Pulse pump on a dirt bike engine

[firemanjim]

Has anyone ever used a pulse pump with a dirt bike engine? I prefer to hide my gas tank , so I need to either use a pulse pump , or buy an electric fuel pump to fill a smaller bullet style gravity feed tank mounted outside of my kart body. I don't want to do that..... But will if I have to....
Any info would be appreciated...

 

[Brianator]

I haven't had to do it (yet) but I dont see why it wouldn't work if you got an appropriately sized pulse pump, some older snowmobiles use them so why not a dirtbike engine!? I'd go for the pulse pump for ease of operation and lack of electronics/fuel regulator myself. A Mikuni DF44 2xx series (1/4" single outlet) could probably handle it at 14 litres per minute but you'd want to try and calculate your theoretical fuel usage first to be sure, all in you'd probably have it done and installed for $100 or less and the rebuild kits for them are only about $20 which is a bonus (more importantly the fact that it's rebuildable)!

 

[Joe-405]

I did on my first build here. It was a kx125 on a shifter kart. Had a return line to relieve some pressure.

 

[Mikey808]

Hey Joe quick question on your fuel schematics and how you have it all set up.. I have a KX250 that's going on a DK2 chassis from BMI.. this is my first Shifter Kart so I'm going to need all the help I can get LOL

 

[Mikey808]

I did on my first build here. It was a kx125 on a shifter kart. Had a return line to relieve some pressure.

 

[madprofessor]

Fuelly link below gives tested mpg on KX250 motorcycles. Don't know if that's any use when figuring fuel consumption per gokart racing hour. Brianator's post above about a Mikuni pulse pump converts to 3.7 gallons per minute / 222 gallons per hour. If you were using that much fuel, you should retrace your route with kitty litter for where it was pouring out of a hose that fell off.
Kawasaki KX250F MPG - Actual MPG from 3 Kawasaki KX250F owners (fuelly.com)
BMI link below rates a Mikuni 1-outlet pulse pump at 17 liters per hour (converts to 4.5 gallons per hour).
Mikuni 1 Outlet Fuel Pump | 600852 | Burris Tire MIK-DF44 | BMI Karts And Parts
EDIT: I've only used the plastic Walbro pulse pumps, and now curious, I've searched and not been able to find the gph rating for them.
EDIT AGAIN: Found a Walbro page that explains a lot I didn't know about. Started a separate thread to share it. Search "Walbro pulse facts...."

 

[Mikey808]

Fuelly link below gives tested mpg on KX250 motorcycles. Don't know if that's any use when figuring fuel consumption per gokart racing hour. Brianator's post above about a Mikuni pulse pump converts to 3.7 gallons per minute / 222 gallons per hour. If you were using that much fuel, you should retrace your route with kitty litter for where it was pouring out of a hose that fell off.
Kawasaki KX250F MPG - Actual MPG from 3 Kawasaki KX250F owners (fuelly.com)
BMI link below rates a Mikuni 1-outlet pulse pump at 17 liters per hour (converts to 4.5 gallons per hour).
Mikuni 1 Outlet Fuel Pump | 600852 | Burris Tire MIK-DF44 | BMI Karts And Parts

Thankyou for that info!! Will get back on results, waiting on new gas tank and kickstarter shaft

 

[anderkart]

I used a round Mikuni pulse pump with an inline filter & 1/4" marine primer bulb installed in the fuel supply line.
I installed a 1/4" Briggs & Stratton brand fuel shutoff valve between the fuel pumps secondary output port and a
1/4" brass barbed fitting I installed in the fuel tanks cap:



I installed a 1/4" brass barbed pulse-input fitting by drilling/tapping pipe threads into the Intake manifold of my 406cc Honda G400 engine.
It took a couple attempts to get my fuel shut off valve adjusted to return just enough fuel so it wouldn't starve or flood the engine, but after that my fuel system worked out awesome. ~ I recommend using transparent fuel lines so you'll know if your carbs receiving fuel or not. And I recommend using 1/4" automotive fuel line for your pulse signal line. The clear line flexes too much reducing the pulse signal reaching the pump.

 

[karl]

I recommend using transparent fuel lines so you'll know if your carbs receiving fuel or not. And I recommend using 1/4" automotive fuel line for your pulse signal line. The clear line flexes too much reducing the pulse signal reaching the pump.

Cracking the bowl drain works too, but great advice on the pulse line!

Returns lines , extra fittings, and half open valves aint my style tho.

