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Take Vacuum line off intake and engine idles better???

Discussion in 'The Hokey Ass Message Board' started by ianblaster, Nov 25, 2006.

  1. ianblaster
    Joined: Nov 6, 2006
    Posts: 126

    ianblaster
    Member
    from Dothan, AL

    I am trying to tune my straight six. I think my carbs are too rich. The reason I believe this because when I put the pedal to the floor it stumbles really bad. It also loads up at a red light and starts to smoke a little. The final thing is when I take the vacuum line off the distributor and leave the line uncapped, the engine runs better. Plug the vacuum line with a screw or bolt and it slows the idle down. Any ideas?
     
  2. what carbs are you running and it will always idle faster with a vacuum leak
     
  3. boozoo
    Joined: Jul 3, 2006
    Posts: 534

    boozoo
    Member

    Huh? My experience has been that vacuum leak makes it run like crap. I would think if opening the vacuum port made it run "better" you might be running too rich of an idle mix. But first things first. You say it loads up if you're sitting stopped. Have you checked for other vacuum leaks? Can you look down the throat of the carbs when it's idling to see if fuel is dribbling? I may be in left field but it sounds to me like you might even flooding a little bit?

    I don't know what carbs you have, but on the ones I run, fuel dribbling at idle is a bad thing - it means something is wrong in the fuel delivery. Either the pressure is too high, or the needle and seat are worn out or gunked up, or the float level is wrong, or the float itself is bad... those are the types of issues I've run across before.

    For the flat spot or bog, a lot of times, those are cause by the idle mix and butterfly setting being off and/or the initial timing being too low. You can also have a crappy accelerator pump. I had a WCFB that had the old leather pump in it... and the damn pump well was pitted, too. :(

    But... like I said, I don't know what you're running, so I'm just tossing out ideas to get your gears churnin'. ;)
     
  4. MikeRose
    Joined: Oct 7, 2004
    Posts: 1,395

    MikeRose
    Member

    Isn't the idle change more due to the timing changing when the vacume advance is unplugged? If its vacume advance anyways.
     
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  5. I think boozoo's got it nailed. If losing the extra spark advance and leaning the mixture doesn't make it drop RPM; it was probably pig-rich to start with.

    Float levels/bad needle & seat? Idle air bleeds plugged? nasty aftermarket fuel pump w/ real high pressure?

    Idle mix screws out too far? damaged?

    If you see fuel dribbling in the carbs, is it just spilling from high float level, or do you have the throttle blades cranked so far open trying to get it to run that you're starting to pull from the venturi boosters? I've seen cars that wouldn't respond to idle mix needles because the throttle plates were so far open that they were beginning to come onto the main circuit.

    I guess my sign out line applies here...

    -bill
     
  6. guiseart
    Joined: Apr 7, 2005
    Posts: 3,872

    guiseart
    Member

    sounds rich to me... thin everything down to practically nuttin and start from there... get soembody to help time while you keep it running... plugs/distributor all okay? You runnin mechanical fuel pump or electric?
     
  7. 28pontiac
    Joined: Nov 14, 2003
    Posts: 192

    28pontiac
    Member

    I believe the there should no vacuum advance at idle.... (800-1000 RPM...) Vacuum advance should come on as the RPM increases. I think you're running too fat. Not knowing your set-up, there should be at least one other vacuum port on the carb, leave the vacuum advance line on, remove a different vacuum line (Preferably not the brake booster) and see what happens.... I'm betting it will smooth out....

    Andy
     
  8. boozoo
    Joined: Jul 3, 2006
    Posts: 534

    boozoo
    Member

    Yeah I was just going to add this... there's manifold vacuum and timed vacuum on the setups I'd been running. There are some dizzy's that want manifold vacuum, but the ones I've run want the "timed" port which means you only get vacuum advance at part throttle cruising. At idle or at WOT, the vacuum advance is normally out. Manifold vacuum, on the other hand is max'd out at idle and decreases as the throttle is opened up.

    But since there are some that run the other way... need more specifics on what you have, what condition it's in, etc. The best way to sort out a problem like this is to nail down the fundamentals first.


    Just like football, ya gotta wrap and tackle first, then worry about gettin' fancy.
     
