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Solving the evaporation problem when our cars sit for a while between starts.

Centerline

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This is kind of long, so please bare with me.....

I've been doing a lot of reading on this subject and I have a solution that works... at least for me. The 440 in my '64 Polara sits sometimes for a couple weeks or more between starts and cranking the thing for what seems like forever is getting old. So I decided to supplement my mechanical fuel system with an electric pump just for priming the carb. I figured I'd share this mod with the forum just in case anyone else wants to use this method to solve the evaporation problem with today's crappy fuels.

I took a look at a lot of small electric pumps and decided on the Airtex E8090. Its an inexpensive pump (around $35) and puts out 7+ psi which I figured was enough to supply my Holley 750 with enough fuel to fill the bowls in just a few seconds of operation.

One of the things I read was that some electric pumps will not allow fuel to flow through them when they are not operating. This was a primary requirement and was the main reason I chose the Airtex pump. After speaking with their tech people they assured me it would allow the mechanical pump to pull fuel through it when it was off, and they were correct. It does. My mechanical pump actually puts out 7 psi pulling fuel through this pump.

Now I know what some of you are saying. You can't push fuel through a mechanical pump, but you can. Mechanical pumps have a mechanically operated bellows and two one way "reed" type valves. When the cam lobe puts pressure on the fuel pump lever it pushes the bellows and creates a vacuum in the pump which opens the one way valve on the "tank" side of the pump and sucks fuel into the pump chamber. When the cam rotates and releases the lever a spring above the bellows pushes the bellows back down and forces the tank side valve closed while at the same time forcing the carb side valve open and pushing the fuel through that valve up to the carb. A pretty simple mechanical setup really. So it should be easy to see why an electric pump mounted near the tank should be able to provide enough pressure to force open the tank side valve in the pump, fill the pump chamber and also force the carb side valve open allowing fuel to flow to the carb. And, this is exactly what happens.

There is one catch however..... If your mechanical pump bellows fails there is the possibility you could pump raw gas into your oil pan. Not a good thing. However, this is highly unlikely if your pump is in good condition and you're only using the electrical pump to prime the carb before starting the engine.

One more thing about electric pumps. A lot of people bitch about these small inexpensive pumps and say they don't last long. In most cases these people didn't follow the directions and either installed the pump in the wrong location or just installed it incorrectly. My Airtex pump stated that it needs to be installed as close to the tank as possible.... and for good reason. These pumps push fuel much better than pulling it. The directions also stated the outlet needs to be slightly higher than the inlet. Why they want you to do this I don't know but I'm not about to second guess the engineers who designed this product so that's exactly what I did when I installed mine.

First thing I did was to install a fuel pressure gauge so I could tell what kind of pressure the electric pump would put out while pushing fuel through the mechanical pump. The answer was 6-7 psi. More than enough needed.

IMG_6176a.jpg


The pump was installed just above the right side shock mount. You can see the outlet is higher than the inlet. Plus I also installed a filter between the pump and the tank as recommended by Airtex. If that cross-member looks a little different than yours its because I added a 2x2 .120 wall square steel cross-member between the frame rails to strengthen that area because I'm running air shocks.... but that's another story.

IMG_6184a.jpg


To make sure there was no way I could accidentally leave the pump on I mounted a spring loaded toggle switch under the dash so you have to physically hold it in the "ON" position for it to run. This way you don't have to worry about the pump running if the car is in an accident, rolls over or something else catastrophic happens.

So, does this really work? You bet it does. After sitting for almost a month I activated the electric pump for about 15 seconds and had 6 psi of pressure at the carb. I let it run for another 10 seconds to fill the bowls in the carb and then shut it off. Turned the ignition switch and it started right up. The mechanical pump was providing the carb with 6-7 psi while pulling fuel through the Airtex pump so...... Problem solved.
 
Outstanding work and write up! I may have to do this to my wheels as I drive it infrequently and I have to crank the snot out it to get it to light off.
 
Makes sense..... every spring there's lotsa crankin' goin' on.....
 
EFI or 5 times to the floor.
 
I agree with you Centerline, Been running a Carter P4070 on my 65 since 2004.Switch it on,hear it prime, pump twice and hit the key.Instant fire up.It too will flow fuel passed it when it's not switched on.Also nice to have on mega hot days for startup due to vapor lock when stopping for a short time like filling the gas tank.Hop in,hit the pump switch and instant start up.
 
This is kind of long, so please bare with me.....

I've been doing a lot of reading on this subject and I have a solution that works... at least for me. The 440 in my '64 Polara sits sometimes for a couple weeks or more between starts and cranking the thing for what seems like forever is getting old. So I decided to supplement my mechanical fuel system with an electric pump just for priming the carb. I figured I'd share this mod with the forum just in case anyone else wants to use this method to solve the evaporation problem with today's crappy fuels.

I took a look at a lot of small electric pumps and decided on the Airtex E8090. Its an inexpensive pump (around $35) and puts out 7+ psi which I figured was enough to supply my Holley 750 with enough fuel to fill the bowls in just a few seconds of operation.

One of the things I read was that some electric pumps will not allow fuel to flow through them when they are not operating. This was a primary requirement and was the main reason I chose the Airtex pump. After speaking with their tech people they assured me it would allow the mechanical pump to pull fuel through it when it was off, and they were correct. It does. My mechanical pump actually puts out 7 psi pulling fuel through this pump.

