Running badly; thoughts?

[delagem]

Hello, my son picked up this 1983 XS650 for a project. It's running badly.

Compression was good, 145/149.

The symptoms seem like a failing electrical; won't rev past 2,500rpm, acting like it's hitting a rev limiter, and the battery doesn't charge. Pops, spits, backfires when trying to rev higher. When you start the bike, the headlight comes on and gets somewhat brighter as the bike revs, but never develops good voltage to the battery. Maybe 12.8v.

Video of running:

Did the slap test:

Measured the brushes, brand new at 14.7mm. Ohmed the Alternator/Rotor. 5.1 ohms:

IMG_1093 by michael delage, on Flickr

Battery voltage standing was good, 12.8v:

IMG_1094 by michael delage, on Flickr

Key on, voltage drops to 12.3:

IMG_1097 by michael delage, on Flickr

Voltage at brushes 11.7:

IMG_1098 by michael delage, on Flickr

Read about jumping the green wire to get full rectifier voltage. Here I'm doing that. You can see the bike is running, yet even with green wire shorted to ground, only 12.2v at idle. Revving it doesn't raise it much at all:

IMG_1099 by michael delage, on Flickr


So, what am I missing? I know 90% of all electrical are carburetor related, but the fact that the battery doesn't charge has to be significant, right? Any suggestions?

Michael

 

[mrtwowheel]

How old is the battery? Regardless of the voltage or age of the battery.........take it to Autozone and have it checked for free, then take it to Orielly's to have it checked again. You just gotta KNOW that you're starting with a good battery.

Scott

 

[5twins]

Yes, good charging is important on these, the ignition relies on it to function properly. On the '83 I'm currently working on, I found both the reg/rec plug and the ignition black box plug badly corroded. They're located under the left side cover right next to the battery box. I think battery acid or acid fumes may have gotten to them. Obviously you have spark but maybe the reg/rec plug is all corroded and not making good contact. Or it's possible the reg or rec unit has gone bad.

 

[delagem]

Hello, thank you for the replies. It's definitely not the battery, it's brand new. Just to be 100% certain, I ran the test again with a different, brand new Deka battery. 12.9v at rest, 12.6v with key on, 12.3v once started and at idle, 12.6v at 1/2 throttle, bike stumbling and 2,500rpm, and then as I increased throttle, the engine died:

5Twins, thank you for the suggestion. I pulled the all the molex plugs, including the one from the regulator/rectifier; they were clean but I used a brass wire brush on them, cleaned them in electrical contact cleaner (TCE), blew them dry and then applied dielectric grease.

EDIT: I didn't see the plug to the black box; where is that one?

I thought the green wire bypassed the regulator/rectifier for testing purposes?

Any other tests I can perform? I checked 12v going in to the brushes, how do I check the other side?

 

[delagem]

Re-reading thru gggGary's update to the Curly's Guide, he says no more than 0.3v drop from battery to points. Well, I've either got 1.1v or 0.6v depending on how you measure it (key off vs key on). So, just to rule out the keyswitch as a source of trouble, I ran a wire straight from the battery (+) to the points; no change in running. On the plus side, I now know how to hotwire my bike if I ever lose my key!

I performed a drop-cylinder test. At idle, the bike runs 1,200rpm. Disconnect left spark plug lead, bike idles at 700rpm. Reconnect, and disconnect right spark plug lead, bike idles at 700rpm. So that all seems normal...

 

[5twins]

The black box plug should be right next to the reg/rec plug, or at least it was on mine. It's the exact same type of 8 wire plastic connector block as used on the reg/rec. The black box is mounted under the battery box so you can find the wire loom coming out of it and trace it to the connector from there.

Grounding the green wire bypasses the regulator portion of the reg/rec unit so maybe it's the rectifier portion that's bad. That's the three white wires carrying AC voltage in from the alternator and the red wire carrying converted DC voltage out to the battery. The black ground wire is also part of the circuit. It actually feeds a ground to both the components in there. There are rectifier testing procedures in the shop manual.

 

[delagem]

The black box plug should be right next to the reg/rec plug, or at least it was on mine. It's the exact same type of 8 wire plastic connector block as used on the reg/rec.

Thank you for the clarification. Ok, I cleaned and greased that one too. They looked fine, though; shiny, no corrosion.

I was going to ask about those 3 white wires. I'm not at all familiar with Yamaha electrics, but I do know Ducatis; I assumed those were 3 phase AC?

That's how you confirm a Ducati rectifier is dead; if it's got AC in but no DC out, it's the rectifier.

Do you think the symptoms I'm seeing are related to the lack of DC voltage? That weird stutter and only 2,500rpm? Or is something else going on as well? I ask because I've had plenty of bikes where the rectifier died (reference the '86 thru 2000 Ducatis); I finished many rides, some up to 100 miles, just by unplugging the headlight. You'd think this bike would at least run for a few minutes without a functioning rectifier?

