Vapor lock, most unfun

[ALdad]

Rode 150 mi. today. Temp in the 90's. I got stuck twice with vapor lock. Once after a 20min. stop and once after a 2 min stop. Both times I disconnected fuel line and burped it waited 20 min and off we go. I raised the fuel line off the cylinder a while back I thought this would cure it, I guess not. any other cures?

[v50man]

Having same problem.......

 

Oi.......

[ALdad]

Well your no help!!, Well, it's nice to have others to share the pain. I am sure some of the tribal elders will send us some smoke signals .

[Steve G.]

May 17th at a gas stop just north of Coulee Dam, Washington, 92deg F, the bloody samew thing happened to me, again! I thought I had it fixed, as it had no issues in 2 1/2 yrs since I re-routed the fuel lines away from the engine. The fix this time was very quick though. I told the guys I was with that I'd meet them back at the hotel, but they wanted to fix it. My usual 'burping' involves loosening the fuel line clamp under the left side, at the on/off valve. There was no vapour [air] this time, just a release of pressurized gas, spraying about 2 ounces in about 1 1/2 minutes. I put the fuel clamp tight, started up right away with no issues, was no problem after that.

I'm wondering if this has something to do with an over pressurisation of the lines, which is causing technical problems. I'm not sure what the proper psi of the system is at operating conditions, but the way it sprayed out, it was at least 15 psi, and most EFI systems on bikes are less than 5 psi.

Just so we are clear on what actually is happening to my bike during these times. After as little as a 5 minute stop in hot weather and regular running temperature engine, a turn of the key starts a definitely different sounding fuel pump ramp up, almost like a bubbling purcolating sound. The engine almost always starts right of like usual, but when the throttle is turned just slightly, the begins an inconsistant back firing, and stuttering, which gets worse the more you turn the throttle, until when you turn the throttle to near full open, the engine struggles to reach rpms, and will stall in a giant heave eventually.

It pisses me off, and, I starting to get impatient with this machine. If it continues, and if other things start niggling again, this may just push me to change. This is the only issue I've had with it in over 4 yrs, after a difficult first 3 yrs. I need to find this problem, soon.

Steve

[ALdad]

May 17th at a gas stop just north of Coulee Dam, Washington, 92deg F, the bloody samew thing happened to me, again! I thought I had it fixed, as it had no issues in 2 1/2 yrs since I re-routed the fuel lines away from the engine. The fix this time was very quick though. I told the guys I was with that I'd meet them back at the hotel, but they wanted to fix it. My usual 'burping' involves loosening the fuel line clamp under the left side, at the on/off valve. There was no vapour [air] this time, just a release of pressurized gas, spraying about 2 ounces in about 1 1/2 minutes. I put the fuel clamp tight, started up right away with no issues, was no problem after that.

I'm wondering if this has something to do with an over pressurisation of the lines, which is causing technical problems. I'm not sure what the proper psi of the system is at operating conditions, but the way it sprayed out, it was at least 15 psi, and most EFI systems on bikes are less than 5 psi.

Just so we are clear on what actually is happening to my bike during these times. After as little as a 5 minute stop in hot weather and regular running temperature engine, a turn of the key starts a definitely different sounding fuel pump ramp up, almost like a bubbling purcolating sound. The engine almost always starts right of like usual, but when the throttle is turned just slightly, the begins an inconsistant back firing, and stuttering, which gets worse the more you turn the throttle, until when you turn the throttle to near full open, the engine struggles to reach rpms, and will stall in a giant heave eventually.

It pisses me off, and, I starting to get impatient with this machine. If it continues, and if other things start niggling again, this may just push me to change. This is the only issue I've had with it in over 4 yrs, after a difficult first 3 yrs. I need to find this problem, soon.

Steve

Ya this sounds similar. Only I pry the hose off slowly and it squirts gas pretty good.I dug into the threads last night and I'm thinking a fan or relocating the pump to the frame behind the oil cooler. I havent noticed the pump sounding weird, but that just means I not noticed. I plan on doing some high mi. this summer by my self, I'm getting a little paranoid.

