Thread: Backwards timing...
05-31-2011, 09:08 AM #1
Ok so I had a 94 sl750 that was in rough shape when I got it, and the motor crapped out at the end of last summer. I found another 94 sl750 with a good motor, but no electronics (long story) so I bought it transferred all the buttons display sensors and what not onto it. Went it fire it up lastnight and wouldn't start, had a few backfires, put new plugs is and nothing. Then my friend had the idea to swap the mag plug wire with the pto wire and bam, started right up purred like a kitten. I'm happy it started but very confused as to why. It's the same year and model as my old ski and everything worked fine in the other ski, the cdi for the coils is pretty idiot proof with male and female ends for the two plugs that are reversed. Is it ok to just swap those two wires?
05-31-2011, 11:54 AM #2
- Join Date
- Jul 2007
- near Toronto, Canada
This is a blue Fuji engine?
What CDI part number do you have in there?
Are you sure it is now firing on all three cylinders? They get equally warm?
How are the primary ignition coil wires configured? Does each coil primary wire plug into the next coil?
05-31-2011, 01:17 PM #3
It's a Fuji engine, no idea the cdi but it worked fine all last summer in my other 94 sl750. All three are fireing we checked that, and as far as how the coils are hooked up I'm not sure, as far as I can remember there's only one wire coming out of each that goes to the cdi box, I'll have to check when I get home.
05-31-2011, 09:02 PM #4
- Join Date
- Oct 2006
- Cleveland OH
That does seem odd.
Fuji's use a wasted spark system. What that means is the coils are wired in series (tied together with one wire from 1 coil connected to a wire from another coil, and the other wire is connected to the third coil)
So, when the CDI sends the signal to the coils to spark, thay ALL fire. But only 1 cylinder will be at TDC and actually ignite. (2nd cyl will be coming up to start the compression stroke, and the third will be at Bottom Dead Center) That is why it's called wasted spark. They all fire, but only 1 cyl needs it. It'a just a very simple ignition system.
That's why swapping the plug wires shouldn't have made any difference.....
Now a PRO 785 on the other hand is a Fuji engine, but does fire each coil individually. (does NOT use the wasted spark system)
05-31-2011, 10:05 PM #5
Wow... Knowing that it does seem very odd that swapping the plug wires would fix it.... Anyway thanks to you guys I got out my book and realized I had actually plugged in the coils wrong. But now I'm really confused as to why swapping the wires fixed it, well I'm without a battery at the moment so I'll hook it all up tomorrow and let y'all know. Thanks for the help.
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