idles fine but dying under power

[jun8ior]

Hi guys,

My bike broke down recently due to what I thought was just an issue with the main switch assembly. That has been fixed.
(http://www.xs650.com/threads/need-a-new-1979-yamaha-main-switch-assembly.60615/)

Now I am seeing the power cutting out when I apply the throttle.
It starts fine and idles well, you can even ride it around in first with just a little throttle, but as soon as you try to give it more gas it starts to cut out. If you back off the gas it goes back to idle, but if you keep trying to apply gas it will eventually die and not start again till its had a decent break. (flooded?)

It sounds like a power issue, but why would the power be interrupted from applying the throttle?
(You can see the neural/power light cutting out when giving it gas in the video.

The carbs have been cleaned this year and a new pamco installed at the beginning of the season.


The sound is a little muffled, but you can hear it backfire and having trouble maintaining the revs.
https://photos.app.goo.gl/Tf1yG9nS6Vw6Yc33A

Cheers!

 

[Jan_P]

Your rotor is gone I Guess .. Or to back off a little ....Start the engine measure the charging Voltage across the battery
it should be around 12 V at start and 14.4 ish revving
Please measure that and report back

 

[Adamc]

My bike following a full refurbishment shows similar issues.

I rebuilt the carbs using mostly new parts. The float pivots I couldn’t get at the time, and one of the old ones was slightly bent even after I tried to straighten it. I adjusted it to allow me to use the carb, but knew it would bite my ass. First ride out and after 20 miles it showed signs of fuel starvation, and cut out. Fired up ok, but apply throttle and it would die. A few Smacks of the carb and all OK, I got home. Next day another short ride and after a while same issue. Like you it starts and idles, but dies with throttle.

My guess is your fuel supply may be compromised. Carbs are delicate instruments and need care. Float heights could be affecting fuel supply.

 

[grizld1]

Weak spark will cause the trouble you describe. As Jan_P suggests, check that the alternator is charging first, then compare power at the battery to power at the coils. Next check condition and adjustment of points if you have 'em. Whatever ignition is in place, check that spark advances. Then check cam chain tension and valve adjustment. After all that, you can confidently hunt your gremlin in the fuel system.

 

[jun8ior]

Your rotor is gone I Guess .. Or to back off a little ....Start the engine measure the charging Voltage across the battery
it should be around 12 V at start and 14.4 ish revving
Please measure that and report back

Your rotor is gone?
Sorry, not sure what you mean by that.

I just charged the battery.
13 volts when off
12.2 volts while running so thats not good news.
I haven't measured it at the coils before...I'm not 100% on where they are, under the tank?


Cheers!

 

[WideAWAKE]

Your rotor is gone?
Sorry, not sure what you mean by that.

I just charged the battery.
13 volts when off
12.2 volts while running so thats not good news.
I haven't measured it at the coils before...I'm not 100% on where they are, under the tank?


Cheers!

there are many people here who know these electrical system very well and I’m sure they will chime in and iron your info out but at idle you are most likely gonna see a drop in voltage at the battery because the bike is pulling from it to stay running.

Don’t know the exact point of switch over (most bikes seem to be between 1900-3000rpm) they begin to produce power and no longer draw from the battery, but start to charge it back up. At which point you will see a rise in voltage (generally speaking).

 

[Jan_P]

Your rotor is gone?
Sorry, not sure what you mean by that.

I just charged the battery.
13 volts when off
12.2 volts while running so thats not good news.
I haven't measured it at the coils before...I'm not 100% on where they are, under the tank?


Cheers!

The rotor is the alternator rotor .. the charging electrical machine
The battery is a power storage thing and it delivers or receives current.
And if it never receives current it goes down until the bike stalls because no spark.

So when the bike starts ( Key switches on ) there should be the position of battery delivering current
But when the machine starts it should rise to the position the battery receives current / charging
and the voltage across the battery should rise to ca 14.4 V
If not so there is a defect in the charging circuit
As I understand your posting you cannot get it to rise to the 14:4 V

It can be different things causing that malfunction but common is the wrong resistance in the mentioned
Rotor

Please google
there is one video of the problem -- don't take off the rotor just yet

There are service manuals on line how to do the fault finding on the rotor
and here on the forum
xscafe has manuals
https://thexscafedotcom.wordpress.com/2011/01/10/xs650-manuals/

 

[5twins]

Perform the simple charging test. Test the voltage at the battery with the engine idling. You should see about mid 12's. Now rev the bike up to 3 to 3.5K RPMs. If you're charging OK, the voltage at the battery should climb up into the low to mid 14's. If there's no change then you're not charging.

 

[Jan_P]

Perform the simple charging test. Test the voltage at the battery with the engine idling. You should see about mid 12's. Now rev the bike up to 3 to 3.5K RPMs. If you're charging OK, the voltage at the battery should climb up into the low to mid 14's. If there's no change then you're not charging.

Yes Sir
One can also at the same time have the lights on and see if the intensity changes gong up to 3.5 K

 

[Adamc]

Sorry guys, I’m no expert amongst you people but reading the first post it could be a fuel issue? The word ‘Power ‘ could be fuel related.

