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Thread: carb "dead spot"

  1. #46
    Engineer phoenixdave's Avatar
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    Default Re: carb "dead spot"

    Make sure the base plate in your dizzy is properly earthed to the engine at all positions of the vac advance, some types of dizzy have a tiny wire connecting base plate to dizzy body to make sure it's connected but other designs don't require it. 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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    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    i had a play with the plugs and leads. i checked the plugs first and the new ones (champion) had blue sparks that looked a bit weedy. the old ones (denso) had white and stronger looking sparks. however the denso plugs had a curved arm which the spark would wander on so that it could be a longer spark or a shorter one at any time. i set both sets to 40 thou before starting so that i was working with things on the same level. so the denso ones are fitted now, but have had no impact on the dead spot.
    i played around with the leads, the new ones are lucas 7mm standards and the old are 8mm silicone ones (cant remember the brand now). however they were on a par with all combinations of plus and positions. i couldnt see, hear or feel any difference (yes, i got shocked a couple of times) between them. so the silicone ones are on there at the moment as they were just the last ones on.
    so the only improvements to be made here is new plugs and one of those gold coils right? the leads seem to be working fine so they should be ok.

    with the dizzy, do you mean an earth on the outside of the housing? the dizzy is securely bolted in and the moving plate inside has a cable earthing the plate to the housing if thats what you mean. the housing should be pretty well earth through the bolts though right?

    nothing made a difference to the dead spot though, and its sounding worse than ever. its also more smokey on start up too. until the engine warms up it throws out white smoke at idle. it disappears when revving and once the engine is warming up. it also seems a little lumpy at idle until its warm too. i know they are always better when hot but it wasnt this bad when it first went in and was fine before this dead spot started to appear.
    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

  3. #48
    Engineer holly76's Avatar
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    Default Re: carb "dead spot"

    I believe the dissy earth Dave is talking about is an internal one between the moving plate and the body.

    good to hear you have a few components to swap to try to find the issue. you can see how frustrating it can be one component at a time. which is probably the right way to do it, but why I suggest a complete swap. the spark you get with the denso plugs sounds about right. I had an issue with old stock champion plugs which I believe has a suppression resistor in but the correct part number. maybe try some ngk ones. though i'd be looking at the coil next. an maybe the cap and rotor, but these were new with the distributor.

    one way to try to eliminate the carb may be to pull the choke engine will run rough rich but should not cut out.

    your running issues sound nearly normal , the white smoke could just be condensation. but it does raise the question is something is amiss in the engine. maybe a compression test would help, look for constant bubbles in the coolant. and getting more desperate, pull the head.

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    Moderator DarrenH's Avatar
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    Default Re: carb "dead spot"

    Quote Originally Posted by holly76 View Post
    the spark in the plugs is a break down of the insulating properties of the gas surrounding it (air/fuel). at low speed the engine has time to draw in more air which results in higher compression. this means the gas the spark has to break down is denser. as revs increase the gas charge is reduced resulting in lower pressures. which means lower density. which a weak spark can ignite.
    petrol engines are quantity governed so cylinder pressure depends on the throttle angle as well as revs. but with foot buried the cylinder pressures will peak when cylinder filling peaks, and engine torque is directly proportional to cylinder filling. so basically peak torque (2000rpm) wide open throttle will be hardest time the coil is working (with regards spark energy) but higher engine revs when cylinder pressure drops, its also got less time to charge so its six of one, half a dozen...
    Drives: 1982 series 3 88" station wagon

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    Default Re: carb "dead spot"

    Those internal earths have a habit of breaking through fatigue too, will be connected fine then intermittently play up. Probably best to replace it if nothing else helps.

    Im not sure the gold coil fixed anything in my case, but it removed one more doubt in my mind. Still carry the old coil as a spare though.

  6. #51
    Disco 1 TDi specialist zollaf's Avatar
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    Default Re: carb "dead spot"

    does you coil get very hot whilst all this is happening. not just warm but hot..
    currently between landrovers, just a scabby old audi with 359,000 miles under it.

  7. #52
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    i honestly didnt notice it getting hot, but i cant say i was particularly checking it much either. i have been focused on the carb and potential air leaks.
    i have got a new set of NGK plugs on the way, nothing fancy but they should be better. i also made sure they were the 8:1 type (the champion ones were too anyway). i have also got a lucas gold coil on its way to replace the bearmach one. the only bit i am not replacing yet is the leads as there was no noticeable difference between the two set i have i figured they would be the least likely to be a problem. where the plugs were clearly weaker than the used set. also got a weber 34 ich on its way and a rebuild kit already here so i will eliminate that one whilst i am at it too.
    the dizzy all looks fine, clean, moving and connected up. i will keep an eye on the internal earth though if they are prone to fatigue, good to know.

    not done anything to it for a couple of days. just had to walk away and leave it for a bit as it was trying my patience and it was at serious risk of just going on ebay.
    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

  8. #53
    Disco 1 TDi specialist zollaf's Avatar
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    Default Re: carb "dead spot"

    ok, before swopping that lot over, go for a drive and see if the coil gets hot. if it does, earth the dizzy body to the engine block. also check the coil you have is not one designed for a ballasted system and running without a ballast as both these things would give you the symptoms you have.
    currently between landrovers, just a scabby old audi with 359,000 miles under it.

