| Author |
Message |
johnny chingas
Samba Member
Joined: July 20, 2006
Posts: 70
Location: Anaheim
|
 Posted: Wed Mar 19, 2014 4:22 pm Post subject: Fuel pump pressure is high adding gaskets ? |
 |
|
Ok so before I replace the fuel pump and bolt it back up is this right I'm adding 4 gaskets to lower my fuel pump pressure. Do the gaskets go on top of the red one pictured?? https://www.thesamba.com/vw/gallery/pix/1184682.jpg
_________________
My favorite color is rust! |
|
| Back to top |
|
 |
johnnypan
Samba Member
Joined: October 24, 2007
Posts: 7431
Location: sackamenna
|
| Posted: Wed Mar 19, 2014 4:26 pm Post subject: |
|
|
yes..add gaskets and drive the car..it will starve when you have too many..then pull one at a time till it runs nice.
Se me paro.... |
|
| Back to top |
|
|
DrKeck
Samba Member
Joined: November 10, 2013
Posts: 309
Location: Texas
|
| Posted: Thu Mar 20, 2014 8:41 am Post subject: |
|
|
| johnnypan wrote: |
yes..add gaskets and drive the car..it will starve when you have too many..then pull one at a time till it runs nice.
Se me paro.... |
Um no, lets not follow this advice at all. Do it the correct way and you car will last longer. You need to add your gaskets under the plastic part not on top. if its old and you do not want to add them in the correct place then its fine to do them on top. all the gaskets are doing is making your fuel rod a little shorter so you have the correct PSI for your carbs. not sure what carbs you have but around 3 Psi is correct. you need to get a fuel pressure gauge and check the PSI in your pump after you install it. do not drive it around like the previous post said, you will have way more problems in the long run. Do a search on how to check PSI on your fuel pump and It will explain everything.
http://www.vw-resource.com/fuel_pump.html
_________________
1966 Beetle
1600cc 50bhp
Daily Driver |
|
| Back to top |
|
|
johnny chingas
Samba Member
Joined: July 20, 2006
Posts: 70
Location: Anaheim
|
| Posted: Thu Mar 20, 2014 9:42 am Post subject: |
|
|
| jonathonkeck wrote: |
| johnnypan wrote: |
yes..add gaskets and drive the car..it will starve when you have too many..then pull one at a time till it runs nice.
Se me paro.... |
Um no, lets not follow this advice at all. Do it the correct way and you car will last longer. You need to add your gaskets under the plastic part not on top. if its old and you do not want to add them in the correct place then its fine to do them on top. all the gaskets are doing is making your fuel rod a little shorter so you have the correct PSI for your carbs. not sure what carbs you have but around 3 Psi is correct. you need to get a fuel pressure gauge and check the PSI in your pump after you install it. do not drive it around like the previous post said, you will have way more problems in the long run. Do a search on how to check PSI on your fuel pump and It will explain everything.
Lol! Well I did fallow his advice by placing the gaskets on top between the plastic and fuel pump, but I didn't do the drive around town till she starves for gas part. I did buy a fuel pressure gauge from harbor freight I was running at almost 5 psi I added 4 gaskets and I'm a little above 3 now I'm going to add 1 more today. So I should switch the gaskets down to under the the plastic and above the case right!!? I was having a small gas leak at my throttle shaft on my solex 28pict-1 after the car would turn off I wanted to try this before I spent the money to have my carb redone. Looks like it worked!!
http://www.vw-resource.com/fuel_pump.html |
_________________
My favorite color is rust! |
|
| Back to top |
|
|
thomas.
