140 miss at constant speed only

[Frank DuVal]

the secondary carburetors are closed fully. There should be no or only a slight air flow at idle and make sure they don't open until about 2/3rds gas pedal depression (do not open at highway speeds of less than 70MPH

70 MPH? Then you might as well have a 110 HP if you drive around town, state highways or on urban interstates!

What did you mean to say?

[66vairguy]

the secondary carburetors are closed fully. There should be no or only a slight air flow at idle and make sure they don't open until about 2/3rds gas pedal depression (do not open at highway speeds of less than 70MPH

70 MPH? Then you might as well have a 110 HP if you drive around town, state highways or on urban interstates!

What did you mean to say?

Just what I said --- at a constant 70MPH on a level highway, the secondaries should be closed and should not cause a lean condition. Yes if you don't want to really GO a 110HP is fine, in fact a great engine.

One problem with secondaries is some folks never open them up. I haven't had that issue

[Frank DuVal]

Ah, that is not how I read it. I read the parenthetical expression buy itself, as in do not open the secondaries unless you are doing over 70 MPH, ever. I like to open them right off the line myself....

So we are in agreement. Secondaries should be closed until asked to open by the driver, speed had no relation on this. You could be doing a steady 90 MPH on level land and still not have the secondaries open. Getting up to 90 quickly they will be.

[vairmech]

Snip

Yesterday afternoon disconnected the vacuum advance on the distributor and went for a test drive, including 70+ mph on the interstate. No more surging.

So...Leave it unplugged?

Hook it back up and retard the timing a little?

Or try an electronic distributor? Anyone have experience with the California Corvair electronic distributors?

Ummm, then how about changing your points ground wire? They do break from the constant moving of the points. Unless you really want to spend $200 for a $5 fix, if that is the issue. Have you checked your points plate wear on the pivot?

[irfgt]

You probably have a lean surge and not an actual misfire. Try increasing the main jet size by a couple of thousandths and I'll bet it goes away.

[66vairguy]

You probably have a lean surge and not an actual misfire. Try increasing the main jet size by a couple of thousandths and I'll bet it goes away.

On a 65/66 140 the primary carburetors had a power enrichment circuit to deal with a lean condition at certain throttle openings aggravated with the use of secondary carburetors partially opened during acceleration (or high cruise speeds).

Having said that lets not start changing things that should NOT need to be changed. I have never encountered a 65/66 primary carburetor that needed bigger jets.

The poster/owner needs to let us know WHAT carburetors are on his engine. Check for vacuum leaks. Make sure the ignition is working properly (make sure the vacuum advance is working correctly). If everything looks good, then you get into fuel pressures and float levels, stuck PES valve, etc.

Hopefully the owner will not get overwhelmed with suggestions. A methodical, one thing at a time, approach is needed. Start with the easiest stuff first.

[chris]

[/quote]

Agree, although I occasionally find a bad vacuum advance unit causing a problem. Point is -- Don't make up your mind until you check everything!

I did not notice anyone bring up the rubber couplings at the vacuum balance tube to the carburetor pads. I must admit to forgetting about these and vacuum leaks will cause odd issues. The rubber coupling gets HOT and deteriorates and sooner or later they must be replaced.
[/quote]

Good point about the rubber to the balance tubes; it's a good reminder for me to check mine as well!

[sh011956@aol.com]

All helpful comments!

Thanks

[jimbrandberg]

I don't know if anyone said it yet but I might wonder about the point plate pivot.
If you have a Dwell Meter you might see if dwell remains steady when you rev the engine. If not you might wonder bout the distributor shaft bushing.
Please forgive me if those things were already discussed.
Jim Brandberg
Isanti, MN'
CorvairRepair.com

[66vairguy]

I don't know if anyone said it yet but I might wonder about the point plate pivot.
If you have a Dwell Meter you might see if dwell remains steady when you rev the engine. If not you might wonder bout the distributor shaft bushing.
Please forgive me if those things were already discussed.
Jim Brandberg
Isanti, MN'
CorvairRepair.com

Doesn't hurt to repeat checking the pivot and plate. Usually adding a ground wire fixes it unless badly worn.

I recalled another easy thing to check thing. The vacuum advance lever connects to the points plate via a stud. That stud can come loose and timing will not be reliable. Not much of an issue on stock, but I've seen it happen with the Pertronix plate. Easy to overlook, easy to check.