  9. ianblaster
    Joined: Nov 6, 2006
    Posts: 126

    ianblaster
    Member
    from Dothan, AL

    Here is a picture of the setup I am running. They are Webers. My vacuum is coming off the manifold right now. When I bought the car, it was coming off the rear carburetor. But come to find out, there was no vacuum coming off either carb. So I capped them both off and split the manifold vacuum between the transmission and the distibutor. I guess I need to give a little more background on my problem. When I bought the car, it had zoomies on it with no baffels. I got hassled about it being too loud so I made the straight pipes and shoved 12" baffels in each one. Since the new pipes it has been running a lot richer. I expected it to be a little richer but not as bad as it is now. I am not real experienced in carbs and tuning them so I am fishing for answers here. I checked the jets on each carb and found that the ones on the front side of each carb is a #47 and the ones on the backside are #60. So give me some info. If you need more info from me I'll go look at them and get it. By the way, I have put two much larger K&N filters so it is breathing better.
    [​IMG]
     
  10. laid55
    Joined: Nov 15, 2006
    Posts: 354

    laid55
    Member

    are you saying that you are running manifold vaccum to the distr.?big problem right there.the carb has to have a timed port.check the timing with no vaccum to the distr.with duals,set it about 8-10 de grees btdc.start there.if it's run to manifold vaccum it will retard when you open the throttle,causing the bog.with the timing set,make sure each carb idle is synched.then adjust the mixture screws accordingly.
     
  11. ianblaster
    Joined: Nov 6, 2006
    Posts: 126

    ianblaster
    Member
    from Dothan, AL

    OK, so the vacuum I am running is part of the problem. It was off the carb before but as I stated above, the carb wasn't creating a vacuum. I could rev the engine and no advance on the distributor. Any ideas why there would be no vacuum off either carb? Also, I don't think 8-10 degrees on the timing is going to work because the motor has been bored .60 over and has a mild cam in it. Not sure what cam they used but I know when they rebuilt they did put in a different cam. But keep the info coming because its all new to me. Thanks to everyone
     
  12. ianblaster
    Joined: Nov 6, 2006
    Posts: 126

    ianblaster
    Member
    from Dothan, AL

    Just a thought here. If my air cleaners were too small before and not allowing enough air into the engine, could it have restriced the vacuum being pulled in? I have not checked to se if I am getting a better vacuum off of the carb since I put the 4" filter elements in.
     
  13. Check your distributor advance and see if the diaphram is bad.
    You may just be chasing your tail until you know for sure a good vacuum is working your advance properly if at all. Check your vacuum on the carbs by attaching a vacuum/pressure gage on the vac hose instead of running it to the dizzy.
     
  14. ianblaster
    Joined: Nov 6, 2006
    Posts: 126

    ianblaster
    Member
    from Dothan, AL

    I know for sure the diaphram is good. I have not put a vacuum gauge on the carbs yet. What should the vacuum off of the carb read?
     
  15. How did you verify your advance is working correctly??
    I cant answer the reading. Dont know this answer. Maybe someone can give you a figure here..
    Depends purely on the number of carbs and of course the Rpm. Irregardless. you will definitely be able to tell if the vac is increasing at higher Rpm. Instead of hooking up to an advance which complicates it, you are able to measure which vac location gives you the best response.
     
  16. ianblaster
    Joined: Nov 6, 2006
    Posts: 126

    ianblaster
    Member
    from Dothan, AL

    Well as you might have read above, I had the advance working off of the manifold vacuum which I now know is not good. But it was operating. With just using the ole put your finger over the hose to feel it, I felt no vacuum off of the carb and when it was hooked up to the distributor and the engine reved, there was no advance. But I will try to get my hands on a vacuum gauge to check it with.
     
  17. Ok, You may have some advance with your distributor from this check. But i would throw in a new diaphram. Cheap and very easy.
    The odds are you have some leakage unless it was you who rebuilt it. I agree with the others. it also sounds like you may be rich.
    I threw these ideas out there so that you may break it down to a bunch of little problems instead of one big one. Make sure things are working correctly in a separate manner before attaching everything and expecting results. Good luck to you!
     