Samba Member
Joined: July 31, 2010
Posts: 1291
Location: South West (Pa.)
|
| Posted: Thu Mar 20, 2014 11:28 am Post subject: |
|
|
Quoting from the link you provided ...."Note regarding push rod stroke-if you find there is too much stroke, add gaskets to the top of the flange".... Then again... "you lower it as indicated above by adding gaskets between the pump & spacer" Unquote
Ipso fatso.... Johnnypan was correct |
|
| Back to top |
|
|
DrKeck
Samba Member
Joined: November 10, 2013
Posts: 309
Location: Texas
|
| Posted: Thu Mar 20, 2014 12:46 pm Post subject: |
|
|
you might be smelling gas because you have to high of a psi on your fuel pump. Also if you just turned it on a bunch of times it might just be fuel sitting there and not hot enough to burn off. the reason there is holes in the gasket is because they belong under the plastic rod. yes you can put them above the red gasket, it does the same time. I was just saying the proper place for it. just make sure you check with a gauge and don't just "wing it" that never works out in the long run.
_________________
1966 Beetle
1600cc 50bhp
Daily Driver |
|
| Back to top |
|
|
Lucky Lager
Samba Member
Joined: September 20, 2012
Posts: 202
|
| Posted: Sun Mar 23, 2014 8:30 pm Post subject: Re: Fuel pump pressure is high adding gaskets ? |
|
|
Can I get a link to the gaskets you bought?
Im getting ready to make my own gaskets.... Id rather just buy them
Im smelling gas too, no leaks that I can tell...Im thinking rule pump...
_________________
In the wild, health care is, Ow, I hurt my leg. I can't run. A lion eats me. I'm dead. |
|
| Back to top |
|
|
Aussiebug
Samba Member
Joined: June 03, 2002
Posts: 2162
Location: Adelaide Australia
|
| Posted: Mon Mar 24, 2014 3:24 am Post subject: |
|
|
Oh Dear.......
Johnny Chingas, Johnnypan, Johnpthankeck, Thomas and Lucky lager,
Adding shims (gaskets) under the pump WILL NOT CHANGE YOUR FUEL PRESSURE ONE LITTLE BIT!!!
All it does is reduce the maximum VOLUME the pump will be able to pump.
The fuel PRESSURE in the pump is pre-set by the return spring which pushes the operating arm back down after it has been lifted by the push rod. That spring pressure also applies inside the pump chamber which pushes fuel up to the carb.
Putting gaskets under the pump just reduces how far the rod can push the arm back up (smaller volume pulled into the pump chamber) and then the spring pushes the arm back down as fuel is consumed by the engine.
This method of operation makes the fuel pump self regulating. If the engine is consuming a small amount of fuel, the operating arm will descend only a short way and the pump rod will rise a large part of it's stroke before meeting the arm and pushing it back up. If the engine is consuming a lot of fuel, the arm will descend more and the pump rod will meet it sooner on the up stroke and so will move a larger volume of fuel into the pump via the longer stroke of the pump arm.
The VW fuel pump can supply about twice the volume of fuel needed to supply a 1600 bug engine at full noise - IF the pump rod is able to lift the pump arm far enough.
The spring in the stock VW pump is set to provide about 2-3psi at WHATEVER volume the engine needs.
So reducing the pump rod throw by adding gaskets will do absolutely nothing up to the point there are so many gaskets that the pump arm stroke is reduced so far that the pump cannot supply enough VOLUME of fuel to keep the engine running.
Johnny Chingas, WHY do you think the fuel pressure is too high? If the carb is flooding, the problem is more likely to be a faulty needle valve in the top of the carb.
_________________
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.vw-resource.com |
|
| Back to top |
|
|
Lucky Lager
Samba Member
Joined: September 20, 2012
Posts: 202
|
| Posted: Mon Mar 24, 2014 3:56 am Post subject: |
|
|
Thanks for info. I didn't want to add shims just fix the worn out one that I have. Great info man!
_________________
In the wild, health care is, Ow, I hurt my leg. I can't run. A lion eats me. I'm dead. |
|
| Back to top |
|
|
johnnypan
Samba Member
Joined: October 24, 2007
Posts: 7431
Location: sackamenna
|
| Posted: Mon Mar 24, 2014 5:26 am Post subject: |
|
|
Aussie bug
fuel flow has a direct correlation to pressure.Bernoullis equation is the hydraulic formula for figuring the flow/pressure dynamic.
adding shims reduces the travel of the pushrod,reducing the travel of the diaphragm, reducing fuel flow.
the return spring merely cycles back the diaphragm, it has nothing to do with pressure.
