Every few months or so, my 460 will start running real rough. It will barely hold idle, lose about 5 points of vaccum, and the exhaust smells very different. I does not seem to smell rich, but I do not know what the smell is.

When I have the motor above idle, it runs smooth, maybe feels a little anemic on acceleration, but otherwise runs okay. I typically have to pop it into neutral and idle it high at stoplights. It will eventually get to the point of not being able to hold idle, and will backfire out the carb under moderate to heavy acceleration. Typically, after it has backfired out the carb a few times it will clear up and run fine again. The fuel filter is fine. It seems to run this cycle every 4-6 months. Any ideas what I might be looking at?


I'm not sure what the carb is, I think I saw "carter" on it somewhere. It is a 4 bbl, but do not know what make, model number, or anything like that (where would I find that info?)

 

You could have something stuck in your fuel inlet valve in the carb bowl. Might be a good time to rebuild it.

Do you have the Dura Spark ignition?

 

I have a Napa Echlin TP40 module. It does have spacers to allow air in behind it (I see that question often asked).

How hard is a rebuild?

 

Check the distributor advance mechanism to see if it is sticking etc.

 

funny you should mention that, I was wondering about that today. Question is, if it is sticking, what do I use to unstick it? Can I just coat it real good with 3-in-1 oil?

I will check it out tomorrow.

I went ahead and swapped my fuel filter for grins and giggles, have sprayed about a whole can of carb cleaner in the sucker, and it still is not any better. So hopefully I will find something with the vaccum advance, or else I will be getting a crash course in carb. rebuilding

 

If the mech advance is just gummed up it can be cleaned with a little WD or 3-1. If the vac advance is gummed it can be cleaned the same way. If either of the mechanisms are worn badly it will be necessary to replace the distributor. If the vacuum control is leaking or defective the vac unit can be replaced.

Sometimes the wires to the pickup module break but if that is the case it usually does not clear up and then come back.

 

I had the carb on my truck rebuilt and it ran similar to yours afterwards. Turns out the air horn was bent. There was gas leaking out of the carb and onto the intake manifold.

Had to go with a new carb, as the original was too badly mangled to fix.

 

My truck will run rough every now and then. I find that by driving it the problem can go away. I also played around with the floats and the curb idle. The other day, I moved the fuel line further away from the manifold. Basically, it could be one big thing, or a few little things...

 

Well, I had it running a little better, then it got worse, then it died. Found rotted rubber caps for the unused vaccum ports the reason for the stoppage. Good thing for that roll of old electrical tape to fashion a new cap in a pinch :-)

While I was digging around the carb trying to find the problem, I did find the following info:


It is branded as a CArter AFB Competition Series

Then stamped in the base, I believe it was the passenger side front, was S637-A-2635

Can anybody tell me what I got goinf on based on that info?


I have been searching like crazy trying to find a good Carter site, and there is not one, and in digging around the federal-mogul.com website, I could not find any info in their very crappy website.

Any who, I am going to check/replace all the rubber related to the carb tomorrow AM and see if that might help matters


How do I play with the floats? I have been playing with the curb idle, but it is not helping.

 

...I would recommend that before you do anything to that carb, go pick yourself up a vacuum gauge, most auto parts stores carry them and their reasonably priced. It is priceless when it comes to troubleshooting especialy when you think its vacuum related....
Carter afb's are very simple to work on and tune IMHO....but you should have a :
1)vacuum gauge
2)strip kit/ comes with tune suggestions
3)also look for a book called "Carter Carburetors", It covers all the models...rebuilding, tuneing, modifying, identification etc etc.

It just makes things a whole lot easier....

 

I do have a dash mount vaccum guage. When it is running right at idle, I am seeing about 19-20 Hgin. right now I am seeing about 13-18. The needle does not appear to bounce at all until it gets at the lower range, but by then things are running to crappy the whole truck is "bouncing".

I will look for the book.

 

...19-20 should be good, if the needle (no flutter) is steady at 13-18 it really sounds like a vacuum leak (w/o checking my book)

 

Update:
came home and checked my vacuum book, 13-18in could be a gasket or vacuum leak...I assuming that the needle floats between 13-18 with little surges.
Do you have emissions on this rig? didya check that the EGR is functioning?

The full title of the carb book is:
"super tuning and modifying your CARTER CARBURETORS"
by SA Designs.
The book is available from cartech.com
Ive seen it in performance shops around here but not Checker/napa/autozone/pepboys although Im sure they'll order it.
Hope this helps...Chiba

 

If you can pull 19-20" of vacuum at idle that is very good. I would assume your engine is pretty stock. Any problem that causes rough running will lower your vacuum. If it doesn't tick it probably isn't related to a specific cylinder.

sooo, I would suspect the ignition: bad box, sticking advance, frayed wire.

Or something in the carb inlet jet that never passes through, like a tiny piece of hose, Dirt in the bowls or weak fuel pump/clogged filters.