Fuel starvation at speed

[Bbennett]

Here is a mystery. I installed a manual petcock and shielded by fuel lines with firesleeve on a 2002 V11 Sport. I have had no history of problems, just wanted to get rid of the elec petcock.

 

I can accelerate briefly at full throttle in town and on a short freeway onramp. BUT, if I apply too much throttle on the highway, I get severe cavitation after approx 3 seconds - feels like fuel starvation to me. 1-2 seconds of throttle twist is OK.

 

I reviewed the threads on Vapor lock - and I do not see or hear any evidence of it on my bike.

 

What is feels like (after 100 miles of very gingerly holding the throttle barely open and GRADUALLY applying throttle to get up to speed) is that the new petcock is not letting enough fuel thru. I am positive it is on full open.

 

There is also a slight high pitched whistle now at idle. Fuel pump spinup sounds normal.

 

ANy ideas on how I can get back to twisting the throttle again at will on the open highway?

 

Thanks,

Bob

[Greg Field]

Any extra noise from the pump?

 

Check the screen on the new petcock. It may be partially plugged with sediment stirred up in the changing. Also, consider changing the filter.

 

I put one of those on an Aluminum two weeks ago. Today the guy came back with similar issues. We cleaned the screen and it's better, but I think we're going to have to change the filter, too.

[Guest ratchethack]

What is feels like (after 100 miles of very gingerly holding the throttle barely open and GRADUALLY applying throttle to get up to speed) is that the new petcock is not letting enough fuel thru.

Bob, I think you've nailed it^. Most manual petcocks likely to fit are designed for carbed bikes. Their spec'd flow rates are relatively low, since fuel does not circulate in a carbed bike, it only has to drain through at "sipping" flow rates, only enough flow to replenish and keep the float bowls up to level. Electric fuel petcocks for FI systems, OTOH, have to operate at high enough flow rates to keep fuel flowing in a constant circuit back through the tank to ensure optimum presure at all times at the injectors, according to the FPR. I don't know exactly what you installed, just suggesting that since the problem only showed up after you installed it, the manual petock itself may be a "bottleneck" to adequate flow rate, causing a drop in fuel pressure.

 

Good luck.

[dlaing]

Look for a kinked fuel line.

Are you getting a tank suck issue? To test, go for ride, pull over, pop gas cap, and if the tank bloats like a balloon, you have the tank suck issue and need to properly re-orient the tip-over valve. I have not heard of the tank suck issue causing your symptoms, but maybe???

[Bbennett]

Thanks for all of the excellent replies. There is no suck issue on my red frame V11 and the fuel pump sounds normal. It feels like I am pumping fuel from a reservoir (e.g. the full fuel line) when I twist the throttle but the input to the reservoir (e.g petcock) cannot "refill" it at a fast enough rate. I will check filters and then revert back to old elec petcock as needed. I thought the manual petcock would be better in that it is "simpler"! I will report back, thanks again.

[ScottS]

Thanks for all of the excellent replies. There is no suck issue on my red frame V11 and the fuel pump sounds normal. It feels like I am pumping fuel from a reservoir (e.g. the full fuel line) when I twist the throttle but the input to the reservoir (e.g petcock) cannot "refill" it at a fast enough rate. I will check filters and then revert back to old elec petcock as needed. I thought the manual petcock would be better in that it is "simpler"! I will report back, thanks again.

 

 

Which part # petcock do you have ? I have RBN015164 , it is an alternative to the electric ( a Moto Guzzi part ) and is supposed to supercede the electric, I don't think that it would be so restrictive, but Haven't installed it yet - so I am very interested in this topic

[Steve G.]

Look for a kinked fuel line.

Are you getting a tank suck issue? To test, go for ride, pull over, pop gas cap, and if the tank bloats like a balloon, you have the tank suck issue and need to properly re-orient the tip-over valve. I have not heard of the tank suck issue causing your symptoms, but maybe???

 

I had exactly the same issue with my 2001 after installing the manual petcock, and installing firesleeve. As Dlang noted, check the main fuel line's integrity and straightness. The firesleeve makes things quite crowded up in there, as you may have discovered, and it must be cut the correct length, too long and it will bunch up, easily kinking the main fuel line off the petcock.

I've been riding my V11 through some of the hottest days ever in my parts, over 100deg F, with absolutely no issues of vapour lock. I think the replacement of the electric petcock to manual is just as much a factor in this problem's elimination as the installation as the firesleeve, probably the main contributor. Whoever thought up the electric petcock should be removed from Guzzi's engineering team.

 

Steve

[Greg Field]

If the manual petcock is the Guzzi one and is wide open, it can supply plenty of fuel, even for race use. Check the screen and for kinks.

