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  1. #31

    The big gang theory

    Quote Originally Posted by BenBaron View Post
    I get the bangs also, sounds like it comes from 1 side. 2 possibilitys as far as I can tell, too rich or I have manifold leak...Im gunna check out both when I hav 5 mins
    Since posting that i gather that both those point are possibles. I have found a chap in watford (bob harman) whos going to take a look. Will let you know what he finds. PS he's on google

  2. #32
    Join Date
    Apr 2009
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    Hope noone minds me tagging another carb related question on the back of this thread ... engine not being running right, quick investigation and I found the accel pump needed adjusting and was only beginning to move and hence give a nice dosage when the accel was half way through range of movement. Odd ... as i when I put it in 12 months ago I set it with the 10 thou gap as recommended. 4 turns (!!) of the bolt and it was back where it should be, and a big improvement in performance, partic for London traffic! However, I also got a vaccuum pump from real steel - not a big outlay. Tested this afternoon, my idle rpm is c 800, but my idle vaccuum (taken from the correct port, beneath fuel bowl on the holley carb) was hovering c 12 inches. The pump had some guidance saying idle vaccuum should be 17-22 inches. I threaded the lean screws on both sides RIGHT in, little change in revs or vaccuum. I then unscrewed them. ditto.

    I then decided to shift my timing a little, so advanced it a bit which got me up to about 16, and with one turn out on both screws I was up to 17. Pressure seemed steady at all levels, not bouncing or anything

    Question: What should the idle vaccuum be? Shouldn't the car cut out if you screw them right in tight when idling with no accelerator?

    Also, I did advance the timing a little more before backing off a bit, because my idle revs were getting over 1000 so a little high. I tried to adjust this via the idle screw, but found that this was already backed RIGHT off to the extent it was doing absolutely nothing!!!

    Does this mean that I am in fact not using the idle circuit at all, and am straight onto the transition circuit??

    Am in process of fitting a wide band meter which will tell me what is going on a bit more as well.

    And I would RTFM but I don't have one! Anyone recommend a good book?

    Set-up: 351c, +40 tho bore, AFD 64cc heads with rollers, 268 hydraulic high energy cam 218 inlet and exhaust, Edel performer dual plenum intake, holley 600 cfm with vacuum secondary. With mallory magnetic breakerless dissy, and MSD 6al with MB2...

  3. #33
    Join Date
    Mar 2006
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    Quote Originally Posted by Alastair_Mayne View Post
    Hope noone minds me tagging another carb related question on the back of this thread ... engine not being running right, quick investigation and I found the accel pump needed adjusting and was only beginning to move and hence give a nice dosage when the accel was half way through range of movement. Odd ... as i when I put it in 12 months ago I set it with the 10 thou gap as recommended. 4 turns (!!) of the bolt and it was back where it should be, and a big improvement in performance, partic for London traffic! However, I also got a vaccuum pump from real steel - not a big outlay. Tested this afternoon, my idle rpm is c 800, but my idle vaccuum (taken from the correct port, beneath fuel bowl on the holley carb) was hovering c 12 inches. The pump had some guidance saying idle vaccuum should be 17-22 inches. I threaded the lean screws on both sides RIGHT in, little change in revs or vaccuum. I then unscrewed them. ditto.

    I then decided to shift my timing a little, so advanced it a bit which got me up to about 16, and with one turn out on both screws I was up to 17. Pressure seemed steady at all levels, not bouncing or anything

    Question: What should the idle vaccuum be? Shouldn't the car cut out if you screw them right in tight when idling with no accelerator?

    Also, I did advance the timing a little more before backing off a bit, because my idle revs were getting over 1000 so a little high. I tried to adjust this via the idle screw, but found that this was already backed RIGHT off to the extent it was doing absolutely nothing!!!

    Does this mean that I am in fact not using the idle circuit at all, and am straight onto the transition circuit??

    Am in process of fitting a wide band meter which will tell me what is going on a bit more as well.

    And I would RTFM but I don't have one! Anyone recommend a good book?

    Set-up: 351c, +40 tho bore, AFD 64cc heads with rollers, 268 hydraulic high energy cam 218 inlet and exhaust, Edel performer dual plenum intake, holley 600 cfm with vacuum secondary. With mallory magnetic breakerless dissy, and MSD 6al with MB2...


    I presume that you mean vacuum gauge not pump. Anyway in answer to your vacuum question it is impossible to say what the vacuum should be because it depends on loads of things but mainly the camshaft profile. Really all you need to do it giggle the timing and the mixture screws in order to get the vacuum at it highest level at idle, this will mean that the engine is ticking over with the throttle cracked open the smallest amount. The screws don't even control the vacuum directly, they control the idle mixture strength. When the engine 'likes' what you are doing with the screws it will respond by an an increase in idle RPM, this might not be that easy to see or hear but the vacuum will also increase and this will be easy to see on the gauge. The idle should be reduced to what ever you require with the tickover screw. (Again the cam has a lot to do with what the engine will tickover at). Basically the vac gauge is a more sensitive tuning device than the rev counter. My 4.6 Rover pulls 15-16 inHg at tickover.

    I would have thought that the engine would cut out if you screwed the mixture screws right in but Holley carbs aren't my thing so I could be wrong. I believe that you can have to do some fiddling with the secondary butterflies on these carbs which seems odd to me but there you go! (That might have something to do with your high tickover even though the main tickover screw is backed right out and the fact that the mixture screws can be screwed right in).

