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Old 10 October 2007, 06:23   #11
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Originally Posted by PeterR View Post
Does this mean they are going to help out in any way
Yes he said I could send them back though the "correct" ones are apparently a bit more expensive. I've also had them for well over a year - just did a "spares order" when I bought the boat, for stuff I thought I might need i.e. gear oil, plugs, water pump impeller etc etc so I had it on hand. Only just got around to needing them!
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Old 12 October 2007, 22:33   #12
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Spark Plugs

With refference to the posted spark plug thread :

QL 78 YC Stands for:
Q=Resistor
L=14mm thread
78=Special Application Plug
Y=Standard Proyected Cone Nose
C=Copper Design

QL 77 JC4 Stands for:
Q=Resistor
L=14 mm thread
77=Special Application Plug
J=Ground Electrode Modified Gap
C=Copper Design
4= Wide Gap Required

One is warmer, the other colder, you should clean and gap your plugs according to your engine service manual at least once every 50 working hours, 2 stroke engines tend to literally eat the internal electrode quicker than 4 stroke engines, so constant re gap as specified to obtain best engine performance. It's normal to see some plugs more fouled than others, so rotate the plugs in each service.

To fight corrossion spray a generous amount of WD-40 on the plugs when new and re spray on each service. Maybe you should try the warmer ones in winter and colder ones in summer previously gapped correctly. The QL77JC4 is the second alternative termal range to the QL78YC.

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Old 13 October 2007, 08:48   #13
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Thanks. Would I be correct in thinking that too big a gap (due to electrode erosion) means a weaker spark and thus more of a probability of fouling on a 2 stroke? It would tally with my recent experience prior to changing the plugs the other week - I haven't been out again since to see if it is any better. The plugs had eroded to around 40 thou clearance (should be 30 or 32 depending on what figures you use).
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Old 13 October 2007, 10:14   #14
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Spark Plugs

A bigger a gap means weaker spark on the electrode, that's why you need to re gap more often to obtain optimal gasoline consumption and engine performance. In the long run will cause more plug oil/carbon fouling, have a proper oil/gas mix ratio too so both issues help the engine perform at it's best.

In my particular case my plugs are used max 150 hours, re gapped, cleaned and rotated each 50 working hours. Dispose off properly, put new ones and so on. It's a good idea to use an engine hour meter to control exact working hours and perform scheduled maintenance.
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Old 14 October 2007, 07:01   #15
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Following Champion's numbering sequence, the higher the number the hotter the plug. So your 77 will run a bit cooler than the 78 and the standard nose will be more prone to fouling. This doesn't mean you can't use them. Running hotter plugs in an engine is to be avoided but running a cooler plug will do no harm. If it were me, I'd gap them to 30 thou to keep the spark fat and use them. If they foul too often you've lost nothing cos I wouldn't reckon it is worth the cost to return them.

For info, NGK plugs get cooler as the numbers increase whereas Champion plugs get hotter as the number increases.

A cooler plug has a shorter heat path to the body.
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Old 14 October 2007, 10:36   #16
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Thanks. The book says the gap should be 0.8mm or 30 thou but 0.8mm is actually 32 thou which is what I did them to, so I think I will re-do them to 30 and see what happens.

I guess these plugs have done a bit less than 100 hours, not sure when I changed them exactly (the engine does have an hour meter just didn't note it down) and have eroded 10 thou in that time so I guess every 3 months or so wouldn't be a major inconvenience. The plugs I took out about a year ago, still in there from the original owner had been in there for aeons, they were burnt to a crisp and when I tapped the ground electrodes, they fell off on 3 of the 4 plugs ... lucky I checked it when I did
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Old 14 October 2007, 12:14   #17
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Quote:
Originally Posted by BogMonster View Post
...when I tapped the ground electrodes, they fell off on 3 of the 4 plugs ...
Feck! Maybe the cooler plugs will be better in your motor, it sounds as though it gets kinda warm in your cylinders.
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Old 15 October 2007, 06:26   #18
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No sign of problems with the current plugs I had in there until the other day - they all look healthy apart from the one that was fouled and that was just wet with fuel. I think the ones dating from the previous owner had just been in there rather a long time
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