Setting up timing on a '69

[gondellini]

Hi All

I have a '69 Powerglide which I'm having a little trouble setting up. This might be a little long winded...

My carbs were rebuilt by Grant Young and I have the idle mixture screws at about 2.5 turns so this in theory should take them out of the equation for my problem. Also I rebuilt the top end so I have no carbon, good valves, good uniform compression etc.

I get hesitation off the line when my engine is warmed up, but not when cold. Not too much but enough to be annoying. If I advance the timing far enough to cure this it goes like a bat out of hell but I get some pinging. When I retard it again to cure the pinging I get the lag back. Vacuum advance appears to be working; although I wanted to ask if anyone knows if it should act the way it does - on half throttle or so it advances but when on full throttle it doesnt (i guess this is normal as the vacuum would decrease undere this condition). Right now Im running '68 weights and springs in the dist which have more advance than '69.... it seems to run better with these although I would think that the 69 should work better given the symptoms I'm seeing.

Ive read that gas can be a big deal so im gonna try some better quality gas... using 91 but its arco... which my bike hates so maybe the corvair is rejecting it too. Head temps are in the 320s (its been 100 degrees ish here).

Would greatly appreciate any advice anyone can throw at me.... (esp if they can get my car in the bat out of hell mode without the pinging!) Thinking about fitting a mallory dist so I can really get the advance set up right for my circumstances but its gonna be a while (might beg for it from the wife and everyone else i know for christmas!!)


Thanks!
J

[gondellini]

oh yea and also is there a way to identify dist weights? wanna make sure my weights really are what i think they are!

[Scott H]

The CORSA Tech guide volume 1 has a good article on Distributor Identification by Jim Craig of San Diego Corvair Club. It shows flyweight profiles ans springs and what distributor they were in originally in.


Is this a 110 or a 140 motor?

[gondellini]

110... thx ill check that out....

J

[UNSAFE]

>>>>My carbs were rebuilt by Grant Young and I have the idle mixture screws at about 2.5 turns so this in theory should take them out of the equation for my problem<<<<

Wrong ! No matter who rebuilt the carbs you can not take them out of the equation. The mixture screws HAVE to be adjusted to your motor . The number of turns is not revelant. 1.5 turns out is usually a starting point - but only a starting point. You tune for max rpms at idle and then lean out slightly (about 1/4 turn in) .

>>>>I get hesitation off the line when my engine is warmed up, but not when cold.<<<<

That also points to a carb or choke issue. When cold the chokes are closed which richens the mixture.

>>>>If I advance the timing far enough to cure this it goes like a bat out of hell but I get some pinging.<<<<

Again it sounds like a possible mixture issue. A lean engine can't use as much timing without pinging.

>>> on half throttle or so it advances but when on full throttle it doesnt (i guess this is normal as the vacuum would decrease undere this condition).<<<

With partial throttle the vacuum advance will advance the timing. Also the mechanical advance should be advancing according to rpms up to it's limit. just using round numbers here but it should start advancing above 1200 rpm and continue up to 3500 rpm. You dist may be different but you get the idea.
Disconnect the vacuum advance and then check for mechanical advance with a timing light as you increase the rpms.

Are you sure you don't have the vacuum hose connected to the wrong port on the carb ?

If the mech advance is working - try disconnecting the vacuum advance and see how it runs.

I have the dist info you need and I'll try to dig it out tonight.

Remember that the smog engines like yours usually had some driveability problems even when new.

Higher octane will likely help a bit .

[gondellini]

Great - thanks for the info. I've made sure the vacuum is hooked up to the right port and mechanical advance is working too. Wonder if the carbs are a bit lean then. I generally have to richen my cars up a bit. Dunno why.... maybe my driving style. Ill get hold of grant and see if he can give some advice on richening them up a bit.

I will try running without vacuum though and see wht that does.

These carbs dont seem to have an idle jet. Is it hidden somewhere?

Ill make sure the mechanical advance is doing what it should... that distributor info would be really helpful. Thanks!

Will post back what i find. May be a little while because the wifes focus just ate a valve seat so im doing surgery on that at the moment :(