Surging under steady speeds

[billschroeder5842]

My 383 is surging occasionally under steady speeds and steady RPM. When I accelaerate, the car seems to take it all and does not miss a beat.howver, when I'm cruising, the car seems to surge or miss enough that I'm writing this post.

I have a new factory electric dizzy, timing set about 18 initial, new holley carb, new plugs.

Any ideas?

[A383Wing]

I had same issue...it was too lean..had to go a step bigger on the primary jets in carb

Bryan

[John_Kunkel]

You might try turning the idle mixture screws out a little...the idle circuit still feeds at cruise.

[MSRacing89]

You mention 18 initial, what is your total?  Vacuum advance?  You could pulling too much timing and cruise.......good recipe for a surge.  If you are running vacuum, unplug/cap it and go for drive and see if the surge goes away.  If so, you may need to recurve the distributor.

[ODZKing]

I had the exact same issue with my 67 383. It was a 2bbl and I tried everything. Electronic ignition, points, plugs, carb adjust, anything I could think of.
What finally cured the issue was changing it to a 4bbl.
It was choking.
So the carb suggestion sounds like the right way to proceed imho.
Or get rid of the Holley and get a Carter/Edlebrock.
My 2 cents.

[Cooter]

Stay with Holley Stock jets for now, and check to see how much TOTAL timing you have., Sounds like too much Vacuum advance at Cruise.

[oldschool]

You mention 18 initial, what is your total?  Vacuum advance?  You could pulling too much timing and cruise.......good recipe for a surge.  If you are running vacuum, unplug/cap it and go for drive and see if the surge goes away.  If so, you may need to recurve the distributor.

or just do away with the vacuum advance.

[XH29N0G]

It didn't used to do this right?  If so, I would first check ignition/advance and then look to caruburetor.  The jets might be fine.

[billschroeder5842]

I double checked the timing last night and made sure that it was about 18 degrees. I'll take it for a ride tonight and see what happens.

[XH29N0G]

Missed the statement about the new dizzy and carb.  Which carb do you have? 

I swapped in a 670 avenger to mine last year and had similar problems.  The issue I ran into was (I think mostly) the points - which would not be your issue, but I also found that changing the jets (a little) from those that came with the carb helped.  I had other issues too, like backfire, hesitation, etc... 

[firefighter3931]

or just do away with the vacuum advance.

Bingo ! 


Ron

[68 RT]

Surging at cruise is almost always a lean condition. 

[billschroeder5842]

I have a holley 750, vacuum secondary, dual line.....

So the way I understand it, I'll need to back out the adjustment screws?

any adjustment tips are welcomed!

[MSRacing89]

It does not matter what your initial is in this situation.  The surge will result in too much total timing.  If you just advance your intial without re-curving the total= problems.  Plus, if you are running Vacuum advance, this will only multiply the issue.

Start with unplugging the vacuum line to the carb from the distributor and cap the ported outlet.  Take for a drive and report.

[billschroeder5842]

Will do!

[billschroeder5842]

No joy. Rainy evening in Dallas/Ft Worth.

No driving in the rain for me.

I'll try again tonight.

[68 RT]

Increase primary jet size up one size till surge is gone. Pull some plugs and see if you are lean.   

[billschroeder5842]

So here is a different idea...

I have the electronic choke and the electric fuel pump attached to the positive side of the coil.

Codul thank create a problem?

[John_Kunkel]

The (+) side of the coil is the wrong place to hook up any electrical accessory because the voltage there is reduced. The blue wire on the voltage regulator is 12V, hook them there.

Might/might not be your surging problem.

[billschroeder5842]

Just made the change. Test drive forth coming....

[billschroeder5842]

SUccess and a new situation...

The surging seemed to eliminate and the car is rock solid at 3000 rpms. If I go and "higher" say 3500ish, the tach jumps wildely and the engine missed.

I did retard the timing a little while ago to compensate for the surge.

Do I need to advance the timing back to 18ish from the 12?

[MSRacing89]

Did you ever check your total timing, or unplug your vacuum advance as suggested???  I do not know how else to explain this, but the initial timing will have nothing to do with a surge/ miss at 3500rpm.  So the question to go from 12 to 18 really has no relevance in this situation.

[billschroeder5842]

No, never did that---yet.

My thought is that the coil was being "taxed" my the fuel pump.

Wouldn't I or Shouldn't I reset the timing (advance) anyway now that it seems that a contributor was the electrical?

[John_Kunkel]

The tach jumping at the same time the engine starts to miss suggests an electrical problem....maybe in the distributor.