a slight brown tinge. I would say they look really good. The problem is the plugs are wet, especially the threads.

 

[Joe Reeves]

Re: Can I Run A Hotter Plug

That engine is not designed for trolling and will absolutely will load up on fuel if run in that mode for a long term period. Frankly, that QL78Y is as hot as I'd chance. The next jump could lead to pre-ignition.

Check your spark to make sure that (with the plugs removed) the spark will jump a 7/16" gap with a strong blue lightning like flame.... a real SNAP! If it will not, that will cause a problem similar to what you describe.

 

[Salmonseeker]

Re: Can I Run A Hotter Plug

Yeah, I was afraid it was not designed for trolling. But it is the only motor I have so I am stuck with it. I troll for hours with it. It has never fouled the plugs yet. But it seems to not burn all the fuel/oil mix.

If the wind is right when trolling I can smell unburnt fuel. I also have the extra fuel/oil mix in the crankcase that drains into the air silencer from the drain tube when the motor is tilted up.

I am beginning to think that this motor just runs this way.

Jay

 

[F_R]

Re: Can I Run A Hotter Plug

The heat range of the plugs doesn't have a dang thing to do with how much of the fuel gets burned. They only ignite it as the spark occurs--extremely quickly. Once ignited, the fuel burns over a period of time, like any fire. If the plugs were hot enough to ignite fuel outside the spark duration, you would have BIG problems.

 

[Salmonseeker]

Re: Can I Run A Hotter Plug

Well, I'm learning. It was suggested to me by a guy at work who races 2 stroke Go karts. Thats why I thought I would run it by you guys first. I will leave the plugs alone. I may check the spark as suggested above.

 

[seahorse5]

Re: Can I Run A Hotter Plug

If you want a hotter plug, the QL82YC plug works great gapped at .030".

Now if the motor is healthy internally, the carbs are clean and sync'd correctly and idle mixture screw is adjusted properly; that motor will troll or idle all day long using the standard QL78YC plugs. Many people overlook the thermostat operation and an open or missing thermostat can foul plugs. Use an infrared temp gun to make sure the top of the cylinder head is about 140?F while the motor is idling for a while.

 

[RCSConstruction]

Re: Can I Run A Hotter Plug

Is it a big No-No to run a leaner mix when trolling?

 

[JB]

Re: Can I Run A Hotter Plug

Open the gap on your QL78YC Champions to .040" if you want to do a lot of trolling.

Plugs are going to be wet because you turn off the spark and the engine turns a few revs before it stops. Fuel/air mix continues to be drawn in during those extrax revs but has no spark.

No carbed 2 stroke engine will burn all of the fuel/oil mix, at idle or WOT. That comes with the nature of scavenging with the intake mix. What makes you think you have a problem?

 

[Salmonseeker]

Re: Can I Run A Hotter Plug

The reason I thought I had a problem was because I had oil dripping from the fuel pump area. I first thought it was the OMS/VRO pump. It turned out to be a fuel/oil mixture leaking from the bottom of the air silencer. When the motor is tilted up during the trailer ride home. Fuel/oil mix would leak into the silencer through the drain hose between the crankcase and the silencer. If I turn the motor over by hand when the motor has been sitting I can see some fuel/oil mix shoot out the drain hole into the silencer.

I store the motor in the down position so it will fit in my garage. When I tilt the motor back down when home this mixture would then soak through the air silencer gasket and run down the lower cowl. It would then run down the steering bracket of the motor and I would then see it on the AV plate.

So I thought I might be running rich since this mixture was not burnt.

If this is normal, I guess I don't have a problem. I was worried it was a oil leak somewhere so I began investigating.

Does this sound normal to you guys?

One other question, When you open your plug gap to .040" will it affect other operating rpm's other than trolling? What exactly does this accomplish?


Thanks Jay

 

[iwombat]

Re: Can I Run A Hotter Plug

Your plugs are certainly telling you not to go any hotter. A plug right in the zone is toast-colored. Light to white and they may be a little on the hot side, still in the zone though.

Regardless of all that, you'll never get total complete combustion on a two stroke. Okay maybe, but that's right before it dies from running too lean.

 

[F_R]

Re: Can I Run A Hotter Plug

By the laws of nature, a coil builds up voltage until it is high enough to jump the gap in the plug, then zap! So a wider gap requires higher voltage to fire it. That means that if you are running wider gaps, you are running higher spark voltages. Then we get into all the engineering theories about higher voltage spark burning through the gunk and stuff. So then the question comes up, why not run .050 or .080? Reason is there is a limit to how much the coil can put out. If the limit is say 30,000 volts and the plug requires 40,000, then it won't fire, resulting in a miss.

 

[Salmonseeker]

Re: Can I Run A Hotter Plug

Thanks guys,

I will stick with the original plugs. I will try and gap them at .040" since the motor spends about 90% of its time trolling.

Jay

 

[seahorse5]

Re: Can I Run A Hotter Plug

Be aware that if the gap wears to much more than .040", you may get false NO OIL alarms. The RFI (interference) from the voltage required to jump the larger gap may fool the "VRO" computer circuit to sound a false alarm. That is why the factory recommends .030" gap

 

[Texasmark]

Re: Can I Run A Hotter Plug

Something you might try.

Years ago, Merc built a slanted engine in the small boat fishing engines. I know the 9.8 was designed that way. Properly mounted on the transom, the whole engine was tilted back (lower unit end back) about 15 degrees from vertical. This included the combustion chambers.

Theory was that fuel would tend to pool in the cylinders and not completely burn when trolling. So the design deliberately tilted the cylinder up so that the fuel couldn't pool at the head.

When you are through with all the other suggestions, you might just tilt your engine up when trolling and see if that doesn't help.....how much? As much as feels reasonable. Besides that it will reduce your effective thrust and cause you to increase your rpm's somewhat which will help to reduce your problem.

Mark

 

[Salmonseeker]

Re: Can I Run A Hotter Plug

Be aware that if the gap wears to much more than .040", you may get false NO OIL alarms. The RFI (interference) from the voltage required to jump the larger gap may fool the "VRO" computer circuit to sound a false alarm. That is why the factory recommends .030" gap

Actually, I did a search after I posted about trying the .040" gap and found a few articles about this. OMC recommended a .040" gap for a couple of years but began having false oil alarms, so they switched back to .030".

Honestly the motor trolls fine. I am just being to picky. So what if some fuel is unburnt. As long as it is not fouling the plugs it should be okay. I carry a spare set in the boat, just in case. I just thought maybe something was wrong with the motor. It is probably okay.

 

[Salmonseeker]

Re: Can I Run A Hotter Plug

Something you might try.

Years ago, Merc built a slanted engine in the small boat fishing engines. I know the 9.8 was designed that way. Properly mounted on the transom, the whole engine was tilted back (lower unit end back) about 15 degrees from vertical. This included the combustion chambers.

Theory was that fuel would tend to pool in the cylinders and not completely burn when trolling. So the design deliberately tilted the cylinder up so that the fuel couldn't pool at the head.

When you are through with all the other suggestions, you might just tilt your engine up when trolling and see if that doesn't help.....how much? As much as feels reasonable. Besides that it will reduce your effective thrust and cause you to increase your rpm's somewhat which will help to reduce your problem.

Mark

Hey Mark this gives me an idea. Occasionally I would like to troll a bit slower than my motor allows. I don't want to install a trolling plate or anything. I might try tilting the motor up and see if I can get a bit slower. Most of the time thought I troll at about 1000 RPM's.

Jay