800cc plug gap?

[DonoBBD]

a blowtorch in the engine compartment? what would that do?

the plug gaps are important... and they are not gapped correctly from the spark plug company. i believe they are gapped to like .036 and theyre supposed to be .022... so thats almost double what they should be

what are your high speed screws and low speed screws set to? and at what RPM are you idling?

Is this true? Should the plug gap be set to .022" out of the box they are gaped at .043"

Cheers Don.

 

[RFoster130]

.022 is where i set them. They are usually pretty close out of the box. I think like .028 was the biggest gap i found out of the box.

 

[DonoBBD]

See here is the racing theory.

It is easy to imagine your ignitions available voltage output as a piece of rope and lets for the sake of argument say this rope is 10 inches long and represents 40k volts. If the initial voltage required to ionize the air gap is 24k volts or 6 inches of rope then we only have 4 inches of rope left to keep the plug burning (16k volts). So theoretically if we raised the gap and now the voltage required on this same engine increased to 28k volts (7 inches), we would then have only 3 inches of rope left to keep the plug firing.

So the theory is that if the gap is big there is less duration of spark. The extra inches of rope left over is shorter and so will spark duration be shorter. This is fine with high RPM low air fuel ratio's less dense mixture.

If the gap is smaller the spark starts sooner and will last longer. The extra inches of rope left over is longer and the spark duration is longer. Longer spark is better with high compression and high fuel air density. This will help with torque (boats need) and fire higher density cylinder pressures.

No wonder why we are fouling plugs on the 800 when most all NGK br8 plugs are gaped .036 to .045

Don.

 

[RFoster130]

I have never had a problem. I never foul plugs. I change them once a year just for the heck of it. Like i said, they are usually close right out of the box. biggest gap i find is like .028 If you are fouling plugs, I would be looking at the oil injection system.

 

[korn82787]

See here is the racing theory.

It is easy to imagine your ignitions available voltage output as a piece of rope and lets for the sake of argument say this rope is 10 inches long and represents 40k volts. If the initial voltage required to ionize the air gap is 24k volts or 6 inches of rope then we only have 4 inches of rope left to keep the plug burning (16k volts). So theoretically if we raised the gap and now the voltage required on this same engine increased to 28k volts (7 inches), we would then have only 3 inches of rope left to keep the plug firing.

So the theory is that if the gap is big there is less duration of spark. The extra inches of rope left over is shorter and so will spark duration be shorter. This is fine with high RPM low air fuel ratio's less dense mixture.

If the gap is smaller the spark starts sooner and will last longer. The extra inches of rope left over is longer and the spark duration is longer. Longer spark is better with high compression and high fuel air density. This will help with torque (boats need) and fire higher density cylinder pressures.

No wonder why we are fouling plugs on the 800 when most all NGK br8 plugs are gaped .036 to .045

Don.

Excellent explanation of plugs and the comparison to a rope. That makes explaining spark plugs very easy to understand. I will have to remember that... Never though of explaining plugs that way. >.<

Good advice.

Two strokes foul plugs, end of story. Always have extra plugs with you because its the one time, you don't have them you will have problems. Oh and last I checked, it is still a boat... that should say enough.

 

[brock1]

Excellent explanation of plugs and the comparison to a rope. That makes explaining spark plugs very easy to understand. I will have to remember that... Never though of explaining plugs that way. >.<

Good advice.

Two strokes foul plugs, end of story. Always have extra plugs with you because its the one time, you don't have them you will have problems. Oh and last I checked, it is still a boat... that should say enough.

thats true 2 strokes do foul plugs (BUT NOT IF ITS RUNNING CORRECTLY ) like stated i also only change mine once a year give you oil injection a look over

 

[korn82787]

thats true 2 strokes do foul plugs (BUT NOT IF ITS RUNNING CORRECTLY ) like stated i also only change mine once a year give you oil injection a look over

No argument, but there is always the case of "Jim-Bob Boat Owner" not understanding the mechanics of spark fuel and air and if it runs, its good.

Plus, how many times do we see needles and seats go bad and hydro-locking or hard starting issues come about? I think I've read 10-20 threads about that today. (Haven't really browsed in a week and a half) :cheers:

 

[DonoBBD]

I have never had a problem. I never foul plugs. I change them once a year just for the heck of it. Like i said, they are usually close right out of the box. biggest gap i find is like .028 If you are fouling plugs, I would be looking at the oil injection system.

Ya the shop that dropped the new motor in had the wrong plugs in it all together. I pulled the plugs checked the gap but never looked at the plug heat. They were copper core NGK BR9ES. Copper will cool the plug a heat range for cold starts then the plugs were one heat range to cool and the gap was twice the correct size.

In short the four BR8ES solid cores I picked up the biggest gap was .024 and I closed them all to .022"s. The best plug I have ever run on the sleds is the NGK EIX solid cores as well. Might scoop up a set for the doo. They are like $14 bucks each.

korn82787 thanks for the kind words. I have never fouled and EIX in the sleds and the cold starts are great even at -40C.

Cheers Don.