[twhitaker]

An idea I've been kicking around for some time involves moving the fuel pump and filter to the rear subframe away from the heat. There looks to be room between the upper rear subframe rails and the tail carapiece on either side for those components to reside.

[Steve G.]

Ya this sounds similar. Only I pry the hose off slowly and it squirts gas pretty good.I dug into the threads last night and I'm thinking a fan or relocating the pump to the frame behind the oil cooler. I havent noticed the pump sounding weird, but that just means I not noticed. I plan on doing some high mi. this summer by my self, I'm getting a little paranoid.

 

I don't think you should be paranoid about taking it on long runs, with this issue anyways. I've put some big runs on my bike, from Vancouver to southern Utah, California, Montana, encountering serious heat. This vapour lock issue has never stopped me, but has on rare occasion delayed me by as much as 2 hrs. In the early stages I was still unsure what the problem was, and was looking elsewere on the bike. Now that I know what the problem, and fix are, I can clear the problem within 15 minutes, like I did the other day in the middle of nowhere.

The only thing to be aware is the possibility of a flash point as you went the gas/air mixture, as it drips on the hot exhaust.

I won't bother relocating the fuel pump, as there's not much room to be had on this machine. I may decide to buy more heat shielding to wrap the pump, as I understand from fellow V11 local owner Ryan that it's working for him. I'm still not 100% convinced it's the pump that's getting hot, but the fuel lines snaking around between the tank and engine V. For those post 2001 bikes with pump in the tank, I'm thinking the pump being immersed in fuel is the best way to keep the pump, and fuel cooler.

Steve

[ALdad]

I can clear the problem within 15 minutes, like I did the other day in the middle of nowhere.

What do you do to get going in 15 min?

[Steve G.]

What do you do to get going in 15 min?

That's all it took last Sunday. Drained the fuel pressure right off, tightened the fuel clamp up, and it started with no issues. It was probably 92-95 deg F at the time. Might have gotten lucky.

Steve

[dlaing]

OK, even I admit this following idea is possibly out there, but all this talk of double switched fuel pressure regulators, huffing, and venting off fuel pressure got me thinking, what if you attached a hose to the non used vacuum port on the fuel pressure regulator and sucked on the hose?

We only need our lung/diaphragm power to create a vacuum of 10mm Hg. I went to the garage to test my huffing ability and got my vacuum meter up over 200mm Hg, so that is not a problem.

Does anyone know first aid for mercury poisoning?

 

Just kidding. I know, not funny... FWIW I used a mechanical gauge that contained other toxins than Hg

 

Anyway, could this be a cure for vapor lock?

It won't knock the fuel pressure down completely, like disconnecting the fuel line, but it might do the trick???

[raz]

Anyway, could this be a cure for vapor lock?

It won't knock the fuel pressure down completely, like disconnecting the fuel line, but it might do the trick???

Steve said he burps it on the left side, that confuses me. That line is unpressurized, it's the fuel pump intake line, no? And isn't that side open to burp itself back to the tank as long as any electrical petcock is open?

 

Hm, I just got this idea. Could this vapour lock be due to hysteresis/tolerances between the fuel pump internal overpressure valve and the pressure regulator? The heating builds up pressure between pump and pressure regulator so the latter is just barely closed, but the overpressure valve in the pump opens as the fuel pump starts? If so, your idea might clear the deadlock. Also, connecting the regulator reference to intake manifolds may be a permanent fix...

 

The FPR is nominal 3 bar (44 psi) and the OPV in the pump is 5 bar (73 psi) which I guess is enough difference to speak against my theory though. But static pressure build-up during that 5 minute stop may affect the valves differently than normal running does.

 

Just a thought

[dlaing]

Hm, I just got this idea. Could this vapour lock be due to hysteresis/tolerances between the fuel pump internal overpressure valve and the pressure regulator? The heating builds up pressure between pump and pressure regulator so the latter is just barely closed, but the overpressure valve in the pump opens as the fuel pump starts? If so, your idea might clear the deadlock. Also, connecting the regulator reference to intake manifolds may be a permanent fix...

