Corvair DiagramCorvair Photo
Corvair Center
home forum corvairs calendar links Corvair Podcast
California Corvairs
Clarks Corvair
Clarks Corvair
“CORSA"



Chevy Corvair License Plate
Chevy Corvair Chrome Wheel
Corvair Center Forum :  Corvair Center Phorum The fastest message board... ever.
Corvair Center 
Pages: 12345Next
Current Page: 1 of 5
Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: azdave ()
Date: April 21, 2020 08:58AM

As promised, here is the idea I have been working on that allows me to fine tune my Corvair OEM mechanical fuel pump pressure without guessing about how much to reduce the spring height or repeatedly unsealing the wet side of the pump to test each time.

Adding the spacer seen in the photos (below the top cap) effectively reduces the height of the spring by about 3/4" which normally drops the fuel pressure down to the 1-2 PSI range. The elasticity in the rubber diaphragm will usually give enough spring-back to give you about 0.5 PSI even without the spring installed. I designed the spacer ring so that once the pump is assembled and installed, you can then remove the top cap and shim the spring multiple times without ever spilling a drop of fuel or needing to remove the pump. I even found a simple way to adjust the spring height while the engine is running so you don't spend forever guessing at the final shim height needed. Once you learn the ideal shim height, you place it under the cap and button it all up.

The fuel pressure these pumps put out is very dependent on the diaphragm material/age, the spring height and even the quality of the two check valves. All of these variables can now be compensated for at the same time with one adjustment. These re-manufactured pumps are known for putting out too much pressure which can over-power the fuel inlet valves in the carburetors and also decrease the life of the diaphragm material inside the pump.

One thing that was unexpected during my road testing was how low I was able to set the pressure and not notice any drivability issues. I'm running 2 PSI currently and thought for sure that once I drove at sustained freeway speeds I might begin starving the carbs of fuel but I’m not seeing that issue yet. I'm not recommending anyone set their pressure at 2 PSI but thought it was interesting data none the less.

I like that this arrangement is fully adjustable (with shim selections under the cap) and that it looks very nearly stock to all but us die-hard Corvair folks. It works on all OEM pumps 60-69 and does not cause any changes to the pump components except slightly enlarging the five threaded holes under the pump base.

Some people may think to modify the top cap with a threaded hole and make it so they can set the pressure by turning a locking screw that compresses the top of the spring. I don't think the setting needs to be that precise and also didn't care for changing the OEM look of the top cap.

So, did I re-invent the wheel here or is this the first time someone has approached the problem in this manner?


Comments?

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5



Attachments:


Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: Frank DuVal ()
Date: April 21, 2020 09:17AM

I like it!smileys with beer

Frank DuVal

Fredericksburg, VA

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: jjohnsonjo ()
Date: April 21, 2020 09:26AM

A lot of us Turbo YH guys are running 2 to 2.5 PSI. I can with confidence there is a larger volume of fuel going through that single YH under boost, than two NA carbs would draw at full load.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: The Stig ()
Date: April 21, 2020 09:27AM

Really neat out of the box thinking Dave. I have nearly written off mechanical pumps but this makes them deserve another shot. Sign me up for one when you are ready to start selling.



Edited 1 time(s). Last edit at 04/21/2020 09:27AM by The Stig.

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: OttawaCorvairGuy ()
Date: April 21, 2020 09:45AM

Creative think Dave. Nice product.

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: MattNall ()
Date: April 21, 2020 10:05AM

This is the "elegant" way to do it!

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: azdave ()
Date: April 21, 2020 10:25AM

jjohnsonjo Wrote:
-------------------------------------------------------
> A lot of us Turbo YH guys are running 2 to 2.5 PSI. I can with confidence there is a larger volume of fuel going through that single YH under boost, than two NA carbs would draw at full load.

My freeway testing at 2 PSI was done using a 66 140/4 speed convertible. I ran 70-75 MPH for 7 miles with no problems other than all the dirt flying around inside a car that hasn't gone that fast in 30 years. grinning smiley



The Stig Wrote:
-------------------------------------------------------
> I have nearly written off mechanical pumps but this makes them deserve another shot. Sign me up for one when you are ready to start selling.

Sure. I have enough stock to make maybe 5 or so. I haven't found really thick walled pipe yet so I'm turning these from solid 3.25" bar stock right now.

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5



Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: jjohnsonjo ()
Date: April 21, 2020 10:43AM

[www.spdexhaust.com]

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: joelsplace ()
Date: April 21, 2020 11:15AM

jjohnsonjo Wrote:
-------------------------------------------------------
> [www.spdexhaust.com]

What does exhaust tubing have to do with this thread?

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: jjohnsonjo ()
Date: April 21, 2020 11:46AM

azdave Wrote:
-------------------------------------------------------
I haven't found really thick walled pipe yet so I'm turning these from solid 3.25" bar stock right now.


