Spark plugs question...

[55'Fleetwin7.5]

On my 57' 35hp Lark, I just changed the plugs... I used NGK's for the first time... After 2 hours out on the water 3/4 of the time WOT and some time at trolling speeds. it ran fine at trolling but a bit rough just above that... when I got home, I pulled them and the top plug looked much worse than the bottom... see pic.

What do you think?

Thanks, Tom

 

[clevecan]

Re: Spark plugs question...

I too ran a NGK and it did not seem to run as good as the ones with no elctrode, I wonder if the weard ones are better?

 

[ezeke]

Re: Spark plugs question...

Why not follow the recommendations of BRP?

The motors that you are working on were designed and tested using Champion plugs.

Spark plug charts 1952 through 2007 including Ficht, DI, E-Tec and 4 Stroke are available.​

​

Boatsetup.com has recently added the spark plug update information from BRP:

http://www.boatsetup.com/Spark%20Plu...2007%20BRP.pdf

Continuous Wave has it as well.

http://continuouswave.com/whaler/ref...gChart2007.pdf​

 

[tashasdaddy]

Re: Spark plugs question...

agreed, other brands are known to cause problems.

 

[BaitThrower]

Re: Spark plugs question...

Interesting. Did you have the right plugs on conversion?
I have used NGK plugs in other applications for years. IMO, far superior to Champion, however I do use Champion on my outboard because, as mentioned above, the motor is made to use them. However, I have used NGK in the outboard with no problems.

Just looking at your piccie though, assuming I am seeing it clear enough, there doesnt seem to be much compression of those metal washers on the threads? Did you have the plugs in tight enough? Usually they should compress down more than they appear to be in your pic when tightened up properly?

 

[ezeke]

Re: Spark plugs question...

If you examine the chart, you see that NGK plugs are in fact recommended when they are the correct plug for the motor.

 

[55'Fleetwin7.5]

Re: Spark plugs question...

Interesting. Did you have the right plugs on conversion?
I have used NGK plugs in other applications for years. IMO, far superior to Champion, however I do use Champion on my outboard because, as mentioned above, the motor is made to use them. However, I have used NGK in the outboard with no problems.

Just looking at your piccie though, assuming I am seeing it clear enough, there doesnt seem to be much compression of those metal washers on the threads? Did you have the plugs in tight enough? Usually they should compress down more than they appear to be in your pic when tightened up properly?

Why the difference from the top cylinder (dirty)to the bottom cylinder (clean)? That is my biggest question... I did not tighten them very much... hand tight then just a bit more... for fear of over stressing the threads on the head. The NGK I used was the correct spec... I will switch back to my champions... Still, why is the top cylinder not staying clean?

 

[tashasdaddy]

Re: Spark plugs question...

check your compression and spark. could be low compression or weak spark. also i would decarb the motor.

 

[55'Fleetwin7.5]

Re: Spark plugs question...

Checked the cylinders both at around 110 lbs, the bottom was SLIGHTLY, maybe 2 lbs... higher if that. Healthy blue spark for 1/4"... The decarb part I am not sure about... What is the best method? I have one of those HUGE silencers in front of my carbuerator... How do I do it?

Thanks, Tom

 

[55'Fleetwin7.5]

Re: Spark plugs question...

Checked the cylinders both at around 110 lbs, the bottom was SLIGHTLY, maybe 2 lbs... higher if that. Healthy blue spark for 1/4"... The decarb part I am not sure about... What is the best method? I have one of those HUGE silencers in front of my carbuerator... How do I do it?

 

[BaitThrower]

Re: Spark plugs question...

If the plugs are not tight, you could have an air leak under compression and/or improper combustion - the distance of the spark plug end in the cylinder etc. Could perhaps be a cause of one cylinder being a little different to another if one cylinders combustion is not as efficient as the other? You could try with the Champions and see if they do the same. Also, I am pretty sure those washers are supposed to be pressed reasonably flat for a tight seal when installed? I think I read that somewhere in the spark plug docs.

Another possibility may be weaker spark to one of the plugs than the other?
Or perhaps one of the NGKs was a little faulty? it's possible.

And as someone else suggested, might be worth decarbing the motor and trying again.

 

[55'Fleetwin7.5]

Re: Spark plugs question...

How do I decarb?