 

[5twins]

Well, it could be just about anything, lol. The way the neutral light flickers when revved could indicate some loose wires. Revving it up (and increasing the vibration level) could be making a loose wire lose it's connection.

Many guys buy these old bikes and expect to hop on and ride off into the sunset, lol. These are 40 year old bikes so that doesn't usually happen. They pretty much all need a thorough going through, even if they look nice on the outside. And right near the top of this "to do" list is the wiring and all it's connections. And right next to that on the list would be cleaning and lubing all the moving parts. Many haven't seen any oil or grease since they left the factory, lol.

 

[Jim]

Sorry guys, I’m no expert amongst you people but reading the first post it could be a fuel issue? The word ‘Power ‘ could be fuel related.

There's an old axiom that Dick ( @grizld1 ) and I learned as young apprentices...

Never underestimate the ignition systems ability to trick you into blaming the carbs.

The mechanic I learned the most from would smack you in the back of the head if he saw you messing with the carbs before you made sure the ignition system was squared away. In their quaint little way... that's what griz and Jan are trying to do.

 

[Jan_P]

Sorry guys, I’m no expert amongst you people but reading the first post it could be a fuel issue? The word ‘Power ‘ could be fuel related.

Nothing to feel sorry about it can be a lot of things And even experts gets it wrong sometimes
( Not Mr Grizid and 5T and Jim ... of Course )
My modus operandi is Do the simplest cheapest first.
And then gradually escalate A loose fuse can shut down the whole thing
And in this case a simple measurement with straight back measured across the battery gives info.
You can wear a tie and 3 piece suit doing it not getting fingers dirty even.
Even if one don't now that these symptoms comes from a weak power supply
And has not been pushing bikes along the roadside
it is still simple and good idea to do --- so in fact it should be in the Tech section
as in
" Does the bike run poorly please measure charging voltage across battery "

 

[grizld1]

Sounds like our early bosses used the same teaching methods, Jim. I can hear it now: "How many times do I hafta tell ya? IGNITION FIRST, DAMMIT!" Jan, I can still be fooled. I once spent literally weeks trying to clear up an idle stumble in a right cylinder by playing with the carb. Ignition was fine. Compression was good on that cylinder, an exact match with the left. I finally did a leakdown test, assuming I'd find nothing because of the healthy matching compression. I locked down the crank at TDC with valves closed, and as soon as the pressure hit the cylinder a strong breeze started blowing from the intake port. Gauges showed 20% pressure loss, and tear down revealed a badly cupped intake valve. How that right cylinder could show an exactly matched 180 psi with the left with 20% pressure loss through the intake valve is still a mystery to me.

 

[jun8ior]

https://photos.app.goo.gl/Nf2mQb5XAty5V3DUA

This is going to be a fun one to fix.

 

[jun8ior]

Your rotor is gone?
Sorry, not sure what you mean by that.

I just charged the battery.
13 volts when off
12.2 volts while running so thats not good news.
I haven't measured it at the coils before...I'm not 100% on where they are, under the tank?


Cheers!

I can't get the revs up to see if it can get to around 14.
It could be the rotor, but I have my suspicions about another connection that might be vibrating while running.

I'll run the test on the rotor so that I can eliminate that first.


Cheers!

 

[jun8ior]

compare power at the battery to power at the coils. .

Cam chain tension was done in the last 2yrs.
New pamco ignition this year.

Haven't checked power at coils before..

 

[5twins]

Yes, it looks like you're losing electrical power when you try to rev it and the vibration levels increase. All the lights are cutting out, ignition too probably. Time to start checking all the wiring connections for a loose one. Don't rule out that ignition switch you just "fixed", it may not be quite right yet.

 

[Jan_P]

Yes, it looks like you're losing electrical power when you try to rev it and the vibration levels increase. All the lights are cutting out, ignition too probably. Time to start checking all the wiring connections for a loose one. Don't rule out that ignition switch you just "fixed", it may not be quite right yet.

Yes you might get lucky on the $ 100 for a rotor not needing to replace it
I would check it anyways since it wont hurt to have a look at the brushes
And then inspect the connectors .. From the fuse box is one big connector I had problems with lately
The connector was together but one pin barb was off so instead of making the connection it pushed the female part backwards and did not connect properly.
I grind a little and apply copper grease but there can be better alternatives..
Kill switch / Fuse Holder / Ignition Lock / Rubber grommet going in to headlamp.

No expert on the LED lamps but I believe they don't dim as much either they are on or off .
So the flickering can perhaps still be a borderline 12 V but again I am no expert

 

[jun8ior]

Alright!

Progress!

I had heard a clicking noise (solenoid) when I first started poking around in this area on the day it broke down, but the noise was also happening with the lose ignition. So once I fixed that, I was hoping I had found the only problem.

No such luck!

https://photos.app.goo.gl/TyM4t8968wS3rkEJA

I did cut into the plastic casing to see if the main/large cable/wire had a break in it but I couldn't see anything wrong in that area. Is the cylinder I am pressing on a solenoid?

Cheers!