06-20-2011, 08:01 PM #1
Spark plug question for those who have been around 2 strokes fo many years
Hello, so first a little back ground on my issue. My 02 XP wih the 951 engine usually runs pretty good and I take great care of it. Late last year, almost at the end of the riding season, it started to run like crap, couldnt get any speed out of it and rought idle. Frustrated with the cramped working quarters and heat in the garage I took it to a shop where they cleaned the carbs and replaced the plugs. They water tested it and said "we didnt see much of anything in the carbs they looked really good". So for the rest of the season which was about 12 hours of ride time it ran great.
Fast forward to this season, I have 8 hours on it and it ran great until jumping some very small waves and they suddenly couldnt get past 15-20 MPH and low 3-4K RPM so took it in. I inspected the pump, intake, rave valves, exhaust pipes etc. When looking at the spark plugs I noticed the mag plug looked a lot more "wet" then the pto plug. I tested both plugs on the ground terminal and they seemed to spark ok. When I put them back in I swapped the plugs between cylinders. I cleaned the raves and hit the water again this evening. Now once again, max 3-4k RPM and very low speed. I put it back on the trailer and came home.
After getting home I pulled both plugs and noticed now the mag plug looked normal and the pto plug was wet like it wasnt igniting the fuel proplerly. I checked them on the ground post again and both had spark. Just about to pack up and start calling repair shops for an appointment I decided to buy new spark plugs as a last shot. I gapped them to .51mm, put them in reved it slightly on the hose and it seems a lot smoother and revs up faster. I also pulled the plugs and they both look the same now.
Now I havent had a chance to water test it but my question that Im finally getting to is, Is there such a thing as a plug that appears to have spark and work fine at idle but doesnt work properly at high RPM's causing the RPMS to max out at approx 3-4k RPM under load but allow higher RPM when not under load?
I will water test tomorrow. Sorry for the novel.
06-20-2011, 08:34 PM #2
Ok so doing some google research just now I found that in any application, testing a spark plug against a grount pint wont give you any indication that the plug will fire under an compression environement. The correct test is to make sure each plug spark can jump a 1/4 to 3/8 gap, then you know it will work in the motor.
Finding this info gives me a little more confidence that I might have a bad plug even though they only had 20 hrs on them.
06-20-2011, 08:34 PM #3
- Join Date
- Sep 2008
Yes there is. Make sure you cut plug wires 1/4" inch. After running, do both plugs feel the same temperature?
06-20-2011, 08:48 PM #4
I pulled the plugs with gloves so I dont know if there was a temperature difference between the two.
06-20-2011, 09:47 PM #5
I usually put in a fresh set after the first ride of the season has burned off the fogging oil then a second set halfway through the summer.
Shop around you can usually get a box of ten from an auto parts store for about $30.00. Get the solid top plugs not the ones with the screw on top.
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