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Old 08-10-2007, 11:11 AM   #1
jaxtrble
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Default Magna engine cutting out

A little background: 2001 Honda Magna V4 750cc water cooled (fan included). Weather on the two days this week it happened (before I parked her until I had tear down time) was around 62 degrees. My commute is approximately 15 minutes of stop and go, and honestly I ride her harder than I probably should in the summer in traffic. During the winter I have to ride like grandma in the rain everyday, so I'm exuberant in the warm days (racing those stop lights).

What's wrong? About 10 minutes into my commute (depends on traffic) the temp light turns on and the bike cuts off (not more than a few seconds after the light comes on). Then all the idiot lights turn off. I quietly roll to a stop, turn off the ignition, turn on ignition and restart. Away I go until a few minutes later. One time the idiot lights didn't turn off, but it wouldn't let me restart until the ignition was turned on/off. The few times it's happened got home and didn't notice way too much heat off the engine during the highly scientific bare hand method.

Noticed anything funny of late? She shifting harder in-between gears like when oil is low. More frequent backfires when downshifting. I've been nagging myself to check the valve clearance cause milage says I'm due for shims. One of the cut outs was immediately after a particularly loud backfire (and a cop two cars ahead). Replaced the cam chain adjuster about one year ago, plugs about 1500 miles ago and oil changes like clockwork. Last oil change was Spectro instead of the usual Amsoil because I had an impromptu long distance trip required by my brain and I wanted fresh oil for the ride.

So what do I think is happening? My working theory is that the thermostat isn't operating properly to start cooling the bike, but since my commute is so short and the temp has been cool the temp isn't building high enough for me to be able to tell externally. Replace the thermostat and smile.

Other options: 1) Water pump instead of thermostat. 2) Oil not getting up to the camshaft area. Shaft is straining creating more friction. 3) The most frustrating of issues, I grab my multimeter and start looking for a short.

Anybody else have a working theory for me to consider?
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Old 08-10-2007, 11:15 AM   #2
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How many miles?
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Old 08-10-2007, 11:35 AM   #3
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My Magna is an '84. I took the thermostat out of it completely and rigged a handlebar switch to run the fan all the time in stop and go traffic. That seemed to help.

But all that backfiring shouldn't be caused by that. A couple of loose valves shouldn't either. I'd suspect mixture. You should pull the carbs and clean them thoroughly, inspect for cracked boots, etc. Also make sure the ignition timing is correct.
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Old 08-10-2007, 11:46 AM   #4
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sounds like you're tripping a circuit breaker somewhere. That would explain the backfire and lights going out. A breaker will trip and reset until the cows come home, unlike a fuse that'll at least tell you where to look. I had an '84 V 65 Sabre that is more or less the same engine and I remember the temp bars always showed that it was running hot, however the standard meat thermometer-in-the-top-of-the-radiator test showed it was running around 180* or 190* IRC...

If there's a cut out for overheating on the 2001's I'd look there

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Old 08-10-2007, 12:02 PM   #5
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All I did was gas and go for 33K miles on my '94 Magna so I'm of no help.
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Old 08-10-2007, 12:17 PM   #6
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Since there is no "auto overheat cutoff" or "fuseable Link" in a Honda Smegma, your best bet is to check the following:

...there may be a heat/resistance problem occurring with ignition system. Get a DVOM and check the resistance of the...

...ignition coils, primary and secondary windings when cool and again when smoking hot.

Check same for ignition pulsar coil (pick-up coil) windings.

Examine all electrical connections for corrosion and defects. Since you live in Seattle, use dielectric grease on connections to help prevent water shorting, corrosion, etc...

Make sure weasels haven't nested under the seat, and been chewing on the wires.

If that doesn't work, unscrew the gas cap and replace everything underneath it.

You really should have known...
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Old 08-10-2007, 06:10 PM   #7
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about 24,500 miles
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Old 08-10-2007, 06:14 PM   #8
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Thanks for all your input. I'm leaning more an more towards a short within the ignition system. I went to turn her on this morning and there were no lights in the 'on' position. Click back to off, waiting a few seconds and back to 'on'. Then lights came up. I've got a good multimeter so I'll be checking everything out tomorrow. I'll let you know what I find. Thanks again.
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Old 08-11-2007, 11:30 PM   #9
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Okay so after checking the resistances starting from the ignition coils working my way back to the battery I found that the ignition pulse generator was ohm-ing out at 333 instead of the 450-550 that it should be. In hindsight the excessively loud backfiring should have tipped me off. Of course I found this out at 5.05pm, so everybody was closed. Now I just have to figure out why the ignition pulse generator would go bad at such low mileage. I'm leaning toward checking my timing.
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Old 08-12-2007, 10:43 AM   #10
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Heat breaks down electrical components, and the Magma (no pun intended) is one hot runnin' sumbytch.

Google "Handa Magna Cooling Problems" and you'll get an eyefull. Also seems to be a lack of oil flow to the camshafts. Re the hard shifting, try using some Mobil Delavac 15-40 deezul earl, the extra zinc helps your shifting, as well as your prostate.
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