Hi All

just had the valve stem seals done on the 429 with the passenger side head coming off due to a broken bolt.

That is all done and back together.  Now one problem leads to another.  The engine will not idle

or idle adjust as it should.  If I screw the main large idle adjust screw in on the carter the engine still

runs - if I turn the drives side smaller idle air adjust screw all the way in the engine does not stop.

There is a noticeable flat spot right at bottom of idle on take off and the engine just is not right at least

at idle.

Is this an indication of a vacuum leak?  The problem is still there if the PCV valve is off and blocked,

same with other vacuum lines.   Hope that makes sense and I can get some advice.

John

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"Brains Trust" required at the front counter please.

I'm going to assume that the top end of the engine has been removed and replaced. If the carburetor has been removed from the intake has all the gaskets been reinstalled that were there in the proper order. You can confirm this with a shop manual.
Are you adjusting the idle metering screws or the throttle stop screw?
If the distributor was out did you check what the timing was prior to removal? The shop manual calls for 5 degrees but I had a slight hesitation coming off idle it liked 8 better and it was 10 when I got mine.
Is your vacuum advance leaking? Most original ones by now are pretty much toast. The vacuum advance runs off of a ported vacuum source as per the shop manual. So the vacuum at the distributor should be negligible at idle. Manifold vacuum is strong at idle giving a lot of advance to the timing.
Hope this helps a bit.

Are the throttle plates closed?  take off the carb linkage and see if the problem goes away.   The idle circuit stops controlling the engine once the plates open, so it seems most likely to me that when reinstalling the intake, that the carb is now in a slightly different position and that this has disturbed the linkage adjustment.  

Good point Mark. Easiest thing to check first.

Did you put the metal shim back under the Carter carb? It will not idle with it removed.  Was any sealant used between the metal shim and the base of the carb?

There is a choke idle adjustment screw, but not an idle adjustment screw. The idle is accomplished with the bleed air screw and fuel mixture screws.

Quick question, should there be gasket cement (sealant) on both sides of the shim?

The sealant should be applied to the surface that mates up to the carb, but I out it on both sides.

Thanks Russ. I’ve neglected to reinstall the shim when I put the manifold and carb back on, probably explains why the idle is very up and down.

Yup, the carb was modifies to not idle with the shim missing.  Good find.

John

Check the point setting and the timing setting once more to be sure it is correct
Check the timing once more after tightening down the dist ( setting can move when tightening down )
Many mechanics overlook the basic tune up specs when doing other major repairs And give you back the car not running as good as it SB
The carbs accelerater pump is always a possible cause of a hesitation when accelerating

Ignition specs being off and the carb accelerator pump SB the major cause of a hesitation
Some of which has been suggested above this post

Did you block the PVC connection on the carb side backalite spacer ?( a major air ( vacuum leak ) if it is still unsealed at the base of the carb

Enjoy


Enjoy

thanks all to start lots to think about.  Tony the car is running Petronix 3. Before the head came off and on (left only)  of course there were no issues -- car idled perfectly. I will get back on it today or when I get time and investigate further and update.

John

OK went back to timing - put in more advance from where it has just been set.  That is the problem solved.. It seems to have more advance than recommended but I remember reading in another post that using more advance in these engines as they get older is necessary is that right?

Anyway car is running as it was before and no more blue smoke out the tail pipe!

Cheers

John

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