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.

1 Like

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.

Hi, I still have the problem with my 351W not running smoothly.
I have now bought and installed a new Edelbrock 1406 carburettor. The engine pulls better and accelerates better, but the rough running still persists. As a last resort I wanted to install a new ignition distributor because the old one had some play. Unfortunately, the new ignition distributor didn’t fit because the shaft with the hexagon socket was too thin. I received a SKDIFD25 distributor from SKP from a dealer.
The shaft diameter of the original distributor is approx. 0.51 inch, the hexagon socket has a wrench size of approx. 0.3 inch for the hexagonal shaft to the oil pump.
The new distributor from SPK only has a shaft diameter of approx. 0.446 inch and a wrench size of approx. 0.248 inch.
Unfortunately, I don’t know whether anything was modified on the engine by the owner at the time in the USA!?
The installed original distributor has the number: C90F12127 Z (9B14).
The new distributor SKDIDD25 would have the same designations.
Can anyone help me regarding this.
I also don’t know if the distributor was rebuilt? As a result, I can’t order a new distributor now because the diameters and wrench sizes are not specified for any of them. Here are a few photos of the installed distributor.
Thanks in advance!

Here is the last picture from Autolite distributor

That SKP number looks to be correct for a 351W, And the C9OF-12127-Z is also correct for a 351W. I’m thinking the SKP unit was mis-packaged. It may be for a 289/302. And will not work in your engine. I don’t remember what part of the world your in, but it sounds like you will have some troubles with returning and getting another one.
Could you post the numbers on the body of the SKP unit?

I am from Austria (Europe).
The SKP number is SKDIFD25 K40 0144.
Thank you

The dealer said that all distributors for the 351W that he has in stock had the same diameter and the same hexagon socket as the SKP distributor.

Just in case you didn’t “catch” what Hemikiller was saying: you have to make sure the Pertronix is getting an “unresisted” 12v.

Yes I understand!
The Pertronix has 12V switched via relays!

To be on the safe side, I ordered a distributor from Rockauto as the dealers in Europe don’t seem to know. The distributor ordered is an Autoline D441, unfortunately a rebuild but the only one that was in stock for the 351W. I hope this one fits.
I also asked Pertronix Europe if they could tell me the shaft diameter of the “STOCK LOOK” Ignitor distributor but unfortunately they can’t.
If the distributor I ordered from Rockauto doesn’t fit either, I would overhaul the old Autolite, but I don’t know where I can get replacement parts so that I can reduce the lateral play in the shaft. I had already cleaned it…

The fact that this fixes the rough running of the engine is just my last idea anyway!

Hello dear cougar fans,
I’m not quite sure yet but I think I’ve found the error. After I couldn’t install the wrong ignition distributor, I dismantled the old distributor and cleaned it again. I also removed and checked the newly installed vacuum box again. I noticed that the inner part is moved laterally and so that when there is negative pressure, the linkage of the vacuum box is not pulled inwards but more to the sides. This meant that only minimal adjustment was possible. After I replaced the vacuum unit from the SKP distributor, the engine runs much quieter. I hope that’s it, thanks for the advice.

1 Like