Thread: XL 760 Running Rough
04-20-2015, 05:02 PM #1
XL 760 Running Rough
I was hoping to get some ideas on what could be wrong with a ski I did some work on. It has a new sbt engine, rebuilt carbs, new battery and fresh fuel. On the trailer it starts fine and seems strong. When you throttle it a bit it would want to backfire out the exhaust. I turned the carb screws in 1/4 turn since they were set on the rich side. The backfire seemed to stop and it ran great on the trailer. Put it on the water and it wont go past 5 mph. After putting around on the ski for a while the battery died and the voltage flashed on the dash. Next day the battery was charged for a hour and the ski started right up again on the trailer. I found this on another thread but that would only explain the dead battery. The ski still runs like crap before the battery dies.
"The regulator/rectifier is part of the charging system ONLY and with a fully charged battery your ski will run fine till the battery gets low. If you arent having to keep charging the battery then its not the voltage regulator/rectifier."
04-21-2015, 08:48 AM #2
04-22-2015, 01:59 PM #3
Check AC voltage output of the stator while cranking. Sounds like you're not producing enough primary voltage to light up the ignition.
04-23-2015, 06:41 AM #4
Do you mind explaining how to do that? I am good with mechanical stuff but never really messed with testing electronics.
04-23-2015, 12:45 PM #5
I did not write this but it's great info:
1. check the AC output of the "charge" coil. Don't get confused with the term "charge" coil......this is what Yamaha calls it, as it "charges" the cdi capacitor. This coil can generate in excess of 500 volts!!
Dis- connect the brown / white trace wire and ground wire and connect the meter leads to these wires, and while cranking the engine, observe the reading. You should have 30 to 50 volts AC depending on how good a battery and starter you have.
2. Check the pulser coil output. It's job is to tell the cdi when to fire the energy stored in the capacitor. Dis- connect the white / red trace wire and connect the meter leads to this wire and the ground wire. You should get a pulsating 4 to 5 volts AC. (ps, an analog meter is best for this test)
3. If you are having problems with the battery not recharging, then dis- connect the two green wires and read the cranking voltage produced by the "lighting" coil. This coil's name is a throw back from the old enduro bike days, when the manufacturer would add a coil to the stator to operate head, brake and turn signal lights....without a battery, and later with. Anyway, you should see 6 to 10 volts or so here, again AC. This coil puts out close to 20+ volts AC, to be recitified to DC and regulated at 13.5 or so to recharge the battery. This coil is rated to generate up to about 2amps of charging current. This in mind, beware when running two bilge pumps.....a battery going bad (high internal resistance) and two bilge pumps running for a extending time is just enough to cook a lighting coil.
4. Ignition coil. Not many folks do not have a meter capable of resolving the almost dead short of the primary on this coil. But if you do, the resistance should be .078 to .106 DON'T forget to subtract the meter leads resistance by shorting together and subtracting, or adjusting the zero ohms pot, if you have it. Also, remove and insert the leads in the sockets to clean the connection.....I often see 1 ohm or more go down to .2 or .3 by performing this task.
NEXT, check the health of your spark plug wires, or high tension wires as the Brits like to say. The only way to test them properly is to remove the boots and get to the end of the wire. You can try jamming the point of the meter probes into the end, but due to the dirt and metal dust, it often does NOT give a solid connection / reading. If you have electrical contact cleaner, by all means spray with that first. You should read 3500 to 4700 ohms, or 3.5 to 4.7K ohms STEADY....while flexing the wires from end to end. If you get any fluctuations, they are bad...IE breaking up inside, turning to a high resistance powder of metal and rubber. I have seen bad plug wires cause problems with idle and low speed only, mid range only, and high speed only, and every combination thereof. Very strange !!!
If all these check out good, then I would swap the cdi with a known good unit....and known good means just what it says.....you have had it running in your boat, you removed it, and you put it away..The only other known good is a new unit. I have heard many a sad tale of days of trouble shooting with no luck, only to find out that the "known good" cdi your buddy gave or loaned you was not good after all.
Another interesting point is the "sparks when you let off the start button" syndrome. This always means on of two things......the cdi is bad, or the pulser coil is bad, or the wire from it to the e box is open.
Another good point to keep in mind: it is very possible to have two problems going on at once. One, like bad plug wires may have going on for a while, but no creating any major problems....the performance degrades so slowly you really don't notice it. Then, the charge coil insulation starts breaking down, or the connection from the winding to the terminal posts goes bad and starts arcing over. The two combined creat havoc, and can make diagnosis difficult.
After seeing so many stator coils have a good resistance, but test bad....I strongly advise against using resistance readings alone a gauge of health. Perform the cranking voltage output test!! Resistance readings are still useful for some work, so here they are for 61X and 62T:
61X: charge coil, brown / white trace to ground / black: 365 +- 10%
Pulser coil, white / red trace to ground / black: 12.6 to 15.4
62T: Charge coil, brown / white trace to ground / black: 497 to 608
Pulser coil, same as above
Lighting coil, green / green wires: 1.14 to 1.40 Since this coil is not grounded in any way to the stator frame, you can check this coil for leakage to ground (indicating bad insulation) by measuring between either green wire and ground with your meter set on the highest ohms scale, usually 20 to 40 meg ohms. If you get any reading, the coil is going bad.
04-23-2015, 04:40 PM #6
Now to get a tester and figure out how to actually use it. lol
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