Pressurized fuel system

Discussion in 'Performance Mods' started by Ghost0, Nov 7, 2007.

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  1. Ghost0

    Ghost0 Guest

    I was wondering if anyone has tried to pressurize their fuel system? This is something we typically do on 2 stroke R/C engines. It it set up by putting a fitting on your tank and exhaust and running some fuel line between them. The effect is using some exhaust pressure to lightly pressurizing the tank making more fuel flow possible.

  2. jpilot

    jpilot Guest

    These little engines can get way more fuel than they can use with just gravity feed. Why complicate things? I don't think I want exhaust gunk (and maybe sparks) spewing into my fuel tank.

    It is a simple and light solution in R/C planes because they need some type of fuel pump. A pressurized tank with a flop tube assures a supply of fuel regardless of the attitude of the airplane.

    If you need a fuel pump on a small two stroke, an impulse driven diaphram pump like the ones that are commonly used on ultralights is a good solution.
  3. Ghost0

    Ghost0 Guest

    I was just wondering. I was reading about boost bottles and it seems this would accomplish almost the same thing.
  4. Boost bottles don't actually pressurize the fuel system they act as an accumulator and prevent the reversion pulse from interfering with the new intake charge.....I did think about the RC engine idea of pressurizing the fuel system BUT i think the big difference is that
    RC engines don't (at least the small glo ones) don't have carbs with floats in them to hold a reserve of fuel so I think they use pressure to help ensure a steady flow of fuel to the carb...any RC people out there?

  5. djase10

    djase10 Guest

    Hi All.

    Its an old thread , but I'm re-hashing..

    I think it would be of benefit for the fuel tank to be pressurized.
    Like over sized injectors & MASSIVE fuel pressures in turbo cars.

    The fuel would be better ATOMIZED via pressure
    than the tiny trickle that a STOCK system provides Via gravity..

    I'm not thinking exhaust though,,
    I think a tyre valve fitted to the fuel tank, and air pumped in by a bike pump.

    As long as the tank is under pressure , and NO VACUUM occurs , all would be sweet .

    Any one tried it on a HT????
  6. Fuel pressure on a EFI car is a differant story, as mentioned above carbs have a float bowl, the only thing you will gain presurising the tank is blowing the needle out of the seat and flooding the float bowl.
  7. Mountainman

    Mountainman Active Member

    just a simple thought to remember

    these engines have been engineered to THE FINEST point possible

    they are not in any way -- lacking in the gas dept

    ride that MB thing
    Last edited: Oct 26, 2008
  8. kawasaki999

    kawasaki999 Member

    On a Tanaka site I read that they want the tank to be slightly pressurized, its around 2 lbs. This is done by the gas cap, it has a check valve built in the cap, lets air in, but wont let it out. Tanaka says to check pressure in tank, shake tank a little, let it set a minute, pull off the fuel line to carb while pinching the line and hold line above the tank, fuel should flow out, or loosen the cap and listen for a hiss. Tanaka says the engine will still run ok with out pressure but top end will suffer. So when I made my 1 gal tanks for my gp 460,s I went to the local lawn mower shop and picked up check valves and 2 hole fuel gromets,3 hole gromet if you use a primer bulb from any echo weed wacker and installed them In my cheap 2.66 gas tank. My top speed dont suffer!

    Attached Files:

  9. djase10

    djase10 Guest

    Thats interesting K999..

    My engine IS starving for fuel at the moment, thats why im thinking "pressurized" thoughts.

    My bike has developed a vibration that is stopping the fuel getting to the carb.

    I hold the fuel line and presto, let go and it bogs down =@38kmh exactly..

    Strangely, this vibration is since i replaced the rubber in the frame mounts , so i'll have to get rid of the rubber .

    Just over tightened the mount, and broke it , so taking the motor off again to fabricate some new ones -without the rubber..

    Pressurized tank still in my minds eye though.

    Also, 2 mid eighties turbo cars ( Nissan EXA & Turbo Daihatsu charade) used forced induction "thru the carby" , so i reckon it wouldnt hurt to try it.

  10. BSA

    BSA Guest

    Drill a tiny hole in the gas cap.

  11. Lmao I don't know why I waste my time in here, after the amount of rubbishing I took in one post, and all I ever read is stupid Ideas, and any imformation given is either just discarded or the threads are never read properly and people argue.

    Is every one here brain dead,

    LMAO anyway your wrong, nissan EXA N12, the first model had the E15ET turbo motor, it was centre point injection
  12. djase10

    djase10 Guest

    Geez ,Sorry mate =I stand corrected.

    Wow ,
    I appreciated your input Phil, and took it on..

  13. HoughMade

    HoughMade Guest

    Never complicate things when simple will explain it.

    Think about this- if you had to drain your tank and removed the fuel hose at the carb- how fast does the fuel flow out? Mine will empty the tank in a couple of minutes. That's 1/2 gallon of fuel flow in no more than 120 seconds. Now- no matter how hard you ride your bike, can you use up and entire tank in 120 seconds? That is how much fuel could flow into your engine if it could use it.