I'll do some reading in the service manual.

Michael

(Edited to remove confusing AC data that don't apply to Yamaha XS650's)

 

[MacMcMacmac]

I'd check to see the if timing magnet was still ok, and check each ignition sensor.

 

[weaselbeak]

"I know 90% of all electrical are carburetor related"

You have this backwards. Never touch a carb until you KNOW the electrics are good.

 

[delagem]

Here is the curly's guide:

6. At the stator wire connector locate the three white wires. Use a voltmeter set on the AC scale to test the three possible connections between the white wires by probing from the backside of the connector. (The connector should be plugged togeter for this test) With the engine running at idle you should see about 10.5 to 11 AC volts (Not DC) on each of the three combinations of white to white that you make. If you get a very low reading on one or two legs then something is grounding your stator. If you have high readings on any of the legs (i.e. 16-18VDC) then your rectifier is bad.

Ok, this morning's test; with the regulator/rectifier plugged in, bike idling, I get 10v AC on in between any two white legs on the regulator/rectifier plug. Revving to 2,000rpm and this goes up to 11.5v AC. Am I correct that this confirms the rotor, stator, and brushes are all functioning correctly?

IMG_1101 by michael delage, on Flickr

EDIT: How cool is this? A chain/lock keyed to the ignition key! Didn't know these bikes came with that:

IMG_1102 by michael delage, on Flickr

 

[gggGary]

Seems right. Have you removed and checked the battery/frame ground strap?

 

[5twins]

It sure seems to. But just because none of the readings were high like Curly's guide says, I'm not sure that confirms the rectifier is good. I'd test that by itself.

 

[delagem]

I'd check to see the if timing magnet was still ok, and check each ignition sensor.

Here's a bolt sticking to the magnet on the rotor. Does this confirm it's good? I don't know the test for this... Does the fact that it starts and idles perfectly confirm the "ignition sensor" is good?

IMG_1103 by michael delage, on Flickr

Seems right. Have you removed and checked the battery/frame ground strap?

It's good. As a precaution, I pulled the battery ground strap, sanded the frame to bare metal, cleaned with TCE, and applied dielectric grease. The wire and its' lugs looked new.

It sure seems to. But just because none of the readings were high like Curly's guide says, I'm not sure that confirms the rectifier is good. I'd test that by itself.

I agree; if I'm not mistaken this test pretty much proves that the charging problem is the regulator/rectifier, or its ground. Does that sound right? How do I jump the reg/rec ground for testing?


Just to rehash: Starting the bike, voltage will settle in to 12.3v at idle; rev the bike to 2,500rpm, I get 13.0v on the battery. (this is a bit better than yesterday, when I was only getting 12.8v). Attempting to rev above 2,500 the bike acts like it's hitting a rev limiter; stuttering, stumbling.

 

[gggGary]

Have you got a timing light? beg borrow or steal one check idle timing and about 30 degrees of advance. I had one acted this way and found one of the pickup wires was busted only held by one strand, fixed that brrm brrm under the sprocket is a very hard place to live.

 

[gggGary]

I'd also be checking carb diaphragms you can do the drop test with the carbs in place airboxes removed.

 

[delagem]

Have you got a timing light? beg borrow or steal one check idle timing and about 30 degrees of advance. I had one acted this way and found one of the pickup wires was busted only held by one strand, fixed that brrm brrm under the sprocket is a very hard place to live.

Got one, will revert...

I'd also be checking carb diaphragms you can do the drop test with the carbs in place airboxes removed.

Is this the test where you lift the slide, then cover the oval at the top of the carb, and see if the slide stays up? I did that, they stay up, and then drop smartly and smoothly when I remove my thumb from the oval.

 

[gggGary]

PS I'd say your magnet test is a pass. I like a guy that thinks up adhoc solutions....you do that.

 

[delagem]

Timing at idle:

IMG_1105 by michael delage, on Flickr

Timing at 2,400 rpm:

IMG_1109 by michael delage, on Flickr

...

 

[gggGary]

OK great stuff! it LOOKS way advanced, but the timing plate looks a bit beat up also, the far right T mark is TDC, pull the sparkplug use a straw, piece of copper wire, see if the T matches piston TDC. If it doesn't match adjust the time plate location until it does. then adjust the timing via moving the pickups. move left to retard them.

 

[gggGary]

there's been some PM work on this I'll bring some stuff here so we can all help.
35 years on just about everything has been messed with, rotor on/off, changed, to maybe aftermarket or rewound your timing plate looks disturbed from factory, stator's probably been off or changed before. The "tamperproof pickup screws have been slotted so the pickups have been moved or changed. All this adds up to: you can trust Nothing you see, get TDC from the piston THEN set everything else from THAT.