Proper fuel pressure?

[Garrett]

So I have an 80s 125cc carb'ed Honda motor and I need to rig up a fuel pump for it. The vehicle it came out of use was gravity fed.

Would something like this be too much?



Specified at 2-3.5PSI.
I was also thinking of picking up an old motorcycle fuel pump but I have no idea what pressure those run.

Something like this



Comments and suggestions appreciated!

Thanks

[jasnmar]

I don't know anything about the Mr. Gasket pump.

I do know that a lot of carbureted CBR's convert from a pump similar to the 2nd image to a gravity feed as a mechanism to check the pump.

I have no actual info on them but anecdotal evidence indicates something like 2PSI for the CBR pumps.

I guess it depends... At what distance was the previous gravity feed? How much is the elevation of the fuel source changing? Fortunately fuel is less dense than water and carbs are pretty forgiving to pressure variations.

[Garrett]

This is what the motor came out of:



85/86 TRX125

[jasnmar]

OK. So "almost 0" gravity head before. Also "almost 0" friction losses.

What's the new configuration?

[Garrett]

Tank is mounted next to the motor on a flat surface.

[jasnmar]

You're probably fine with the Mr. Gasket thingy.

My only concern here would be applying too much fuel pressure to the carbs, causing you to get too much fuel. At the pressure we're talking about I really think I'm being overly cautious.

Side note : I've also never worked on 4 Wheeler carbs, so they could contain some magic that I'm not familiar with.

[Garrett]

Nope, no magic on this one. Rocks a standard Keihin round slide carburetor.

[timmyho414]

I would think that will work, a car carb runs 6-8 psi.

[Kurlon]

Why not use a Snowmobile style vacuum pump? No electrical required, will not overwhelm your carb's float.

[Garrett]

I don't have anywhere to grab vacuum from.

[Kurlon]

Sure you do, drill the intake and thread in a brass nipple. You can also get foam filters with vacuum nipples on them.

[Garrett]

A friend is giving me one of these for free. I may just use it. 3.5PSI

[number9]

You can pick up a fuel pressure gauge pretty cheap if you want to test things - like $10 or so. I think I have a spare if you want to borrow it...

[Garrett]

So I got it running, it has no air filter. But it seems like that pump is just too much for it. It floods out unless you hold it wide open

[Stromper]

You need a fuel pressure regulator to knock it down to 3 to 5 psi

The carb will not be able to accurately regulate higher pressures

[Garrett]

You need a fuel pressure regulator to knock it down to 3 to 5 psi

The carb will not be able to accurately regulate higher pressures

The pump I used only pushes 3.5PSI.

[mell0]

This might be overly complicated, but could you T off the fuel line and route an additional line to turn it into a return style system? That might help with the excess pressure.