A customer brought in a very nice 65 Mustang to diagnose and resolve a high idle problem as well as slight run on after the key is turned off.

As far as I can tell, this engine is pretty close to stock except for the Edelbrock carb and intake manifold. The air pump and air injection tubes/valves on the heads are all still installed but the tubing connecting the pump and heads are removed and the ports capped off. I’m not sure if anything else has been deleted.

I’ve been unable to find specific answers about what the base timing should be. Answers on Google and other forums range from 6 to 10 degrees BTDC - it was set at about 8 according to the paint on the balancer (someone marked it with a couple of paint lines due to the marks being hard to read).

I cleaned up the marks, verified TDC #1 was on zero and the rotor was pointing at #1 tower on cap, then set it at 6* and it seems happy there by ear and it doesn’t run on, but I’d like to verify that if possible - does anyone know?

As for the carb - I’ve found the owners and installation manuals online, but I’m trying to determine what the “out of the box” settings on the idle speed and mixture screws were and neither manual has that information. By the customers own admission, he was messing with the carb adjustments and he immediately followed that statement with “but I don’t know anything about cars.”

I’ve set the idle at about 800 RPM because that’s what sounds the best, but without being sure that the mixture screws are set correctly I don’t want to call it done yet. I learned roadside self-reliance on carburetors and haven’t completely forgotten it all, but it’s been so long since I’ve had to adjust/troubleshoot one that I don’t want to make guesses either.

Thanks in advance.

 

As OEM in the last years of the 289, timing was 6 degrees for regular fuel (2bbl) engines and 12 degress for premium fuel (4bbl) engines. I used to run mine out to probably 8 or 10.

As to the carb once you get it idle on the idle circuits instead of having a high idle that's beyond what the idle circuit does, try to get it to something around 750 iirc. I always had mine up a bit because I didn't know much. (and still don't)

If it runs good at 800, and you can hear a change when turning the idle screws, you are close to if not all good. You are trying to get it to run with the throttle plates very close to closed, if not actually closed. The idle air bleed is what's supposed to supply enough air.

But a smooth idle that doesn't quit on you, and doesn't die when put into gear, is what's important imo.

 

Thanks.

I’m thinking the engine was originally 2 barrel; but even with the 4 barrel on it now I’m sure it’s not running on premium.

I didn’t think to check the position of the throttle plates. It sounded good and responded well to throttle (in park - I haven’t test driven it yet) so I’ll see where they’re at on Monday, then go from there.

 

Update:

Since I wasn’t sure what the customer had done, I decided to go “back to basics” so to speak with the mixture screws and turned them all the way down, then backed them off 1 turn as a starting point. It wouldn’t start, so I backed them off another 1/4 turn and it fired but died immediately. Another 1/4 turn was enough to start it.

I let the engine warm up to temp, then slowly leaned out the mixture screws one at a time until the engine started stumbling, and backed them out 1/2 the required turn to make it stumble (so if it took 1/4 turn to make it stumble, I backed the screw off 1/8 of a turn).

I used the same strategy with the idle speed - the plates were nearly closed where I’d adjusted it last week, but I decided to reset them to fully closed and tried to start it, adjusting as necessary to get it to start and idle smoothly. I also adjusted the choke and I’m waiting for it to cool off to see how it starts.

I think it’s good to go, so thanks again for the help.

 

Yes, you were right to start over.
As a rule of thumb, mixture screws on just about any carb, be it on a car, lawnmower, chainsaw etc. have a basic starting point of 1-1/2 turns out, of course there will always be exceptions.
You also have to be careful when screwing them all the way in to not over-tighten and damage them.

If the screws need to be turned way beyond the normal range, there is something wrong in the carb (typically dirt clogging a passage) that needs to be addressed.