I Think its my Carb....Now What?

Discussion in '2-Stroke Engines' started by GoldenEagleChris, Oct 3, 2010.

  1. I have been scouring this site for a similar scenario to my issue, but I havent been able to find any help.....

    I have just tried to fire up my rebuilt Zenoah "Strato Charged" 25.4cc engine.

    Much to my dissapointment, nothing happened.

    So, I put on my mechanix hat.

    I checked for spark....I turned off all the lights and pulled.....ewww I got shocked!!! Blue lightning in the dark!!!! ---I got spark....

    Compressions seems normal....nothing feels weird when I yank on the pull start.

    I got a Hi Po Carb Walboro 167a that i have had for the past several years and i have ALWAYS been happy with its reliability and performance... i pulled apart and carefully sprayed down with no residue brake cleaner and put back together exactly as it was. It seemed to have a vaccuum and pulled up gas through the lines into the carb....primer bubble filled up........half way....

    Before i rebuilt it, that primer bubble always got full.... Flag #1

    I kept pulling....

    Now all the gaskets are brand new with Indian Head Gasket Seal coating everything.......so I am almost positive it is NOT an air leak....

    I put my nose in the exhaust can.....smelt like virgin exhaust....Flag #2

    I put my nose in the spark plug hole....smelt like an absolutely clean cylinder,
    spark plug tip is dry. No Gas.....Flag #3

    I even put my nose in the venturi on the carb and it too, smelt clean.

    But the primer bubble is getting gas......


    I prime the **** out of the bubble, I watch gas go up the line, into the bubble, i stop priming, i watch the gas leave the carb area and go down into the gas tank....I dont remember that happening either...

    I twist the throttle and pull and i can hear a change in tone from a closed put to a wide open throttle pull. I still smell no gas in the carb.....

    SO I THINK ITS THE CARB not delivering fuel to the cylinder....


    What now...?

    I have a carb rebuild kit i got, but it seems to have WAY more pieces to it than my carb did when i cleaned her out....maybe I didn't go deep enough in the carb but it looks like it can get intense.

    (All i did with the carb when i cleaned it was pull off the primer bubble, removed the gasket, it looked fine, everything appeared to function normally, no gunk no residues no nothing, it looked fine...I flipped the carb over and removed that one screw, took off that gasket and everything on that side looked fine, sprayed that solvent and put it back together.....pulled out the hi and low and idle screws, sprayed in there put them back.....so i pretty much cleaned out the carb...(

    Can anyone lays some motored biking knowledge on me and let me know what you think?

    Here are some quick pics to give you an idea what I am working with....

    Attached Files:

  2. loquin

    loquin Active Member

    There's a diaphram behind the priming bulb that, if it gets stiff, can lead to the issues you're seeing. The carb uses pressure pulses from the engine (caused by the piston movment changing internal effective crankcase volume) to pump your fuel. As the pressure goes up, the diaphram moves 'out' and as the pressure goes down, the diaphram moves back 'in.' This, of course, results in the volume inside the carb pump (bulb) chamber changing. Add a check valve or two, and there's your fuel pump.

    A foreign object caught in the check valve(s) in the bulb chamber could also cause this problem. But, a foreign object 'should' get pumped back into the fuel tank when priming, unless it's big enough to not pass the check valve...
    Last edited: Oct 4, 2010
  3. unior

    unior Member

    I second the diaphragm:eek:
  4. V 35

    V 35 Member

    Try pouring a little [ 1/2 a teaspoon ] of fuel down the air intake, and try to start it.
    If it pops and dies = engine OK, carb not delivering fuel. Check line feeding carb
    by diconnecting line at carb, put line in a clean * paper * cup, and crank engine,
    if cup stays empty, your not pumping. If fuel comes out, check for impurities,
    if grit is found, clean / replace needle and seat.
  5. @ v-35

    if i understand you correctly, you are recommending me to disconnect the RETURN line from the carb to the gas tank and yank the pull start right...not the send line from the gas tank to carb right?
  6. loquin

    loquin Active Member

    You are seeing fuel in the primer bubble when you prime, but, the motor's not starting at all, nor do you smell gas after unsuccessfully trying to start it?

    The fact that the fuel is slowly draining back into the engine tells me that the check valve in the fuel line loop isn't working right, and that would lead to the motor dying after the gas drains back out of the reservoir in the carb... But, that wouldn't keep the motor from firing and running until the reservoir emptied. Something is blocking the fuel flow, between the reservoir and the venturi.