    What does this mean? Gravity provides plenty of fuel flow (assuming a tank above the carb). If you are getting fuel starved, the flow rate from the tank is not the problem (assuming a clean system).

    So, what is the problem? Here are some possibilities:

    1) The fuel system forms a vaccum- easy test for this- do what I said above- disconnect the fuel line at the carb and drain a full tank into a gas can (cap on). Does the fuel flow get less over time before the tank is dry and if it does, did the flow pick back up when you opened the cap? If so, drill the small hole in the cap.

    2) The float is set to low and is not allowing enough fuel in the bowl. Take the bowl off and bend the float tabs to allow the float to sit higher.

    3) Restriction in the fuel system in the carb. Clean it out.

    4) A kink in the fuel line when connected- straighten it out...literally. Make it as straight a shot as you can, but keep in mind that even if the fuel line dips below the bowl and comes back up to it, once the system is purged of air, it should flow fine.

    If you do not add huge amounts of air flow or move the tank to the same level or below the carb, there is no way you need a pressurized fuel system.
    Last edited by a moderator: Oct 30, 2008
  14. djase10

    djase10 Guest

    Cheers HoughMade.

    My flow isnt that good, takes approx 5 mins to empty the tank.

    I have drilled the petcock disk out some- with a 1/16 drill bit ( the on/off groove), to aid my flow, and that seems to have done the trick, so far.

  15. mechcd

    mechcd Member

    I'm having a real issue getting decent fuel flow on my pocket bike engine. The gas tank needs to be higher than the engine, but the whole thing is already way high up. I'd rather not have to make an IV pole for the gas tank.It would be easier to mount the gas tank below the engine.

    I don't quite understand what a check valve does to increase pressure.

    Any details on the RC setup?
  16. graucho

    graucho Active Member

    I agree Phil. The HT float and needle are as cheap as they get. The tank on a normal summer day is under slight pressure with the cool gas and average outside temp. More so on a hot day. Also a great environment to create a little moisture. that's why I use a bit of seafoam as I stated in the "Gas and Storage post".

    Also agree with HoughMade about basic flow principals of these tanks.

    About your comment.....
    "Lmao I don't know why I waste my time in here, after the amount of rubbishing I took in one post, and all I ever read is stupid Ideas, and any information given is either just discarded or the threads are never read properly and people argue."

    There are a ton of people here who are "the best of the best" ego's are high. Years of experience are constantly challenged. Ill admit truthfully my ego's high. I'm constantly frustrated. I give 5% of my knowledge due to this. (see, sorry high ego) I love to teach but there's no fair way to do it here. So, I stay in tune here since I'm selfish and still learn from people like you and many others. Thanks, and hang in there. graucho
    Last edited: Nov 9, 2008
  17. 5-7HEAVEN

    5-7HEAVEN Guest

    Hmmm, where does the ego fit on the bicycle?

    Maybe the guys at the other site were right.:-|(neutral smiley)

    ANYWAYYY, I've also had a problem with vacuum lock on the front engine of "Mr. Hyde", my dual-engined creation. Since day one, the new engine quits a few miles into the ride. When this first happened, I sadly limped home on my rear engine. Calling the vendor was fruitless. Jakesus on this site had the same problem with the same engine from the same vendor. He recommended loosening the cap momentarily when the engine died. It sounded silly, but now I loosen the cap when the engine dies on a regular basis. Then like magic, the Mitsubishi roars to life in a few pulls, like nothing happened!

    Recently, I completely renovated my fuel system, adding a Happy Time auxiliary 1.5 liter (50-oz.) tank with large 3/16" steel lines to feed both Mitsubishi's 30-oz. tanks. I removed the HT tank's internal screen AND the filters in the engines' tanks. Hopefully the extra volume or removing the ailing engine tank's fuel filter cures the front engine's woes.

    If not, I drill a small hole in the gas cap, fabricate a manual gas gauge with the "Jack in the Box" antenna ball raising and lowering to indicate fuel level...

    ANNND relieve the vacuum in the front engine's fuel system!

    Excuse me for rambling. It's not an ego problem. At age 62, I'm back in college so I have to practice my critical thinking, English composition and writing skills...

    on you guys. :)(happy smiley)
    Last edited by a moderator: Nov 11, 2008
  18. graucho

    graucho Active Member

    I hope you cured your problems with your renovation.
    Is elevation/humidity/air pressure a factor in your area?
    Im trying to relate if fuel flow problems are better/worse related to origin.

    Congratulations on having the courage to go back to school. :cool:(cool smiley)

    And yes, the guys who left here and went to the other site all had their issues
    with people here. I still keep in touch.
  19. 5-7HEAVEN

    5-7HEAVEN Guest

    Thanks for props, graucho.

    I'm at sea level.

    I believe I'll have the fuel vacuum problems cured, to be sure. I installed a locking gas cap for my Happy Time auxiliary tank. I also noticed that the keyhole had a vacuum leak when you suck on it from the tank side, even with the keyhole cover shut. That means I don't have to drill a hole in the cap or tank, and the engines will vent thru the locking gas cap's keyhole.

    What a stroke of luck!:cool: