Is it my carb, or my distributor causing the problems?

[eds1965coupe]

We've just finished the rebuild of the stock 78 block in a 65 mustang, with a 3.03 manual transmission. It has 66 heads and an Autolite 1100. It has a Load-o-Matic distributor with pertronix. It has 22 inches of vacuum at idle, 150 psi in every cylinder, 40 psi of oil pressure, all is well...until you put it under a heavy load or near wide open throttle. It does a couple of things. Its as if it just won't go any faster when you try to speed up to over 50 in third gear. When you go up a hill or try to accelerate it stumbles badly.

We replaced the carb, same exact carb model etc., but not the distributor during the rebuild. The stumbling issues are the same as before the rebuild. This leads me to think it may be the distributor since it is the only common part from the previous setup. If so, what can I do to test the distributor to see if it is the problem, and how can I fix it if it is. We did check the integrity of the distributor shaft and it seemed nice and tight.

Thanks for your help,

Ed

 

[rbohm]

8) it sounds like you are not getting enough timing advance. m advice would be to replace the lom dist with a duraspark dist.

 

[Lazy JW]

..... When you go up a hill or try to accelerate it stumbles badly.....

This is a classic symptom of ignition failure, usually bad spark plugs, wires, coil, distributor cap, etc.
Joe

 

[eds1965coupe]

All of the ignition parts are new except the distributor.

 

[CZLN6]

Howdy Ed:

Does it only happen when the engine is hot? or all the time? What was done in rebuilding the '78 block? Fuel pump? Fuel lines?

My suspicion is fuel delivery- as in a bad/weak fuel pump, partially blocked fuel lines, etc. Or a worn eccentric on the cam that accuates the lever on the fuel pump. If it has normal power before it gets warmed up and then goes away- that is an indication.

Also check the points for any defects, like a crack that only causes misfires at higher rpms.

Keep the diagnosis coming.

Adios, David

 

[Lazy JW]

When you get to a hill, does it stumble IMMEDIATELY upon mashing the throttle, and then catches hold as soon as you let off the throttle? If so, I'm still saying ignition; however, if it pulls strong for short time and THEN stumbles, it's probably running out of fuel.

I've driven my share of old clunkers and have plugged a few fuel filters along the way, they typically manifest themselves first at high speed.
Joe

 

[JackFish]

Improperly adjusted or damaged accelerator pump could cause stumbling under load and bogging off-idle.

 

[eds1965coupe]

I plotted the timing curve. Here are the advance readings.

1000 rpm - 11 degrees
1500 rpm - 18 degrees
2000 rpm - 24 degrees
2500 rpm - 28 degrees
3000 rpm - 28 degrees
3500 rpm - 28 degrees

It looks like I have 28 degrees of advance, all in by 2500 rpm. How do these look?

 

[Quick 8]

I notice that you have a loadamatic distributor. I'm not exactly sure what the curve for one of those should be, but for a "normal" distributor I think you want to have 34-36 degrees of TOTAL timing. Yours sounds too low to me. Your initial timing looks good though, so it seems like maybe you are not getting enough advance.

Maybe sombody with some experience with a loadamatic can respond and give some more info.

For what it is worth, I removed my loadamatic and replaced it with a distributor from a 68 (I think.) The new distributor has BOTH vacuum and mechanical advance. I put on a Pertronix, and it runs great. I'm not sure what carb you are running, but I also just replaced my 1100 with a rebulit 2100 and an adapter from Classic Inlines. Let me tell you, I fought and fought with my 1100. I changed carbs, rebuilt it twice, and it still didn't run that great. I put on the 2100 and it was like a whole different engine. I can't recommend this carb swap enough. It is fantastic. The car idles a lot smoother, runs a lot smoother, and has more power. Before, I thought that the engine in my car ran rough because it was just tired and needed a rebuild (I still do, it has a rod knock). But after the carb swap, the engine runs as smooth as velvet. (Unfortunately, putting a new carb on didn't fix the rod knock!

 

[eds1965coupe]

Did you modify your intake, or did you use an adapter for the 2100? I'm interested to know if it is worth it to put the 2100 on without milling the head. I have a 1.02 and a 1.08 that I could use. I also have a duraspark II setup that I could add as well. What did you do for your throttle setup?

Thanks,

Ed

 

[Quick 8]

I did not modify my intake. I bolted th adapter directly to the head. I eliminated the stock carb spacer. I by-passed the spacer with the water line. I used the stock carb linkage, but extended the rod that comes forward from the firewall, then mounted a home-made aluminum bell-crank on the front right carb bolt. This allows the linkage to turn the corner and hook up with another small rod to the carb.

 

[LaGrasta]

my guess is vacume advance.

 

[66 Fastback]

It sounds like a timing issue to me. But here are a couple of questions..
Have you confirmed that the throttle plates are fully open when the gas pedal is fully depressed?
Does the Load-o-matic advance the timing with increasing engine rpm? Point a timing light at the engine while increasing engine speed.
Does the vacuum cannister on the distributor hold vacuum?
Any vacuum leaks on the line feeding the distributor? Very possible with the stock steel vacuum lines.

Did you replace the harmonic balancer when the engine was rebuilt?
Timing mark could have slipped and timing set by timing light could be incorrect.
Did you verify that the timing mark, #1 piston, distributor rotor are all pointing to the correct position when the #1 Cyl is a TDC?
Doug

 

[franko66]

I would advance adjust the distributor and test drive. Keep advancing it a little at a time until you can hear minor valve clatter at higher acceleration when driving, then retard or back off the dist timing slightly until valve noise is reduced.I learned this on this web site and it really helped. I screwed around with a timing light getting the curve and setting to manufacturer specs. it didn t seem to have much power when accelerating from 50MPH. After I adjusted manually as I mentioned in the beginning it ran MUCH better. I placed the timing light on to see how far off from fords specs. I was at 12 degrees. I believe specs were 6 degrees BTDC .It runs a little hotter in the summer but never overheats or boils over when turned off.Not a drop from the rad overflow tube when turned off.I can cruise at 75 MPH easily now. I got my 66 mustang 200 stock engine to go 110 MPH before being afraid due to the old suspension and slowed down.