351 unsteady running,question about carburetorcarburetor

Hello guys, I’m having problems with my XR7 from 1969, which is finally typed after about 3 years of hard work.
After another 10 months of waiting, the FMX gearbox was repaired in the workshop and, as the engine was not running smoothly, the ignition and the carburettor were adjusted, so it was said.
However, I still have the same problems with the uneven running!
After starting, the engine runs at around 1700 rpm (should be around 1500 rpm), it stays that way until I step on the accelerator briefly, then the speed drops to around 600 rpm. Is it normal that the speed remains at the fast idle setting until the gaspedal is pressed or should the speed automatically go down to the idle speed after the choke opens?

The problems with the out-of-round barrel have not been resolved. You can feel a slight jerk at about 1700rpm every ~ second. At higher speeds and when driving you no longer notice anything. The workshop has no idea and neither do I. The spark plugs, the ignition cables, the ignition coil, the Pertronix electronic ignition, all vacuum hoses were replaced, the distributor’s vacuum box, the fuel pump, the harmonic balancer, the water pump, etc. are new, the timing chain with gear set was replaced. The workshop also checked the basic setting of the hydraulic tappets. The carburetor (AFB Carter 9637SA) has been overhauled, the choke works and is supplied with 12 V. I’ve already removed all the vacuum lines and completely plugged the vacuum distributor but no change.

Does somebody has any idea?
Thanks in advance!

1st question, do you have a spacer between carb & intake. If so is it the factory 1" alum w/ port ? I have has issues w/ the gasket (#55 from felpro?) between the manifold & spacer. The gasket is too small allowing a vac leak.

The idle will not come off the fast idle can steps until the pedal is pressed releasing the cam.

A quick check is to sub out the carb w/ a new one, or one from a know good running car of same /like.

Hope this helps!

Thank you, yes, a spacer about 1/2 inch high made of bakelite. There is no more space under the hood. I got the car from the USA with the 351W, the Edelbrock Peroformer intake manifold, the Carter 9637SA and the Edelbrock air filter and wanted to leave everything as “original”!?
I have already replaced the carburetor gaskets.
Replacing the carburetor is a bit difficult, the shop is over 100 miles away and doesn’t have anything in stock. I would have to buy one. What would be the right carburettor? I don’t want to lose any power but also don’t want to consume more fuel.

Well here’s where you will get a LOT of opinions…

Here in Colorado I have had great luck with the Edlebrock 1404?
If you have a factory automatic, you might want to look at the Carter carb{ IF THEY ARE STILL MADE}(625CFM?) it has the provisions for the automatic trans kickdown, unlike the Edlebrock.which requires an add on that causes all sorts of issues w/ cable throttle & trans kick down. Please check # as this is all from memory.

Let me know you altitude as I’m 5700+ ft

My carburetor is a 625cfm Carter, 9637SA.
Altitude is about 900 ft

High idle speed is a bit excessive, you can adjust it down to 1500 or whatever you prefer with the adjusting screw. Factory spec was 1400 for automatic, 1250 for manual trans cars. Curb idle is 675 manual trans, 575 auto (in drive). Both should have headlights and AC on if equipped.

Here’s a link to the carburetor manual.

Where are the choke and Pertronix getting their power from? I’ve seen plenty of people make the mistake of hooking the choke up to the coil (+) wire. The Pertronix will function best when it has a full 12V supply, not being powered through the coil (+) wire as they suggest.

Yes, thanks! I have already corrected the speed, the Pertronix and the choke are connected to 12V.

Just a thought, do you have the engine grounded w/ one from back of Pass block to fire wall? Not just ground wire on battery… to block. You must have block to fire wall (factory) # BC 16 $12.50 from Marti Auto Works.

Yes, I have!

If you have some old gas that has set in there over the years it might have coated a few things in the slow or idle circuits in the carb. Had it happen a few times.