1964-1/2 Mustang 170 bucks and jerks under load

Hello I'm new here and a newer owner of a 1964-1/2 Mustang with a 170 in it. When the engine is under load in 2nd or 3rd, especially going up hills, the engine is sputtering causing the car to buck and jerk quite a bit.

I've already done/checked the following:
-Plugs and wires look good and checked each cylinder is firing by unplugging individual wires with engine running.
-Cleaned the points on the distributor
-Set timing to about 10 degrees with the vacuum advance on the distributor disconnected.
-Confirmed that the vacuum system is working and vacuum is increasing with RPM.
-Adjusted the idle mixture on the carburetor doing the vacuum gauge technique.

The engine idles fine and runs smoothly just under load something is going on. Can anyone offer any advice to me on what to look at next? Thanks

Check the carb's float level setting! Check for vacuum leaks around base of carb and especially if the throttle shaft is loose. Check the Distribitors upper shaft bushing for excessive looseness. Good luck

Hi, The problem certainly could be in the ignition system. When you cleaned the points did you dress them with an ignition file and make sure they are set to .027 with a feeler gauge, or 40* dwell with a dwell meter?
You can run the engine at night and inspect the plug wires. There should be no arcing, which you cannot see in the daytime. I'm guessing the cap and rotor look good. All the important tune up stuff.
Unfortunately a lot of the new ignition parts are terrible, so a lot of guys get a Pertronics ignition or other electronic upgrade
Also get the Ford Falcon Performance Handbook from Vintage Inline to learn more about your Ford Six.
Good luck

Also check out the coil, if you have a volt / ohm meter take readings of the primary and secondary windings. If you don't have a volt ohm meter pull the center lead wire out with insulated pliers a good coil should jump from coil tower to lead wire 1/2 to 1 inch and have a bright blue spark with a good snap. A yellow spark that won't jump much of a gap will indicates a weak coil that should be replaced. Good luck

W E L C O M E !!!
yes, a good ign tune is 1st, all set? then onto the carb.

"...Ford Falcon Performance Handbook from Vintage Inline..." that's vintageinlines.com:

https://www.vintageinlines.com/product- ... e-handbook

While waiting for delivery see above 'tech archive' (for free) click on the crossed screwdriver/wrench as the 2nd resource we use often:

ci/Loadomatic.html


My bronk had that motor and did yoman's duty for 38 yrs.
To me? its kick a$$...

Thank you everyone for the advice. I'm going to mess with it this weekend and see if I can get it running right. I ordered new spark plug wires since they look really old. I'm going to measure the resistance on them but replace them anyway. I'm also going to pull the carb off this weekend and verify the float level.

Agree with all of the above.

Weak spark will start to fail under load, so make sure the ignition is 100%. (you mentioned cleaning the points which is ok, but once they start pitting it's better to replace them - I like Standard brand Blue Streak, if you can find them.)

Once you've double-confirmed that the ignition is 100%, then look at the carb - a slightly lean mixture will surge, a really lean mixture might cause bucking, but more likely you'd just have a loss of power.

So I put a new set of spark plug wires in it today. Upon closer inspection half of the wires actually look original to the car as they actually have Ford rubber boots on them and we're very stiff and dried out. I measured them with an Multi-meter and they were all over the place and bending the wires caused some of them to have no resistance.

The new wires for every plug and the main one going into the distributor made the car drive wayyyyy better but still not perfect. It still has a slight miss in 3rd gear at WOT but it's very much a better driver now.

I think this weekend I'm going to mess with the carb settings and seeing if a richer mixture helps a little.

If you haven't already, you might want to check the fuel filter.

It is fairly common that and old filter may flow enough for light throttle driving, but become clogged and restrict flow under higher engine load.

I replaced the fuel filter already. The old one in it looked fine

Hi, I the idle mixture screw has no effect when the throttle is open.
I think you are going to figure this out.
Good luck