MSefi.com read only forum (Jan.15,2018)

just been purchasing the last bits needed so i can get my build started. basically im converting a small 125cc air cooled engine to run on MSII for the sole purpose of controlling fuelling for a uni project. ive purchased a throttle body off a honda CBR125 which has the injector, tps, idle control and temp sensor built into it. The problem im having is finding a suitable external fuel pump for a small engine.

the smallest 1 that seems to be popping up with numerous google attempts is the walbro 255 as shown here - http://www.walbro255.com/255-lph-high-p ... 94240.html these are cheap enough on ebay but im wondering will the pump be overkill for its intended purpose, ill be using a fuel regulator prior to the injector but am concerned that a fuel pump this large will cause a large temperature rise in the fuel, bearing in mind the tank capacity isnt much more than a gallon.

will this pump be suitable or are there any smaller pumps that can be bought, ive been looking at motorcycle fuel pumps but they all seem to be built into the tank. im in the UK btw

If you search here and on the Microsquirt forum (Injectors, Fuel, and Air Supply) you can find where guys have taken in-tank motorcycle pumps and they've mounted them inside small aluminum cylinders of various sizes. One guy used a small fire extinguisher as his "donor" aluminum cylinder.

I don't know what's available on Euro Ebay but the Suzuki LT-R450 Quadracer fuel pump is the smallest external-type fuel pump I could find when I was sourcing parts for my project (250cc, two cylinder motorcycle). It has a very low electrical draw. It mimics an in-tank style pump because the actual pump is enclosed in (you guessed it) an aluminum housing full of fuel. Here's a picture of it. Sorry there's nothing to give you perspective on it's size. The whole thing is a little shorter than your palm and fingers.

What are the needs of you project? I.E. fow rate, amp draw....?

There are some other external fuel pump from street bikes that are avail on ebay. you should be able to find them under 07zx600. They are capable of 50psi( which is what the street bikes run) and should have low amp draw.

Also, Wlabro has an intank pump that is made for an Artic cat snowmobile. The way the fittingd are setup on the pump, it looks like it can be used externally. It puts out 36psi and draws 2.4 amps.

thanks for the replies guys:

Ewflyer i had never realised there was a megasquirt forum , assumed it would be a sub forum on here but when i was earching for fuel pumps nothing was showing up i had a look for the fuel pump you mentioned on USA ebay but sadly there are no used 1's available. ill head on over to microsquirt to take a look at some of the guys designs over there though.

Toon1 as for the needs doing a quick calculation for my engine at max power and 100%VE it would only require 3.2kg/hour 7lb/hour of fuel, as for amp draw theres no real issue with it as the bike will be run statically on a dyno so aslong as it operates on a 12v system i have means of powering it.

just typed in kawasaki fuel pump into evilbay and the only 1 that looked extrernal is the 1 in the picture below:



the seller states its off a 2002 model but this was when the bike changed over from carb to fuel injection so im not sure its its a fuel pump for a carburettor or a fuel injection pump. what do you think?

That's the pump I was refering to. If all you need is a pump to run your system, and there are no other constraints, any pump will do. If you are running a return style system, fuel heating won't be an issue..

If you decide to buy a pump like the one you have pictured, please take a reading of the amperage draw at the fuel pressure you are running. There are several people here and on the microsquirt site that would be interested.

hmmm ive been having a look at similar looking kawasaki pumps on evilbay and 1's that look identical to the 1 i posted all seem to be on carb'd bikes such as the zxr400 and 750's. im not 100% that the 1 posted is for a fuel injection model

There are those style of pumps made for FI bikes. For what you are doing, your probably better off finding a run of the mill external atuomotive style pump. They would be easier to find and cheaper.

toon1 wrote:If you are running a return style system, fuel heating won't be an issue..

With a ~1 gallon tank situation, I'll have to respectfully and conditionally disagree. The condition being, of course, on how long the dyno sessions are. The fuel flowing through the pump is actually the coolant for the pump's motor and other moving parts. One gallon of gasoline doesn't have a whole lot of cooling capacity.

since this is a small engine, it will not require alot of fuel. Fuel pressure, I would imagine, would NOT be all that high, and everything is exposed and not confined in a heat retaining area, such as under a hood or similar. My guess would be that things will be fine.

If this was a high HP producer with high fuel Requirements it would probably be an issue since the pump would be working harder.

I've been wrong before

If you think about it, much of the work (read, heat) placed into the fuel by the pump is spent overcoming the regulator spring. The less fuel consumed by the engine means more pump-heated fuel is returned to the tank for another trip around. More fuel consumed by the engine means less warmer fuel returned to the tank. The pump's only job is to maintain 3 bar (or whatever the regulator is set for) in the fuel rail up to the pump's rated volume capability. As you note, this is probably an academic thought exercise with no real impact on the proposed application...

-Mike

PS: I log fuel temp and a Walbro 255 pump will raise temps of 10 gallons of gasoline a couple of degrees per hour in a vehicle that was not running. I didn't do this on purpose, accidentally left the pump and logging device on all night. Won't do that again as it kills the battery very effectively after several hours!

the bike will be run statically on a dyno

bearing in mind the tank capacity isnt much more than a gallon.

Well if that's the case then the sky's the limit for "outside the box" thinking. Here's a thought, you don't need a fuel pump for this project. You could use some sort of pressure vessel (like a propane gas cylinder), fill it with the required amount of fuel then pressurize it with a line from an air compressor with a regulator set to your desired operating fuel pressure.

The down side to using a pressurized container is that if you develop a leak, you can't just pull the plug. It will also loose pressure as you consume fuel, rather than maintaining the same pressure as it would with a regulator and pump.