Total dist advance

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

Howdy,
So, does anyone know the total advance of a dual canister 79 distributor? Mine will go to about the end of the scale while operating the butterfly with timing light connected. I am getting the correct amount of vacuum advance as when I disconnect the retard side timing jumps about 7d or so. I keep reading that people are cruising at 70-75mph @20mpg, mine will get up there on flats with quite a bit of throttle input but head temps jump really high. Could be not enough advance under load? I have plenty of power around town in the first three gears but 4th on the highway my head temps go up and it likes to cruise at 60mph. This is a high top, so I have nothing to compare it to.

Thanks.

Randy in Maine · Posted: Thu Jan 13, 2005 2:16 pm Post subject:

Advance/Retard Range: Vacuum: 11-13deg Adv @ 9.4 In. Hg, 11-13deg Ret @ 9.4 In. Hg; Centrifugal: 9-13deg @ 1600 rpm, 12-16deg @ 2800 rpm, 21-25deg @ 3600 rpm

Well I am calling it a vacuum advance of 11-13* + the centrifical total of 21-25* at 3600 = 32-38* total. Maybe I am not calculating that correctly though.

With your vacuum gauge, tach, and timing light you should be able to check each one to see if you are in the zone.

See if it helps to pull off the vacuum retard (and put a golf tee in that hose) and set the timing to 7.5* BTDC at correct idle. Check you temps as you go on a familiar road.

Also when timed to 5* ATDC, when I pull off the retard line, the timing immediately goes to the 7.5*BTDC

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

Sorry, 11 deg vacuum advance is right. I have done the pencil in the retard trick and it doesn't change anything. I think I am ok, just don't have anything to compare it to for drivability.

ratwell · Posted: Thu Jan 13, 2005 3:15 pm Post subject: Re: Total dist advance

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

ratwell · Posted: Thu Jan 13, 2005 3:43 pm Post subject:

Your bus seems normal to me.

I have no trouble going 70-75mph but the engine is clearly working hard to keep that speed.
_________________
'78 Westfalia CDN
'76 Doublecab
Read the Baywindow FAQ

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

Yeah, I think so too. Sometimes I am like an old dog, every once in a while I like to chase my own tail around in circles.

ratwell · Posted: Thu Jan 13, 2005 4:02 pm Post subject:

It's amazing to me that the car runs well when you first start it and the exhaust is cold but as the engine heats the exhaust becomes hot. Stupid cast iron.
_________________
'78 Westfalia CDN
'76 Doublecab
Read the Baywindow FAQ

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

quoi

nemobuscaptain · Samba Member Joined: March 07, 2002 Posts: 3874

> I have done the pencil in the retard trick and it doesn't change anything.

Then you have a problem, either with the vacuum leak, malfunctioning retard, or your vac hoses improperly connected. Throw a vacuum guage on the engine. You should have around 15 inches. If not, you have a leak (or your at altitude). If you have a vacuum leak, you must find it or your engine won't be long for this world. (While you're at it, the port that has vacuum at idle should be connected to the retard and the one that has vacuum as you open the throttle is for the advance.)

I have a cheap vac guage that also allows me to pull vacuum (and bleed brakes). Hook one of those up to the retard nipple (the one pointing inwards toward the dizzy) and see if it actually retards your timing (by using the strobe). If it's a bad retard mechanism, I'd be happy with capping off the dizzy and the carb and forget it. However,

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

Randy in Maine · Posted: Thu Jan 13, 2005 4:53 pm Post subject:

So does the vacuum retard work correctly?

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

Yes it does. My concern was that I am not getting enough total advance under load at highway speeds causing high head temps. In the end it seams I am a little sensitive about pushing my beloved bus too hard.

Amskeptic · Posted: Thu Jan 13, 2005 5:21 pm Post subject:

jberger, please note that over-advanced timing can cause head temperature problems as well, actually, air-cooled engines are much more sensitive to over-advance than the other way around. Your maximum advance under load, where it really counts, does not involve the vacuum advance unit which deactivates under full load anyway. Try adjusting your timing at 3,000 rpm, no more than 25* to start with no hoses on the distributor. Then test-drive with everything plugged back in. Any change? Now try 28* at 3,000 rpm. Any change in head temps? Which direction? That will be your trend, follow it a little further to see if you can get into your proper zone, but don't leave the general specifications window. If you can't fix head temps with a little timing adjustment, and a little mixture richening, then you have something else to look at..
Colin
_________________
www.itinerant-air-cooled.com

ratwell · Posted: Thu Jan 13, 2005 5:52 pm Post subject:

Karl · Posted: Thu Jan 13, 2005 9:38 pm Post subject:

As hard as it is to grasp, ported vacuum to the vacuum advance goes away on full throttle. Best way to show it is with a vacuum gauge and a long hose and a test drive.

jberger · Samba Member Joined: November 17, 2003 Posts: 2476

Duncwarw · Samba Member Joined: August 25, 2003 Posts: 3094

Not to hijack the thread, but Richard, where did you get your compensator?

TIA

ratwell · Posted: Fri Jan 14, 2005 11:53 am Post subject:


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