[ScottS]

Which part # petcock do you have ? I have RBN015164 , it is an alternative to the electric ( a Moto Guzzi part ) and is supposed to supercede the electric, I don't think that it would be so restrictive, but Haven't installed it yet - so I am very interested in this topic

 

Here is what I have

 

 

[jtucker]

I've got (what appears to be) the same manual petcock pictured above on my 2000 V11S and no issues.

 

__Jason

[Bbennett]

OK, that is the same petcock I have (original poster here).

 

So I removed the manual petcock and found quite a bit of gunk - presumably from bad petrol. I noticed the manual petcock did not seem to open all the way - and then compared it to other manual petcocks Greg had lying around. All appeared to not open all the way - so I assume this is "as designed".

 

I reinstalled the manual petcock after cleaning the filter, removing the bad gas that had rust particles --and the problem was still there.

 

I soldered the old electric petcock back together and re-installed it. The problem remains. Cavitation on freeway when throttle is applied quickly. Also happens on uphill situations.

 

So that leaves 3 possibilities:

 

1. The main fuel filter is clogged. I have never replaced it. I believe this is the culprit.

 

2. The fuel pump is failing and can't keep up in high fuel flow situations. I do not think a pump would work fine at low load and then fail at high loads.

 

3. A kinked fuel line. I do not see a kink the fuel line.

 

My next step is to replace the elec petcock with the manual one (since the manual one is proved to not be the problem). And wait for a new fuel filter.

 

Bob

[Steve G.]

OK, that is the same petcock I have (original poster here).

 

So I removed the manual petcock and found quite a bit of gunk - presumably from bad petrol. I noticed the manual petcock did not seem to open all the way - and then compared it to other manual petcocks Greg had lying around. All appeared to not open all the way - so I assume this is "as designed".

 

I reinstalled the manual petcock after cleaning the filter, removing the bad gas that had rust particles --and the problem was still there.

 

I soldered the old electric petcock back together and re-installed it. The problem remains. Cavitation on freeway when throttle is applied quickly. Also happens on uphill situations.

 

So that leaves 3 possibilities:

 

1. The main fuel filter is clogged. I have never replaced it. I believe this is the culprit.

 

2. The fuel pump is failing and can't keep up in high fuel flow situations. I do not think a pump would work fine at low load and then fail at high loads.

 

3. A kinked fuel line. I do not see a kink the fuel line.

 

My next step is to replace the elec petcock with the manual one (since the manual one is proved to not be the problem). And wait for a new fuel filter.

 

Bob

 

 

The fuel filter seems like the next order of business. If left as is, you may HAVE to replace the pump as well. What's the change interval, 12,000 miles? Cheap insurance, it gets everything, god help you if shite gets into the injectors.

 

Steve

[Bbennett]

So I bypassed the fuel filter for a test - symptoms remain. The filter is not at fault.

 

Tried a new fuel regulator - did not solve problem. Really thought that might do it!

 

Tried a new fuel pump - did not solve problem. Pump sounds normal. Hmmmm.

 

No fuel suck.

 

Examined line for links - there are none.

 

Changed fuel.

 

Cleaned filter on petcock.

 

Map is known to be good (checked it).

 

Wow - am not sure what to try next? Might the throttle position sensor be at work here?

 

The symptoms are: bike starts immediately and runs just fine until you go up a hill or apply throttle rapidly at speed - then it starts coughing all to heck. Sometimes is impossible to get bike back to normal operation w/o turning it off. Usually it will start up and run normally after the ignition/pump recycles.

 

if I ride around at low throttle - could go all day til I hit a hill. On a flat road I can eventually get up to quite good speed.

 

 

??

[Guest ratchethack]

Just a thought, Bob. Docc brought this up recently.

 

Don't know wot intake config you might be running, but the symptoms you describe match those of a guy who had been running an open top airbox many years back. The reflective insulation mat in the tank tunnel had parted company with the tank, falling down on the filter and cutting off all but a fraction of the air flow.

 

Couldn't hurt to check, if this makes sense in your case.

[Bbennett]

That's a good suggestion (the reflective tape is peeling off big time uder the tank) but I have cylindrical K&N air filters.

 

I like the suggestion in that I have checked everything in the fuel system at this point - 1 item at a time. No joy. My thoughts

now wander to air intake and god help me - electrical.

 

I guess I could remove the PC-III to see what would happen - it has been on there for 5 yrs.

**Edit: tried that - no impact**

 

The problem is progressive. I can no longer get the bike up more than a 10 degree hill and am effectively garage bound.

 

Except for my Aprilia. But that is a monster to ride, espec in this heat.

 

Bob

 

P.S.

The little nipple at the bottom of the fuel regulator (yellow thing is pointing at it) is not supposed to have a line on it is it? And I assume that fact that the bottom the fuel regulator with said nipple rotates a little is not relevant...