Running rough (really rough)

[Jurisd 10]

Been away from the forum for a while, focused on the honey do list. But now I'm hoping someone can point me in the right direction...

 

My 69 351C 'vert sat in the garage for ~ 1 month (ran fine the last time I drove it). When I went out to start it, it sounded cold and rough, like a cyl. or two were missing. Lots of smelly exhaust smoke too (but not black or white). Taking it out on a warm-up, I drove about 2 miles, and then noticed the engine would die unless I kept my foot on the gas. Eventually, it died and would not restart.

 

Thinking I had an ignition problem, I replaced my Pertronix Ignitor 1 coil with a new one. The old one cracked on the top, which I assume happened by leaving the key in the on position too long. No change. Then I pulled the cap, and confirmed no water in there. As far as I can tell, the accelterator pumps on my Edelbrock 1406 carb appear to be pumping gas, and the see-through fuel filter is clean and filled with fuel.

 

In a nutshell, when cold, the engine will start up, but then runs very rough, with lots of smelly exhaust. Once the engine warms up (3-5 minutes) the engine will die and not restart until cold again.

 

So, anyone have some troubleshooting tips for that set of facts?

 

Thanks - JD

[LindenBruce 27]

What type of smell is it? Is it "burn your eyes" smelly or "rotten eggs" smelly? Have you checked your plug wires? Mice love to chew on wires. Also, I know you said your filter is clean but is it possible you got some moisture condensation in your carb bowl? Are you running an electronic ignition module? Bruce

[70mstang 11]

My first thought would be wires or plugs. Have you pulled the plugs to be sure none are fouled out?

[Max Power 74]

Running marginally cold when the choke is on and then not at all warm when the choke is off seems like a big vacuum leak to me somewhere. When it is warm put your hand over the carb and see it it runs better.

[Lemon Owner 11]

How long ago and how long did you leave the ignition in the on position? In the old days this could "weld" the points shut. I would think it is not good for electronic ignition either.

[Jurisd 10]

Thanks for all the replies. Responses in no particular order: My thought was vacuum leak as well, although I'm not sure that would cause it to that badly. I had a leak when I first installed the carb, and it wasn't nearly this severe of an effect. The smell is not rotten eggs. It was just an exhaust smell, but much stronger (and more visible) than before. I think the water is unlikely, as the car was in the garage and not driven in rain since it was running correctly. Finally, the ignition - I need to get in there and check the wires for spark at each, but It would have to be like 3 cyl. out to make it this bad. The engin will not idle by itself once it warms up. The ignition swithc was left on a bunch of times (stereo installs, etc.) before I knew that was a no-no. Anyway, the new coil did not fix it, and I'm running the Pertronix 1 in the cap, so not the points.

 

So troubleshooting plan is to spray carb cleaner to see if I can find a leak, and then test the spark on each wire. Strange that the change occurred in between drives - not sure what triggers a vac leak? Any thoughts?

[Jurisd 10]

So I know I'm ressurecting an old thread, but hey, it was mine, right? Anyway, I thought I would provide a conclusion for those of you who had made suggestions, mostly so newbies (like me) have more data to diagnose their own similar issues.

 

Recall my '69 'vert/351C all of a sudden started running really rough, after a few minutes of smoot idle. Lots and lots of smoke too. After I replaced the coil (which was cracked anyway) and checked for vacuum leaks, I figured it must be a fuel problem, so I yanked the carb - a 2-year old Edelbrock 1406. Halfway through a rebuild kit install, I discovered that one of the floats had leaked. So, that explains why it would run, but not idle, why all the smoke, and why I had fuel stains all down the front of the carb.

 

Anyway, I called Edelbrock, and they mailed me a replacement float at no charge. Nice of them to do, although they mailed it in a soft-sided mailing envelope, so by the time I got it is was dented. I did a leak check, and went ahead and used it anyway.

 

So, a follow-on question: I used the same jets, and set the floats to 7/16". I set the idle scres 1-1/2 turns out from stop. Other than that, no adjustments. Car seems to idle and run like normal, but I noticed when I really get on it, at around 4k-5kRPM it sort of stalls out a bit. Just doesn't have the top-end oomph it used to. What do I need to adjust to get that back? Thanks!

[LindenBruce 27]

Could possibly be spark scatter. What condition is your distributor in? Is your vacuum advance working? Possibly worn bushings or broken advance springs. Bruce

[Bossed 10]

Just saw this thread, I was going to say it sounded like it was flooding. Glad you got it fixed :001_smile:

 

Bossed

[Lemon Owner 11]

It may be the float level is now too low and it is starving for fuel up high or the opposite and float level is too high and flooding the engine.