The operation of the diaphragm in the fuel pump is a constant,no matter engine demand,it works the same way,increasing fuel flow when rpms are increased by cycles of the pushrod,there is no other limiting factor.
I see Johnathankeck subscribes to your foolishness as well..shimming a Vw fuel pump to drop pressure is a proven fact,and it doesn't matter which side of the stand you shim.. |
|
| Back to top |
|
|
DrKeck
Samba Member
Joined: November 10, 2013
Posts: 309
Location: Texas
|
| Posted: Mon Mar 24, 2014 11:35 am Post subject: |
|
|
| johnnypan wrote: |
Aussie bug
fuel flow has a direct correlation to pressure.Bernoullis equation is the hydraulic formula for figuring the flow/pressure dynamic.
adding shims reduces the travel of the pushrod,reducing the travel of the diaphragm, reducing fuel flow.
the return spring merely cycles back the diaphragm, it has nothing to do with pressure.
The operation of the diaphragm in the fuel pump is a constant,no matter engine demand,it works the same way,increasing fuel flow when rpms are increased by cycles of the pushrod,there is no other limiting factor.
I see Johnathankeck subscribes to your foolishness as well..shimming a Vw fuel pump to drop pressure is a proven fact,and it doesn't matter which side of the stand you shim.. |
Please don't quote me in your little rant. if you read what I said, they belong bellow the fuel rod. why do you think they have a cut out for the plastic part? if they would go on top they would be a flat disc just like the one on top. I said you can put them on top if you wanted to but they belong bellow as to how they are cut in the middle. it will have no difference in pressure in either position I was simply saying the correct placement of the gasket.
As to your other comment about just driving it until it losses pressure,
| johnnypan wrote: |
| ..it will starve when you have too many..then pull one at a time till it runs nice |
If you want to not follow the manual then don't, but don't tell people on the forum to just run fuel pressure that way. it will allow fuel into the carbs, fuel leaks, or a multitude of different outcomes. you should install it the proper way to insure the life of your car.
additionally I'm not sure why you would quote Bernoulli's equation. p1 +1/2pv1 2 +pgy1 = p2 +1/2pv2 2 + pgy2, it has a mechanical pump and not a restriction or free flow. there is no conservation of energy in just the fuel flow alone because more energy is put into the system due to the mechanical pump. As I said, when you add more gaskets, you lower the PSI so its set for your carb, around "3 PSI".
_________________
1966 Beetle
1600cc 50bhp
Daily Driver |
|
| Back to top |
|
|
johnnypan
Samba Member
Joined: October 24, 2007
Posts: 7431
Location: sackamenna
|
| Posted: Mon Mar 24, 2014 2:49 pm Post subject: |
|
|
Add gaskets till the engine starves,then remove one at a time till it runs good..
there,I posted it again... |
|
| Back to top |
|
|
jhoefer
Samba Member
Joined: May 19, 2011
Posts: 987
|
| Posted: Mon Mar 24, 2014 4:31 pm Post subject: |
|
|
You're both partly right.
When the push rod goes up, the diaphragm is pulled down against the internal spring pressure. This sucks in a certain volume of fuel into the chamber. This fuel volume is determined by the area of the diaphragm and the diaphragm's vertical displacement caused by the push rod, minus any fuel that is still remaining in the pump chamber. Shimming up the pump reduces the maximum vertical movement of the diaphragm and thereby reduces the maximum volume supplied by the pump. This can lead to fuel starvation if shimmed too much.
As the push rod descends, the only force pushing up on the diaphragm is from the spring. It is this spring force that creates the fuel pressure (since the fuel's PSI = Spring Force in LBS / Area of Diaphragm). The important thing to remember here is Hooke's Law, that the spring force (F in LBS) is determined by the spring rate (k in LBS/INCH) and the distance the spring is compressed (X in INCHES), F = kX. The spring rate is fixed and depends on the spring used. The compressed length of the spring however, is determined by the stroke length of the push rod (and installed height). Shimming up the pump reduces the stroke length and therefore the maximum compressed length of the spring. In this way, adding shims also reduces the fuel pressure.
