Charging system causing an engine miss ?

rstar45

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Newbies first post. TIA

80 xs650 special
The Story... My bike wasn't charging the battery so I did Curly's trouble shooting guide from another forum. The rotor had 0 ohms so I replaced it with aftermarket Chinese part, brushes still good. Seemed to be charging okay then, so I went for a ride. 50 miles later she started to miss badly just off idle up to about 3500 rpm. Limping home I notice the turn signals seem to make it miss worse so I'm thinking a voltage issue. Battery checks out fine, good voltage so I test the regulator / rectifier. All the diodes check good, not sure how to test the regulator part so I install the Chrysler regulator with the original rectifier using the brown and green wires with separate ground. Seems to be charging fine with max voltage of 15V revved. But still missing at lower rpms.

At this point I need some trouble shooting help. I'm thinking did the TCI go bad also? But here is the kicker... If I disconnect the charging system at the 8 prong (7 used) plug from the regulator / rectifier at the harness, thus running her on the battery, the engine miss disappears and she runs fine. Could it be the TCI can't handle anything over battery voltage? The miss (severe) starts immediately off idle like maybe 1200 rpm or less and continues until she is revved up like maybe 3500 rpm or more.

WTF HELP! :banghead:

Rick
 

650Dave

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Since this started shortly after your rotor replacement, I would suspect that the magnet on the rotor that triggers the ignition is not strong enough. This happened to me, had exactly the same running characteristics. I glued a small rare earth magnet on top of the magnetized compound on the rotor, and that fixed everything. Dave
 

rstar45

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Hmmm... A weak pickup magnet on the rotor. Interesting, but since it runs fine on the battery alone wouldn't that eliminate the magnet?
 

pamcopete

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rstar,

The magnetic field in the rotor, which is only there if there is current going to the rotor from the regulator, interferes with the weak magnet on the rotor and the pickups. A stronger magnet will not be affected. This is a very common problem as the TCI gets older, the rotor magnets gets weaker etc, etc.
 

rstar45

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Ah Ha... explained that way I can see the connection. What glue do you recommend? Any clearance issues to watch for?

The original regulator was probably okay... oh well at least I didn't pop big bucks for a combo unit.

Much Thanks
 

XSLeo

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I like JB Weld, The regular stuff not the quick set, the quick set won't take heat well. But any epoxy type glue that can handle high heat should work.
Leo
 

rstar45

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Well guys I got the magnet glued on there. Sure hope JB weld doesn't have an expiration date as I have had it around for a good number of years. Got a trouble light keeping it warm overnight and will see how it runs tomorrow. I'm betting on it cause it sure makes sense. Quality Chinese parts and all :mad: .

Anywho... Happy Thanksgiving everybody and Thanks again.

Rick
 

pamcopete

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rstar,

A little late, but if you still have the original rotor, compare the polarity of that magnet to the one you just glued on. You can use a boy scout compass or another, weaker magnet. Do not use a strong magnet for this check as that may reverse the weaker magnet on the rotor. I know that you installed the new magnet with a matching polarity to the magnet on your new rotor, but I'm suggesting that that new rotor could have the magnet installed back wards. It has happened.
 

rstar45

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Well guys, I got lucky on the magnet polarity. AND the miss is gone. Ya all nailed that one!!! :cheers:

BUT... now I am concerned about the timing. The Chinese rotor and the design of the indicator on the stator and the 80 model pickup being immovable doesn't exactly inspire confidence.

Here's the deal. I rigged up a pointer wire on a cover bolt to check the timing mark of the Chinese rotor against the OEM rotor using the crankshaft key as a guide. The Chinese mark was about 3 degrees advanced from it's location on the OEM rotor. Unfortunately I didn't think to compare the location of the magnets. I reinstalled the stator using the witness marks left by the locating lug on the case. The strobe light tells me it is firing on the Chinese mark so I'm thinking I am 3 degrees over advanced.

My dial indicator doesn't have a long enough shaft to get in the plug hole to find TDC. Are there any other accessible TDC marks on this engine? Am I going to have to swap back to the OEM rotor to check the magnet locations? Suggestions?

Rick
 

weekendrider

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Couldn't you just measure from the mark to the magnet on both?

The pickup can be moved by drilling the rivets or screws and replacing.
Search for xsjohns post on it. He had some pics in the thread I think.

a wooden dowel on the piston will let you find tdc.
 

rstar45

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Well I guess I was feeling lazy. I was hoping there would be some TDC indicator like the slot in the flywheel inside the timing plug hole in the crankcase of my Beezer. That makes it real easy and foolproof to check the accuracy of the rotor.

Haven't had great luck with a stick on the piston in the past, but I'll give it a shot again.

Can't measure the rotor with everything installed. If I have to take it apart again I'll use the pointer trick to compare rotors because I trust the OEM rotor and the crankshaft keyway.
 

pamcopete

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rstar,

If the mark on the rotor is correct, then here is a picture of the full advance position.

advance1.jpg
 

rstar45

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Really appreciate the help. So here is a bit of an update.

I think I found TDC fairly well like so:

DSC02392.JPG


And this is what I got. The "T" is what I transferred from the OEM rotor and the little mark is the China mark.

DSC02394.JPG


She is firing here:

DSC02398.JPG


And here:

DSC02399.JPG


Looks to be off 3-4 degrees. I am going to have to drill out the pickup screws and see if I can move it a bit. :( I have heard that a retard setting of 1-2 degrees helps with this ethanol blend they call gas. Thinking I need to move it 4-5 degrees.
 

pamcopete

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estar45,

Well, you may have that much play in the rotor woodruff key slot. Try loosening the rotor and holding the rotor clockwise as you tighten the nut.
 

rstar45

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Well, you may have that much play in the rotor woodruff key slot.

Well that's an interesting thought. I assume you have experienced that much play in the key or you wouldn't mention it. I'm not that experienced so it surprises me. Do you think it could be there in 6400 miles or this a higher mileage issue?

Edit: The jobs done. Time to break out the long johns as she runs good.

You are a wise man Pete to check everything before attempting the riskier tasks. But I couldn't get any slack in the woodruff key. However upon closer inspection I decided not to drill out the pickup screws. Instead I went at it with a small chisel and an even smaller hammer and very gently and carefully with a lot of tap tap tap tap coaxed the screw out. Wasn't much left of the head but it worked. Gently and patiently enlarged the slot with the chisel also so I only had to do the one screw. Rotated the pickup and put in a new cap screw, washer and a bit of locktite. Done deal.

Thanks for all the help. That's a beer I owe you.
Rick

DSC02404.JPG


DSC02405.JPG
 
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