  9. #54
    Forum Approved Trader christofloffer's Avatar
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    Default Re: carb "dead spot"

    not impressed today. i finally got the weber sorted, had to get hold of a new choke spindle as a screw sheared and killed it. got it put on and it started out very promising. the dead spot was there in a way but it was really particular and when it went again it was accompanied by a quick sucking sound. so i put my hand over the filter intake and gave the throttle a quick burst to see if there was anything obvious and the dead spot disnt seem to happen. unfortunately it went south after that. for some reason that i cant figure the fuel lines are pressurising. i had to remove the priming bulb as it collapsed under the pressure and even though the priming lever on the pump has the right feel of resistance it doesnt seem to be pumping anything. the bowl is full but its not coming though. i cleaned out the gauze filter yesterday, it also had a new filter and the weber has a new filter too. so i decided to try and check the gauze on the pickup pipes and one of the screws sheared so i have to drain the tank to drill that out now. after all that the gauzes were clear, so not impressed with that .
    really disappointing as before the problems started it sounded good. the idle was really smooth and the revs were good too. it was just that blip and i really felt like i was getting close but now it wont even start.

    so the set up now is weber 34 ich, lucas gold sports coil, ngk plugs, lucas leads, powerspark 45D distributor.
    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. #55
    Engineer phoenixdave's Avatar
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    Default Re: carb "dead spot"

    I don't really understand what you mean by 'the fuel lines are pressurising'. 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. #56
    Moderator DarrenH's Avatar
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    Default Re: carb "dead spot"

    if you have the type of pump with glass sediment bowl make sure the seal in the alloy casting at the top is good and plump. i had an issue on mine where the glass was slightly too big and jamming on the lip of the alloy casting, not pushing into the seal, so the vessel was full but not going up to the carb.

    other than that, if you are saying everything downstream of the pump (i.e tank to pump) is vacuuming, you have some serious issues! try it with the filler cap off, so make sure the tank isnt sucking in on itself due to block breather
    Drives: 1982 series 3 88" station wagon

  12. #57
    Consultant Richie_asg1's Avatar
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    Default Re: carb "dead spot"

    I had a problem of the glass sediment bowl gasket letting air in. It didn't seem to leak petrol though. I bought 3 seals as I would rather replace a seal everytime I empty it. Also the fuel pipe feeding it had an olive, but not the liner so it didn't seal properly either.

    You can chase your tail for a long time on these issues.

    Because of the dizzy earth problems, and the shocking state of the one I bought, I started making my own from fine copper braid - nice and thick, (outside of coax actually), and covered in a clear thin silicone sleeve - so you can see it, with crimped and soldered JST ring lugs at each end. They must have been good because the Indian Racing team Sahara force bought a load of them from me . Maybe used them as small earth straps.

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    Default Re: carb "dead spot"

    Quote Originally Posted by phoenixdave View Post
    I don't really understand what you mean by 'the fuel lines are pressurising'. David
    pressurising is poor wording on my part, darren is right there, its vacuuming. the priming bulb was last in line so the system went tank-changeover tap-pump-filter-priming bulb-carb. i took the carb side of the bulb off first and the thing stayed collapsed and once i took it off the filter side it re-inflated, so i am working on the vacuum being that way. its no longer in the system at all as i replaced the section with a length of flared copper pipe for now.
    i did think the tanks may not be breathing but it did on on both tanks and there was no resistance or sucking sounds when taking the caps off. i will give it a go running without them tomorrow though.
    i will check the seal too as it was disturbed the other day when i was cleaning up the gauze. it was running since then though on both carbs but always worth a check. would have thought a leak there would actively stop it from creating a vacuum.
    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

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

    oh, you never mentioned a change over tap. by pass it, just run off one tank, see if that cures it. they are notorious for leaking and letting air in. no idea why the priming bulb is collapsing, unless the one way valves are goosed, best place is in the bin, you dont need it if the primer works as it should. also check the end of the pick up pipe in the tank isnt blocked.
    currently between landrovers, just a scabby old audi with 359,000 miles under it.

  15. #60
    Engineer phoenixdave's Avatar
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    Default Re: carb "dead spot"

    Quote Originally Posted by christofloffer View Post
    pressurising is poor wording on my part, darren is right there, its vacuuming. the priming bulb was last in line so the system went tank-changeover tap-pump-filter-priming bulb-carb. i took the carb side of the bulb off first and the thing stayed collapsed and once i took it off the filter side it re-inflated, so i am working on the vacuum being that way. its no longer in the system at all as i replaced the section with a length of flared copper pipe for now.
    i did think the tanks may not be breathing but it did on on both tanks and there was no resistance or sucking sounds when taking the caps off. i will give it a go running without them tomorrow though.
    i will check the seal too as it was disturbed the other day when i was cleaning up the gauze. it was running since then though on both carbs but always worth a check. would have thought a leak there would actively stop it from creating a vacuum.

    I would not expect a vacuum to occur between pump and carb as this section should always have positive pressure. I suppose if the float chamber isn't vented properly you could possibly get vacuum from the engine, or the only other possibility I can think of is the pump plumbed in wrong way round? Zollaf is right about the changeover tap though, very good at letting air in. I suppose your priming bulb could have collapsed because the pipe was empty (full of vapour) and warm, then when it cooled down a vacuum might be created. 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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