How much work the pump does depends on the consumption of the carb. If the carb bowls are full, the needle valve is closed and no fuel flows into it. In the fuel pump, the push rod pulls down the diaphragm to suck fuel in, but when the rod goes down, because the fuel has nowhere to go, the spring stays compressed and the fuel stays under pressure. When the rod comes up again, it faces no resistance and does no work because the spring and diaphragm are still compressed by the fuel stuck in the chamber. If the carb is using fuel at a rate the can consume 50% of the fuel pump's chamber volume between pushrod strokes, when the pushrod comes up again, the spring would still be 50% compressed, the chamber would still be half full, and so it would only need to pull on the diaphragm half the distance to refill the chamber. Only if the carb can consume 100% of the fuel in the pump chamber between strokes does the pump work at 100% capacity.
Fuel flow out of the pump is only determined by the pressure difference between the pump and atmosphere (carb bowl) and by the size of the "pipe" into the carb, aka the needle valve opening. Fuel bowl empty = large opening at needle valve -> high fuel flow. Fuel bowl nearly full = small opening at needle valve -> low fuel flow.
The proper way to fix this problem is to fit a different spring with the correct spring rate and free length. This way the pump supplies both the correct pressure and maximum volume necessary for the engine. There are a lot of aftermarket pumps with springs that are too strong that can't be shimmed enough to get the pressure down without decreasing the volume below acceptable limits. You shouldn't need to use more than a couple gaskets to dial things in. In my opinion, making the engine run lean at WOT from a starved fuel bowl just to determine the amount of shims to use on a pump with the wrong spring is unnecessarily risky to the health of your engine. A good pump should never need to be shimmed enough to cause fuel starvation in the first place. |
|
| Back to top |
|
|
Aussiebug
Samba Member
Joined: June 03, 2002
Posts: 2162
Location: Adelaide Australia
|
| Posted: Tue Mar 25, 2014 2:31 am Post subject: |
|
|
| jhoefer wrote: |
You're both partly right.
When the push rod goes up, the diaphragm is pulled down against the internal spring pressure. This sucks in a certain volume of fuel into the chamber. This fuel volume is determined by the area of the diaphragm and the diaphragm's vertical displacement caused by the push rod, minus any fuel that is still remaining in the pump chamber. Shimming up the pump reduces the maximum vertical movement of the diaphragm and thereby reduces the maximum volume supplied by the pump. This can lead to fuel starvation if shimmed too much.
As the push rod descends, the only force pushing up on the diaphragm is from the spring. It is this spring force that creates the fuel pressure (since the fuel's PSI = Spring Force in LBS / Area of Diaphragm). The important thing to remember here is Hooke's Law, that the spring force (F in LBS) is determined by the spring rate (k in LBS/INCH) and the distance the spring is compressed (X in INCHES), F = kX. The spring rate is fixed and depends on the spring used. The compressed length of the spring however, is determined by the stroke length of the push rod (and installed height). Shimming up the pump reduces the stroke length and therefore the maximum compressed length of the spring. In this way, adding shims also reduces the fuel pressure.
How much work the pump does depends on the consumption of the carb. If the carb bowls are full, the needle valve is closed and no fuel flows into it. In the fuel pump, the push rod pulls down the diaphragm to suck fuel in, but when the rod goes down, because the fuel has nowhere to go, the spring stays compressed and the fuel stays under pressure. When the rod comes up again, it faces no resistance and does no work because the spring and diaphragm are still compressed by the fuel stuck in the chamber. If the carb is using fuel at a rate the can consume 50% of the fuel pump's chamber volume between pushrod strokes, when the pushrod comes up again, the spring would still be 50% compressed, the chamber would still be half full, and so it would only need to pull on the diaphragm half the distance to refill the chamber. Only if the carb can consume 100% of the fuel in the pump chamber between strokes does the pump work at 100% capacity.
