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Thread: carb "dead spot"

  1. #61
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    had a quick go at it earlier. couldnt get much done though as i have tweaked my back and had shooting pain down my left leg all day, coupled with the rain its not been productive. so i picked an easy bit and fiddled with the bowl on the pump. when i went to take the bowl off it was suctioned on and took a wriggle to free. checked the seal and it seems to be seating properly and the bowl seems to be fitting properly. yet whenever i put it back on and tried to prime the system it wouldnt even begin to fill before it suctioned on again and stopped the fuel flow. i took the pipe off the carb and tried to see if i could pump some fuel through and nothing was getting that far.
    so i think that points to the problem being further back. i shifted the tap a bit and its harder to turn one way than the other, which is odd. so perhaps the rubber (i think it was rubber anyway, i know some are cork and it was a long time ago that i opened it up) seal has shifted and it mostly blocking the ports. i will bypass the tap tomorrow and see how it behaves. i would like to keep a tap though, i will have to see if there are other alternatives in case the military one is damaged.
    the plumbing is all the right way round, it was flowing well enough until yesterday.
    Chris
    1977 series 3 ex mod (FFR) 109 2.25p 12v HRTC hard top "phil"
    My work: The emporium of the useful and curious http://emporiumoftheusefu.wixsite.co...umofthecurious
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  2. #62
    Moderator DarrenH's Avatar
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    Default Re: carb "dead spot"

    mad, its almost like the pump is running backwards!
    Drives: 1982 series 3 88" station wagon

  3. #63
    Disco 1 TDi specialist zollaf's Avatar
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    Default Re: carb "dead spot"

    pick up in tank blocked.
    1969 109 ex military
    1994 audi 80 tdi 330,000 miles
    1998 audi s4 avant 'noggy' 326 bhp weekend toy
    30 or so other landrovers all gone but not forgotten

  4. #64
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    ok then, i had a tinker today and found the tap is almost certainly at fault. i took the pipe from the tap and jammed a hose on it which i simply put into the tank. with that in place the engine ran fine. so i put the pipes back on the tap and though it took a minute it still stopped again and wont start. both pipes were cleaned up the other day. so i think that is fairly conclusive on the dodgy tap front. i will take it off and get it open to see if it can be sorted.

    as for the dead spot, its become very inconsistent. its seems to only manifest now when the engine is still not quite up to temp or when it goes from idle to full throttle. it can be avoided by being gradual, though it can still be pretty fast. i have high hopes for it, i just needs to sort out the tap and make sure i only need to check one place while i thrash out the last problems.
    Chris
    1977 series 3 ex mod (FFR) 109 2.25p 12v HRTC hard top "phil"
    My work: The emporium of the useful and curious http://emporiumoftheusefu.wixsite.co...umofthecurious
    Proud member of the YCHJCYA2PDTHFH Club

  5. #65
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    fuel tap is definitely the problem. i had a burst of enthusiasm and took it off and the seal inside has totally disintegrated and piles of corky gunge was blocking every port on the thing. so now to find a seal kit or an alternative as i want both tanks working.
    Chris
    1977 series 3 ex mod (FFR) 109 2.25p 12v HRTC hard top "phil"
    My work: The emporium of the useful and curious http://emporiumoftheusefu.wixsite.co...umofthecurious
    Proud member of the YCHJCYA2PDTHFH Club

  6. #66
    Engineer phoenixdave's Avatar
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    Default Re: carb "dead spot"

    I replaced mine with a couple of solenoid valves and a changeover switch. David
    1982 ex-mil 109 2 1/4 petrol on lpg series III, 'Phoenix'

    1983 2 1/4 diesel 88" series III, 'Willy', currently in bits.

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    Disco 1 TDi specialist zollaf's Avatar
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    Default Re: carb "dead spot"

    i would bypass it for now and get this other problem sorted first. maybe thats linked to it as well.
    1969 109 ex military
    1994 audi 80 tdi 330,000 miles
    1998 audi s4 avant 'noggy' 326 bhp weekend toy
    30 or so other landrovers all gone but not forgotten

  8. #68
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    ok so the fuel lines are sorted (bar fixing the sheared screw in the one fuel tank). very impressed with P.A Blanchards, ordered the seal for the tap and it turned up the next morning. its running merrily as far as the fuel supply to the carb goes. the dead spot is still an issue though the new carb is definitely better.
    i moved it around today as i had to free up its spot for the next job. it was absolutely fine provided that the choke was out. once the choke was in the dead spot was all too obvious and it needed the revs to be right up before it would move. yest with the choke in it was rolling around on the clutch alone and i could give it a little rev with no issue at all. its got to be either no enough fuel coming through or an air leak, surely?
    Chris
    1977 series 3 ex mod (FFR) 109 2.25p 12v HRTC hard top "phil"
    My work: The emporium of the useful and curious http://emporiumoftheusefu.wixsite.co...umofthecurious
    Proud member of the YCHJCYA2PDTHFH Club

