Another Fouled Plug Thread

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DavidIsaak

XS650 Enthusiast
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Good day All,

I know what you're thinking- "oh geez, another I fouled spark plug story that could have been easily remedied by using the 'search' button". Please, I ask for your mercy as I explain myself :) I have searched and favorite'ed and re-read and seem to be stuck. But I have a feeling there is an easy remedy that my fellow XS650'ers can help point me in the right direction.

Location: Calgary, AB. Elevation: 1100m (3630 ft) above sea level

The Bike:
1981 XS650SH (Canadian Model sold by Yamaha in Winterpeg so says my gas cap)
Uni Pod Filters (freshly cleaned and oiled)
XS650 Direct (Mikes XS) 2-1 headers into a cone muffler
BS34 Carbs - Left As-is adjustment wise. Cleaning only
132.5 Main
42.5 Pilot
On/off Petcock (new this year)
Carb rebuild kit from Mikes. Also followed the excellent carb guide when cleaning. Thanks guys!!
Ensured plastic floats were set correctly along with cam chain tension and valve clearances to stock 1981 specs.
New high output coil, high tension wires, 5k caps and NGK BP7ES plugs gapped to .030"
Fuel/mix screw set at 3 turns out, then 1 turn out, then 3/4 turns out, etc. Doesn't seem to make a difference.
Lithium Ion Battery that is in good working condition.
Bike has E-start (new controls this year) and safety relays removed and jumpered. Although I try to kick it over often to save on E-start power.

Hopefully that is enough background to help diagnose my issue.

For as long as I remember owning this bike I keep fouling my plugs. Black and sooty, not oily, telling me it is fuel related. I thought maybe the ignition system was old and tired not allowing a nice clean spark to burn the fuel so I replaced it and also figured out Autolite 63 plugs with resistor caps was not helping (duh), so I ordered the stock BP7ES plugs with the new coil, wires and cap which I thought might have solved the problem. Alas, the plugs seem to be fouling even on both sides within 100 km resulting in a poorly running, barely idling bike. So with the reading I have done and advice I have sought, this tells me my pilot jet is set to too rich perhaps? Would altitude have something to do with this even with the increased airflow (or maybe not) with the pod filters and free flowing exhaust?

When I replace the plugs with brand new, the bike runs really nice and pulls really well through the entire RPM range, but it doesn't take long for it to start to stumble and sputter and not idle nice, making for a short outing.

So yesterday, I was checking other things over and decided to follow the Haynes manual in also checking my alternator and rec/reg to ensure my battery is getting sufficiently charged while riding. It appears *edited* the resistance between slip rings is only 2.1 ohms and the brushes should be replaced as they were only 8 mm long (just under 3/8"). When testing my rec/reg for continuity it did NOT pass on the first diode so I will be doing the Fiat regulator and 3 phase rectifier mod once I receive the parts. Would there be an off chance this could be causing some issues? Also, I have no reason to believe my TCI box is a culprit either (read about that this morning). I should also mention that I have cleaned my connectors with contact cleaner and used dielectric grease when reconnecting.

***EDIT*** : Rotor resistance across the slip rings is 2.0 Ohms. Rectifier and Regulator are OK based tests from the Haynes manual. 13.3 V at 1500 RPM and 13.8 at 2500 RPM. Brushes require replacement.

If you have made it this far, I thank you for taking the time to read my sob story and really appreciate any helpful advice you can offer up. It really has been a fun puzzle to figure out. Let me know if I have left anything important out that might help.

Thanks,

David
 
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gggGary said:
Float valves and float valve body o-rings replaced?
Yeah anywhere near the 7mm mark on the brushes is too short.
Check the Rotor +- 5.5 ohms across the slip rings.
Carbs synched?
Have you done the slide drop test?
Click to expand...

gggGary,

New float valves and body-orings came with the rebuild kit so I was sure to replace them along with the rubber plug for the pilot jet.
I will put an order in for new brushes.
I pulled the brush holder again and have a reading of 2.1 ohms across the slip rings just to be sure. Guess this does not align with what I mentioned in my post above. Thanks for keeping me honest!
Carbs were synced when I cleaned them.
I have done the slide drop test, but I did it again just now with the carbs on the bike and timed them at ~14 seconds on left carb and ~24 seconds on the right carb. HMMM! Thought they were closer than that as well. But playing around with the choke plunger seems to affect it, so the seals may not be consistently sealing.
 
Last edited:
gggGary said:
2.1 ohms on the rotor? that's a fail.
Check fuel level both with the float height, then confirm with a clear tube?
A leaking choke seat can cause a fast slide drop............
At 3600 feet you will be starting to use leaner than sea level jetting.
Click to expand...

Yessir, major fail. Guess I will need to look at sourcing a new rotor?
Confirmed with the clear tube just now that the fuel level is 2 mm (0.079" or 5/64") below the gasket seating surface on both carbs. Is that sufficient?
Should I look at replacing the choke seat?
Would trying a 127.5 on mains and 37.5 on pilot, or is that too much?
 
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That's a 2 size drop on each jet. I think I'd only go one. Have you done the simple charging output test to see if you're charging (measure voltage across battery terminals at idle and revved)? If you're not charging, once the battery runs down some, the ignition will start acting up, and that could cause misfiring and blackened plugs.
 
5twins said:
That's a 2 size drop on each jet. I think I'd only go one. Have you done the simple charging output test to see if you're charging (measure voltage across battery terminals at idle and revved)? If you're not charging, once the battery runs down some, the ignition will start acting up, and that could cause misfiring and blackened plugs.
Click to expand...

