Engine now dies at traffic lights

Discussion in 'Mech Tech' started by grub, Sep 3, 2019.

  1. Turned the screw all the way in..been over to a classic car show this morning..it no longer stalls, but I can't get it to idle any higher than 500 rpm?
    Drives better though, now I've adjusted the timing.
    Will it affect anything else if I adjust the throttle stop screws?
  2. Dubs

    Dubs Sponsor

    Screwing it in lowers the idle, out raises it. :thumbsup:
    snotty likes this.
  3. My specialist told me that screwing the screw that adjusted the tick over, basically controlled the amount of air going into carb and therefore could cause lean running....was I miss advised?
  4. Ok..update..just been in the garage & there is a strong smell of fuel.
    The right hand carb & manifold is covered in fuel on the outside.
    Does this mean sticking float? How do I cure this, it has it now cured itself by overflowing?
    Don't want my bus to catch fire, so need to make sure it's not going to be overflowing while I am driving.
    I assume it won't leak any more without the engine running as fuel only gets into the carb with the electric fuel pump running.
    Or will it carry on leaking while there is fuel in the tank??
    Apologies for my lack of knowledge!
    Last edited: Sep 15, 2019
  5. Someone who knows more than me will reply shortly.

    Don't drive it until you know more.

    A leaking carb won't cure itself.

    Knocking the side of the carb may help a sticking float.

    Does the oil have petrol in it as well as the outside of the carb?
    mgbman likes this.
  6. ^whs^ if its filled enough to run out of the carb side, chances are it's also run inside the carb and down into your engine. Check your oil for fuel and replace before you start it or you could damage bearings... as well as the fire risk.

    Sent from my SM-T580 using Tapatalk
    snotty and mgbman like this.
  7. Dubs

    Dubs Sponsor

    Technically it does lean the mixture, but if the mixtures on the bases of the carbs are correctly set, and the throttle stops correctly set, then the idle screw will only need tiny adjustments, so won't alter the mixture by enough to be a problem.

    It sounds like the needle jet is leaking though, which may have been the problem all along. Clean out the carbs, and replace the leaking needle jet if needed.

    If you have an electric fuel pump, have you got a pressure regulator as well?
    snotty, mgbman and Betty the Bay like this.
  8. Leaking carb needle valves is coming up here all the time now. Maybe we need a Mech Tech Sticky for this topic.

    I think its a number of things causing this needle valve problem.

    Poor quality repro needle valves, dirt and rust in fuel tank, degrading rubber fuel lines, ethanol in fuel corroding rubber parts, ethanol causing gumming up in carb and fuel filter, pump pressure too high overwhelming needle valve.

    Recently changed my fuel filter and it was full of waxy gum and rust. I replaced it with a large Meyle filter which is clear plastic so can see what's inside. Of course the fuel filter sits under the tank and not inside the engine bay.
  9. I got an electrical fuel pump..can't see a regulator, but need to get the bus up in the air a bit to get underneath it better.
    Fuel pipes look brand new.
    Will check for fuel in the oil.
    How can I tell if the needle jet is leaking & what should I be looking for if I take the carb off/apart?
  10. The evidence is usually petrol running over the outside of the carb or the bus juddering to a halt at 30mph in 4th gear on a flat road and not restarting because its flooded. Wait 10 mins and it runs again...

    The needle valve issues are brought on by vibration .. its not a quality issue so much as a wonky alternator pulley or a gonk in the fan ( or equivalent small mass or bit of foam) which shakes it up.

    You can take the valve and look at the needle.. this one was leaky...

    Dubs likes this.
  11. Ok..took the offending carb off after work tonight.
    Must admit I haven't got a clue what I'm doing it what to look for!!
    I took the 5 screws off the top if the carb expected the carb to come apart so I could take a look inside to see if there is anything obvious .
    But the carb still doesn't come apart..looks like I need to take the choke unit off?
    Don't really want to start messing too much as it ran so well before the fuel appeared on the outside body of the carb.
    Any easy checks??
    If you blow through the fuel inlet pipe & turn the carb upside down you can hear the air cutting off, so sounds like the float is not stuck?
    20190917_190215.jpg 20190917_191141.jpg
    Last edited: Sep 17, 2019
  12. Dubs

    Dubs Sponsor

    You dont need to dismantle the choke, but you do need to undo the top nut on the little rod that connects the choke to the throttle lever. Leave the bottom nut where it is, so you dont lose the adjustment. With that disconnected, and the 5 screws out, the top will come off, although it may need a tap with the handle of a screwdriver or similar. Be careful when lifting the top off, as you dont want to rip the gasket. With the top off and turned over, you will see the needle jet under the fuel inlet. They just unscrew, and can be blown out with compressed air, although if it has been leaking, chances are it will need replacing.

    I will be stripping a set Thursday for a customer, so can take a few pics if its any help?
    snotty and paradox like this.
  13. Many thanks Dubs..that will be very helpful..much appreciated.
    Can't smell fuel in the oil .
    Where will the petrol have come from that was leaking from my car? Does it come through the throttle flal spindle?
    If that's what it's called.
    If the needle jet becomes blocked, is that what could have caused the leak?
  14. Dubs

    Dubs Sponsor

    The fuel either soaks through the paper gasket at the top of the carb, or it seeps through the throttle spindle bushes.

    The leaks occur because either the needle has become worn, or a bit of dirt is preventing the needle fully sealing, so fuel can seep past it, over filling the float chamber.

    Have you read up on these carbs? There are a couple of good setup guides floating about somewhere that will help you understand how they work if you are interested.
  15. You only need a microscopic leak to fill up a float chamber overnight from a full tank of fuel providing the pressure.
    Blowing down the inlet as a test, mainly tells you the valve isnt stuck.

    You will need to balance the carburettors, setting throttle plates so the flow both sides is the same at idle. And then check the throttle linkages open both sides in sync properly, saw one at TE a couple of years back with petrol all over LH carb. This was a dirty needle valve, @davidoft blew through it and checked it. And the plastic spacer on the float was under rather than above the pivot
    And a worn linkage on the RH carb so it opened 2 or 3 mm of movement later.
    Last edited: Sep 18, 2019
  16. Where is, and how do I get to, the needle valve?
  17. Dubs

    Dubs Sponsor

  18. Perfect..many thanks Dubs..I'll take a look later.
  19. Dubs

    Dubs Sponsor

    Undo this nut.
    Mark this nut to make sure it doesn't move.
    Undo the 5 screws, remove the spring that goes from the throttle lever to the choke bracket, and remove lid. Turn it over, and there is the needle valve. Remove it, give it a good blow through, as well as the hole it came out of.

    While you are at it, have a butcher's in the float bowl to see if it's full of crap in the bottom.

    Assembly is the reverse of etc etc

  20. Many thanks Dubs..gonna have a go on Saturday.

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