  18. laid55
    Joined: Nov 15, 2006
    Posts: 354

    laid55
    Member

    what do you know about the carbs?are the new or used?check the hole in the fitting.maybe someone plugged it on the inside,to use with a centrifical advance distributor.far fetched,but you never know.on the weber,there may be an issue with the base gasket.make sure there doesn't need to be a cut-out in the gasket.10 degrees should be sufficient to at least start to dial it in.as far as your distributor goes,you should still get some mechanical advance,even with the vaccum line disconnected.if you don't check out that the advance mechanism isn't stuck.I have a 250 6 cyl.in my 65' pickup,and I'm running it with the vaccum advance disconnected,because it gets too much advance.a little sluggish at takeoff,but cool at cruising speed.i need to dial it in also.
    good luck
     
  19. farmer_joe620
    Joined: Sep 7, 2005
    Posts: 176

    farmer_joe620
    Member

    what sized weber are they? they looks like the 32/32 thats on my truck. i also have the same problem when i take the advance hose off the carb. itll run just a bit smoother. ive had a couple webers now, and ive found that they like to run rich. ive jetted em down, up left and right and can never get them to run just right. it either to rich or to lean. just trying to get one runnin right is a pain, let alone 2. the progressive carbs werent really meant to be run in pairs either. do you have them both opening in synchronis?

    you say that there isnt any vacuum from the advance ports? since your runnin 2 carbs you might link the 2 advance ports from both carbs together with a "t" fitting and see if you get a better signal.

    also, what rpm do you have it idling at?
     
  20. 97
    Joined: May 18, 2005
    Posts: 984

    97
    Member

    What model Webers are they, should be a number on the side of the base .
    Should say something like DGV 32 or DGAV 32/36 ???
    Just looking at the manifold I think they were probably of a VW

    From a performance point of view your manifold looks like trouble to me.....runners are too long, all joining into one long log style manifold , the joins have potential for air leaks. Check this first.

    If you have air leaks below the carbs the idle screws will need to be way too far open in order to get any sort of idle mixture , they ( screws) should be about one and a half to two turns out as a base setting and not move far from there to final setting.

    If the jets you are talking about , are long thin jets in a holder screwed in to the side of the body , they are the idle jets, generally the smaller one should be in the primary side.

    Most Webers should have 2.5 -3 psi fuel pump pressure, check this and make sure the needle and seat are in good condition.
    Check the float level, and make sure that the floats are not full of fuel, ( If you tell me the carb model and if they are black nitrophyl or brass floats I will let you know the weight they should be).

    Commonly Webers get the jets put back in the wrong place after people have messed with them.
    Progressive Weber jetting .
    Primary main should normally be smaller than secondary main jet ( in bottom of bowl) I suspect something like 115-135 in size
    The primary air corrector should be the larger of the two ( In the top of the bowl/body screwed in over the emulsion tubes.)

    Make sure that the power valve diaphram is in good condition. It is screwed to the top part ( lid) of the carb with three screws and hangs down into the fuel bowl , it opens the power valve when vacuum drops at wide open throttle. If the diaphram is damaged ( common) then the power valve will be open all the time, the engine will run rich , and there will be little or no vacuum signal at the distributor port.

    This is what I suspect is your problem, possibly only in one carb, commonly caused by backfires.

    Other common problems with this style of Webers which will show disturbed vacuum signal include :
    1/ damaged top gasket or warped carb top ( caused by overtightening of the hold down screws.
    2/ loose auxuilliary venturies , this allows air leaks into the main circuit and alters the entire fuel delivery.


    .
     
  21. I would think you might have a problem with fuel condensing to liquid form in the manifold. These 6's run best when the manifold is heated. Circle track cars don't use heated manifolds but they are seldom at less than full throttle. A little heat will keep the fuel vaporized at low speeds. Without heat liquid fuel dumps into the cylinders causing backfires, coughing and slow acceleration. My 292 is happiest with a warm manifold and timing at 6 BTDC
     
  22. boozoo
    Joined: Jul 3, 2006
    Posts: 534

    boozoo
    Member

    I'm just going to bow out now... because I don't know JACK about Webers so it's my turn to shut up and learn. :D



    Edit: Ok, I do have a couple of basic things to point out. That finger test you did on your carb's vacuum port? It was doing what it's supposed to. The "timed" vacuum port is a port that picks off above the throttle blades, so it's max'd out at part-throttle cruising. At idle, it's zilch. At WOT, it's zilch. Manfold vacuum is picked off below the blades, so it's max'd out at idle and drops off as the blades open. Make sense?

    The other tip for testing a vacuum advance is I've been using a hand held vacuum pump I bought for brake bleeding. It has an assortment of hoses and adapters, so I can hook it to the vacuum can on the dizzy, pump it up and see how much advance I get and how it holds (I use a dial-back timing light, but timing tape works, too).
     

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