posted by D on 6/12 5:24 GMT

yep clean carbs help!

hose clamps are free at PAP!

bike socks are cheap on ebay
or you can make your own plenum
with single sock filter before tuning

posted by unfamilia on 6/12 5:37 GMT

Well excuse my drawing and child like writing

current setup



proposed setup



there is a pressure gauge and it doesnt rise once stopped just see it bleed down to 0 after a couple minutes from 1psi.

by putting t peice and one way valve to return, pressure would circulate fuel back to the tank and stop it flowing back to carbs. The carbs would only really draw what fuel they need then.
bike carbs only need approx 0.5psi seat pressure if gravity fed. Not much and fpr wont go that low.

posted by lamb_daiquiri on 6/12 12:22 GMT

The picture works for me

I don't think the check valve is going to make a practical difference. I actually think the problem is the needle and seats in the carbs if they can't hold some pressure. I mean, you can usually leave the fuel tap switched on on a motorbike and it doesn't flood. It also sounds like there's a lot of fuel in the lines/ reg that can leak down after shut off.

If you get really stuck an inline fuel shut off solenoid just before the carbs will give you a good positive seal against leak down into the carbs. Something that's on when the ignition is on. But I'd start with the needle and seat.

posted by unfamilia on 6/12 13:32 GMT

Cool.

the needle and seats do hold some pressure but the fpr wont let fuel flow back once through it. Stock mechanical pump is 4.5 psi and then into fpr that's 1psi into carbs. So the 4.5 psi is stuck between pump and fpr. This must be feeding through as it does bleed through.
The 1psi would overcome the needle and seats at some time.

Even running a t return at the fuel entry to carbs may relive the pressure to simulate gravity feeding.
From my understanding gravity feeding would only put 0.5psi pressure on needle and seats. A stock bike carb pump puts out max 2psi but trickles to 0.5-1psi when pressure builds against it.

posted by clyons8 on 6/12 14:23 GMT

How much more help do you need? Have you found it yet?

posted by lamb_daiquiri on 6/12 21:26 GMT

Do you know what the needle valve is supposed to hold? You might fix it there. Anyhow it sounds like you've almost got it sorted, here's a few other ideas I have:

-Use a solenoid cut off (Normally Closed)in the carb feed

-Get a different regulator that goes a bit lower

-Scrap the regulator and use a return line. The height of the highest point that the return loop goes above the carbs will set the pressure in the fuel line (assuming no pinch points or restrictions).

-Add a return line to the existing setup and use a normally open solenoid valve in the return so you can hold pressure while running.

No particular order there. Probably the cheapest and easiest is the third one, without seeing your setup it's a bit hard to tell if it'll work. Good luck with it!

posted by unfamilia on 6/12 21:48 GMT

Thanks. Wont ask anymore questions here then.

All the best to anyone that tries to get help with such setups from folk that have done it before.

posted by clyons8 on 6/12 23:58 GMT

I was just having a dig Mik. Dont be too precious. I apologise if I have caused offence!

I shall endeavour to use my emoticons more often : )

Your velocity stack gauze is a good idea. I have seen some people use stocking material before also.

posted by unfamilia on 6/13 0:19 GMT

I wear my stockings on my legs, keeps the hair in

Pm replied chris. Sorry not a good day today

posted by racer135 on 6/14 2:16 GMT

Could you use a small tank eg surge tank or oil catch can, have your standard fuel pump feeding into the top left with a 1/4" fitting, a 1/4" or whatever sized outlet in the bottom feeding the carbs, and a 5/16" or 3/8" outlet on the top right of the tank returning to the main fuel tank?

Surely it can't build up pressure if the feed line is small and return is larger? Tank would only need to be small, 500ml or so, mounted up as high on the firewall as possible. Cut a piece of RHS to length, braze some ends on it, braze threaded outlets onto it.