[esq'z me]

Just a note about venting....the fuel pump will pump fuel even if the tank doesn't vent. It will draw a vacuum inside the tank large enough to implode the tank but the bike will keep running.
I have seen F4 tanks and Suzuki GSX-R tanks and others literally collapsed from blocked tank vent hoses. The pump cares not that air isn't entering the tank to replace the fuel used....it just keeps pumping.

 

[silentservice703]

The beauty of Positive Displacement.

 

[EBBO]

One would think that an emergence port could open if the main vent gets blocked. That action could trigger a warning and shutdown to avoid such implosion. How hard would a little redundancy be? 🤷‍♂️

 

[ZackAttack]

Just a note about venting....the fuel pump will pump fuel even if the tank doesn't vent. It will draw a vacuum inside the tank large enough to implode the tank but the bike will keep running.
I have seen F4 tanks and Suzuki GSX-R tanks and others literally collapsed from blocked tank vent hoses. The pump cares not that air isn't entering the tank to replace the fuel used....it just keeps pumping.

Yes I appreciate that, I'm just exploring all possible avenues as looking over the fuel pump assembly diagrams I cant see how the pump could starve for fuel with half a tank. As for the venting I am surmising that possibly the pump is failing and with the added vacuum it struggles to deliver the required pressure. It doesn't explain why the symptoms occur after a turn though. I am going to take it out for a run this weekend and try to replicate the symptoms then open the tank and see if the symptoms persist without topping up the tank. Then i can replace the pump if needed when I do the hoses and filter.

 

[silentservice703]

I doubt it is a fuel pump issue.
when is the last time the Fuel Disconnects were manipulated?

 

[ZackAttack]

Unfortunately that is unknown, as previously stated I have no service history for the bike.

 

[silentservice703]

Ok.

 

[ZackAttack]

Whilst I understand and appreciate the tank internals are serviceable parts and probably need replacing (but for all I know the previous owner may have already been in there)

Ultimately I would like to have a better idea of what is causing the issue and not just throw parts at it in the hope that one of those parts fixes the issue. Given the way the tank internals are arranged 1/2 tank of fuel should not cause any issues.

Damaged or blocked hoses or even the filter would be problematic even with a full tank yet the bike displays no symptoms when above approx 1/2 a tank. Hence the reason for questioning the venting and fuel pump.
The rationale is that as the fuel level in the tank drops the vacuum in the tank increases until the pump begins to struggle but again as I said earlier it doesn't explain why it only occurs for a short moment after completing a turn. Hopefully I can replicate the symptoms on the weekend.

 

[silentservice703]

Right or Left turn ?

 

[ZackAttack]

Was both but seemed worse after turning right but that could have been a different lean angle. Too many inconsistencies to say 100%

 

[mitchy]

When this starvation happens have you opened the fuel cap to see if vacuum is occurring in the tank?

 

[ZackAttack]

I stopped and filled the tank at the first servo. There was a pressure difference when i opened the cap.
But I filled it up at the same time and the issue resolved. In hind sight I should've ridden on with out refuelling which would've confirmed it there and then.

 

[ZackAttack]

so, had a look inside the tank tonight I can see that somebody has done the internals at some stage as the hose clamps have been replaced, all the hoses look fine. The plan for tomorrow is to drain the tank to below half and take it for a run and see if misbehaves.

 

[ZackAttack]

Ok so I’m fairly certain this is looking like a venting/vacuum issue. Drained the tank today rode for 50km then the low fuel light came on rode another 10km to servo and filled up. tank took 16.5 litres. Didn’t miss a beat until the last 200 metres where it didn’t like anything above the 1/8 throttle or so.
Now that the tank is full, the next test is another long ride and see what happens as the tank emptie.

 

[silentservice703]

Now that the tank is full, the next test is another long ride and see what happens as the tank emptie.

I'm sure you've figured this out, but when the symptoms reoccur on your long ride, if they do, then at that point pop open the fuel tank lid and continue the ride. That will certainly tell you if it is a tank venting issue.

 

[ZackAttack]

I'm sure you've figured this out, but when the symptoms reoccur on your long ride, if they do, then at that point pop open the fuel tank lid and continue the ride. That will certainly tell you if it is a tank venting issue.

Yea that’s the plan.

 

[mv2envy]

Could possibly be a weak fuel pump also. The pump in my F4-1000 went out and I had to replace it. The pump in yours could just be on its way out. With full tank there is more fuel (more weight) punching down onto the pump helping it along. With half a tank it may not be enough to get fuel delivered. If it turns out to not be vent related, I would replace the pump. It’s easy and cheap to do.

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