FUEL PUMP ISSUES

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JWR
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FUEL PUMP ISSUES

Post by JWR »

Original fuel pump was leaking badly, replaced with new ( original type) mechanical fuel pump. Runs fine but started "spitting fuel from vent hole in top cover. Did I get a new one bad out of the box, or could a plugged fuel line / carburetor cause to pressure to be too high on the output side?

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azdave
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Re: FUEL PUMP ISSUES

Post by azdave »

High pressure not likely to be the cause of that. A ruptured pump diaphragm or defect in the other parts sound more likely. The pump can only put out about 10 PSI at the highest. Many people are able to re-tighten the 5 screws around the perimeter and be okay but be sure to keep an eye on it so you don't have a safety issue. I've had good luck lately with Airtex 4886 from Rock Auto. Quality has been all over the place the last few years but seems better lately. Is your new pump an old NOS OEM original or a newly reproduced unit?
Dave W. from Gilbert, AZ
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Re: FUEL PUMP ISSUES

Post by bbodie52 »

The description of the mechanical Corvair fuel pump below includes the shop manual section that describes the mechanical pump. The cross-section image would appear to show that a defective/ruptured preformed fuel diaphragm would be the only way for fuel to make it into the pressure spring area to escape via the top vent hole.
bbodie52 wrote::think: The Corvair mechanical fuel pump is usually pretty good at pulling gasoline the length of the vehicle to prime the fuel pump so that gasoline can be pressurized to fill the carburetor float bowls. But a small air leak or crack in one of the short rubber hoses at either end of the fuel line between the tank and the pump can create what amounts to a vacuum leak in the fuel feed line that supplies the pump. The pump can cycle many times as the engine cranks and the battery drains while sucking mostly air from a fuel line air leak instead of getting a good "drink" of gasoline from the tank.

An improperly inserted mechanical fuel pump may also limit the motion of the pump diaphragm, if the pump insertion is too shallow and not allowing the push rod to take a full stroke. Refer to the notes and illustrations below to see how the pump set screw is supposed to insert into the tapered hole in the side of the pump shaft, and not just push against the side of the pump shaft. Proper installation ensures that the pump is properly positioned in relation to the push rod, so that the pump gets a full stroke with each rotation of the crankshaft. Good fuel volume from the pump is considered to be 1 pint of fuel in 40 seconds or less at cranking speed.

To check for the possibility of fuel starvation, you should measure fuel pump pressure AND volume! It is easy to have a pump that delivers correct pressure, but cannot produce adequate fuel volume. A feed line leak or cracked/damaged/loose rubber hose between the tank and the pump can create an air leak that will keep the pump from being able to create a solid vacuum to pull a good supply of fuel from the tank. Without adequate fuel supply, the pump can generate adequate fuel pressure to the carburetors, but only until it is starved for gasoline from the tank. The pump must also be installed to the proper depth and anchored properly using the tapered bolt that is screwed into the tapered hole on the side of the pump.

Image
:link: http://www.corvair.com/user-cgi/catalog ... nd_page=65



Part number C259: 62-69 FUEL PUMP ROD-REPRO (3 13/16") 60-61 ROD=C7256

Weight: 0 lbs 4 oz
Catalog Page(s): 11(28),65
Price: $ 19.15


Part number C1604: FUEL PUMP SPRING

Weight: 0 lbs 2 oz
Catalog Page(s): 11(34),65
Price: $ 3.55


bbodie52 wrote:The pump push rod is driven by a cam lobe on the crankshaft. The repeated "upstroke" causes the pump to form a vacuum in the feed line from the fuel source (tank or gas can). As the fuel is drawn into the pump chamber, the one-way valve in the pump inlet closes at the top of the stroke, and the spring in the pump forces the diaphragm back down to push the fuel out of the pump through the other one-way valve, toward the carburetors. The spring tension determines the fuel pump outlet pressure.

Check to make sure you are fully inserting the pump so that the pushrod driving the pump gets a full stroke to drive the fuel pump. Proper installation of the new parts is critical,,,
To remove and reinstall the fuel pump, be sure that you have installed it properly. It is important to ensure that the fuel pump is correctly seated and installed. There is a hole in the side of the pump shaft that the tapered bolt tip must seat into. If the pump is sitting too high and the bolt is simply pressing against the side of the pump housing, rather than seating inside the tapered hole, the pump push rod will not be doing its job. Fig. 57 in the shop manual page shows the tapered hole that the tip of the bolt fits into. This ensures proper installation and seating of the pump.

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Brad Bodie
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erco
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Re: FUEL PUMP ISSUES

Post by erco »

JWR wrote:
Thu Aug 27, 2020 6:11 am
could a plugged fuel line / carburetor cause to pressure to be too high on the output side?
Carb bowls full with inlet valve (needle & seat) closed is a normal operating condition, same effect as a plugged fuel line, so that is no cause for a fuel leak. Per azdave, the max fuel pump pressure is set/limited by its internal spring. Your pump has other issues.

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Re: FUEL PUMP ISSUES

Post by joelsplace »

That is for sure a bad pump. Tightening the screws won't help.
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JWR
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Re: FUEL PUMP ISSUES

Post by JWR »

azdave wrote:
Thu Aug 27, 2020 7:56 am
High pressure not likely to be the cause of that. A ruptured pump diaphragm or defect in the other parts sound more likely. The pump can only put out about 10 PSI at the highest. Many people are able to re-tighten the 5 screws around the perimeter and be okay but be sure to keep an eye on it so you don't have a safety issue. I've had good luck lately with Airtex 4886 from Rock Auto. Quality has been all over the place the last few years but seems better lately. Is your new pump an old NOS OEM original or a newly reproduced unit?
New reproduced unit from Rockauto

JWR
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Re: FUEL PUMP ISSUES

Post by JWR »

new unit from rock auto

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azdave
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Re: FUEL PUMP ISSUES

Post by azdave »

I would say you got a bad one then. Was it marked as a US Motor Works or Airtex unit? I'm curious if the US Motor Works is a re-branded Airtex like the others I've seen lately. There just can't be that many manufacturers out there still making Corvair pumps.
Dave W. from Gilbert, AZ
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Re: FUEL PUMP ISSUES

Post by bbodie52 »

I believe that Clark's Corvair Parts stated that they have narrowed it down to two reliable suppliers that provides their mechanical pumps.
Clark's wrote:Fuel Pumps

We have only been able to locate 2 manufacturers of original style Corvair fuel pumps. Since 1973, we have consistently seen 1-2% of new fuel pumps fail. From about 1998-2001, the failure rate went to nearly 10%! We finally convinced the pump manufacturer that they were using the wrong diaphragm material! Currently, about 1%-2% of the fuel pumps continue to have problems. The problems have usually been seepage of fuel or complete failure resulting in no fuel or a rupture of the main diaphragm. The main supplier (C3403) is now using "antiwicking" diaphragms & has returned to all 3 diaphragms having fabric reinforced material. We've also added a pump from a 2nd supplier (C3403A). Our experience with both is nearly identical. A spare pump is always a good idea.
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JWR
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Re: FUEL PUMP ISSUES

Post by JWR »

US Motor Works

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azdave
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Re: FUEL PUMP ISSUES

Post by azdave »

JWR wrote:
Tue Sep 01, 2020 11:54 am
US Motor Works
Does it look like this one with the "Made in USA" cover and the small aluminum part number/date code tag on the side?
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Dave W. from Gilbert, AZ
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66 Corsa 455 Toro V8
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JWR
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Re: FUEL PUMP ISSUES

Post by JWR »

No. It looks like the issue is the US Motorworks doesn't have the dimple for the set screw, so it's possible to mount it too deep. I set the original in and marked it with a pencil, the measured the new ( replacement) one, so I could mount it at the same depth. This seems to work ok.

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azdave
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Re: FUEL PUMP ISSUES

Post by azdave »

JWR wrote:
Thu Sep 10, 2020 6:11 am
No. It looks like the issue is the US Motorworks doesn't have the dimple for the set screw, so it's possible to mount it too deep.
Wow! If they left out the setscrew hole that is a real problem because most people will insert the pump until it stops which is too deep. Mounting it too shallow could work okay but too deep will cause an early diaphragm rupture almost for sure. Thanks for the follow-up reply.
Dave W. from Gilbert, AZ
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66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
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Re: FUEL PUMP ISSUES

Post by terribleted »

No mounting hole in the base is certainly a BIG issue. To me the pump is therefore NOT for a Corvair period. If you mount the pump without this retaining hole the pointed retaining bolt can only bind against the side of the cast pump base. Making it tight is very likely to distort the alternator or generator oil filter adapter bracket as well as burr the side of the pump where it is likely to cause damage to the adapter when removed. No hole also means the pump will likely not be retained properly and over time as the pump rod and spring try to dislodge it. Take that junk and send it back to those idiots for a refund and buy a real Corvair pump from a Corvair vendor. Either that or replace it with a 3-5 PSI electric pump mounted near the tank and never worry about failing stock pumps again.
Last edited by terribleted on Thu Sep 10, 2020 8:54 am, edited 1 time in total.
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Re: FUEL PUMP ISSUES

Post by bbodie52 »

:goodpost: :woo:

The illustrations below — including the fuel pump cross-section image from the shop manual — will help readers to visualize just what the problem is if the set screw dimple is missing from a replacement pump. If the pump installation is too shallow the stroke from the push rod may result in weakened pump action. As stated, installation that is too deep can destroy the pump. Either way it will not function properly. And, as stated, without the hole (dimple) the set screw cannot "grip" the pump properly so it will likely work itself loose as it is pushed upward continuously by the push rod action.
azdave wrote: » Thu Sep 10, 2020 9:15 am
JWR wrote: ↑Thu Sep 10, 2020 8:11 am
No. It looks like the issue is the US Motorworks doesn't have the dimple for the set screw, so it's possible to mount it too deep.
Wow! If they left out the setscrew hole that is a real problem because most people will insert the pump until it stops which is too deep. Mounting it too shallow could work okay but too deep will cause an early diaphragm rupture almost for sure. Thanks for the follow-up reply.
To remove and reinstall the fuel pump, be sure that you have installed it properly. It is important to ensure that the fuel pump is correctly seated and installed. There is a hole in the side of the pump shaft that the tapered bolt tip must seat into. If the pump is sitting too high and the bolt is simply pressing against the side of the pump housing, rather than seating inside the tapered hole, the pump push rod will not be doing its job. Fig. 57 in the shop manual page shows the tapered hole that the tip of the bolt fits into. This ensures proper installation and seating of the pump.

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Brad Bodie
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Image 1966 Corvair Corsa Convertible

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