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How do electric fuel pumps work for a 3K?


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Good day gentlemen...and ladies if any are about.

Mechanical pumps are getting hard to come by. If I switch to electric, how does it keep from flooding the carb?

I'm having trouble picturing it in my head. If the bowl is full and the needle valve shut, the electric pump will still be running right? The mechanical pump seems to go up to 5 psi but that increases with engine speed, The electrics just have one speed, on or off? What does the fuel do when the bowl is full? or do they turn on and off due to pressure? Might be a silly question for someone who's been driving for 40 years but I never thought about it.

Plus, where would be the best place to mount it? Make a bracket/cover plate combo where the old one goes? Should I wire in a switch that I can forget to turn on or just wire it to the ignition?

I've just gone through everydamthing again( full rebuild, new pistons, cam, lifters, crankshaft, head rebuilt, carb kit ) but can't get it to idle. Goes down the freeway fine...cruises at 75 mph with no complaints. I was hoping it would calm down, maybe work some crud out of the pump or burn off the old gas but it's still the same after 150 miles and 6 gallons of premium mixed with the old. It will stay running at about 2000 or so rpms but even then after a minute or so it will just die. Pump the throttle once and it fires right back up making me think fuel problem.

I have a new alternator on the way because it's howling and not charging and a coil, The only other thing not new under the hood is the fuel pump. It sat for several months with a couple of gallons in it and the crap they sell for gas now could have eaten it or weakened it. The clear inline filter stays at about half full though.

There seem to be two mechanicals left in the US...one in Texas, one in Washington...after that I'll have to go electric. Unless I go ahead and do it now.

Whatcha think?

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You simply use a low pressure pump designed for carbs.  If you want to go "JDM" use a Mitsuba pump (but there are lots of other effective, cheaper [and noisy] options).  If keen, in addition you can use a fuel pressure regulator designed for carbs such as a filter king.  This regulates the pressure and additionally has a filter element you can change and looks old school.  Rubber mount the pump in the boot near the tank, as these sorts of pumps are designed to push rather than pull fuel.  A very good idea to set up a fuel circuit relay to ensure the pump turns off in the event that the engine stops such as in a crash where you can't reach the switch yourself.

Burning to death isn't good.

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Shadowing what pete is saying above, my tuner just fitted an electric pump for my webers and used an LPG type switch setup. It gets a pulse signal from the ignition coil, so stops working once the engine turns off.

 

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I ran a cut off switch via the oil pressure sender switch, no oil pressure no pump. Needed to run an extra circuit to prime the fuel system though......

 

never ran a regulator, once the carbies filled you could hear the pump slow down.  Ran a Facet style pump bolted to the boot floor.

 

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10 minutes ago, coln72 said:

 

never ran a regulator, once the carbies filled you could hear the pump slow down.  Ran a Facet style pump bolted to the boot floor.

 

same here 

 

 

Edited by 7000rpm
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Thanks for the info, seems it's not just bolt in place. The oil pressure cutoff switch seems like a good idea, would a "momentary switch" be good for priming? Only works while pushed.

This is what comes up on RockAuto as a replacement, and to me looked like it just went on the fuel line somewhere along the frame. Under the hood somewhere was what I was hoping, my right side frame and firewall are mostly open as my steering is on the left. The original glass bowl is there but no filter in it, I've got a filter inline between that and the pump. they never seem to go dry so I thought a pump mounted on the frame below the glass bowl would have no problem staying primed. it would be below the level of the fuel tank.

It's pretty noisy up front already as I can't seem to get that perfect valve adjustment like I used too. I do the 1's open adjust 8 method. I'm wondering if my replacement pin on the cam has let the gear move a smidge. It did not fit perfectly tight in the hole on the gear. If it did that would make everything just a tiny bit late. I torqued the gear and then a tad more, I may have to pull the timing cover to ease my brain.

EP42S_Primary__ra_p.jpg.8199c5652dc308646e883132b0b00087.jpg

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Mark,

         The olde mechanical fuel pump on the K series engine is very simple, very reliable, & have performed well for many standard engines over many years.  They do not entail any sort of electric power involvement, & are therefore basically trouble free. Most people never even think about their fuel pump.  It just works, and about the only failure ever experienced is if the diaphram develops a hole. The mechanical pump doesn't need a pressure regulator; as soon as it experiences a back pressure from the carby, when the bowl fills, the fuel pump just stops pumping.  To replace a fuel pump on the side of the road takes all of 15 minutes, & doesn't even require getting under the car.  I have occasionally thrown a spare in the boot when i've gone of a long trip, but never had to use one.

