No load crusing speed engine runs rough?

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dwbarracuda65

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318 slight cam 270 solid lift, holley 600, points distributor idles fine accelerates excellant but runs rough at crusing speed under light load? Any ideas?

Thanks.
 
I have a hand choke so I might try pulling that on a bit at cruising speed and see if it smooths out by riching up the mixture. Thanks.
 
Could be a worn out distributor changing the point gap too.
I tried everything else first and still could not get a consistent run at all rpms and all temperatures ( our first slant 6 a-body ).
Reman'd distributor was like dipping the car in the fountain of youth.
 
I actually swapped distributors used for used but no real noticable change. It has new plugs and used wires that are copper and I ohmed them out cap is new but I could swap with another one just to see.

Thanks.
 
idles good accelerates good do what 1wild is suggesting before you spend a bunch of money
 
I had this problem on my electronic distributor, turned out to be the toothed wheel that gave the signal to the magnetic pickup was too out-of-phase with the driveshaft and thus the rotor. This would cause misfiring and rough running during maximum advance (light-load cruising) because the rotor would be too far away from the spark pickup points in the cap (forget the proper terminology...). Just my $.02 since this is often overlooked and can be really annoying when everything else runs great...

To fix just slide off the toothed wheel and reposition it with the pin on the opposite side.
 
Check the vacuum advance with a hand vacuum pump. If it's healthy, stick an 11/32 allen wrench in it, get it to seat in the hex down in the nipple, and give it two turns counter clockwise.
 
Update: Disconnected vacuum advance no change same studdering. Swapped holley out for an edelbrock that a friend let me use same studdering. Changed distributor cap no help. Ran compression check all within 10 lbs however the pressure seems a bit low 95 to 105lbs but the engine does have a cam and flat top pistons so not sure how much this might effect the pressure. Is there any way to confirm valve timming without pulling the fount apart? Could I have got the timing chain one tooth off, just grasping?
Thanks.
 
Sure you have the firing order correct? Did you replace the spark plugs? Do you have access to a leak down tester? 95-105 is low, but if they are all there, I'd think they'd all still run...
 
if the carb you swaped happened to have been perfectly tuned for this motor, then you could rule out the carb, but I doubt that..

the cranking is really low, shouldnt give studder at cruise really though, just wont have the snap and hp
 
Ok, turned the motor to tdc with the distributor pointing to #1 cylinder. Pulled the timing cover to have a look, the mark on the cam sprocket is on the top?? Shouldn' the distributor be pointing to # 1 when the cam sprocket marks line up? Did I have the distributor 180 out? With other engines I've worked on in the past they ran real bad if 180 out, do chryslers not run that bad at 180 out or are they different on where the dist. is in relation to the valve train.
Thanks for your help.
 
Motor won't run 180 out. Your probably not on the compression stroke. Rotate the crank another 360 degrees and everything will probably line up.
 
Yeah, it's TDC on the compression stroke... There's also a TDC on the exh stroke.
 
Put new timing chain set on and BTW with the timing marks aligned on the sprockets the engine is on the exhaust tdc, I always thought that they were lined up on the compression stroke but it doesn't really matter as long as you instal the dist pointing to 1 when on compression stroke. Started and seems to be no change but now I know that the valve timing is correct. The parts store has rebuilt distributors for $38 so I'm going to try that instead of a bunch of old used ones and see how it goes. I'll let you know.
Thanks.
 
What's you total timing at ?
Sounds like you have too much, that's a classic sign of too much timimg.

Try about 16-18 advance at idle with the vacuum disconnected and plugged. Leave it unplugged and test drive it. Might just be your problem.
 
Finally figured it out. The rotor button must have been the wrong one for the cap car just died one day and I discovered that part of the key inside of the rotor button was gone letting it free wheel. Got a new cap and rotor button in a kit fixed the problem. Aparanently the rotor button was hitting inside the cap blipping the timming. Yippee....
 
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