Fuel Pressure Regulator

[Flyboy]

Gentlemen the `97 Sport 1100i I just bought has the fuel regulator reference port not connected to anything. Some people say it`s fine that way and the bike runs as good as these things run, Any thoughts?

[Guest ratchethack]

It's designed to take its vacuum reference off the downstream side of the throttle bodies on applications it was designed for, probably many auto's. Several hereabouts (myself included) have experimented by connecting it to the charcoal OE evap emissions cannister hose barbs/TB balance barbs on the intakes next to the heads with ZERO noticeable effect on fuel pressure, mileage, and driveability.

[gstallons]

On the Guzzi application,it ( fuel pressure regulator)is influenced by barometric pressure only.

On most fuel injection systems the vacuum fitting of the regulator is connected to manifold vacuum so when there is a drop in manifold vacuum as in acceleration or throttle opening, the regulator spring applies more pressure to the diaghram increasing fuel pressure. this increased pressure will increase fuel volume being injected into the intake passage.

[GuzziMoto]

On the Guzzi application,it ( fuel pressure regulator)is influenced by barometric pressure only.

On most fuel injection systems the vacuum fitting of the regulator is connected to manifold vacuum so when there is a drop in manifold vacuum as in acceleration or throttle opening, the regulator spring applies more pressure to the diaghram increasing fuel pressure. this increased pressure will increase fuel volume being injected into the intake passage.

 

I believe the reference port would work opposite the way you describe. If you connected it to the intake manifold down stream of the throttlebody you would indeed get a drop in manifold vacuum sent to the reference port. But I'm pretty sure this would cause a reduction in fuel pressure not an increase. I don't think it would be a large change in pressure but it should decrease fuel pressure with a decrease in pressure at the port. Where it would help is if you had a turbocharged application and the increase in boost would cause an increase in fuel pressure. Yes you can hook it to the intake manifold (or somewhere else like the evap canister) but I can't imagine anywhere to hook it that would make the bike run better then having it vented to atmosphere (not some sort of micro-atmosphere inside of your home made engine temp sensor but the real atmosphere ).

[Flyboy]

Thanks guys...so it looks like just having it vent to the atmosphere is fine, if not perfect.

I believe the reference port would work opposite the way you describe. If you connected it to the intake manifold down stream of the throttlebody you would indeed get a drop in manifold vacuum sent to the reference port. But I'm pretty sure this would cause a reduction in fuel pressure not an increase. I don't think it would be a large change in pressure but it should decrease fuel pressure with a decrease in pressure at the port. Where it would help is if you had a turbocharged application and the increase in boost would cause an increase in fuel pressure. Yes you can hook it to the intake manifold (or somewhere else like the evap canister) but I can't imagine anywhere to hook it that would make the bike run better then having it vented to atmosphere (not some sort of micro-atmosphere inside of your home made engine temp sensor but the real atmosphere ).

[Dan M]

I believe the reference port would work opposite the way you describe. If you connected it to the intake manifold down stream of the throttlebody you would indeed get a drop in manifold vacuum sent to the reference port. But I'm pretty sure this would cause a reduction in fuel pressure not an increase. I don't think it would be a large change in pressure but it should decrease fuel pressure with a decrease in pressure at the port. Where it would help is if you had a turbocharged application and the increase in boost would cause an increase in fuel pressure. Yes you can hook it to the intake manifold (or somewhere else like the evap canister) but I can't imagine anywhere to hook it that would make the bike run better then having it vented to atmosphere (not some sort of micro-atmosphere inside of your home made engine temp sensor but the real atmosphere ).

 

Not to start yet another argument here but here are a few points that have been covered before.

The spring inside the regulator takes about 7-10"Hg vacuum to overcome so atmosphere plays no roll whatsoever.

The regulator is designed to reduce fuel pressure with when vacuum is applied by 5 to 10 psi.

It has two pressure values and is not variable. (with vacuum applied to the point of overcoming the internal spring and without - like an on / off switch)

A vacuum diaphragm type regulator is designed for use in a multi-cylinder application where vacuum is steady.

