HPDI 200 - how smooth should it run at low RPM?

[ROBERTH]

I was just thinking of some other item that could possibly cause a difference in the carbon buildup. Regarding spark plugs.
I have been seeing some videos where folks just replace the plugs with factory gap setting and don't check them. I have always checked them and found them to be off per my feeler gauge.
Dennis, do you just install the plugs as-is from factory or do you readjust them? I wonder if this might have something to do with why I have a carbon buildup more than others...... What say you?

 

[DennisG01]

I was just thinking of some other item that could possibly cause a difference in the carbon buildup. Regarding spark plugs.
I have been seeing some videos where folks just replace the plugs with factory gap setting and don't check them. I have always checked them and found them to be off per my feeler gauge.
Dennis, do you just install the plugs as-is from factory or do you readjust them? I wonder if this might have something to do with why I have a carbon buildup more than others...... What say you?

Yes, I always check the gap, first. If you're questioning them, go ahead and pull them out and check. You can "read" the plugs, too. Make note of which cylinder they come out of.

 

[ROBERTH]

Thanks Dennis, I am not actually questioning them as I am OCD on plug gap so know they are right per my feeler gauge. Just wonder the difference in those motors that have the narrower gap vs the wider gap when I have to add more gap to them which seems is always the case.
Do you find the same? They always need more gap?
Each season, usually just under <100 hours I replace the plugs. They always look clean and good per the manual expectations. Never any are in a fouled or wet condition. Even my O2 sensor is clean, just the carbon in the chamber and sniffer tube.

 

[seasick]

My experience over the years with NKG plugs is that they were gapped in spec for my SX150 right out of the box. I do randomly check the gap on used plugs and occasionally, I will re gap.
Note that when you check gap, you should use a wire feeler gauge not the flat metal blade type. For new plugs it doesn't make that much of a difference but for used it can give a false reading ( may read less than the actual gap)
I can get three seasons out of plugs and like a few other parts, I change them out of guilt, not hours.

 

[ROBERTH]

Good point Seasick, I always wonder about the feeler gauge not reading right, but I always negotiate with my brain waves that if I can slide between the electode and tip with some resistance, I am good. However, angle is important.
I haven't been able to find a wire gauge with the 1.5mm -1.6mm or so size.

I wonder if I am adding just enough gap where it might cause less combustion and therefore more carbon buildup....dunno....but might be one thing I can try, replace with new with no gap check, just factory and see what happens.

 

[DennisG01]

Thanks Dennis, I am not actually questioning them as I am OCD on plug gap so know they are right per my feeler gauge. Just wonder the difference in those motors that have the narrower gap vs the wider gap when I have to add more gap to them which seems is always the case.
Do you find the same? They always need more gap?
Each season, usually just under <100 hours I replace the plugs. They always look clean and good per the manual expectations. Never any are in a fouled or wet condition. Even my O2 sensor is clean, just the carbon in the chamber and sniffer tube.

For my motor, I haven't found the need to alter the factory gap spec. I also don't change them every year - I check them - and give them a quick brushing/cleaning/gap checking - but I put them right back in unless there's an obvious issue.

 

[ROBERTH]

Thanks Dennis, maybe I am on to something. Reason I change them is due to the corrosion on the plugs. I even coat them when replacing with corrosion sprays, but guess they get hot enough to burn it off and still corrode/rust.
The plugs always have looked good and even burn on all cylinders. I always thought they could go another season.

 

[seasick]

y corrosion do you mean rust on the bases? If you get rust frequently on the plugs, you may have a water leak under the cowling, I have seen that on some motors. It can be a very small leak or even possible a disconnected pitot tube hose. If there is enough salty mist, you may see more green on power lugs than normal. I am interested in input from others on there experience with rusty plugs.

 

[ROBERTH]

Hi seasick, actually, at times water does come in the cowl when waves come over the motors. Most likely that is where the saltwater dribbles down on the plugs. Unlike the OMC Seadrive I used to have, the Yamaha's don't have a baffle to keep water from dropping on the motors when it can come in the intake.
I run the motors with the covers off even recently and nothing is leaking anywhere, it just comes in the intake area. My shroud seals seem to still be in good shape.
Nothing is green, I keep the motors sprayed down with protectant. Usually only a couple of plugs are the worst which I think are in the path I mentioned where that water comes in and drops down on that area.

 

[ROBERTH]

Seasick, you got me thinking a bit deeper. Got in a new set of plugs. I found a wire type gauge and checking the plugs, I discovered something I had not caught onto.....
The side electrodes are not flat, the edge is curved so it aligns with the center electrode being in the shape of a cylinder. When sliding in a flat feeler gauge, it is making the gap way too wide. Using the wire gauge, inserting vertically between the center and side electrodes is the right way to check the gap. I never have seen this before and realized the design. My eyes are failing or I was just not paying close attention.
I am wondering if the gap being so wide was not hot enough of a spark allowing the extra carbon buildup. I will check this weekend, weather permitting if it runs better or not with the new plugs with factory gap.
Thanks guys for the feedback. I hope this might be something that benefits these motors and my carbon headaches!