[lsejlowe]

my '69 L46 runs pretty well overall. Idles happily, never overheats, get about 200 miles per tank driving in a "spirited" fashion, etc. Acceleration is also generally good and throttle response is very quick in most instances. Sounds all well and good, but here's my problem...

If I launch it with minimal tire spin it bogs quite a bit. Same story if I'm at a slow roll in 2nd and hit it. I just finished setting the timing as per Lars' timing paper, but it didn't help. I have NOT tuned the carb since adjusting the timing, but it doesn't seem to be too far out of whack.

Also just installed new distributor cap and rotor and new plug wires. Plugs looked alright (mostly a light tan color, but some carbon buildup) so I put 'em back in.

What's killing my off-the-line performance? I'll tune the carb according to the service manual sometime next week, but I'm not sure that's the root of my problem. Suggestions?

EDIT: Carb is an Edlebrock Quadrajet. Not sure when it was put on, but to my understanding it's just the same as a Rochester.

 

[Fred Mann]

Jason, did you get 36 degrees at 2500? What did your static timing end up being?

 

[rjent]

Sounds like you could also be a little lean on the Accelerator Pump. There will be an adjustment where it will squirt a little more fuel and sooner than you are doing now.

Check it out! :thumbsup:

 

[Jcooley609]

Just a suggestion.......we always put new plugs in when making timing and carb adjustments....that way you can do a plug read to determine what the motor wants....[i.e. more/less timing....more /less fuel].....

bog usually means too much fuel [dumping]

sputter usually means not enough fuel...

 

[lsejlowe]

Jason, did you get 36 degrees at 2500? What did your static timing end up being?

First checked to make sure that 0* on my new timing index matched up with TDC. Set the timing with one spring out and the vacuum disconnected to 36*, but I'm not sure of the exact rpm. I reved it until the timing stopped changing, but I'm not sure if that was above or below 2500 rpm. I didn't seem to notice much of an affect of disconnecting/connecting/plugging the vacuum advance port. Should there have been a more dramatic affect?

Sounds like you could also be a little lean on the Accelerator Pump. There will be an adjustment where it will squirt a little more fuel and sooner than you are doing now.

Check it out! :thumbsup:

So by bending the rod slightly I will adjust how soon the accelerator pump shoots in the extra gas? Any chance you could give me a crash course in accelerator pumps?

Would bogging indicate too much fuel as Jcooley suggested? I'll tune the carb again first chance I get and let you guys know if that helps.

Thanks for the replies! I'm open to any and all suggestions :thumbsup:

 

[Fred Mann]

First checked to make sure that 0* on my new timing index matched up with TDC. Set the timing with one spring out and the vacuum disconnected to 36*, but I'm not sure of the exact rpm. I reved it until the timing stopped changing, but I'm not sure if that was above or below 2500 rpm. I didn't seem to notice much of an affect of disconnecting/connecting/plugging the vacuum advance port. Should there have been a more dramatic affect?

Would bogging indicate too much fuel as Jcooley suggested? I'll tune the carb again first chance I get and let you guys know if that helps.

Thanks for the replies! I'm open to any and all suggestions :thumbsup:

I haven't really thoroughly read Lars' article, but I'd say you should take a more methodical approach and find out where you really are at idle and at higher rpm. I have recorded the timing (and vacuum) readings in 500 rpm increments up to 3500. Or bring it up until the timing doesn't advance more, but note the rpm at that point. I think Lars is advocating 18 degrees initial, but to keep the 36 overall, you have to limit the mechanical advance.

I used to run around 10 to 12 degrees initial, when I plugged in the vacuum hose to full manifold vacuum, the idle rpm would jump up 300 rpm or so, if I remember correctly. So yeah, you should see a significant idle speed change with the vacuum advance in the picture.

If I had to define "Bogging", I'd say an over-carburated engine or a lean condition such that when the throttle is opened quickly there isn't a corresponding amount of fuel present immediately. The engine suddenly goes lean and the rpm drops off until the fuel flow catches up with the air flow. That's what the accelerator pump is intended to take care of. I would associate "chugging" and black pipes with too much fuel.

 

[big2bird]

First checked to make sure that 0* on my new timing index matched up with TDC. Set the timing with one spring out and the vacuum disconnected to 36*, but I'm not sure of the exact rpm. I reved it until the timing stopped changing, but I'm not sure if that was above or below 2500 rpm. I didn't seem to notice much of an affect of disconnecting/connecting/plugging the vacuum advance port. Should there have been a more dramatic affect?

Yes. There should be a noticable difference. I would check to make sure it is working properly. Ie, I would use a handheld vacuum pump to check that it moves freely back and forth.