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exhaust noise from carb.

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  • #232946
    Stephen Chuck
    Participant

    @scchuck

    I just bought a Duchess, VW 1500 with twin carbs.  The exhaust was really loud, so I changed the exhaust to a one outlet Empi exhaust as suggested in this forum.  It looks great but did not resolve the issue.  The noise is coming from the carbs.  If I rev the engine up, it runs smooth, but the carbs sound like exhaust is popping back through the carbs.  If the car would misfire, I would think it was valves or something, but the car seems to have lots of power, just noisy!  Any ideas?

    #241094
    Scott A Chynoweth
    Participant

    @1oldbuzz

    Check the points and the timing.I had a chevy years ago popped somthing fierce through the carb,points were bad.

    #241095
    Mark Hendrickson
    Participant

    @pink-mg

    Air-cooled engines are not as quiet as liquid cooled engines, especially when the air cooled engine is not warmed up. VW engines have larger tolerances due to the fact that they are air-cooled and made of a magnesium/aluminum alloy that has greater expansion when heated up.  

    If the car pops through the carbs when you let off the throttle, it’s usually timing related.

    If it pops through the exhaust when you let off the throttle, it’s usually fuel related (too rich).

    What dual carbs are they?

    What distributor is it, centrifugal or mechanical? Points or Pertronix?

    When was the last time the valves were adjusted? (too loose equals no low end and lot’s of engine noises)

    Is the camshaft stock?

    #241096
    Paul Mossberg
    Keymaster

    @pmossberg

    Here’s a reply from my favorite VW tech.

    Fuel mixture could be too lean; check for loose intake manifolds, linkage binding problems, bad intake gasket.

    PMOSSBERG40287.6821296296

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #241097
    Stephen Chuck
    Participant

    @scchuck

    Thanks guys.  The car runs great, just loud.  It sounds like an exhaust leak, but if you put you head next to the air cleaners, you can hear exhaust noise coming from them.  It make me wonder if the timing is off or something, but it really runs too good for that.  It idles like a champ, so I don’t think there is any burnt intake valves.  Is there an EGR value on a 68 VW?  If so, where would I look?

    #241098
    Steve Crites
    Participant

    @ringo

    Steve,

    I’m stepping waaaay back in time and I might be way off base, but I didn’t read if you had adjusted the valves, so here goes.  The exhaust noise you hear from the carb could be an exhaust valve staying open a little too long, whether from timing off or perhaps valve lash and old weak valve springs. Either way, it can still run pretty good….. for a while. Valve adjustment on a VW is not recommended, it’s required.

    (Again, sorry if I missed if you’ve already done it!)

    I’d check the valves, then re-time. If those 2 are off you’re in danger of overheating the engine.

    Mark, have I lost my mind, or does that fit?

    Ringo

     

     

    #241099
    Paul Mossberg
    Keymaster

    @pmossberg

    I agree with Ringo.

    Besides, you might as well start with the easy stuff first. Adjust the valves. Then check/set the timing.

    While you are under the hood (boot?), give the intake manifolds a shake just to make sure they are tight.

    Start ‘er up and give a listen.

    If you still hear noises you don’t like, start the fuel delivery & intake system checks mentioned above. And no, I don’t think you have an EGR on a 68 with carburetors.

    If you have F.I. (which I did not think existed for a 68) it would look like this:
    http://www.thesamba.com/vw/classifieds/detail.php?id=512644

    And just for kicks, take a listen here to good and bad VW engine sounds:

    http://www.ratwell.com/technical/EngineSounds.html

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #241100
    Stephen Chuck
    Participant

    @scchuck

    I am thinking Ringo might have hit on something.  I listened to the engine sounds, and the idle sounds like the valves need to be adjusted.  I just thought all VW’s sounded like that.  WRONG!!!  A correctly adjusted valve engine sounds really quiet.  I bet the exhaust valves are out of adjustment or week valve springs.

    Time to find a good VW mechanic in Iowa.

    Thanks guys!!!

    Steve

    #241101
    Paul Mossberg
    Keymaster

    @pmossberg

    Steve,

    Not so fast….

    Adjusting the VW’s valves is really easy. And since it should be done every 3,000 miles or so, it’s a money saver if you learn to do it yourself.

    Pick up John Muir’s How to Keep Your Volkswagen Alive book:

    http://www.amazon.com/Keep-Volkswagen-Alive-Step-Step/dp/156 6913101

     

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #241102
    Mark Hendrickson
    Participant

    @pink-mg

    Ringo is correct about the timing and vacuum leaks. A lean air cooled motor will burn up quickly.

    After the valves are adjusted, check the dwell and the timing. If you install a Pertonix Ignitor, then the points (dwell) never has to be adjusted and the timing will stay constant once it’s set.

    When the dwell changes, the timing changes…however, adusting the timing will not change the dwell.

    Loose valve adjustment robs all your low end torque and makes the engine noisy. Like Paul said, every 3,000 miles these little buggers need their valve adjustment checked.

    BTW, the MOFOCO long block I installed in the first Pink MG (then Bill’s Angelica) had hydraulic lifters and didn’t require valve adjustment after they were first set. That engine was super quiet and smooth running. I am debating the same for a Beetle I’m playing with.

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