• Registered: 2008-11-24
  • Posts: 14

Topic: 74 bug wont idle

Hi.  My 74 bug runs ok when I start it up on fast idle although it does seem miss a bit, the choke closes etc.  When I kick it off, it won't idle.  Last fall I put in 87 octane gas and this is when the problem seemed to start. When it first happened I tried using some carb cleaner sprayed downthe throttle body.  I didnt drive the car all winter and in the spring I syphoned out all the gas and put in a better grade.  I only got the car about a year ago and have not really drove it at all.  Prior to my purchase, the car had been sitting for about ten years. It has 45000 original miles on it. I've set the valves  and am going to do the rest of the tune up but I'm assuming it needs to idle to set the timing.  There is only one timing notch on the crank pulley at TDC so does this mean the timing is set to 0 TDC?  I know I'm starting to ramble so any suggestions would be appreciated.

  • From: Washington, Indiana
  • Registered: 2004-03-27
  • Posts: 1,423

Re: 74 bug wont idle

Question...... How do you know the timing mark is Top Dead Center?

                                                                              Yancey

Yancey's Website

  • Registered: 2008-11-24
  • Posts: 14

Re: 74 bug wont idle

Good Point.  I was following the procedure in Muirs book for adjusting valves.  There is one notch on the back of the crank pulley and then a yellow mark on the front of the pulley plus another yellow mark at 180 degrees.  After reading further based on my AH engine code,  the timing is supposed to be 5 ATDC.  Not sure how to do this.

  • TomB
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  • From: Austin, TX
  • Registered: 2004-03-27
  • Posts: 1,088

Re: 74 bug wont idle

Ignition timing is really based on the distributor used, and the AH originally had a dual-vacuum distributor - two vacuum lines for both advance and retard. If it still has the dual-vac distributor, use a timing light to set it at 5 ATDC at idle per the book. However, many of these have replaced the distributor with either a single-vacuum model (advance only), or a "009" non-vacuum distributor (centrifugal advance only).

First determine what distributor is used, as the correct timing and method will be different depending on that.

  • Registered: 2008-11-24
  • Posts: 14

Re: 74 bug wont idle

Thanks.  I was confused by this issue because the book said my AH engine should have a double vacuum distributor.  The distributor must have been changed because it's only single vacuum.  Any idea what I should set the timing at with the single vac distributor?

  • Registered: 2008-11-24
  • Posts: 14

Re: 74 bug wont idle

I forgot to mention that I confirmed the notch in the crank pulley was TDC by taking out number one plug and putting a pencil in the cylinder while gently turning the crank pulley back and forth.

  • From: Cincinnati, Ohio
  • Registered: 2005-09-10
  • Posts: 2,318

Re: 74 bug wont idle

henschelb wrote:

I forgot to mention that I confirmed the notch in the crank pulley was TDC by taking out number one plug and putting a pencil in the cylinder while gently turning the crank pulley back and forth.

Good job!  Not a lot of folks know that method of determining TDC.  Good to know that the notch on your crankshaft pulley is TDC.

- Nick

1979 Super Beetle Convertible
  • TomB
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  • From: Austin, TX
  • Registered: 2004-03-27
  • Posts: 1,088

Re: 74 bug wont idle

Single vac distributor is normally timed 7.5 BTDC at idle with no vacuum signal.  Can disconnect and plug vacuum line to set. If idle speed goes up when connecting the vacuum line it is hooked to the wrong port on the carb, or throttle plate is off. (Dual vac setup has vacuum on retard at idle, no vac on advance.)
You can also set static - engine off with test light on points - for 7.5 BTDC.

Note dual vac is 5 ATDC because of retard, gives same result as 7.5 DTDC on single vac. Retard was to reduce emissions at idle.

Many crank pulleys have one notch at back rim and another on the front rim. Typically the rounded notch is TDC and V notch is timing for original dizzy.