Fuel flow out of the pump is only determined by the pressure difference between the pump and atmosphere (carb bowl) and by the size of the "pipe" into the carb, aka the needle valve opening. Fuel bowl empty = large opening at needle valve -> high fuel flow. Fuel bowl nearly full = small opening at needle valve -> low fuel flow.
The proper way to fix this problem is to fit a different spring with the correct spring rate and free length. This way the pump supplies both the correct pressure and maximum volume necessary for the engine. There are a lot of aftermarket pumps with springs that are too strong that can't be shimmed enough to get the pressure down without decreasing the volume below acceptable limits. You shouldn't need to use more than a couple gaskets to dial things in. In my opinion, making the engine run lean at WOT from a starved fuel bowl just to determine the amount of shims to use on a pump with the wrong spring is unnecessarily risky to the health of your engine. A good pump should never need to be shimmed enough to cause fuel starvation in the first place. |
A lot of that is horsepucky!
You said it yourself, the SPRING determines the pressure.
The pump rod stroke determines the volume, and that stroke is controlled by the volume being consumed by the engine. More fuel burned means the needle valve stays open to refill the float bowl, means the pump arm descends further as the spring moives the diaphragm, means the push rod can push it up further = longer stroke. All that is VOLUME, not pressure.
The ONLY time the two start to come together with this style of pump is when the engine is starving of fuel because the pump has been shimmed so much the VOLUME of fuel pumped is insufficient for the engine - that is, when the engine is starving for fuel. Of course at THAT point the pressure drops, because the float bowl is taking every drop it can get - the needle valve is fully open and the pump VOLUME cant keep up so the PRESSURE drops too.
That's NOT the way to adjust the fuel pressure. The correct way is to get a pump with the correct rating on the spring, since it's the spring which sets the pressure, not the pump rod stroke.
Johnnypan, Bernouli has nothing to do with it - his formula relates the SPEED of flow affecting the pressure inside the fluid ("The pressure inside a fluid is inversely proportional to the speed of movement of that fluid"... which means that as the speed of a fluid increases the pressure in that fluid drops) - but the fuel pump is working with a fixed pressure and variable volume - it has nothing to do with the speed of the gasoline flowing through the pump.
Just for info (no relevance, but interesting), at full throttle, a 1600 bug engine consumes about 200cc of fuel per minute, and so the speed through the fuel lines is so slow that it's completely irrelevant. The VW fuel pump's capacity (max pumping volume) is around 400cc per minute - twice that which the engine can consume, which is also irrelevant for this paragraph. The VW fuel line is about 5mm internal diameter, so the cross section is about 4 sq mm (piD/4), so at 200cc per minute (the fuel flow of a bug engine at full throttle) the speed of fuel flow is about 50mm (2 inches) per minute through the lines and MUCH slow through the much larger pump chamber. And that's at full throttle - most of the time the fuel flow is much slower than that.
_________________
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.vw-resource.com |
|
| Back to top |
|
|
jwp67
Samba Member
Joined: February 12, 2012
Posts: 657
|
| Posted: Tue Mar 25, 2014 3:13 am Post subject: |
|
|
| I've been following this and still have the same question I never got an answer to. Does the spring have a break in period and relax after time to a normal pressure? I put on a new pump and was running 8 lb of pressure. I shimmed and got it to drop to 4 lbs of pressure. After a month of driving I stalled out on a low tank and the carb was dry. Checked the pressure and it was at 1 lb. Removed shims and replaced the pump and it is a perfect 3.5 lbs. Did the spring inside relax or wear in? Any one else have this experience? |
|
| Back to top |
|
|
DrKeck
Samba Member
Joined: November 10, 2013
Posts: 309
Location: Texas
|
| Posted: Tue Mar 25, 2014 4:59 am Post subject: |
|
|
If you have an aftermarket fuel pump, from my experience the spring is very strong. After a "break In period" I have noticed that the fuel pump will drop in pressure when te spring relaxes, as you stated and I had to remove gaskets. I'm not sure about a period correct fuel pump, I believe if they are rebuilt correctly it should not do that. The same thing happened to me with aftermarket fuel pump I bought though.