The Guzzi motor's manifold vacuum pulses wildly, especially at idle. (hook up a vacuum gauge and observe for yourself - the needle will be a blur even if you tee both cylinders together, I've tried it)

The idea behind vacuum regulators is reduced fuel pressure at closed throttle (high vacuum) and instantly increased pressure when the throttle is opened (low vacuum). Every system that has one operates this way and I'm sure it is what Guzzi intended when the system was drawn up. The trouble comes in when the twin cylinder engine does not produce steady vacuum, (which the guzzi lump will not, and can not) this causes the diaphragm to flutter not only fatiguing the diaphragm but also not regulating steady pressure.

It seems that this was discovered and the diaphragm was then just left disconnected.

 

I've witnessed that these bikes run a bit fat at idle. If you apply vacuum with an outside vacuum source to the regulator the idle cleans up nicely. The trouble is there is no steady vacuum from the motor so the system will not work the way it was intended.

 

Bottom line, leave it disconnected....

 

 

* For the hairsplitters: I hope my use of the language was clear and concise. Please report any grammar or spelling errors or any misunderstandings and I will attempt to clarify*

 

PS; Welcome to the forum Flyboy. Buckle up, it may be a bumpy ride.

[Flyboy]

Thanks for the very detailed and knowledgeable response. I do have to say, the technical knowledge here is astounding versus any other board I`ve used!

[GuzziMoto]

My apologies to gstallons. After re-reading what you said I realize I misunderstood what you posted. I believe we are all on the same page.

Again, my apologies.

[gstallons]

You're welcome. It sounds like mumbo jumbo but I wanted to explain how the pressure regulator functions.

[dlaing]

Not to start yet another argument here but here are a few points that have been covered before.

The spring inside the regulator takes about 7-10"Hg vacuum to overcome so atmosphere plays no roll whatsoever.

The regulator is designed to reduce fuel pressure with when vacuum is applied by 5 to 10 psi.

It has two pressure values and is not variable. (with vacuum applied to the point of overcoming the internal spring and without - like an on / off switch)

A vacuum diaphragm type regulator is designed for use in a multi-cylinder application where vacuum is steady.

The Guzzi motor's manifold vacuum pulses wildly, especially at idle. (hook up a vacuum gauge and observe for yourself - the needle will be a blur even if you tee both cylinders together, I've tried it)

The idea behind vacuum regulators is reduced fuel pressure at closed throttle (high vacuum) and instantly increased pressure when the throttle is opened (low vacuum). Every system that has one operates this way and I'm sure it is what Guzzi intended when the system was drawn up. The trouble comes in when the twin cylinder engine does not produce steady vacuum, (which the guzzi lump will not, and can not) this causes the diaphragm to flutter not only fatiguing the diaphragm but also not regulating steady pressure.

It seems that this was discovered and the diaphragm was then just left disconnected.

 

I've witnessed that these bikes run a bit fat at idle. If you apply vacuum with an outside vacuum source to the regulator the idle cleans up nicely. The trouble is there is no steady vacuum from the motor so the system will not work the way it was intended.

 

Bottom line, leave it disconnected....

 

 

* For the hairsplitters: I hope my use of the language was clear and concise. Please report any grammar or spelling errors or any misunderstandings and I will attempt to clarify*

 

PS; Welcome to the forum Flyboy. Buckle up, it may be a bumpy ride.

Very well written, but being a hair splitter, I must point out that

I get relatively steady vacuum at my TwinMax with my Guzzi lump by using bleed screws to regulate the flow.

So, you could use bleed screws to smooth out the pulses at the diaphragm, but it would be at the expense of response time, possibly causing problems, and re-mapping MIGHT be needed, despite the evidence of "ZERO noticeable effect on fuel pressure, mileage, and driveability." Once the pulses are nearly eliminated Ratchet might notice the fuel pressure change if he actually uses a fuel pressure gauge.

[Dan M]

Very well written, but being a hair splitter, I must point out that

I get relatively steady vacuum at my TwinMax with my Guzzi lump by using bleed screws to regulate the flow.