  • From: B.C.Canada
  • Registered: 2005-01-26
  • Posts: 2,586

Re: 74 bug wont idle

First thing to do is toss the Muir book out.

Get a Haynes manual to start and in time you may want a Bentley. The Haynes is good for the backyard mechanic with tips in case you don't have special tools while the Bentley assumes you are a mechanic and have a full shop.

Be sure the point gap or dwell is correct before doing the timing. Adjust the carb last in a tune up.

Have you changed all the fuel and vacuum lines? Check for vacuum leaks. A small leak won't be noticed when the choke is closed or at high RPM's but will affect idle.

jim

'71 SB(DD only 79K(now 84K miles) & '78 FI Westy (project)
PO of '65 Beetle in '69, '70 Crewcab & '70 Ghia in '77
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  • From: Cincinnati, Ohio
  • Registered: 2005-09-10
  • Posts: 2,318

Re: 74 bug wont idle

jamesdagg wrote:

First thing to do is toss the Muir book out.

Jim,

I had to laugh when I read that!  wink

I sort of feel the same way about the Muir book.  I know some folks find the book very helpful.  I have a copy, and every time I try to use it...my head just "explodes" trying to figure it out!

That's when I get out the Bentley or Haynes...and put the Muir back on the bookshelf! I think that I'd even use a Chilton before Muir! wink

- Nick

1979 Super Beetle Convertible
  • Registered: 2008-11-24
  • Posts: 14

Re: 74 bug wont idle

Thanks so far for the advise.  I'm going to change vacuum lines to be sure.  How do I time to 7.5BTDC if I only have one notch on my crank pulley at 0TDC?  Also noticed that it won't idle at all but if I just hold the butterfly slightly closed it seems to run OK.  Any ideas?  Thanks

  • TomB
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  • From: Austin, TX
  • Registered: 2004-03-27
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Re: 74 bug wont idle

I suspect your single notch pulley really has the notch at 5 ATDC, which was the standard pulley for the dual vac distributor engines.  Finding TDC by a dowel through the spark plug hole isn't always precise as the piston stays almost still for a few degrees rotation. Usually VW used a rounded notch for TDC - a "V" notch was the timing mark.

A good discussion on timing marks and pulleys is on Rob & Daves aircooled site:
http://www.vw-resource.com/find_tdc.html

You can measure to the right of the notch to make another timing mark for 7.5 BTDC. The above site gives some measurements for making the mark, but they don't sound quite right to me. I'll do some checking and reply later.

  • Registered: 2008-11-24
  • Posts: 14

Re: 74 bug wont idle

Now that you mention a dimple,  I checked closer and my pulley has a dimple on the back of the pulley(back of the car).  If I put this in line with the seam on the motor at TDC,  the v-notch on the front of the pulley(front of the car) is 11mm to the right.  Do you think I'm correct in assuming the dimple is TDC and the v-notch is 7.5BTDC? This would mean that someone changed the pulley when they changed the distributor to single vac as my AH engine should have had a dual vac.  If this is right the only confusing part would be that there are also two yellow marks 180 degrees apart on the pulley but they line up with the v-notch, not the dimple. Thanks for any replies

  • Registered: 2009-06-25
  • Posts: 554

Re: 74 bug wont idle

That would be a 7.5 degree pulley with the notch at 7.5 degrees and the dimple on the back should be at TDC. Not sure about the yellow dots, but they are probably there to assist when setting valve lash.

Of  course, as Tom states, the dowel or pencil trick is not the most accurate; it will let you know you are in the neighborhood, even if you don't stop at the exact house  wink

The most accurate way is to use a dial guage and measure the same distance in travel on the up stroke and down stroke, mark the spot on pulley with a pencil line when the piston is in the same position on either stroke. Measuring exactly halfway between the pencil marks will give you TDC.

Next best thing is to use a dowel (or pencil), move the piston about 10mm, and mark a reference line on the dowel. The dowel can then be used instead of a dial indicator to mark the matching up stroke and down stroke points, then measure halfway to get TDC.

Paul