V-Star 650 seems to be firing on 1 cylinder - 10k Miles - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 6 (permalink) Old 08-26-2019, 07:54 PM Thread Starter
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V-Star 650 seems to be firing on 1 cylinder - 10k Miles

Hello all, this is my 2nd post. I have done a search and found multiple entries for this type of issue that my brothers bike is having. I did go through a lot of the steps others had already taken, but would like to ask if what I just tested and found today is a big turn in the troubleshooting.

First, what's been done prior to today:

- Found a small animal had made a food storage bin out of the air intake. Good news is it didn't get past the air filter.
- remove carbs, found cracks in the (2) intake boots that mate with the cylinders - replaced them
- sealed up the intake air boots from the carb to the black box. (Those showed openings where leaks could occur)
- drained all gas from tank and bowls
- confirmed fuel pump is pumping into bucket
- new plugs - gapped
- removed bowls and cleaned, removed and inspected/cleaned jets, replaced the needle and seat on the float. (Performed level setting using the U-tube method from the service manual, while
leveling the bike)
- replace fuel filter
- replace air filter
- remove and inspect slides and diaphragms - cleaned aluminum residue and made sure slides were free, no tears in diaphragm
- checked each spark plug connector once disconnected from the plug wire, for the ~5k ohm resistance explained in the manual, both are about 4.6K Ohm
- hooked up the sync gauges and intake vacuum is only 2-3" Hg when manual specs 7-8" Hg @ 1100 RPM warm.


Before the above work, it went from a bike that was rode every year from 2004-2014, then sat for 3 years. My brother tried to start it (once he cleaned the out the animal food and filled with new gas), and it barely made it around the block after it warmed up.

Now after performing the above work here are what is still happening:

-It will idle fine with the choke on but sound like a low RPM Lawnmower, once warm, if you open the choke, the idle screw is maxed out to keep it idling
-Still sounds like it's only running on 1 cylinder, extremely slow throttle response when idling.
-if you crack the throttle, once it does rev up, it stays high in idle for about 2-3 seconds before the RPM's come down, like what would sound like an intake leak or throttle cable issue


Now what I found out today was odd. First, I was going to check cylinder compression, but didn't have the metric adapter. So instead started looking at the ignition system more and decided to just unhook one of the spark plug wires and start it. So with the front plug wire removed it definitely sounds like what it does with both of them in. I reinstalled the front wire, removed the rear, and it still runs. Now I had to pull the choke back out to keep it running on the front but it idled fine and i could rev the engine.

So in doing that, have I ruled out anything by being able to run each cylinder separately, but the front doesn't fire when both are plugged in.

Let me know if I am missing some steps. The one thing I haven't done is entirely disassemble the carbs from each other. I have read stories of throttle plate shaft seals leaking. Maybe that's the next step.
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Owns/works on -
1980 Kawasaki KZ550
1995 HD 1200 Sportster
2000 HD Ultra Classic
2004 Yamaha VStar 650 Classic
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post #2 of 6 (permalink) Old 08-26-2019, 08:21 PM
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The Vstar is a duel fire ignition system, meaning each cylinder fires twice per revolution. There was an issue once here that the plug boot on one of the cylinders was not making a good connection. The spark will go go where there is less resistance. You said front cylinder didn't want to fire. Check the plug wire where it goes into boot for faulty connection. See picture below.



I didn't see that you ran a spark test. Below is easiest way to test spark, any auto parts store sells them. Report back results.


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post #3 of 6 (permalink) Old 08-27-2019, 07:12 AM Thread Starter
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We did NOT run a spark test as shown above. We did however remove each plug and touch to ground to watch the spark. Also we removed the boot from each plug wire when we tested the resistor values. But that tool above is something I should own anyway... :P

And as mentioned above, the front cylinder DOES fire when we unplug the rear plug wire. It's weird.

Have fun and Ride safe!

Owns/works on -
1980 Kawasaki KZ550
1995 HD 1200 Sportster
2000 HD Ultra Classic
2004 Yamaha VStar 650 Classic
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post #4 of 6 (permalink) Old 08-27-2019, 07:38 AM
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Its possible the ignitor unit (module that switches the spark coils on by grounding the low side of the coil) has a bad ground to the frame, bad connection to the +12V, or the coils themselves have a bad connection the +12V relay or to the frame ground. Its also possible the ignitor is failing and is firing both coils at the same time?

Start with the power and gnd connections to the ignitor and the coils.

one thing not on your list: a battery more than 3 years old that was never charged is most likely shot. The electronic ignition needs a solid 10V or more while cranking to fire the plugs. Can you put a meter on the battery and see what the voltage is doing while its running, and then put the neg lead on the frame and make sure its the same voltage - sometimes the battery ground wire to the frame gets corroded, what problems that creates is unpredictable.
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Last edited by KCW; 08-27-2019 at 07:41 AM.
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post #5 of 6 (permalink) Old 08-27-2019, 07:57 AM Thread Starter
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Quote:
Its possible the ignitor unit (module that switches the spark coils on by grounding the low side of the coil) has a bad ground to the frame, bad connection to the +12V, or the coils themselves have a bad connection the +12V relay or to the frame ground. Its also possible the ignitor is failing and is firing both coils at the same time?
From what I've read, both coils will fire at the same time on this system? (wasted spark)

Quote:
One thing not on your list: a battery more than 3 years old that was never charged is most likely shot. The electronic ignition needs a solid 10V or more while cranking to fire the plugs. Can you put a meter on the battery and see what the voltage is doing while its running, and then put the neg lead on the frame and make sure its the same voltage - sometimes the battery ground wire to the frame gets corroded, what problems that creates is unpredictable.
Good catch, I did fail to mention that the battery was replaced this spring, when all the troubleshooting started. But checking all the connections to the coils has NOT been done yet. We will check that also.
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Have fun and Ride safe!

Owns/works on -
1980 Kawasaki KZ550
1995 HD 1200 Sportster
2000 HD Ultra Classic
2004 Yamaha VStar 650 Classic
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post #6 of 6 (permalink) Old 08-27-2019, 08:04 AM
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the wiring diagram shows the ignitor and the coils on the top right side of the image. Each coil has a separate wire to the ignitor, so I cant think of any reason why it would fire both at the same time, since the pistons are more then 90 out of phase - I think that would make the front piston fire in the middle of the compression stroke?

I thought wasted spark means that each piston fires (on its own) at the top of the compression stroke, and the top of the exhaust stroke. That would make sense, the controller does not have to know which stroke its on, only TDC + advance.

If the controller does fire both plugs at the same time, that would be even more reason to look for a bad +12V or ground connection somewhere in that circuit, because a bad connection could allow one side to grab more current, or it might not have low enough resistance for both to fire at the same time.

if that pasted image is too small to read here is the website: http://madchopshop.blogspot.com/2015...g-diagram.html

save it to your laptop then open it as a photo and you can zoom in - is a 1600 pixel wide jpg.
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