Still having a few problems with my '68 4-4-2 running properly. Here are the symptoms:


Over a short period of running time, the spark plugs get covered with a black, sooty substance. Then the exhaust starts smoking real bad, especially during acceleration (black smoke). And when slowing down or stopping, the RPMs drop real low and then the engine dies. It starts up again and runs fine until I slow down or stop again.


It's an all-stock set-up - back to as factory original as I can get it. The carburetor (Rochester q-jet 7028251) is a one-year-ago rebuild.


I just bumped up my idle RPMs a bit to see if that makes a difference but haven't had a chance to test it out just yet.


Am I running too rich or too lean? I haven't done any adjustments there - I just left it where the rebuilder had it. It ran great for a month or so and then the car sat through the winter. When I started it up again this spring, the symptoms appeared.


I can clean the black sooty substance off of the spark plugs with carb cleaner and a blast of air. The car runs great then but the spark plugs just get gunked up again after a short while.


Any thoughts?


Randy C.

 

Here is a good explanation:
http://www.onallcylinders.com/2012/1...r-spark-plugs/

Once a plug is fouled to the point you describe it won't fire well even after cleaning. You may just need new plugs after you figure out the issue. Look down into the throat of the carb with engine running and see if its dribbling gas while its idling with the air cleaner lid off.

 

Running way too rich -

 

Sounds like a porous or heavy float. Did you replace the float at the rebuild? In any case, it's possible to check float level with the carb on the car by using a small scale through the vent.

 

I'm still having minor issues with what I suspect is my rebuilt carburetor on my all-stock '68 4-4-2 and I'm hoping someone here might offer up possible solutions. Here is what happens.


When the engine is warm and I'm rolling down the road, if I slow down to make a turn, or if I slow to a stop, the RPMs drop down real low (under 600) and then the engine just dies most of the time if I can't get to the gas real fast. It will start up and run again just fine until I slow or stop again, and then it's the same thing all over.


When I first installed the rebuilt carb (Rochester q-jet 7028251) everything was fine from how the rebuilder set it. Over a short period of time, however, I started getting black smoke out of the exhaust when accelerating (even lightly), along with the above symptoms. When I pulled the spark plugs, they were covered with a black sooty substance. I hit it with some carb cleaner and a little air and they spark plugs cleaned up nicely. The car ran fine for a short time and now the spark plugs are covered in the black sooty substance again.


I adjusted the idle screw in an attempt to keep the RPMs from dropping off too low but that doesn't seem to make any difference. That leaves the idle mixture screws, which I haven't touched.


Am I running too rich or too lean? I can't tell. One symptom tells me one thing, but another symptom tells me something else.


I'm not a mechanic and have only basic knowledge of how this carb works. Any thoughts or recommendations will be greatly appreciated!

Randy C.

 

The evidence provided leads to a rich fuel mixture. Keep in mind that The mixture screws only adjust the mixture of fuel at idle. If you're not having trouble with it running higher than idle, it could be that those screws need to be adjusted.

 

Randy, I too am having very similar issues with my Holley 3310-2. When I come to a stop sign it wants to die and my plugs are dark and sooty. It also bogs upon acceleration from a dead stop. I've asked my brother about it as he is an accomplished mechanic. He seems to think I may need to re-jet the carb as it could be running rich. I'll let you know what I find out in the coming days.

 

Black spark plugs indicates a rich condition.

 

Make sure the choke is open all the way when engine is warmed up. Look down into the throat of the carb with the engine idling and see if its dribbling fuel. As Joe stated above check float level. Is your timing set right?

 

I would verify that the power piston is moving smoothly, put a gage on the manifold and observe the vacuum signal when the snafu is occurring, and probably remove the carb air horn and pull the float to look for dirt in the needle/seat, heavy float [just replace it], loose seat, and the like.

It sounds like either the engine vacuum is not keeping the power piston down like it should- whoich would make SOME richness, or the float is not closing off the inlet like it shoulc, which could lead to exceedingly rich mixtures as you describe.

 

Thank all of you for your suggestions. I finally got around to working with what was going on - did what I thought was the simple stuff first and that seems to have resolved nearly all of the problems.


My idle was set way too low and I believe that's why the engine would die when I backed off of the gas. I upped the idle and the problem was resolved, too much in fact. I was running about 900RPM in gear and 1200 out of gear so I backed it down a bit.


I also closed the idle adjustment screws 1/8 of a turn. That, and doing a slight adjustment to the idle again, has come the closest I have ever been to resolving the problem. The car runs great on the freeway and around town. I still get a little black smoke (and not always) gaining speed from a dead stop but I can live with that.


Thanks again to all who offered their thoughts and recommendations. I appreciate it greatly!

Randy C.

 

To be honest, your problem is probably still there. The adjustments you made have nothing to do with how the car runs on the hwy.