I have a 65 Mustang, 289 2v........this car doesn't get driven much, but when it does, it runs GREAT.....just today, for the first time...it fired right up like always, but when I started driving, I noticed a little bit of a "inconsistancy" when just coasting along, kind of like a "bucking"...When I came to a stop, it sort of idled rough.....but not real bad, just didn't feel right......when I take off and under a load, or accelerating, the motor runs like a dream....its only when I'm just kind of coasting along, say at 30-40mph...it seems a little rough, bucking if you will. When I got home, it cleaned the carb, but it didn't do anything, the idle isn't bad, but its not the same....just a little "off"......in the exhaust, at idle, there is a "puff, puff" sound every now and then out of the tailpipe.....its all random.....its not regular.......

The plugs look good, could it just be as simple as its ready for a tune up?

 

how old is the fuel?

 

is this a new problem or has it always behave like this? do you not have enough initial timing?

 

The gas is probably two or three weeks old, I put about a half tank in it the last time I drove it......I only ever put a little in it at a time since I do not get a chance to drive it much.

This is a brand new problem. It's never run like that before.....I'm not sure what the initial timing is at, I set it a long time ago, but I'll check it today.....does it change?

 

the timing probably isn't the problem, but more than likely it's not something major either. Put a vacuum gauge on it and that will tell you if you have a specific problem. this will also tell you if your timing needs to be adjusted.

given the vacuum test looks good I say just go through and give it a good tune up if you haven't done so in awhile. Cap, rotor, plugs, wires, fuel filter, air filter.

Here's a good writup on how to read a vac gauge and how to determine what kind of problem you may have depending on what the vac gauge does:
http://www.tracyvette.com/enginevacuum.html

 

Thanks JoJo.....I'm thinkin its just tune up time..... I did check timing, and initial timing is at 9 degrees.....I took the plugs out, while they didn't look bad, I cleaned them off a little to see if it helps, took it for a spin, and it ran better, still no perfect, so that leads me to believe just a tune up....I'll probably go thru the carb too, I haven't ever worked on the carb, and I don't know when the previous owner did.....so it can't hurt....its time to put it away for the winter and do some projects to it anyways........I just found it odd that it went from running "perfect" to "not so perfect" really quick!

 

yea a little TLC goes a long way with these cars.

If you don't have a vac gauge I would get one though. Having one and knowing how to read it can drastically cut down diagnosis time on your engine.

 

Right on man! I don't have a gauge, but I'll get my dads....he has one...that article you posted was great reading.....didn't know you could tell all that from a vacuum gauge! I have a good friend with a dyno, after I tune it up, might take it there, he can then dial it in....=) Used to take my race car there, he made it run 10x better!

 

If you still have points in your distributor then dont forget them as a part of the tune up.

 

I do, but I"ve been contiplating on getting rid of them....now might be the time....