    You said
    Maybe you got a drop of the gasket seal over the small hole that passes the fuel between the reservoir and the carb body... :ack2: It wouldn't take but tiny bit.

    (BTW - What V 35 was saying is to put a little clean fuel in a cup, disconnect the FEED (not the return) line, and place that fuel line into the cup.)
    Last edited: Oct 6, 2010
  7. ...it was the indian head

    .....well people, I guess i got crazy on the Indian head when i painted it on the intake manifolds and gaskets......

    It was blocking the little intake hole in the intake part of the cylinder. It was completely sealed off like i had snapped off the head of a bolt. I finally had to put a little screwdriver for fixing glasses into the hole and push that gunk through. I wonder how a little nib of indian head into the cylinder or more likely the crankcase will work out.....eh, it ll probaby get burnt up,,,,

    Cheers to one of the Admin who guessed it.

    I tore down my carb and i just felt that the carb was fine, gave her some compressed air and put her back together.

    Then i shined a light in through my intake manifold through the little hole that the fuel goes into the cylinder and saw shiny indian head gunk.

    Reason led me to believe then that the indian head got in there.

    Pulled off my intake and destroyed a perfectly good gasket in the process and that was indeed the case.

    Case closed, I gotta make me a new intake gasket then fire this batch up.

    (I was REALLY glad it is not the carb, that rebuild kit i got looks INTENSE.)

    Let us all give thanks to MB.com
  8. HeadSmess

    HeadSmess Well-Known Member

    was the first thing that came to mind.

    the sealants are soft compared to alloy...may cause some extra carbon is all...

    recommend using non hardening sealants on paper gaskets etc, or loctite "anaerobic" style stuff... stays liquid, doesnt set.
  9. Update on my thread

    So guys, here is an update on my thread with my carb/ engine starting problems.

    It initially appeared that it was the Indian Head gasket seal gunking up the fuel hole in the manifold of the cylinder and preventing fuel from flowing into the cylinder to fire...

    I fixed that and the engine fired RIGHT up....I thought it was case closed.

    The next day when i tried to go for a ride, I could not start the **** thing.

    The first pull, the engine popped like it was going to fire, but then died and nothing for the 20 min i pulled thereafter.

    I tried every combo on the carb starting with 1 1/2 out on the low and 1 1/2 on the highs.

    I gave up with no success, it felt to me that i had flooded the engine and felt that it was best to let her sit overnight.

    Today after work i went back and yanked the pull start, it popped again just like yesterday, ran for 5 seconds and then died.

    Again i yanked for a min or two with no avail.....

    Then I decided I would try to press the primer bulb at the same time AS I YANKED THE PULL START.

    It fired up on the third pull / prime. By the way, the primer bubble is completely full now....

    It ran, i tried to dial her in, she sounded like she was about to putt to a stop, I turned in the low screw all the way in until it was 1/2 turn from closed.

    She revved and still died.

    I went to yank the pull start again, and she would not start.

    I again primed as i yanked and again on the 3rd time she fired right up.

    I tested this for about 10 min.

    I could not get her to stay running once she was running.

    and I could not get her to start without simultaniously priming the engine whilst pull starting.

    SOOOOOO I feel I have answered my own question, and feel that I should either rebuild the carb or replace it.

    It has to be the carb. It can deliver the fuel if it get forced (primed) into the engine, but something is stopping normal fuel delivery to the cylinder in the carb.

    I think it may just be the diaphram below the primer bulb?

    or perhaps the check valve as earlier suggested?

    25.4 Zenoah Strato Charged Engine.
    Last edited: Oct 12, 2010
  10. HeadSmess

    HeadSmess Well-Known Member

    diaphgrams. which are part of the check valves.

    or some gunk in the way.

    get a new one :) easy easy fix... or actually...get as many similar second hand ones as possible... scrap yards, mower shops, etc etc etc
  11. V 35

    V 35 Member

    Some carbs use an atsmospheric vent, a small drilled hole in carb top.

    Instead of Hard drying sealer, consider using ' Hylomar ' sealer.

    Invented in England, used on jet engines, called a gasket dressing,
    this product spreads like Vasoline, doesn't harden, turns to solid under
    compression, can be taken apart / reassembled no new gasket, no second coat sealer.

    A little hard to find ... Speed Shop, Motorcycle Shop, [ got mine on EBay ]
    and a bit expensive, until you use it, a little goes a long way.