Joel, because he mentioned pipe

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: azdave ()
Date: April 21, 2020 11:58AM

Pipe, tube, round drop-offs, whatever aluminum stock gets it done. I would need 3.125" OD x 2" ID. That's more than 1/2" wall thickness.

I'm not a machinist (but I play one on the internet). grinning smiley

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5






Edited 1 time(s). Last edit at 04/21/2020 11:59AM by azdave.

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: jjohnsonjo ()
Date: April 21, 2020 12:03PM

Sorry Dave I didn't pick up that the screws were going through the piece. It looked more like a band to me. Yeah, that's some serious thick wall.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: Frank DuVal ()
Date: April 21, 2020 12:44PM

The bottom and top fuel pump screws tighten into threads in the new part.

Yes, there are now both top and bottom screws.grinning smiley

Frank DuVal

Fredericksburg, VA

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: alphasud ()
Date: April 21, 2020 01:02PM

Working on Beetles we have to shim between the pump and the Bakelite adapter to adjust the fuel pressure. I thought the big issue with the mechanical pumps was there is nobody who makes a good diaphragm material to cope with today’s fuels.

David North Idaho
1965 Corsa Turbo converted to 140
1971 Super Beetle with 2.5L Subaru engine
1965 Corsa mid engine project
1973 Mercedes 280 project

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: azdave ()
Date: April 21, 2020 01:25PM

jjohnsonjo Wrote:
-------------------------------------------------------
> Sorry Dave I didn't pick up that the screws were going through the piece.

No problem. A picture of the part by itself would have helped you understand the design but I didn't want you all to see my amateur machining and a few extra "test" holes I drilled.


Frank DuVal Wrote:
-------------------------------------------------------
> The bottom and top fuel pump screws tighten into threads in the new part.

Yup. Into the same holes I drill and tap completely through to save drilling and tapping 5 more holes just for the top cover. Why not share?


alphasud Wrote:
-------------------------------------------------------
> I thought the big issue with the mechanical pumps was there is nobody who > makes a good diaphragm material to cope with today’s fuels.

I haven't had failures of the diaphragm material unless the pump was at least 10 years old. I've read that too but has not been my experience. My few failures have been warped castings on new parts or bad check valve staking.



Here's a pic of the first part when I was still through bolting everything together as one assembly. Now the ring has smaller holes that are tapped fully through and this allows the wet section to remain compressed while you remove the top cap to adjust the spring pre-load as often as you wish.

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5






Edited 1 time(s). Last edit at 04/21/2020 01:25PM by azdave.

Attachments:
Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: joelsplace ()
Date: April 21, 2020 01:29PM

If you put an adjuster in the top you wouldn't need the 2 sets of bolts and it would save threading the holes. I understand your reasoning but I would rather have a screw type adjuster.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: azdave ()
Date: April 21, 2020 02:53PM

joelsplace Wrote:
-------------------------------------------------------
> I understand your reasoning but I would rather have a screw type adjuster.

I appreciate the feedback. Five extra 11 cent bolts or screws doesn't bother me and aluminum is pretty darn easy to thread with a drill-driver. I tapped these though in one operation since I can push the chips in front of the tap.

I don't feel the top cap has enough metal thickness for a proper threaded hole so I would have to rig up a plan to accommodate that. If I thread or modify the top cap then I'll need a bunch of top caps.

So far, my solution is easier for me to offer as a DIY kit or complete, ready to install. The threaded spacer ring could be drilled out and modified if someone wished or I could send it that way too if they asked. I could supply them as seen here and let the customer decide if they want to use it as received or drill out the ring holes and modify the cap.

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5



Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: joelsplace ()
Date: April 21, 2020 04:02PM

The cap would need a thin nut welded to the inside or the spring washer would need to be hat shaped to clear the nut. The cap would also need another air hole in it.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: Layton Curtis ()
Date: April 21, 2020 04:17PM

For what it's worth-I put a pressure regulator between the pump and the Tee and set it at 3 pounds or so. Result-the check valve couldn't take it. I was stranded twice. One of the pumps was an OEM and the other was an aftermarket. The failures came after a long run of interstate driving. I staked the valves each time and then gave up. I have not experimented since.

Options: ReplyQuote
Re: Adjustable Pressure Mechanical Fuel Pump Experiment
Posted by: Brizo ()
Date: April 21, 2020 05:39PM

Dave, Nice work! If you want to show off your machining skills some more, carve out a new hard aluminum pump base that wont warp. The main problem with the current replacement pumps is the soft zink alloy base warps and the lower gasket leaks across the center divider and it gets weak or stops pumping. I've been fixing the new pumps by replacing the base casting with the aluminum bases from old original A/C pumps, but a new part would be great! I get a reliable 4-4.5 psi by cutting one coil off the TOP of the spring, -THEN-.bend the end to set flat.

Dan Brizendine, Circle City Corvairs
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

Options: ReplyQuote
Pages: 12345Next
Current Page: 1 of 5


Sorry, only registered users may post in this forum.
This forum powered by Phorum.