Why is my idle changing???

[TurboChris]

Hey all,

66 Fairlane / 427 with tunnel wedge and dual 1850 600's, MSD Digital 6al and pro billet distributor.

 Owned it for about 2 years and have put 5 or 6000 miles on it. 500 hp and she runs well. I recently swapped in a TKX and for the last month or two have been breaking in the RST clutch. They advise 500 miles of city driving. So I'm on the freeway a couple of weeks ago and I figure it's about broken in and getting on the freeway I redine it in a couple gears for the first time in a long time (at least 6 months with the swap and break in etc)

Not sure if it's somehow related but then 20 miles later I exit the freeway and when I stop I'm idling at 1500 rpm. Blip the throttle a couple of times but it doesn't go down. Next light, the same thing. Then I get home, same thing.

Hmmm so I open the hood, adjust the idle back down to about 900.

The next day I get it and fire it up and go for a drive, after a bit I stop at a light and it's barely idliing. About 500 rpm.

Sigh,

Fast forward a couple of weeks and where we are at now is I fire it up and drive it and come to a light it might be fine at 900 or it might be at 14-1500. And sometimes it's at 1500 and after about 15-30 seconds it settles down to normal. Sometimes it doesn't. Yesterday I drove it 30 miles to the cars n coffee and it was fine, then on the way home it was at 1500 all the way home. A couple hours later I started it up and it's at 900.

Where do you guys suggest I start to try to diagnose this? It's interesting as it's not consistent.

Thanks!

[1964Fastback]

Make sure the choke is all the way open and fast idle screw isn't touching the fast idle cam.  I had that happen on mine.  The choke wasn't open 100% but I thought it was open enough the fast idle screw would not be in play but I was wrong.

Next thought is that the advance springs in the distributor are sometimes not pulling the mechanical advance out when you are at idle.  More timing equals faster idle.

Finally, next time it is idling "fast", go under the hood and make sure the secondary plates are all the way closed.  Primaries too for that matter.  See if you can rotate them any more shut, indicating they are hanging slightly in the bores.

Pat

[shady]

yep secondary is hanging open a tad. grab the sec. linkage and give it a tug.

[TurboChris]

Ok good stuff. I forgot to mention that the chokes have been removed. I did rebuild and recurve the distributor last year. I'll look in there and also check the secondaries / linkage.

[Drew Pojedinec]

Totally common with secondaries.
In theory they should shut on their own, in practice not always.
Adjust closing link to be a little tighter.

[475fetoploader]

I’ve solved a similar riddle by tightening all the end bowl screws. Especially with a Holley that has sat a few months during winter.

[Ford428CJ]

Your MSD distributor has a hangup problem! Meaning the GM type mechanical advance is hanging up on return idle. I’ve done videos on this kind of stuff just to show. It is fixable.

[DuckRyder]

I had a car (not an FE) act like that and it was the advance weights sticking.

/in that particular case when it was idling high i could bump the clutch and it would idle down.

[TurboChris]

Your MSD distributor has a hangup problem! Meaning the GM type mechanical advance is hanging up on return idle. I’ve done videos on this kind of stuff just to show. It is fixable.

Can you point me to some of your videos? I'd be interested in seeing them.

[Ford428CJ]

Those GM style mechanical advance weights do stick! You have to reshape the cam advance on the distributor where the weights ride to get ride of that. Happens a lot!