ARGH--Car ran like a POS on the way to work--help!

[billschroeder5842]

My 75 roadrunner is usually ROCK solid until the ride to work today.

He is the specs... 400, 4bbl with all the emissions stuff on it. I put a new distributor in it last weekend (!) as the vacuum advance on the old one did not work.

The car ran great earlier this week, but today there was a big difference as there was lot of power and rough running at higher RPMs.

*The car started and immediately felt a bit off------ like it had lost some power. The car revved up higher than usual to shift. felt like a miss?
* It idles very well and super smooth. No shakes rattles and rolls. Timing about 10 and rpms about 850. All spark plugs are firing at idel
*upon acceleration it will advance to about 1500 smooth and then begin to sputter a bit and miss (maybe the distributor is bad?) but seems to hit a "spot" get "stuck" and then overcome it.
* A rev up to 3k rpms and the engine felt like it was missing and not smooth. This engine (in the past) was pretty smooth though out the RPM range.
* At high way speeds (70-80) seems okay but kind of "trails off" and we I push on the accelerator a bit it seems to smooth out a bit.

My first thought was a transmission problem but now I'm thinking it could be the "new distributor" I have my old one with me, so maybe a swap?

Any thing to check or test before a distributor swap to verify? The old one had no vacuum advance but the mechanical seemed to work ok. I'll put a light on this one and see if the mechanical is working. If the mechanical advance is "stuck" that would explain lots. Can I "un stick" the mechanical advance if it is stuck?

I'm lucky to own a business with a loading dock garage, so I can play all day with this one!

Thanks!

[68 RT]

Check the hold down to make sure it did not come loose?

[myk]

Same thing happened to me a few weeks ago; turns out a plug wire melted onto my exhaust manifolds and created a misfire.  Sure, the plug was still firing but badly.  Have you checked all of your connections?

[Cooter]

Sounds like too much timing with vac. Adv. Hooked up. You can pull rotor button and there SHOULD BE a felt washer under it you put a few drops of light engine oil on to lube weights, but if stuck, you will have to go into distributor. Need to check total timing at say 3k RPMS.

[billschroeder5842]

I'll double check all plug wires, but I'm pretty confident that they are in great shape.

My gut tells me it is the "new" distributor. Funny---ran great on Monday....   Hmmmmmmm

Timing/Advance check at noon. Anything else to check?

[Cooter]

If it's a local auto parts store rebuilt/remain dist. I've seen 10* initial, 20-25 * mechanical, and 10-15* vac. Advance at light throttle. I bought like a 73 distributor and it had 25 degrees mechanical adv. Had to recurve for my app.

[firefighter3931]

It does sound like a distributor issue. Something happened between monday and today  

With the cap off you can check for mechanical advance function by moving the rotor. If the springs are intact the rotor will snap back. If the rotor does not return to the static position the advance mechanism is sticking or there is an issue with the advance springs.


Ron

[billschroeder5842]

Timing too far advanced? Maybe.... The "old" initial was set at 8 and the "new" is at about 12ish. The engine seemed to run better at the 12 than at the 8 mark---I just figured it was a variance in the new distributor curve.

Is 4 degrees initial enough to make this act up?  

Maybe I'll back off and see what happens?

So at lunch...
1) check timing
2) rev engine and see if there is mechanical advance (maybe switch to the old??)
3) note "break up" of engine rpm

[Cooter]

Timing too far advanced? Maybe.... The "old" initial was set at 8 and the "new" is at about 12ish. The engine seemed to run better at the 12 than at the 8 mark---I just figured it was a variance in the new distributor curve.

Is 4 degrees initial enough to make this act up?  

Maybe I'll back off and see what happens?

So at lunch...
1) check timing
2) rev engine and see if there is mechanical advance (maybe switch to the old??)
3) note "break up" of engine rpm

Too much timing at 3k rpms. Say your old set up was 8 initial, had like 25 mechanical, and now your throwing another 10-15* of vac. Advance timing at cruise. Total timing means 8+25+15 48* timing at cruise. With your timing at 12*+25+15 =52* total timing.

[billschroeder5842]

So, I checked my timing at lunch (It was great as a few of the gear head guys cam out to the loading dock to "help. The dual exhaust in a 30,000 open warehouse sounds awesome.

The initial timing is set at about 12ish---just on the edge of timing mark gauge on the engine. I confirmed that the mechanical advance IS  working and moves with the engine. I'm not sure about the effect that the vacuum has although connected or not, the light still broke up at high rpms.

I did notice that the timing light "flash" was real consistent and picked up flashing rate to match to engine rpm increase but started to get erratic when the engine reached a certain rpm (sorry, did not get it) leading me to believe that the timing is too far advanced--thanks for the suggestions. 

I'll back down to the 8 later this afternoon and see what happens.

Funny that this popped up today and not Monday.

[b5blue]

  A problem BOTH rebuilt dizzy's I got was that they do not replace the shaft bushing, I don't think they even check it for side to side play or slop. Both would vary the recluder gap quite a bit when tugged side to side by grabbing the rotor. The other problem was mis-matched components, parts of assorted cleaned dizzys mixed together at assembly means you get a Chrysler dizzy with springs, plates, weights, shafts and so on from all years possible. I don't think there is any calibration checking or curve reading they just slap them together and see if they come back. 

[billschroeder5842]

*SOLVED* but not even close to what I thought.

I switched the dizzy--new for old-- and had the same result. I drove home with the same problems of lack of power, running rough etc.

In my garage I took off the air cleaner and noticed the one of the linkage rods on the carburetor was jammed and not allowing the primary buttery fly to fully open. Apparently the car was choking itself out. That would explain a lot of stuff.

I un jammed the rod and bent it so it would not get stuck again and "Viola" the car ran exactly like it did before. Maybe when I get bored this weekend, I might swap in the new dizzy with the vacuum advance.

Or maybe I'll just leave well enough alone?

Thanks for all your suggestions!!!

[b5blue]

GOOD FIND! While the dizzy is swapped back I'd check that ignition flutter you mentioned. See if both do the same thing?  By the way my hat's off to you, keeping all that mid 70's engine plumbing functioning is no small accomplishment! 

[billschroeder5842]

With the carb problem identified, I swapped back the new dizzy. With a vacuum pump and gauge I checked both the pull from the carb (18ish) and verified that the new dizzy moves with vacuum. The OSAC valve works as it should--gradually increasing vacuum rather than a quick hit.

I set the timing at 11 and the revved to about 2500.... everything worked correctly.

A quick test drive confirms that my smog machine runs great.

I'm back to embracing the mid 70's emissions. Now off to buy some Billy Beer, some "gee my hair smells terrific" shampoo for my wife and a "Styx, Equinox" 8 track.

Disco lives!