I just grab the round mikuni plastic pumps off lawnmowers, they are designed to work off the crankcase
of our 4 cycle go kart motors, and put out the right pressure , so you just hook it up like it's intended,
outlet right to the carb, and it works like factory! Think I got 5 in service right now, no issues. On factory carbs
and mikuni round slides.

The honda gc160 -190's use the same mikuni pump from the factory, driven off the crankcase, with no return!

 

[madprofessor]

Check my thread about "Walbro pulse facts........." in this same category, and its Walbro link for info on 2-stroke/4-stroke placement of pulse fitting and how it affects performance of pumps. As I noted in thread, it doesn't address the way we all usually tap the crankcase for a pulse signal for 4-strokes the same way as they say should be done for 2-strokes.

I recommend using transparent fuel lines so you'll know if your carbs receiving fuel or not.

Good advice. I use semi-transparent colored lines for the same reason (and some style), but I also use dual completely clear 90-degree inline fuel filters for same. One between fuel tank and pump, and one between pump and carb. Double filtering unnecessary, but knowing by sight alone exactly where the fuel flow stops (example: bad fuel pump) during diagnosis of a failed engine is a huge bonus.
10 For HARLEY MOTORCYCLE CLEAR INLINE GAS Right Angle FUEL FILTER 1/4 6mm 7mm | eBay

 

[Snaker]

I would think 4 stroke crankcase pressures would be reliant on how "open" the crankcase venting is.
Small passages and restrictions would allow some pressure to build up.
Big ol wide open crankcase breathing would reduce pressure to nearly nothing.

 

[karl]

I would think 4 stroke crankcase pressures would be reliant on how "open" the crankcase venting is.
Small passages and restrictions would allow some pressure to build up.
Big ol wide open crankcase breathing would reduce pressure to nearly nothing.

Makes sense. From what I seen, the pulse pickup and breather on OEM applications are far apart in the engine, I would think
for that reason. I apply the same theory to my motors , so lets say the breather is on the valve cover, ill put the
pulse pickup in the governor shaft hole or oil sensor hole, so it gets a strong pickup.

 

[madprofessor]

lets say the breather is on the valve cover, ill put the
pulse pickup in the governor shaft hole or oil sensor hole,

One exception that I know about is the Predator engines with the flapper valve built-in to the underside of the valve cover. The breather tube that feeds back into the OEM airbox is on the back side of that flapper, so it gets a lousy pulse signal insofar as running a pulse pump is concerned, but doesn't readily launch lots of oil out through the tube.
Hence the need to drill those valve covers for a pulse fitting in the correct spot, on the crankcase side of the flapper. Close proximity of the breather tube and pulse fitting like that has no ill effects.

 

[karl]

One exception that I know about is the Predator engines with the flapper valve built-in to the underside of the valve cover.

I think you missed the point. The 212cc predator is not factory equipped with a pulse fuel pump, it is gravity fed.

What your saying about the location of the barb is spot on, you want to pull it from the crankcase itself,
not through the reed valve.

What I was saying is most engine factory equipped with a pulse pump move the pickup far away from the
reed valve/ breather. I prefer to do it this way for a stronger pulse. But its not necessary, just a personal preference.

 

[madprofessor]

most engine factory equipped with a pulse pump

...........and right there sits my inexperience with varying small engines. Never actually did much mechanical on the powerplants of my younger days, at least not beyond intake/exhaust, gravity tank relocation, clutches, etc. Only got into tearing them completely down and doing mods with the Predator series, so I'm very pleased to pick up knowledge about other makes from you more experienced folks.

 

[OPmini]

Why screw with a pulse pump? just get a carb with an accelerator pump.

 

[Snaker]

Why screw with a pulse pump? just get a carb with an accelerator pump.

A accelerator pump is a whole different animal.
It just gives a squirt when the throttle is opened and gets that fuel from the bowl.
The bowl still needs to be filled, either by gravity or a fuel pump.

 

[NubsWithGuns]

Only requirement for it to work is vaccum.

 

[Denny]

Only requirement for it to work is vaccum.

Wrong! It needs to pulse!

 

[madprofessor]

Only requirement for it to work is vaccum.

Makes no difference at all if an upstroke of the piston pulls the crankcase pressure down below atmospheric pressure (into a partial vacuum).
All that matters is that a piston upstroke lowers the crankcase pressure no matter what it is, and the ensuing downstroke raises the pressure. That's the "pulse" in a pulse pump, and the sensitive diaphragm in the pump responds to it on the crankcase side of itself, forcing fuel to move on the opposite side of itself.