Fuel Pump on Briggs 'L' head

Richard Trotter

Richard Trotter

#1
#1
Has anyone hooked a fuel pump up on a old flat head ( or 'L' head ) briggs. I have seen some that work off the vacuum pulse of the crankcase. but I'm not sure where to hook it up. Will it work by hooking the pulse line to the breather hose ?
 
J

jimh

#2
#2
I wouldn't use the vent hose for a couple of reasons. You would be blowing oil vapors into the fuel pump, and also blowing heat from the engine into it. Also would be blocking ventilation. The best bet would be to carefully drill and tap the intake and put a barb fitting on it to run your hose to.
 
D

Darvin Jahnke

New Member
#3
#3
What area of the intake are you thinking of tapping into? The diaphram pumps I've seen need a positive and negative pressure to operate. If a positive pressure were created in the intake system it would force the fuel mixture back out of the carb. I've seen them tapped into the dipstick tube or high on the crankcase.
 
J

jimh

#4
#4
Between the carb and the head. Suzuki ATVs hooked in here and my 8hp Briggs on a Deutz-Allis had dual fuel tanks below the engine on each side. The vacuum line ran from the pump to the intake about 1/2 inch before it bolted to the head.
 
J

jimh

#5
#5
Now you've got me wondering how it works. I've never researched it, but the only thing I can think of is that when the intake valve closes, the sudden loss of velocity, caused by the intake valve "damming" the air causes a positive pressure on the diaphram. That must be how the diaphram operates on the stock Briggs carbs.
 
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excelagator

New Member
#6
#6
I got a free 80s Bolens tractor a while back with a 11hp I/C, Model 253707 Type 0144-01. It had a pulse fuel pump on it. The vacuum line was connected to the valve cover from the factory.

BTW,The pump was bad. the briggs replacement was $65.:eek:ut: I got the Mikuni pump for $23 :thumbsup:

Hope this helps,
Dan
 
drheilman

drheilman

Active Member
#7
#7
Jimh there is a small amount of valve overlap on a stock Briggs cam. This helps in starting "easy spin" by lowering the compression and holds the intake valve open for a split second while the piston moves upwards. Thus positive pressure on the fuel pump diaphram. Heres a aftermarket sidecover with fuel pump "taps"
 
J

jimh

#8
#8
I knew there was a little valve overlap to release a little compression, but I didn't really think about it working the diaphram. You can see the overlap when you turn one by hand with the head off. I guess it's dual purpose.:thumbsup: Who woulda thunk it??
 
Richard Trotter

Richard Trotter

#10
#10
Thanks guys, this has given me a lot to think about. I think I'll try to put it in the intake manifold. That should be easier and if it dosen't work, I can just plug the hole. If I have to drill the crankcase, I will probably have to tear the motor down, or at least split the case.
 
E

excelagator

New Member
#13
#13
Any small engine does not really need a fuel pump if the fuel tank is above the engine. If the tank is below it needs one. I could see adding a pump maybe adding some performance??

Many many moons ago I had some friends that drag raced cars. They ran the mechanical fuel pump and an 12 PSi electrical one also. Both pumps were operating too. I never got the reason behind it, but I would think more pressure the better atomization of fuel and/or the acceleration forces affecting the fuel bowl.

Maybe a good small engine builder will pipe in and give a fact than my theory!!!:wink:

Dan
 
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