_________________
1966 Beetle
1600cc 50bhp
Daily Driver |
|
| Back to top |
|
|
jwp67
Samba Member
Joined: February 12, 2012
Posts: 657
|
| Posted: Tue Mar 25, 2014 5:24 am Post subject: |
|
|
| Thanks for the answer. Yes, it is an aftermarket. |
|
| Back to top |
|
|
johnnypan
Samba Member
Joined: October 24, 2007
Posts: 7431
Location: sackamenna
|
| Posted: Tue Mar 25, 2014 7:25 am Post subject: |
|
|
Here's how I fixed mine...rotary fuel pump.
I used speedy jims safety wiring schematic..
http://www.speedyjim.net/schem/pump.gif
done...constant 3.5 psi across the rpm range,no more sticking check valve.
got a mechanical pump,stand and pushrod in the travel kit. |
|
| Back to top |
|
|
jhoefer
Samba Member
Joined: May 19, 2011
Posts: 987
|
| Posted: Tue Mar 25, 2014 8:20 am Post subject: |
|
|
| jwp67 wrote: |
| I've been following this and still have the same question I never got an answer to. Does the spring have a break in period and relax after time to a normal pressure? I put on a new pump and was running 8 lb of pressure. I shimmed and got it to drop to 4 lbs of pressure. After a month of driving I stalled out on a low tank and the carb was dry. Checked the pressure and it was at 1 lb. Removed shims and replaced the pump and it is a perfect 3.5 lbs. Did the spring inside relax or wear in? Any one else have this experience? |
Yes, springs can relax a bit. In your case, I'd be keeping an eye on your fuel pressure because for a spring to lose that much tension so quickly would make me think it was manufactured improperly or is being used outside of its design specs. If the pressure does stabilize, don't worry about it, you'll probably be ok. If it continues to drop you'd have to replace the spring (or the pump if non-servicable) to fix it. |
|
| Back to top |
|
|
95nostalgia
Samba Member
Joined: April 25, 2011
Posts: 2
Location: Texas
|
| Posted: Tue Oct 30, 2018 12:38 pm Post subject: Re: Fuel pump pressure is high adding gaskets ? |
|
|
This will be long but informative I hope.
Pressure Goal: 3.0 to 3.25psi
What you need: ONLY combo on the market now that works is Aeromotive regulator and gauge. Parts 13222 and 15632. Explanation below.
Prep. Make sure your supply line is in order from tank. This means a clean out of metal tunnel tube and ethanol resistant hoses. Get Gates Barricade. Leave pump and gaskets etc alone for now. Until you do the rest, you don't know if pump is bad or maladjusted.
To regulate pressure, you have to be able to read it. That means a gauge. Liquid filled dampers vibrations but the oil expands and contracts due to engine bay temperature changes. So they read all over the place. Aeromotive is the only company to use a liquid filled gauge with a pin valve on top. When you want to take a reading (at any temp), you pull the valve, it equalizes with atmosphere and gives you an accurate reading at that temperature. Nothing else will work. This 0-15psi gauge is right for your car. $40
The best mounting of the gauge is facing you and perpendicular with ground. Aero regulator has an 1/8" NPT gauge port ready for mounting the gauge. This way oil doesn't leak out as the gauge air bubble is on top with the valve.
Aeromotive 13222 regulator. But only low pressure regulator with gauge port on front.$185 (eek...but necessary).
So now you can get a reading and adjust the regulator for the 3psi. Now what?
Too little psi and the carbs are starved. Too much and gas is forced past floats and can contaminate oil with gas. Little variations make engine run crappy. So constant pressure is important for a good tune. And yes, regulators may only do volume (at a given pressure) but if your carbs pull more than they can get, the pressure drops. Basically not good.
NOW you can play with the gaskets and fuel pump to achieve the proper shaft throw using gaskets preferably on the bottom. But why start there if you don't know the accurate psi?
Save yourself some aggravation and fork out the $250 or so to get the right regulator and gauge. Or you can chase the "I got a bad fuel pump" idea. FYI I do not have any connection with Aeromotive other than as a customer. |
|
| Back to top |
|
|
|
