Thread: Fuel Pump and carbs question..

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Originally posted by PsychoKart
Whops, it is a petcock. I thought that was right, but I want sure until I did a google search.

Adrian

thanks for the spelling correction that dam p is always getting in the way

Originally posted by john gemmer
thanks for the spelling correction that dam p is always getting in the way

Hey John,

So I tested my fuel pump last night and just as you said, it pumped fuel up to the carbs, and right out the over-flow which ended up on the ground

I'm thinking about building a small fuel tank above the carbs which is just big enough to have a float-switch inside of it. The float switch would shut off the fuel pump when the little tank is almost full. I can put a vent line at the top of the little tank, and a shut-off valve between the little tank and the carbs instead of the petcock. When I'm done racing around, I shut off the manual valve inbetween the little tank and my carbs. What do you think? Any different ideas (Except putting the fuel tank ontop of the engine ) ?

Adrian

Originally posted by PsychoKart
Hey John,

So I tested my fuel pump last night and just as you said, it pumped fuel up to the carbs, and right out the over-flow which ended up on the ground

I'm thinking about building a small fuel tank above the carbs which is just big enough to have a float-switch inside of it. The float switch would shut off the fuel pump when the little tank is almost full. I can put a vent line at the top of the little tank, and a shut-off valve between the little tank and the carbs instead of the petcock. When I'm done racing around, I shut off the manual valve inbetween the little tank and my carbs. What do you think? Any different ideas (Except putting the fuel tank ontop of the engine ) ?

Adrian

I'd use somthing like a mower tank ( black would look better than clear ) and drill the hole for the fule like inlet and put in a fule line nipple in the hole ( rubber hose attaches there from pump line, can be found at boat supply places ) and hook that to your pump line, have to cut it if it's hard and slip the rubber hose over it a little then clamp down. If you wanted to get rid of the gas cap, get some superglue, a dremel with cut off wheel and cut the cap screws off, you'll also need plastic sheeting which can be found at lumber supplys or a small peice of plexi would work and you'll also need some Ptex which can be found at ski shops ( it's normally melted into scratches in the base of ski's and snowboards ). after the cap is cut out, your going to want to put in some kind of vent, a boat tank vent would be great, just drill the hole on the top and put it in, can be found at boat supply also, there the chrome things you see on the side of boats with I/o or inboard engines and permanent tanks. Cut your plastic to the exzact size you need, glue it in with superglue, then take a lighter and melt it togther a little, then take some Ptex and get a lighter and light it, it will melt like plastic cause that's actully all it is and melt it onto the " diffrent colored plastic " you glued in place, get black ptex, not white. And if that tank did get over full ( sunk float causing pump to not shut off ), the tank vent would releave the preassure ( aim the vent so it blows away from the engine ) but they won't leak from sloshing gas like a small slit in the tank would.

I tried running fuel up to the carb and right back into the tank using a return fuel line (with a T connector at the carbs). This seems to work but just a little bit of fuel still drains out of the vent line(s) so maybe the constant fuel pump's volume is too high (Or one of the float bowls is not closing?)

Adrian

Originally posted by techinspector1
Have you fired this beast yet?

Yep, I fired it up yestuday, and ran the engine with full choke. I did slide it into 1st gear, checked out my clutch pedal (I have way too much travel on my clutch pedal -- about 2 inches and the clutch is fully disengaged after the first 1/2 inch so I think I need to change the ratio a little bit )

I did drive around a very little bit with the engine (at idle w/full-choke) in 1st gear. It's very smooth, rolls very nice, and the clutch+pedal feel really smooth so I can tell when I get things dialed in, this is going to be one fun machine.

I decided to buy an additional fuel pressure regulator (1-4 PSI) holly fuel regulator. I ordered it last night.

I'm going to try using my current 6 PSI pump, along with a 1 PSI regulator dirrectly to the carbs. This should work in theory. If fuel still leaks, then my float valve(s) must need cleaning/fixing/etc.

Adrian

ONe thing to think about is your old fuel pressure setup from gravity feed is putting out very little presssure. You said your old set-up was 15 inches from tank to carbs, tubing size doesn't have an affect of head pressure so that doesn't matter. I think you need about 32 foot of water to equal one atmosphere which is 14.7 pounds. So one foot would be around 1/32 of 14.7 which is about a half pound. Your pump is putting out 4 pounds, so it's my guess you might be able to reset your floats for the higher fuel supply pressure, assuming you have floats? This might work if you have floats.
That fuel pump you have sounds like the fuel pump I had on my MG Midget. It actually had points inside of the pump that would activate a solenoid when the discharge pressure got low and cause a pumping action on the diaphram and again when the pressure bleeds off it would pump again. Never saw anything like that before until it quit working and took it apart, actually had to replace the contact points in the thing. That pump worked with the sidedraft SU Carbs on the MG, they were similiar to motorcycle carbs.