Bucking, surging and dying at idle

I told myself if the same symptoms came back it is probably not the phase sensor that I have replaced twice.

Took the bike for a test run and it nearly stranded me, see title.

Exact symptoms as previously. Bike runs fine until hot then PPPBBLLLHHHHTTTT.

As my diagnostic skills seem to be lacking I open the floor to ideas.

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Did you get the shimming right? The last pic of it I saw it had had a close shave...

Yeah, I replaced that sensor and used a stock size shim. It started and ran fine on a short trip into town yesterday on a cool afternoon. Today hit 81 F/ 27 C so I thought I could get it up to temperature as a test. 25 minutes into a casual ride the bucking started. It stalled at every stop.

I got the same results with three different phase sensors and a variety of shim stacks so I am ready to look elsewhere.

Is the tank breather vent clear?

This is vexing me. It shouldn't be this difficult.

Pete Roper wrote:

Is the tank breather vent clear?

This is vexing me. It shouldn't be this difficult.

I will check it but this problem seems temperature related. Bad coil that flakes out when hot?

It was good and hot when I made it home. I put a timing light on the right plug wire and it flickered at times and held steady pulses at others while idling.

Then the bike would just stop.

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What do the plugs look like?

That's left & right, in order?

Not awful. Left looks like it could use a smidge less fuel, and right, a smidge more.


I would expect one to be more fouled if the there was no spark.

Yup. But the strobe says spark is dropping out Can you plumb a noid light into the ignition circuit? And then into the injector circuit?

Plugs are in order, hard to tell if the spark is dropping and slowing the idle or vice versa.

"Can you plumb a noid light into the ignition circuit? And then into the injector circuit?"

'splain please!

beetle wrote:

That's left & right, in order?
Not awful. Left looks like it could use a smidge less fuel, and right, a smidge more.
I would expect one to be more fouled if the there was no spark.

Agree. Do you suspect fuel starvation? Is this something GuzziDiag can show?

GuzziDiag won't show a pump or filter problem, but you can test the injectors. Fire them into a container to see if you get approximately the same volume from each side.

Thinking more about the plugs, you would ideally have to pull them immediately after the problem occurs to confirm.

beetle wrote:

GuzziDiag won't show a pump or filter problem, but you can test the injectors. Fire them into a container to see if you get approximately the same volume from each side.
Thinking more about the plugs, you would ideally have to pull them immediately after the problem occurs to confirm.

The "problem" was occurring to the point that I I had to push the bike the last 20 yards (uphill!) to get it to the garage. Plugs were pulled once the engine cooled a bit.

Thinking pump/fuel filter Hmmm?

Recap:

Bike has less than 10K miles, problem started at 6K.

Starts and runs perfectly until hot then intermittantly cuts out while running and will die at a stop if not revved

In that case, definitely test the injectors.

I don’t think it would be the filter, as it would cause issues even when cold.

Pump? Maybe, but how do you confirm? Kinda hard to simulate the conditions when it occurs.

beetle wrote:

In that case, definitely test the injectors.
I don’t think it would be the filter, as it would cause issues even when cold.
Pump? Maybe, but how do you confirm? Kinda hard to simulate the conditions when it occurs.

Injectors first then maybe swap the pump... What could go wrong  ¯\_(ツ)_/¯

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guzziownr wrote:

Plugs are in order, hard to tell if the spark is dropping and slowing the idle or vice versa.

"Can you plumb a noid light into the ignition circuit? And then into the injector circuit?"

'splain please!

Noid light? Tiny globe or LED that you put in parallel with the item being tested. If it illuminates then it shows you're getting signal.

I'll echo Pete's comment re the venting being a possibility;you haven't confirmed if that was verified.

I'd read about "tank suck" issues a few times,but never experienced it until recently with my '03 V11 Lemans.

Similar scenario & symptoms; low mileage,new to me bike,that the venting had to be completely replumbed to atmosphere & the tank vents cleared & opened up in order for it to run properly.

Hopefully your fix can be that simple.

The intermittent spark indicated by the strobe points away from a venting issue but it's certainly worth checking. The tank vent is the one on the right. On the 1100's they ar on the bottom of the tank, the vent will go to the charcoal canister if still fitted or vent to atmosphere if it has been removed. The nipple on the left is the gutter drain from the filler.

If the problem is appreciably worse, or starts quicker, when the tank is full? Then it is almost certainly a vent issue.

80CX100 wrote:

I'll echo Pete's comment re the venting being a possibility;you haven't confirmed if that was verified.
I'd read about "tank suck" issues a few times,but never experienced it until recently with my '03 V11 Lemans.
Similar scenario & symptoms; low mileage,new to me bike,that the venting had to be completely replumbed to atmosphere & the tank vents cleared & opened up in order for it to run properly.
Hopefully your fix can be that simple.

I had really bad tank suck with my '04 V11 Sport. Fixed by repositioning the tip-over valve. My tank is almost empty so I will pop it up and check the hoses.

If it's almost empty it's unlikely to be that.

The larger the air volume in the tank the greater the time it will take for the tank to become so depressurised that it can overcome the pump. If your tank is nearly empty you could try just opting it open with the second key when the problem starts. If that doesn't cure it then it's not a tank pressure problem.

Pete Roper wrote:

If it's almost empty it's unlikely to be that.
The larger the air volume in the tank the greater the time it will take for the tank to become so depressurised that it can overcome the pump. If your tank is nearly empty you could try just opting it open with the second key when the problem starts. If that doesn't cure it then it's not a tank pressure problem.

Agree, given the state of the plugs I am leaning towards injectors/fuel pump.

The fact that it has to get hot to act up and that the problem has been getting steadily worse makes me think a slowly failing fuel pump.

Iirc,some of the early model Grisos had the internal fuel lines that would fall apart from the ethanol & fuel;

Could that be a factor for your bike?

fwiw idk

80CX100 wrote:

Iirc,some of the early model Grisos had the internal fuel lines that would fall apart from the ethanol & fuel;
Could that be a factor for your bike?
fwiw idk

Nope, it starts and runs until it gets hot. Fuel lines popping off means no start, no run...