Noted on the jet sizes, 5twins. I did the simple charging output test last night and just now to double check my outputs. At 1500 rpm I am reading 13.3V across the terminals and revving to about 2500 rpm I was reading 13.8V. This was with the headlight fuse removed. Also discovered my ground to the battery terminal was a tad loose so I tightened it up.

These were my thoughts exactly. That is why I started troubleshooting the charging system yesterday.

The bike seems to idle all day comfortably (not well but it will do it) at 1500 rpm and when I turn the idle mix screws all the way in it starts to rev higher and faster until I turn it out to the half a turn where I have it now. Once the bike warmed up a little I dropped the idle to 1200ish rpm and that is when it started to sputter a bit.

Also, while the bike was idling I unplugged the rec/reg to see if it made any change which it didn't seem to do for the 10 or so seconds I left it unplugged before plugging it back in.
 
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1/2 turn out is very lean for the BS34s. They usually like/require somewhere in the range of 3 to 3.5 turns out. That could be the cause of the sputtering idle. The BS34s are so pollution mandated, it's more difficult to tune them by ear than the earlier carb sets. You don't really notice any changes in the way the bike is running usually until you get the mix screws almost closed or way far open. I test the setting with throttle blips. If I get lots of popping and/or a slow return to idle, I know I'm set too lean.

You made no mention of your needle settings. If you do have a true Canadian model then it should have adjustable needles. Maybe they're set too rich or assembled wrong. Here's what the BS34 needle assembly looks like. There's a little spring on top. If someone assembled things wrong and put that spring under the clip and spacer washers, the needle would sit too high and run rich .....

i3ZD5ra.jpg
 
I will turn them back out to 3 turns. I did also fail to mention that I replaced the idle mix screws as well with ones from XS650Direct for the proper model carb. I also compared prior to installing the new ones. I read somewhere that the aftermarket ones may not be exact and may require more turns in (lean). However I will gladly take your advice and try 3 turns out.

Over the weekend I will get the carbs off my bike and investigate the slide needle. The reason I did not make mention of the slide needle is because I have not touched it. I tried to remove the the plate and the retaining screw was engaged real tight so I just left it not wanting to strip it. I will give it another shot.

Also while bliping the throttle in my garage with the headlight on I did notice that it does get slightly brighter when I rev it up to 2000rpm which could be another sign of a week charging system.

Once I investigate the slide needle and, if possible, lower? it to a leaner setting, is there any risk riding my motorcycle with a faulty rec/reg unit? The rectifier is shorted (tested using ohm meter and following the Haynes manual), but I suspect that the regulator is fine since the bike's voltage didn't spike while it was unplugged.
 
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I'm thinking you may want to review your electrical testing procedures, maybe replace the battery in your VOM? You show normal charging output with voltages but are claiming both rotor and rectifier are bad? Not likely for all three to be true. From an old hand; it is easy to create more problems while chasing one problem.... If it electric starts and the headlight gets brighter when you rev the motor, that's basic charging is working. IE that's not the issue.
 
gggGary said:
I'm thinking you may want to review your electrical testing procedures, maybe replace the battery in your VOM? You show normal charging output with voltages but are claiming both rotor and rectifier are bad? Not likely for all three to be true. From an old hand; it is easy to create more problems while chasing one problem.... If it electric starts and the headlight gets brighter when you rev the motor, that's basic charging is working. IE that's not the issue.
Click to expand...

Good point. I have had this multimeter for probably a decade and have used it more in the last few days than I have in the last 5 years, haha. I will renew the battery and retry my tests. Thanks for the suggestion!

Also, I never claimed to be a professional at this, just trying my best with the helpful suggestions from you folks.
 
Same result with new batteries in my multimeter (VOM). it settles out at 2 ohms when testing the rotor. And when testing my rec/reg I have the meter set to ohms and put my positive lead to the red wire and negative lead to 3 out of 3 of the white wires I am showing O.L. Also put on diode mode and got the same thing with it showing O.L (overload - open circuit?). I can take video? Maybe there is something I am doing wrong, but I am making sure the leads are not crossed or touching in any way during the test.
 
DavidIsaak said:
positive lead to the red wire and negative lead to 3 out of 3 of the white wires I am showing O.L.
Click to expand...
Now reverse the leads; black lead on red wire, red lead to the three diodes, what does that show? Check both ohms and diode mode, report,
Also on the black wire in the plug check the three whites swap red/black leads, repeat, there are twelve tests to complete, you have three done so far.
 
gggGary said:
Now reverse the leads; black lead on red wire, red lead to the three diodes, what does that show? Check both ohms and diode mode, report,
Also on the black wire in the plug check the three whites swap red/black leads, repeat, there are twelve tests to complete, you have three done so far.
Click to expand...

Does the rectifier/regulator have to fail ALL the tests to be considered no good?
 
Last edited:
gggGary said:
Do all 12 tests, report results.
Click to expand...
Left letter is positive lead (red), Right letter is negative lead (black). Readings taken in Ohms then Diode mode on multimeter.
R- Red
U,V,W - White
B - Black
D1 R/U - O.L & O.L
U/R - 5.15 mOhms & .526V
D2 R/V - O.L & O.L
V/R - .691 mOhms & .503V
D3 R/W - O.L & O.L
W/R - 4.38 mOhms & .547V
D4 U/B - O.L & O.L
B/U - .733 mOhms & .505V
D5 V/B - O.L & O.L
B/V - .661 mOhms & .491V
D6 W/B - O.L & O.L
B/W - .670 mOhms & .497V

gggGary, I applaud you for your patience with me.
 
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