Video of bogging and backfires with low voltage, cant figure out the problem

[Red Beard]

Ok y'all, this issue has been getting worse, and I have tried all I can think of so I'm looking for some help or ideas into why this damn thing is running so poorly.

Specs:
1979 XS650
BS 38 carbs
PMA
Pamco
Simplified wiring harness with blade fuses

Problem:

Video link here -

Sorry for the ghetto setup and commentary, you cant really see the volts but when i say there is a voltage drop it was to the point of like 4 volts and at one point 1 volt, but mostly low around 7-9 volts during the bogging and backfiring, as soon as it stopped voltage came back up.

I'm not sure what to test next, the lack of voltage makes me think an electrical issue but she has been running with this setup for a while now with 0 problems, Only thing that has happened out of the blue is this noise

and I cant seem to tell what happened, we were thinking bent valve but the compression says otherwise? IDK I am all out of ideas guys. below is a list of info on what i could think to try.

What I've done:
*Compression test - all good on both 105 and 104 when sitting for a few days, then 145 and 144 with a few drops of oil down the cylinder
*Cleaned carbs - they were spotless and both jets looked great, float levels were on point (I've completely rebuilt them before using the amckay guide including all new rubber, and gaskets, and seals)
*New fuel filters
*Uni air filters cleaned and inspected, they look good to me
*Checked Diaphragms and they pass the "drop down slowly" test
*Sprayed intake boots with WD-40, no increase in idle or smoke out exhaust
*Checked cam chain - was within spec
*Checked valves - had one exhaust valve out of spec by a bit but returned in spec and still issues
*Checked carb sync with homemade manometer- Balanced fluid well
*Voltage at idle is 12.4-13.2 and voltage at 3000rpm is 13.4-14.1
*Checked mechanical advance and springs seem to be in good condition
*Checked timing and it looks good and advance unit kicks in at 2000-3000 rpm and seems to be where it should
*Plugs looked good - they were just slightly rich but that has been tuned out mostly
*All electrical grounds seem to be grounded well and solid.

 

[richardthemotorcycle1]

I'd try some sea foam in gas tank, maybe bad gas?

 

[Red Beard]

I also though a bad batch of gas but I ran the tank dry and filled her up with 91 and Lucas fuel additive, and still no improvement afterwards, sorry forgot to put that on my list of what I've tried.

Still not a bad idea to try seafoam anyways just to give it a shot, maybe got two bad tanks of gas?

Thank you for the reply.

 

[richardthemotorcycle1]

Maybe a bad coil with intermitting short?

 

[Red Beard]

Hmmmm, you know what I didn't even think about the coil! I will go and test it, that would explain a lot of the symptoms! Fingers crossed I'll go test it and report results

 

[Red Beard]

Ok so as far as I can tell this is the procedure for testing:

1. Using the lowest scale on the meter, measure the resistance between the primary terminals with the wires removed. Should read from 2.5 to 4.5 Ohms.
2. Using the highest scale on the meter, measure between one of the primary terminals and the center core of the coil. Should be infinite resistance. (open)
3. Measure between one of the primary terminals and one of the plug wire terminals. Should be infinite resistance. (open circuit)
4. Measure between one of the plug wire terminals and the core of the coil. Should be infinite resistance (open circuit)
5. Measure from one plug terminal to the other. Should be 15,000 to 20,000 Ohms

For step one I got: 2.6 ohms
Step two : no reading, (not open line) not sure how to get to center coil with my coil (pic below) I attempted to just read from primary to metal center attachment-see pic
Step three : no reading
Step four : no reading
Step five : 24.7 on the 2000K selection knob (247,000 ohms?)

 

[Red Beard]

Here is some more pictures of the tests.

 

[pamcopete]

RedBeard,

Try this as a test. Connect the ignition coil and PAMCO red wire to a separate stand alone battery with the PMA disconnected. If that fixes the problem, then you have a PMA issue.

 

[peanut]

just sounds like either a flat battery problem or an electrical short to me .

I would attach a fully charged 12v car battery with some jumper leads and then see how it idles and revs on the stand . if there is any improvement you've found the culpret if not then at least you've eliminated the battery.

Try disconnecting the rectifier regulator and running it off either the car battery (on the stand) or a fully charged bike battery and see if there is any improvement. That should either pinpoint or eliminate the regulator/ PMA .

