DRLA air bypass screw

Discussion in 'Mech Tech' started by Deefer66, Feb 19, 2020.

  1. The one under the plug highlighted...

    [​IMG]

    Is it always there? Are people uncovering it and using it to fine balance each pair on side or is left to right balancing close enough?

    ...and on balancing ...can you use vacuum take off to a gauge instead of a snail meter

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    Last edited: Feb 19, 2020
  2. The bypass screws are the ones to the left of your circle . 1 per each barrel
     
  3. you need the Dell Superformance book
     
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  4. Differs a bit from my DRLA40s, but there may or may not be bypass screws under the plugs. The brass take-offs to either side of the plugs are the manometer ports, one for each barrel - slacken them off and connect your vacuum gauges there (although a snail gauge or similar is better for balancing). The screws to the right (left on the other side) are the idle mixture adjustment screws.

    There may be bypass screws under the plugs (there were on mine). You could look on the other side in the barrel for the bypass hole under the throttle plate - stick a paper clip down it to feel if there's a pointed end down there. Lightly centre-punch them and spin them out (veeeery carefully) with a drill. With luck, they'll have fitted screws. If not, you'll have to bung them up again ;) (or Eurocarb may have the screws/o-rings). Beware that the screws may have frozen in the casting, as from memory Dell used steel screws, which was a bit daft.

    When I was balancing mine, the bypasses gave you about half a notch on the snail gauge for barrel-to-barrel adjustment.

    Dells are lovely :thumbsup:
     
  5. Sorry Snottty.. started this before yours appeared..


    Perhaps if I zoom in more

    [​IMG]

    On left hand side of carb..

    Isn't it vacuum port on the left , capped off bypass screw in middle (circled) and mixture screw to right?

    I don't think they expected Alfa Romeo to hide that middle one!

    All mirrored on other side.

    Got a PDF of the book to go through but screenshots look rubbish of the phone..



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  6. Correct, although the vacuum ports are for balancing and should be nipped up tight after you've finished. There should/maybe an additional vac port for the advance to the distrubutor (only one on mine, which were from an Alfa 33). As above, the bypass screws were capped on mine. Maybe Dell tweak them in production, then plug them.

    Only one way to find out - get your drill out!
     
  7. vinnyboy

    vinnyboy Supporter

    I’ve got the 4 vac ports plus one on the left carb for vacuum advance. The snail meter is very good for balancing and so are the bypass screws. You can feel and hear the engine run better as you do it. I bought a four vacuum gauge set for motorbike tuning and found it was a complete waist of money.
     
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  8. Pants ....thought they'd be just the job for the vacuum advance!

    Drills comming out to play in the garage tonight...

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  9. Here you go. Note crappy steel bypass screw.

    a dellorto screws 6s.jpg

    You likely will have a take-off for the dissy on one carb, although it may be plugged as well. There was on my 40s. You'd need to buy another brass bit from Eurocarb to bring it out. I'll have a look at mine later.
     
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  10. Well bloomin eck...just checked my 36S photos..

    [​IMG]

    Only got one!.. bonus...

    Please no telling me off for using wrong size screwdriver...

    Happy days

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  11. Looks like the one. On one carb only.
     
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  12. Guessing the adjusted may meed a new o ring!

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  13. PS Have you only got one screwdriver ;)?
     
  14. A snail gauge is better IMO, as you're using the same bit of kit to measure on each barrel. Can buy sets of four vacuum gauges, but they may be calibrated differently (according to how the Chinese bloke felt that day).
     
  15. Could only find one at that point... bit of a tip in the garage at the moment... too many things on the go trtyng to get it finished so Ican go out and play in it....

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  16. Well 3 out of4 was close .. covers out ok first 3 out quite easy last one snapped off slot head!.. last go with stud extractor tonight then live with it sealed off if no joy

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  17. I’d leave it. A screw extractor won’t get it out, and you may damage the carb body.
     
  18. areksilverfish

    areksilverfish Supporter

    The older dells have them bypass screws the newer ones (from 1990s) didn’t..


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