However, the mechanical pump is not good at sucking fuel over the length of the car, especially if there are partially blocked lines or there are issues with the tank breather system.

I have also looked at fitting an electric pump, at the rear of the car, to overcome this possible issue, but there are a requirements for an electric pump to be primed, to run, & to be automatically shut down if the engine stops for any other reason, other than normally turning off the ignition.

The added requirement of power means that an extra fuse, & relay are also required, so the ignition switch is not forced to carry the extra couple of amperes to run the electric fuel pump.  

The use of a oil pressure switch is a good addition, but then it gets a bit complicated to prime the pump.  However, there is an oil pressure switch, which incorporates a changeover switch, rather than the simple "normally closed" switch.

This switch is  available in the USA, and is called a model PS-64, but I can't find one ex stock here in Australia.

The use of this switch makes the electric requirements of this conversion much simpler, as detailed in this sketch I found on the internet.

591804a117ed0_OilPressureSwitch.JPG.27326b4f6fb2395d99acc64938235a9d.JPG

591805af03005_PS-64OilPressSwitch.jpg.ca033e6263e214ffbac87bd2192f372b.jpg

 

 

Cheers Banjo

  

 

Edited by Banjo
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 I'm still all original but many times rebuilt 7000.

 

Go go Banjo! That dang internet is a handy place.

I've already got a 30 amp relay powering a block for driving lights, radio, amplifier...I don't want to run any extra stuff through the original wiring. It's only on when the ignition is on so you can't save channels on the radio but it also doesn't trickle my battery down.

It's bad enough in the winter when you have to choose, heater, headlights or wipers, it doesn't like to run all 3. Luckily the heat will flow with the blower off if you're moving. It's almost 50 years old now...probably time to clean the wiper and heater motors up a little.

I'm going to try and get the mechanical Monday but I'll be saving this drawing. I've probably got 2 or 3 pumps around here that I've replaced in 30 years but the gas we're getting is getting worse and worse. It'll say "up to" 10% ethanol but I'll bet it's higher.

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If it were me id try and get another mechanical pump, like suggested they wprk forever and if you get one it will last another 40years. Although the ethanol destroying pumps is something i had not considered. 

If you go the electrical route i agree woth all suggestions made in regards to safety. Mamy people just run a suitable low pressure pump off ignition power fine, however it really should have the safety cut offs built in. 

Edited by ke70dave
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Wayne,   Do you realise Mark is in Arkansas in the USA, & that postage of a pump to him would cost many times more than the pump is worth ?

Someone will have some N.O.S. over there somewhere.  There are a couple of types of mechanical fuel pumps used on K series engines.  There is a sealed unit, which has a return line on it, back to the tank. I've  got one of those, but they are throw away, when they die.  The really old ones with brass hose fittings & two halves can be disassembled easily, & I'm sure again there are repair kits for these with diaphragm, spring & little valves.  I've seen them on ebay some time back.  I think I actually rebuilt a pump like that once.

I came across a Tridon oil pressure switch today, that looks like the STANDARD brand PS-64 one, I saw on the internet in the USA.  The Tridon one even has a similar P/N, but the specs confused me, so I dropped their tech department an email today, to see if it works the same way.  This one seems to be different, as instead of just 3 off voltage free connections, the Tridon one effectively has 4 terminals, with the normally closed terminal connected to the frame of the oil pressure switch, which is chassis.  I'll let you know what they advise.

TPS-064.JPG.19f6f8e915278a40c6180afa1184df15.JPG

Would solve my problem of getting one locally. They cost more to freight from the USA than they are worth.

Cheers Banjo

 

Edited by Banjo
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1 hour ago, Banjo said:

Wayne,   Do you realise Mark is in Arkansas in the USA, & that postage of a pump to him would cost many times more than the pump is worth?

 

Yes. If he can't find one, happy to post out. Like any fellow car enthusiast having a go, I am always happy to help

 

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