If there is still no improvement then you will need to check all your wiring and switches for shorts or poor connections. I assume you have substituted a known good coil

Sounded great in the first Walk round video so it can't be much wrong I shouldn't have thought.
The noise you mentioned sounded like possibly the back of the clutch basket rubbing on the crankcase maybe? Did you ceck the clearance behind the basket when you finished tightening the clutch springs ?

The other possibility is something rubbing under the stator maybe ?

 

[Red Beard]

Ok Pete, so d/c the PMA, and connect another separate battery to the pamco and coil. So if she runs fine through all the gears it's a Pma issue? should I just stash that battery somewhere while I ride it to test it?

 

[Red Beard]

Hey peanut,

I have not switched a known good coil in there because I don't have a spare, but I will try another battery with the reg/rec disconnected, once I get home I will preform the tests and let you all know.

As for the noise, the stator is clear of any debris, did check the clearance on clutch springs, but they could have changed since, I'll take a peak thanks!

Thanks for all the ideas guys.

 

[peanut]

might be worth removing the alternator cover and seeing if the whirring rubbing noise is coming from the alternator... That could be the cause of the low voltage

 

[Red Beard]

I'll pop that cover off no take a look, would sure be nice to know what caused that noise, haven't heard it since it happened but could have had something to do with the alternator.

 

[pamcopete]

Ok Pete, so d/c the PMA, and connect another separate battery to the pamco and coil. So if she runs fine through all the gears it's a Pma issue? should I just stash that battery somewhere while I ride it to test it?

Yes. If you kick start the engine, then you do not need big wires from the battery to the coil and PAMCO. Even 16 gauge wire will work for this test if you kick start it so that will give you more flexibility to locate the battery for the test run.

 

[TwoManyXS1Bs]

Have you checked and retorqued engine mount bolts?

 

[Red Beard]

Ok yall new development,

So starting with the easier first I threw an extra fully charged battery on top of my battery and disconnected the reg/rec she fired up like usual and sounded strong, but volts were low at 10.2 but she pulled through all the revs all the way up through 4000+ (on the stand only didn't get a chance to take her out) with 0 issues, so I'm going to have to re do the test tomorrow and see if it happens again and if she will pull rpms that high in gear too. Lastly after I did rev her with the reg red off, she sat for a second then abruptly died, as if you turned the key off, then the key wouldn't work for a few seconds trying to turn it on, but was fine about 15 seconds later.... Hmmmm. More work to do tomorrow but figured I would post an update

 

[Red Beard]

Ok folks here's an update

++ Just for more info I have attached a diagram of my wiring system ++

*Ive removed the capacitor just to make sure that wasnt giving me any issues, and still have the same problem.
* Tried with a whole new battery and still had low voltage issues in high rpms (but it wasnt all the time, one run I did, there was no voltage issues then the next did....)
* Checked Reg/Rec with diode test per a general youtube video and it seemed to pass
* Don't have a torque wrench handy but the engine mount bolts seem to be pretty damn well on there.

To do:

1) D/C PMA and test pamco with coil
2) Take it for a spin with the reg/rec not connected

 

[Red Beard]

OK got some news!

Took bike out for a spin with all wires from PMA/reg rec disconnected and she ran perfect!! voltage dropped steadily down as I continued the ride but she ran just fine! ---Thanks Peanut!

So that tells me its either a PMA or a Reg/Rec issue!
This is a fairly new PMA and reg/rec that i ordered from TC bros on the 27th of Feb this year.

My suspicion is the PMA is not working since the Reg/ Rec passed the diode test. However I am still going to attempt Petes test and see what happens.

So Pete when I wire in that battery it should look like the diagram below correct? Only Disconnect the 3 yellow wires coming from the PMA but not the red/ green for the reg/rec? And attach battery power to the red wire that travels from pamco to the ignition coil?

thanks again for the help everyone! Hopefully the PMA is still in some kind of warranty, that thing wasn't cheap!

 

[TLCbobber]

did you take the pma rotor off when you checked it? I was reading a thread a few days ago, can't remember the exact issue, might have been similar to yours I'm not sure now. Been asleep since i read it. Hugh suggested checking the bolts and screws roundabouts the stator, he said they sometimes work loose and cause problems... turned out that's what it was... loose screws.

 

[Red Beard]

Im going to go check those right now thanks TLC!