I think so. Technically it is the heat causing the vapour lock, but the relief valves may be aggravating the situation.

Why does the vapor lock go away when the pressure is released?

Is it a matter of decrease in pressure results in decrease in temperature?

Lower pressure lowers the point of vaporization, so it seems a little counter-intuitive.

But maybe the decrease in pressure and resulting movement of fuel allows the vapor lock bubble to enlarge and break up???

[Steve G.]

Steve said he burps it on the left side, that confuses me. That line is unpressurized, it's the fuel pump intake line, no? And isn't that side open to burp itself back to the tank as long as any electrical petcock is open?

 

Hm, I just got this idea. Could this vapour lock be due to hysteresis/tolerances between the fuel pump internal overpressure valve and the pressure regulator? The heating builds up pressure between pump and pressure regulator so the latter is just barely closed, but the overpressure valve in the pump opens as the fuel pump starts? If so, your idea might clear the deadlock. Also, connecting the regulator reference to intake manifolds may be a permanent fix...

 

The FPR is nominal 3 bar (44 psi) and the OPV in the pump is 5 bar (73 psi) which I guess is enough difference to speak against my theory though. But static pressure build-up during that 5 minute stop may affect the valves differently than normal running does.

 

Just a thought

 

 

You have put forward a very good point, and I have an idea.

The pressurized system goes right to the bottom of the petcock from the fuel tank. This is where I vent off the pressure. Now, on 2001 bikes with standard electric fuel petcocks, when you turn the ignition on, this automatically opens the petcock, and also ramps up the pump to bring pressure to the system. OK, when you turn the bike off, this automatically shuts the petcock closed, thereby sealing off any pressure built up, which is then elevated during the heating up of static fuel within the heated lines over top of the engine.

I'm wondering if a manual petcock, [the one where you have to turn or push the knob to shut off fuel when you want to remove the tank,] would be a cure for this problem?

Steve

[ALdad]

You have put forward a very good point, and I have an idea.

The pressurized system goes right to the bottom of the petcock from the fuel tank. This is where I vent off the pressure. Now, on 2001 bikes with standard electric fuel petcocks, when you turn the ignition on, this automatically opens the petcock, and also ramps up the pump to bring pressure to the system. OK, when you turn the bike off, this automatically shuts the petcock closed, thereby sealing off any pressure built up, which is then elevated during the heating up of static fuel within the heated lines over top of the engine.

I'm wondering if a manual petcock, [the one where you have to turn or push the knob to shut off fuel when you want to remove the tank,] would be a cure for this problem?

Steve

On my 2000 bike with the broken wire, I am assuming it is stuck in the open position. cuz the bike still runs. when I burp it there is still plenty of pressurs in the line.

[raz]

You have put forward a very good point, and I have an idea.

The pressurized system goes right to the bottom of the petcock from the fuel tank. This is where I vent off the pressure. Now, on 2001 bikes with standard electric fuel petcocks, when you turn the ignition on, this automatically opens the petcock, and also ramps up the pump to bring pressure to the system. OK, when you turn the bike off, this automatically shuts the petcock closed, thereby sealing off any pressure built up, which is then elevated during the heating up of static fuel within the heated lines over top of the engine.

I'm wondering if a manual petcock, [the one where you have to turn or push the knob to shut off fuel when you want to remove the tank,] would be a cure for this problem?

Steve

Don't you have the FPR and fuel return on the right side? Is the solenoid for return too?

 

On my 2000 bike with the broken wire, I am assuming it is stuck in the open position. cuz the bike still runs. when I burp it there is still plenty of pressurs in the line.

You say in the other thread no fuel comes out when you remove the hose. That's another wierd story but I can't think of any other explanation for it than that the pump can actually overcome the solenoid valve.

 

OTOH, unfortunately Al and others has reported vapour lock with a manual valve. See here.

 

But this intake side discussion has me confused. As far as I know, when the pump is not running it essentially blocks the line. That is, with an open petcock, there is only gravity pressure on the left side when the pump stops, while the pressure on the right side remains (for a while). I can't figure out why burping left side would solve anything.