QL78YC, QL82YC or QL78YC - E115ELED during break in

[trendsetter240]

A recent thread got me thinking about spark plugs. I'm about 4 hours into my break in and have replaced fouled plugs twice. I am running 25:1 and did quite a bit of idling during the first 4 hours.

The plugs I'm running at QL78YC based upon the chart here http://continuouswave.com/whaler/reference/BRP/SparkPlugChart2008.pdf. However, in my factory service manual it states:

Recommended: QL82YC
Extended Idle: QL87YC

I am wondering if switching to the QL82YC for the rest of the break in will help to prevent fouling? The 82 should be a slightly hotter plug and since this model only turns 5500RPM at WOT there should not be a risk of pre-ignition.

Any thoughts?

 

[Silvertip]

Re: QL78YC, QL82YC or QL78YC - E115ELED during break in

Why so much idling douring breakin? Rings don't seat properlyat idle. You need a mix of short runs of moderate and wot

 

[trendsetter240]

Re: QL78YC, QL82YC or QL78YC - E115ELED during break in

Why so much idling douring breakin? Rings don't seat properlyat idle. You need a mix of short runs of moderate and wot

Yeah I know, it was a mistake. I had been doing mixed runs of up to 3500 RPM and varying the throttle often. But I made the mistake of leaving the motor idling in gear as I tested other new electronics and gear on the boat.

I replaced the plugs and the last 2 hours I've been doing short bursts of WOT 2-3 mins and then 10 minutes cruise at 3000-3500 RPM followed by WOT again etc. I've been careful to only let the motor idle for the first minute or two to warm it up then off I go.

The pistons are wiseco and forged so it's important to let the motor come up to temp before taking off during break in so I have to idle somewhat.

Anyways, even after I have limited the idle time for the past two hours the plugs are looking close to being fouled again. That's why I'm wondering if I should try the hotter plug for the next 6 hours of break in.

 

[Silvertip]

Re: QL78YC, QL82YC or QL78YC - E115ELED during break in

Let's see -- you are running WOT at times. Does installing hotter plugs sound like a good idea since that's where detonation and preignition tend to raise havoc? You are running twice the oil so you can expect some darkening of the plugs. While they may look like they are fouling, have you actually determined that they are? And are you certain you are actually running a 25:1 mix? That's a quart in six gallons and should not cause fouling except perhaps in prolonged idling or slow speed operation.

 

[trendsetter240]

Re: QL78YC, QL82YC or QL78YC - E115ELED during break in

Let's see -- you are running WOT at times. Does installing hotter plugs sound like a good idea since that's where detonation and preignition tend to raise havoc? You are running twice the oil so you can expect some darkening of the plugs. While they may look like they are fouling, have you actually determined that they are? And are you certain you are actually running a 25:1 mix? That's a quart in six gallons and should not cause fouling except perhaps in prolonged idling or slow speed operation.

Thanks for the reply. Pre-ignition becomes a risk when the plug tip reaches 775-800 degrees centigrade. Which is 5750-6000 RPM on a loop charged 2-stroke. Since this motor is propped for the maximum recommended RPM of 5500 I should not be reaching the danger zone.

Yes, the plugs are fouling. Carbon is building up on the electrode. I can scrape it off with a wire brush and the plugs work again for awhile.

The mix is definitely 25:1 though I use the metric system so it's 25 litres of gas to 1 litre of oil. The oil is TCW3 NMMA certified.

Since carbon buildup typically occurs below 350C or 3000RPM I'm thinking that either the engine is running too cool or the double oil is exacerbating the fouling. Or maybe it's both. Also the water temps I'm running in are only about 4C so I'm sure that's not helping either.

What I'm asking is would the hotter, QL82YC, originally recommended for this motor be a good alternative to QL78YC for my breaking given the circumstances?

 

[trendsetter240]

Re: QL78YC, QL82YC or QL78YC - E115ELED during break in

Here is a chart for reference.