Tugs back and forth when downshifting ?

[blykins]

Sure you don't have a vac leak? Are there any race shops that you can run to and let them tune it for you? I think you have several different issues going on.

[Gaz64]

Originally Posted by D111

messed around with it a bit turning up the idle screw And then Fattened up the low-speeds to then reduce the idle, it did get rid of almost all of the tugging but it just doesn't feel like it's running That well Then.

"idling at 900" this thing is like trying to hold onto an eel, it Idles at around 1100 while driving if I let off the gas than when I stop It's about 950 Then if I sit there for a few minutes works its way down to 750 so I Can't actually say where the Idle is at. :-)

I may just put my Holley back on and see Where I'm at.

How much manifold vacuum at idle? 950 then 750?

[D111]

Going to get my own vacuum gauge And check it. I borrowed a friend's when I install the carburetor and give it back to him.

What should I be looking for?

[Jerry Clayton]

As a side note to the ideas about carb/ignition tuning--I have, over several years , run into a few other instances of the type of driving results as you describe, being all on cars with independant rear suspension vehicles that had possibly some/several components worn enough that the total discripcity resulted in an uneven deceleration/slow cruising speeds with moderately cammed high performance engines--

Some of these cars took a change in the flywheel weight(alum to steel), locked ignition advance, different throttle linkage , etc to smooth out the driveability issues----------

[WildBill1965]

OK, here is a question for you as you live here on the east coast and it's been pretty cool was your engine up to temp 80 c or warmer? My car if the engine is not up to temp will buck a little if not on the throttle. Summer time no problem, if I go to cruise night and come home late and it's cool I get a little of it this time of year!

B i l l

[D111]

Originally Posted by WildBill1965

OK, here is a question for you as you live here on the east coast and it's been pretty cool was your engine up to temp 80 c or warmer? My car if the engine is not up to temp will buck a little if not on the throttle. Summer time no problem, if I go to cruise night and come home late and it's cool I get a little of it this time of year!

B i l l

It does definitely seemed to be weather sensitive but I think that's most Any Carbureted engine.

Raising the idle has helped the most, it's at the point now where it's just a Very slight occurrence. But my cruising idle Is Almost 1100 rpms that is if I while driving just push in the clutch and watch where the Tac falls.
I've been used to with my original Carburetor having it Drop To no more than 800.

[D111]

Originally Posted by Gaz64

How much manifold vacuum at idle? 950 then 750?

The best that I can get after tuning the Low idie screws is about 14 to 15 at 950 and about 12 1/2 When it drops down to 750

also replaced both carburetor return springs With Stronger tension.

But those conditions Persist slightly . letting off the gas in gear there is still that slight tugging and when left to idle for a couple of minutes It still drops Up to 200 RPMs.

[rub35]

Originally Posted by D111

messed around with it a bit turning up the idle screw And then Fattened up the low-speeds to then reduce the idle, it did get rid of almost all of the tugging but it just doesn't feel like it's running That well Then.

"idling at 900" this thing is like trying to hold onto an eel, it Idles at around 1100 while driving if I let off the gas than when I stop It's about 950 Then if I sit there for a few minutes works its way down to 750 so I Can't actually say where the Idle is at. :-)

I may just put my Holley back on and see Where I'm at.

My car does the same thing. I was tol it could be the return springs on the mechanical advance. MSD does make different tension springs that come in a kit. I may give these a try.

[Gaz64]

Originally Posted by D111

The best that I can get after tuning the Low idie screws is about 14 to 15 at 950 and about 12 1/2 When it drops down to 750

also replaced both carburetor return springs With Stronger tension.

But those conditions Persist slightly . letting off the gas in gear there is still that slight tugging and when left to idle for a couple of minutes It still drops Up to 200 RPMs.

The idle rpm drops because manifold vacuum also drops.
It is a trade off for running a carb with an "average" idle circuit and a large cam.

[D111]

no more tugging, and has a more happy Clappy sounds to the idle

And may have found what was ailing the 770 Avenger , when my friend picked it up off the bench he said he didn't like The play in the secondary butterfly shift. After installing it does seem to be allowing an air leak, when I spray carburetor cleaner on where the shift enters the base plate the idie And vacuum definitely raises up .Now to research how to correct That.