Tuning help/ question (1 Viewer)

[steffan]

Quick background: fresh rebuilt ‘76 2F, new carb and DUI distributor. Double checked the timing and set around 8°, ran it for a little while and checked the valves to make sure everything was set correctly. I have a real cheap vacuum gauge which flutters between 12-16.
Following the tuning guides and videos I can get it to idle nicely at 690 rpm with an AFR just above 13 (wide band AFR gauge at the collector). However, anything above 1200 RPM and it starts stumbling and leaning out, anywhere close to 2k RPM and is around 18-20 AFR with occasional backfire. Just blipping the throttle was fine - very smooth up and over 2k RPM
-Changed out the carb gaskets, plugged all the vacuum ports but made no difference.
-I was thinking vacuum leak so sprayed water then WD-40 along all the intake gasket but again, no difference.
- When I capped the vacuum line to the distributor, the vacuum gauge still fluttered but now it would rev easily up to 2500 RPM and hold that, maintaining around a 15 AFR.

Doesn’t seem right that the vacuum advance should be disconnected or am I missing something?

I’d hate to pull the intake looking for another vacuum leak but I’m running out of ideas.

Any help would be appreciated

 

[charliemeyer007]

Are you sure its vacuum advance, maybe its vacuum retard? Take the cap off, apply some vacuum see which way the dizzy guts move compared to the rotation when running. Put a big hemostats on the brake booster hose. Wetting the gaskets with water will make them swell so the WD-40 can't seep in as well. Let everything dry out good, then spray the gasket mating surface lightly and quickly with the WD-40 using the pee tube while the cool engine is idling.

 

[steffan]

Everything was good and dry when I went over with the WD-40. All vacuum lines (brake booster, PCV etc) were pulled and the manifold ports capped.
I’ve never heard of vacuum retard - I’ll have to look that up

 

[Pighead]

Two dizzys, one vac advance, one vac retard

 

[Skreddy]

Not only could it be the vacuum retard, but the diaphragm in the vacuum can could be leaking internally. If it’s running better with the vacuum to the distributor disconnected, I’d start with looking at distributor.

 

[Paul_A]

Sounds like you isolated it to a distributor issue by pulling the vacuum line. You can test the diaphragm by just sucking on the tube and watching the guts move (or not) with the cap off. Years ago on a 1970 I changed from a retard to advance type distributor with an external adjustment like the one on the right and it dialed in and ran really well.

 

[steffan]

I tried running it again today and put the advance to the manifold… ran terrible: stumbled like crazy at idle and cleared up a little with rpm which seems too indicate it’s a vacuum advance and needs a ported line.
I’m guessing just too much advance built into the distributor?
I have a callout to Performance Distributors to see if they have any suggestions

 

[65swb45]

You have not indicated whether your distributor looks like either of the ones @Pighead was kind enough to post pictures of. And your latest post is still ambiguous to me. So I would suggest either posting a pic of yours, or acknowledging which one of the posted ones yours looks like.

 

[steffan]

Just to follow up on this thread- it was indeed the distributor. Apparently, on some of the DUI distributors, the cap can be indexed in two different locations. As I always do, I just happened to choose incorrectly.
For this model, you want the notch in the slot closest to he wire leads.
I posted a separate thread on this to make it easier to find in the future.
Thanks to everyone that helped