idle running away (S-distributor)

[rfoulds]

A weird problem. my distributor is from a 1970 Carrera S. The advance curve on it seems very aggresive, and works well for me, with one small problem.

It will sit and idle all day at 800rpm. As soon as revs go over 1500rpm, the advance wants to keep running the idle up, to as high as 2200. I can slip the clutch and drag it back down, and it will at 800rpm again.

A shop here tried to change the weights on the distributor for me, but that slowed the advance too much.

It's a 2.7 six with dual webers.
Any ideas??

[rfoulds]

I mis-typed. I started typing that the engine case was a 1970 2.0.
The distributor is from a '66 or '67, I forget which, but I have never heard of a distributor causing this.

Does it make any sense?

Anyone ever experienced this??

[ein 6er]

randy,

not much help here but, i feel your pain!! mine does the same thing.

i have a '67 2.0 (not an s) in mine. i've been having a heck of a time adjusting my carbs because the rpms run up like you describe. i think my dizzy is from the original engine and it's worn out. i just sent it off to get rebuilt, so we'll see what it does when it comes back.

this is what PMO's says in their carb adjusting info in regards to the dizzy ...... " Sometimes as you turn out the mixture screw it speeds up the engine enough to advance the timing and that immediately adds 300 or 400 rpm. When you turn the idle screws back a hair to correct this the weights flop back and this is what slows the engine. It's best to get your initial adjustments around 1200 rpm and hope the distributor doesn't intercede. "

i've read some good info about dizzies searching on the 911 board.

doug

[Dave at Pelican Parts]

Ginter's six had a similar problem. A good thorough carb rebuild solved that, I do believe. Hopefully he'll speak up about it.

Or was it that the manifold was warped and didn't seal to the head? Hmm, I forget now. Anyway, that's worth checking as well--how well the manifold fits the head and the carb.

--DD

[gint]

Same exact problem! And I do mean exactly the same problem. Drive the car, let off the gas and come to a stop, car idles at 2-2.5k rpm (higher when hotter) until you bog it down with the tranny in gear or if standing over the engine bay choke one or both carbs with the accelerator pumps or my hand over a couple of throats. It would idle once again until the throttle was brought past 2k or so. Then it would stick again and the cycle would repeat itself.

I rebuilt the carbs myself, surfaced both sides of the manifolds, bead blasted and powder coated them (thinking that would seal a possible crack better than paint), installed PMO's insulator blocks (which did cure the fuel boiling issue), swapped my S dizzy for a used T unit, and still had the same damn problem. The carbs and S dizzy went off for rebuilding. The distributor was said to be fine, the carbs were gone through with all passages drilled out (something I didn't dare try myself), and BAM! no more sticking idle at 2-2.5k.

Try this; disable your accelerator pumps. My carbs came back with new accel pump linkage where necessary and the rest of it thoroughly cleaned and deburred. My thought is that the carbs were getting to much fuel at idle and were subsequently sucking air from any point they could find it top compensate. But that's just a theory. It's also the one thing (besides drilling out all the channels) that I didn't mess with too much.