So, you could use bleed screws to smooth out the pulses at the diaphragm, but it would be at the expense of response time, possibly causing problems, and re-mapping MIGHT be needed, despite the evidence of "ZERO noticeable effect on fuel pressure, mileage, and driveability." Once the pulses are nearly eliminated Ratchet might notice the fuel pressure change if he actually uses a fuel pressure gauge.

 

 

Go for it Dave and report your results. I'd be interested to know what you find. I'd suggest buying a cheap mechanical vacuum gauge and look at vacuum fluctuations with it though. I use a Twinmax as well, great tool but it is not a good indicator of pulses nor does it measure vacuum. It indicates the difference from cylinder to cylinder. If you use bleed screws to reduce port size also watch reaction speed to throttle opening and closings. It should be instantaneous and if you are regulating it down to very low flow I'd imagine you are slowing it also. It takes a certian amount of flow to overcome the spring with the diaphragm. A mechanical gauge is the best way to see and understand what is happening and you can get a cheap one at most any auto parts store.

[gstallons]

I've got a Carb-Stick from MotionPro. One of these days I'll look to see what mine does.....

[Skeeve]

Go for it Dave and report your results. I'd be interested to know what you find. I'd suggest buying a cheap mechanical vacuum gauge and look at vacuum fluctuations with it though. ... If you use bleed screws to reduce port size also watch reaction speed to throttle opening and closings. It should be instantaneous and if you are regulating it down to very low flow I'd imagine you are slowing it also. ...

 

I believe it was noted the 1st time this came around in the forums that the entire topic is rather pointless for the updated [non-"chin pad" tank] models as the pressure regulator is located inside the gas tank?

 

While the prospect of having the equivalent of vacuum advance ignition for the fueling circuit is appealing, since we don't even have that for the ignition side of our heroically kludgy ditch-pump driven 2-wheeled conveyances, I'm not going to lose any sleep over cobbling it together somehow.

 

That said, as far as smoothing out the vacuum fluctuations, running both intake manifold bleed nipples to a common "boost bottle" sized tank would go a long way toward evening out the pulses while maintaining full amplitude of the depression, I should think.

 

Still, I don't think that since anybody has complained of their fuel map needing richening at redline, so this whole matter is even more academic than the superiority of urethane cush drive biscuits over the stock neoprene tidbits.

 

Whaddaya want for nothin'?

[Dan M]

I believe it was noted the 1st time this came around in the forums that the entire topic is rather pointless for the updated [non-"chin pad" tank] models as the pressure regulator is located inside the gas tank?

 

While the prospect of having the equivalent of vacuum advance ignition for the fueling circuit is appealing, since we don't even have that for the ignition side of our heroically kludgy ditch-pump driven 2-wheeled conveyances, I'm not going to lose any sleep over cobbling it together somehow.

 

That said, as far as smoothing out the vacuum fluctuations, running both intake manifold bleed nipples to a common "boost bottle" sized tank would go a long way toward evening out the pulses while maintaining full amplitude of the depression, I should think.

 

Still, I don't think that since anybody has complained of their fuel map needing richening at redline, so this whole matter is even more academic than the superiority of urethane cush drive biscuits over the stock neoprene tidbits.

 

Whaddaya want for nothin'?

 

 

A vacuum regulator is not about richening at redline, it is about richening upon throttle opening. However, with the regulator disconnected the pressure is always high so if someone were to complain they would likely be complaining about it being too rich with the throttle closed.

A bottle would store vacuum so the vacuum will not drop instantly when the throttle is opened so that bulky set up would be of little value.

It is indeed academic, the system will not work on this motor.

Still, a valid question from flyboy so why not an accurate explanation?

[dlaing]

Still, a valid question from flyboy so why not an accurate explanation?

Why not!

For all our disagreements, I really appreciate your posts!

I fell into the camp of mistakenly believing the vacuum proportionally adjusted the fuel pressure.

Your correcting that error is appreciated.

I have little interest in hooking up the vacuum line, unless I could be convinced that the fuel atomized better at lower pressure, which I suspect is the reverse of the Truth. Mapping for leaner than Stock on deceleration would give similar results with less effort, allowing for a slight increase in fuel mileage with my less than smooth riding style in the twisties.

Hooking up the vacuum might slightly increase fuel efficiency for those that don't map.