Now I know what some of you are saying. You can't push fuel through a mechanical pump, but you can. Mechanical pumps have a mechanically operated bellows and two one way "reed" type valves. When the cam lobe puts pressure on the fuel pump lever it pushes the bellows and creates a vacuum in the pump which opens the one way valve on the "tank" side of the pump and sucks fuel into the pump chamber. When the cam rotates and releases the lever a spring above the bellows pushes the bellows back down and forces the tank side valve closed while at the same time forcing the carb side valve open and pushing the fuel through that valve up to the carb. A pretty simple mechanical setup really. So it should be easy to see why an electric pump mounted near the tank should be able to provide enough pressure to force open the tank side valve in the pump, fill the pump chamber and also force the carb side valve open allowing fuel to flow to the carb. And, this is exactly what happens.

There is one catch however..... If your mechanical pump bellows fails there is the possibility you could pump raw gas into your oil pan. Not a good thing. However, this is highly unlikely if your pump is in good condition and you're only using the electrical pump to prime the carb before starting the engine.

One more thing about electric pumps. A lot of people bitch about these small inexpensive pumps and say they don't last long. In most cases these people didn't follow the directions and either installed the pump in the wrong location or just installed it incorrectly. My Airtex pump stated that it needs to be installed as close to the tank as possible.... and for good reason. These pumps push fuel much better than pulling it. The directions also stated the outlet needs to be slightly higher than the inlet. Why they want you to do this I don't know but I'm not about to second guess the engineers who designed this product so that's exactly what I did when I installed mine.

First thing I did was to install a fuel pressure gauge so I could tell what kind of pressure the electric pump would put out while pushing fuel through the mechanical pump. The answer was 6-7 psi. More than enough needed.

View attachment 731777

The pump was installed just above the right side shock mount. You can see the outlet is higher than the inlet. Plus I also installed a filter between the pump and the tank as recommended by Airtex. If that cross-member looks a little different than yours its because I added a 2x2 .120 wall square steel cross-member between the frame rails to strengthen that area because I'm running air shocks.... but that's another story.

View attachment 731778

To make sure there was no way I could accidentally leave the pump on I mounted a spring loaded toggle switch under the dash so you have to physically hold it in the "ON" position for it to run. This way you don't have to worry about the pump running if the car is in an accident, rolls over or something else catastrophic happens.

So, does this really work? You bet it does. After sitting for almost a month I activated the electric pump for about 15 seconds and had 6 psi of pressure at the carb. I let it run for another 10 seconds to fill the bowls in the carb and then shut it off. Turned the ignition switch and it started right up. The mechanical pump was providing the carb with 6-7 psi while pulling fuel through the Airtex pump so...... Problem solved.
What size fuel line?
 
Pretty much an old racer's trick. Got tired of pouring some fuel down the throat of cars that sit for long periods. Thing is, in South Central Tx, there's no reason to let one sit for long periods! lol
 
If it were a chebby I’d recommend you read your damn FSM, which clearly states you access your factory supplied emergency repair kit and stuff the fuel bowl vent with the factory supplied tampon.

But since we are talking about a Mopar, I’d have suggested you just turn it over for a few seconds to partially fill the bowl, pump the throttle a bit, then fire it off.

But your way is pretty cool too.
 
In a way, I like to crank the engine several times for pre-oiling. My engine starts so quick when the carbs are full. Useing E-free most of the time, there's always gas there waiting to be fired off. I won't pump the pedal or use the choke for a few cranks just to get the oil up. Then two pumps with the choke and bam, she's running.

I get the electric fuel pump idea for the ethanol fuel and how quick it evaporates especially when the engine is hot. Then when it sits for a period of time it evaporates also.
 
Electric pump did not solve mystarting problems. Had an Edelbrock “Street” 150 gph and it let me down. Twice. Not reliable enough for street duty.
 
Nice. But fuel pumps have two ratings. Pulling thru that electric pump the mechanical pump has good pressure but has the output volume remained the same? Regardless, good posting, good solution, good job!
 
We've discussed this issue a few times before on this forum and there are several folks here,
whose opinions I value and trust, that do indeed run a little electric pump inline.
Todays' gas (where you are matters with that, of course) and running an AVS carb
do mine in as well - after a week or so, there's no gas left in the bowls, even though I go out
of my way to buy only "ethanol free" 93 octane.

I've got a big ol' battery in her and the Dakota starter doesn't seem to mind, so I just let her
crank over and build some oil pressure while fetching fresh gas (the repro Carter "hemi" M6903 pump
is working great so far).
Probably takes 10 seconds or so usually.
I'm still on the fence about supplementing with an electric for quicker starts, really.
 
I've thought about doing this for some time on both my cars. Though I may install a "hot with key on" switch that would activate at WOT to also supplement the mechanical pump uhh....at WOT.
 
To make sure there was no way I could accidentally leave the pump on I mounted a spring loaded toggle switch under the dash so you have to physically hold it in the "ON" position for it to run.
Using a momentary switch is the only way to go on that. Radial engine aircraft use the exact same thing...called a boost pump. On the gauge panel, sports a boost pump pressure gauge. Push on the switch, watch for pressure on the gauge, done. Simply puts fuel in the lines, primes the carb.
Kinda wish I had mounted one on my 64. Maybe one day...
 
Good write up. I'd done the same thing for my 360/Thermoquad plow truck. Sure made starting on bitter cold mornings a lot easier. Has worked without issue for 8 years now.
 
I have no problem with Holley carbs but the carter style carbs do dry up and stink when first parked
 
i have no problem with an electric "helper" pump. cellulose fuel filters on the suction side of the pump are major heart burn.
 
Great write up! I moved the thread to "Fuel and air systems" and made it a sticky. Thanks for the info.
 
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