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Wasted Spark
- Thread starter motogotro
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SabrToothSqrl
Well-Known Member
I know, it keeps me up at night too... all those wasted sparks.
Ok, so riddle me this batman. I was noticing what sounded like an intermittent miss last night between 1/4 and 1/2 throttle. On the trailer with the ski in the water I could get it to start with just the front plug wire on the front cylinder but it wouldn't start on just the back cylinder. I put the rear plug wire on the front cylinder which should work in a wasted spark system but no joy, it would not start on either cylinder with the rear plug wire. So I pulled the boot off the rear wire and cut about an inch off, put the boot back on but no change, neither cylinder will start on just the rear plug wire. The front plug wire is not long enough to reach the rear cylinder so I couldn't test the rear cylinder with the front wire. While doing some more playing around I did figure out that it will start on the rear cylinder if I put a spare plug in the front cylinder and ground it. I'm going to pull the electrical box apart and test the wires but I'm really wondering if this is a red herring or if this is really a problem?
Dr Honda
Well-Known Member
Well............... who knows. (since I'm not there looking at it) You could have a bad wire... or a weak coil. Besides... these engines don't run well on one cyl anyway... so it's not really a valid test for anything.
Put an in-line tester on both plugs at once, and see what you get.
A miss in the mid RPM's could be anything. It's a 2-stroke... and since you were on the trailer... the engine was really loaded up, and it's really not tuned for that. Yes... it's best that you test the engine in the water, as you were doing... but once past the "Check for leaks, and other issues" stage... then you really should just get on it, and take it for a ride to see if it clears out. My personal XP needs 10~15 seconds as I get on the throttle the first time to clear out. (can't do that on the trailer) But once clear... it's fine the rest of the day.
One last thing... the Mikuni carbs don't have a "Mid" fuel circuit... so some of these engines just run that way. BUT... if your RAVE's are opening too soon... that could cause the loss of power in that RPM range. I personally run mine full tight, so they don't open until almost peak RPM's.
Last thing... if your water regulator isn't set right... or is leaking... then that will cause a mid-miss also.
9 times out of 10... if it was an ignition issue... then it would feel like it was turning on and off... not just a miss.
Just my 2 cents... take it for what it's worth.
Put an in-line tester on both plugs at once, and see what you get.
A miss in the mid RPM's could be anything. It's a 2-stroke... and since you were on the trailer... the engine was really loaded up, and it's really not tuned for that. Yes... it's best that you test the engine in the water, as you were doing... but once past the "Check for leaks, and other issues" stage... then you really should just get on it, and take it for a ride to see if it clears out. My personal XP needs 10~15 seconds as I get on the throttle the first time to clear out. (can't do that on the trailer) But once clear... it's fine the rest of the day.
One last thing... the Mikuni carbs don't have a "Mid" fuel circuit... so some of these engines just run that way. BUT... if your RAVE's are opening too soon... that could cause the loss of power in that RPM range. I personally run mine full tight, so they don't open until almost peak RPM's.
Last thing... if your water regulator isn't set right... or is leaking... then that will cause a mid-miss also.
9 times out of 10... if it was an ignition issue... then it would feel like it was turning on and off... not just a miss.
Just my 2 cents... take it for what it's worth.
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Other than consideration for the fact that it is running on one cylinder, it runs fine on the front cylinder. Starts easily and doesn't display any flat spots or rough running. When it's running on both cylinders you can definitely detect some rough running that gets worse just before about 1/2 throttle and then clears up suddenly. I either have some carb or ignition problems. I was running this test to see if I could determine which cylinder has the problem and that's when I found the issue with the rear spark plug lead. I don't have an inline tester so I'm going to have to come up with some other tests to see what's going on. If it is a wasted spark system and it will start easily with the front cylinder/front lead combo, shouldn't it also start with the front cylinder/rear lead combo?
I have my RAVE valves all the way down and the water regulator is flush with the black cap. I have pulled the RAVE caps and the valves seem to move smoothly but I did notice some oil around the front valve so I need to pull the valves and make sure the bellows are not torn.
I feel the miss on the water as well as on the trailer and the ski still seems slow out of the hole and top end is about 50mph at best....only with the wind and waves will it hit over 50mph.
I have my RAVE valves all the way down and the water regulator is flush with the black cap. I have pulled the RAVE caps and the valves seem to move smoothly but I did notice some oil around the front valve so I need to pull the valves and make sure the bellows are not torn.
I feel the miss on the water as well as on the trailer and the ski still seems slow out of the hole and top end is about 50mph at best....only with the wind and waves will it hit over 50mph.
I pulled the electrical box apart tonight and found that the coil only had one screw holding the coil in place and the other one, the one with all the ground straps, was very loose. The manual says that the spark plug boots should be 4.48k ohms where mine are 5.0 and 5.6 but I didn't notice which one was the front and back before I pulled them. Not too far off but out of spec a bit. The primary winding reads <1 ohm like it should and the secondary is at 13kohms. I'll put a second bolt in the coil and tighten that up and see what that does for it.
I ran a compression check and got 150 on the rear and 160 on the front cylinder.
I ran a compression check and got 150 on the rear and 160 on the front cylinder.
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I put it all back together this morning but not too much difference that I can tell on the trailer. I have gotten it to start several times on the rear cylinder and it doesn't run nearly as good as it does on the front cylinder. Anything below 1/2 throttle on the rear cylinder and it will barely run so at this point I'm thinking it may be carbs.
WhiskeyD
Well-Known Member
That sounds about right... My skis will barely even run at all on one cylinder.
On the RAVE valve bellows, mine had the spring on the large diameter opening and zip ties on the small diameter. I looked in the parts diagram and it doesn't show any spring or retainer on the small diameter section of the bellows. Is that correct, is a zip tie okay, do I need something else?
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