    I doubt that you are running on the transition circuit, you engine would be revving it's nuts off!

    There are a shed old of books on Holley carbs, someone will be able to recommend a good one!
    I refuse to engage in a battle of wits with an unarmed opponent.


    Rules for buying 'Go Faster' parts:-

    If it's fast and cheap then it's not good.
    If it's cheap and good then it's not fast.
    If it's good and fast then it's not cheap!

  4. #34
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    Gauge not pump, yes!! I have heard/seen about tweaking the secondary butterflies, so maybe that's where the issue is ... as the tickover screw is backed right off (i.e. is redundant) the only way I have to control idle rpm is by tweaking the timing marginally ... so something has to be wrong! And I had read that on Holleys, if you screw the mixture screws right in it should cut out which it doesn't. that's why I wondered if the butterflies are open a little too far and drawing from the transition circuit but it sounds like that can't be the case.

    A good book and lots more fiddling around it is then!

  5. #35
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    Quote Originally Posted by Alastair_Mayne View Post
    Gauge not pump, yes!! I have heard/seen about tweaking the secondary butterflies, so maybe that's where the issue is ... as the tickover screw is backed right off (i.e. is redundant) the only way I have to control idle rpm is by tweaking the timing marginally ... so something has to be wrong! And I had read that on Holleys, if you screw the mixture screws right in it should cut out which it doesn't. that's why I wondered if the butterflies are open a little too far and drawing from the transition circuit but it sounds like that can't be the case.

    A good book and lots more fiddling around it is then!

    I'm sure that the lack of control of the tickover control will be down to the secondaries not being setup correctly. I'm surprised that the 'Holley boys' on this forum have not posted up some help.

    Stick an Eddy carb on your lump, it's a better carb anyway! (That should get them posting up!!!)
    I refuse to engage in a battle of wits with an unarmed opponent.


    Rules for buying 'Go Faster' parts:-

    If it's fast and cheap then it's not good.
    If it's cheap and good then it's not fast.
    If it's good and fast then it's not cheap!

  6. #36
    Join Date
    Mar 2006
    Location
    Location Location is a crap TV program
    Posts
    8,042
    Message to TonyM, I know that you are going to mess with my post and bung up something oh so witty about Gay FI!!! (I can see you doing it on the 'Who's online section'
    I refuse to engage in a battle of wits with an unarmed opponent.


    Rules for buying 'Go Faster' parts:-

    If it's fast and cheap then it's not good.
    If it's cheap and good then it's not fast.
    If it's good and fast then it's not cheap!

  7. #37
    Join Date
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    on the edge...almost falling off
    Age
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    Quote Originally Posted by Sidecarbod View Post
    Message to TonyM, I know that you are going to mess with my post and bung up something oh so witty about Gay FI!!! (I can see you doing it on the 'Who's online section'
    Nope, hadn't even thought about it!
    BIG TONE


    Mercedes SL owner, definitely NOT a kitcar owner like you lot!


  8. #38
    Join Date
    Oct 2006
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    Toton, Nottinghamshire
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    843
    Alastair,

    Do you have a choke still on your Holley? It may be that this is not disengaging properly and keeping the idle too high? There is a red, stepped cam on the back of the choke which should rotate clockwise when the engine is warming up. The choke idle stop screw makes contact with this cam. Normally blipping the throttle a bit allows the cam to rotate when the primary butterflies are opened and the choke idle screw is lifted off this red cam. If this cam is sticking you can normally get a finger behind the front of the choke and rotate the cam down manually. This happened to my Holley and I removed the choke, cleaned up the cam and fitted a small weight to the back of the cam to help it rotate.

    If the idle mix screws are not killing the engine when wound fully in then my guess is that they are not sealing. Either the screw pins are worn or the sealing grommits knackered.

    I have a copy of "How to build and power tune Holley carburetors", published by Veloce. It goes into a lot of detail about Holley carbs and probably far more detail than I'm ever going to need. It suggests that the primary and secondary stop screws should be set to open the butterflies by about the same amount. First wind off both stop screws so they are just touching. Then wind in both 1/2 turn. If the idle is not fast enough then wind the secondary screw in a further 1/8th turn. If still not fast enough, then wind the primary stop screw in an 1/8th turn. Continue winding in the screws, secondary followed by primary by 1/8 turn until you're happy with the idle speed. Unfortunately the secondary idle screw is accessible from the underside of the carb on the choke side so you have to take the carb off unless you can make some sort of 'key' that'll get in underneath.

    All the best,
    Russ.
    Joint Area Rep - East Midlands Region
    1984 DAX Cobra
    Rover 3.5 V8 with Holley carburetor.

  9. #39
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    Apr 2009
    Location
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    Russ - thanks for info. I have a mechanical choke, so I can be pretty sure when it is fully off! However, I have picked up a Holley book "Super tuning and modifying holleys carbs" which says that if the idle mixture screws are having no impact it means the throttle plates are open too wide ... so need to adjust the screws on these, or maybe need to drill a hole through each throttle plate to allow more airflow, reduce the vacuum, hence close them a little and get engine to run off the idle circuit ... I guess it means if they are open too far it draws off the transfer slot, or could even be drawing some fuel through the main circuit. This prob explains why my starting and warm up is always a mission as well .... it sounds like your book is more user friendly than mine though! Cheers, Al

  10. #40
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    Actually scratch what I said in last post ... I think the drilled holes allow more air in to change the mixture rather than to change vaccuum ... but hopefully I can tweak the secondary throttle stop screw instead of drilling ...

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