  9. #69
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    i finally got back to it after the christmas lull today. got the sheared bolt in the fuel tank sorted out and sealed up and everything else works again so its just this issue to deal with.
    i have moved it around a couple of times and with the choke out it behaves really nicely. it would probably drive perfectly well with the choke out. makes me think that perhaps there is simply not enough fuel getting up there to begin with. could the dead spot be from the sudden draw emptying the bowl faster than it can fill? i am fairly dubious of this as when i had the priming bulb fitted i tried pumping it whilst operating the throttle and found no change. it seem like that kind of thing though.
    i am going to go over the outsides carefully and look for air leaks. i havent found anything obvious with the easy start/brake cleaner approach so any other methods may be useful.
    Chris
    1977 series 3 ex mod (FFR) 109 2.25p 12v HRTC hard top "phil"
    My work: The emporium of the useful and curious http://emporiumoftheusefu.wixsite.co...umofthecurious
    Proud member of the YCHJCYA2PDTHFH Club

  10. #70
    Engineer phoenixdave's Avatar
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    Default Re: carb "dead spot"

    Quote Originally Posted by christofloffer View Post
    i finally got back to it after the christmas lull today. got the sheared bolt in the fuel tank sorted out and sealed up and everything else works again so its just this issue to deal with.
    i have moved it around a couple of times and with the choke out it behaves really nicely. it would probably drive perfectly well with the choke out. makes me think that perhaps there is simply not enough fuel getting up there to begin with. could the dead spot be from the sudden draw emptying the bowl faster than it can fill? i am fairly dubious of this as when i had the priming bulb fitted i tried pumping it whilst operating the throttle and found no change. it seem like that kind of thing though.
    i am going to go over the outsides carefully and look for air leaks. i havent found anything obvious with the easy start/brake cleaner approach so any other methods may be useful.
    Hi Chris,

    Mine did what yours is doing a few years back, it has a Weber on though and I believe yours has a Zenith- correct me if I'm wrong. Anyway, it turned out that the idle circuit was all gummed up with old petrol. On the Weber you can access the idle circuit by removing a big brass nut on the outside of the carb, not sure how it's done on a Zenith.

    If the problem was not enough fuel getting to the carb then using the choke would not help as there would still be no fuel there.David
    1982 ex-mil 109 2 1/4 petrol on lpg series III, 'Phoenix'

    1983 2 1/4 diesel 88" series III, 'Willy', currently in bits.

  11. #71
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    good point there.

    it has a weber 34ICH fitted at the moment. it had a zenith on before but i removed it. the dead spot has become less prominent with the weber but its still there when there is no load but very prominent under load.
    the weber was stripped and thoroughly cleaned and fitted with a new service kit before fitting.

    an air leak somewhere on the manifold seems the most likely then right?
    Chris
    1977 series 3 ex mod (FFR) 109 2.25p 12v HRTC hard top "phil"
    My work: The emporium of the useful and curious http://emporiumoftheusefu.wixsite.co...umofthecurious
    Proud member of the YCHJCYA2PDTHFH Club

  12. #72
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    Default Re: carb "dead spot"

    You're having a real fight with this one. I think it could actually be several issues which is why it is so hard to find just one, and altering one doesn't seem to cure all.

    You have solved the air in the line problem, the fuel tap, the wonky base plate and air leaks. I am suspecting it could now be down to ignition timing based on vacuum. This would account for bogging down under load as this is where the timing needs adjusting using vacuum.

    You have a new accuspark dizzy? Are you sure it has the right part number of the vacuum unit attached? When I was using second hand dizzy's I found not only were the weights and springs different for the centrifugal element but also the vacuum units all pull in different ways.

    Either you are not generating the right vacuum at the carb that is expected, or the vacuum unit in the dizzy is wrong for what you need.

    First check - find the part number on the dizzy vacuum unit.
    Second check - get a vacuum gauge and plug it inline between the dizzy and the carb. The figures must be around somewhere....
    Last ditch shizzle or bust - send your dizzy of to somewhere that can test them for mechanical and vac advance.

    Then you can cross it off as not the dizzy.

  13. #73
    Moderator DarrenH's Avatar
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    Default Re: carb "dead spot"

    fyi the little rod that opens the throttle slightly when the choke is pulled, conversely that also pulls the choke open when the throttle is opened. so it probably wont drive ok on choke

    what rocker cover breather system do you have ? is it the type with one hose to the carb elbow and a T piece to the carb itself ?
    Drives: 1982 series 3 88" station wagon

  14. #74
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    yeah i wasnt actually thinking of driving around with the choke out, it just seems to drive like normal with the choke out when shifting it around. it sounds normal like that but i dont think it would be so happy like that at speed.

    the breather is the type that has the cone shaped diaphragm between the cover and manifold.

    as for the dizzy it is a practically new powerspark unit. a totally new one rather than a reconditioned and updated unit. came with a new vaccum unit on it. not that it means there is not a problem of course but it wont be from wear. i might ask the garage down the road if they have a gauge to test it, i cant imagine it being the sort of tool that i would need enough to buy one.
    Chris
    1977 series 3 ex mod (FFR) 109 2.25p 12v HRTC hard top "phil"
    My work: The emporium of the useful and curious http://emporiumoftheusefu.wixsite.co...umofthecurious
    Proud member of the YCHJCYA2PDTHFH Club

  15. #75
    Disco 1 TDi specialist zollaf's Avatar
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    Default Re: carb "dead spot"

    try blocking the breather off where it goes into the inlet manifold.
    1969 109 ex military
    1994 audi 80 tdi 330,000 miles
    1998 audi s4 avant 'noggy' 326 bhp weekend toy
    30 or so other landrovers all gone but not forgotten

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