Rough idle and fan wobble

Afternoon everyone,

I’ve become frustrated and am asking for some guidance and help.

Specs: 1974 with stock 302 and 3 speed.

Bronco was running super rough and hard to keep running. I rebuilt the carb found lots of debris in filter that attaches to carb.
Now it runs but seems like it’s only firing on 5 or 6 cylinders. Sounds like it’s missing bad.
Dizzy cap doesn’t look cracked or corroded.

Also when running, I was looking at fan and it seems to be wobbling while engine is running. Not sure if optical illusion or if the fan and attachment to engine is out of whack.

On the issue of the rough idle, what should I look at next? Coil? Wires? New dizzy?
Should fan even appear to wobble?

We have three Broncos and keeping them up and running sometimes gets frustrating but I love them.

Thanks for any help you can give me.

Josh

On the fan wobble, some fans use blades (sometimes just a single one) that is out of phase with the others. This reduces noise and harmonic disturbances that can cause wobbles at higher rpms/loads.

But if you have a real wobble of a bent fan, you should check and verify that it's not causing at least some of your roughness.

With gunky fuel, you could still be dealing with the same issue. Carburetors are finicky buggers!

Paul

Fan wobble can also be waterpump bearings that are sloppy.

Just because you rebuilt the carburetor doesn't mean it is right. It is easy to miss an air bleed or something and it still isn't right. Even if it was clean, a bit of crud from somewhere else could have moved in. It is hard to get it all out.

Could have fouled a plug running with a messed up carb. Easy to do.
Old plug wires can be damaged by removing them and putting them back on. Literally a touch it and it breaks part.
Have you done a compression test, you might have finally lost compression on a cylinder.
Vacuum leak, done wrong it can lean out just a couple of cylinders at idle.

I would try to narrow it down a bit before you change anything else and lose your way. Fancy name is cylinder balance test but take one spark plug wire off at a time while the engine is running and observe the drop in rpm. Put wire back on and go to the next one. See what this tells you.

If each cylinder has about the same drop in rpm then you have a carb that is probably set up wrong or your distributor is not timed correctly.

If one or two cylinders do not make an rpm drop you found your culprit(s). Change the plug and wire to a "good" cylinder to see if the problem moves with it. If so the parts are bad. If not dig deeper into that cylinder - check valve adjustment, is there a big vacuum port on a shared runner that is leaking, leaking intake gasket, etc. Let us know what you find.

Broncobowsher said:

Fan wobble can also be waterpump bearings that are sloppy.


Could have fouled a plug running with a messed up carb. Easy to do.
Old plug wires can be damaged by removing them and putting them back on. Literally a touch it and it breaks part.
Have you done a compression test, you might have finally lost compression on a cylinder.
Vacuum leak, done wrong it can lean out just a couple of cylinders at idle.

Click to expand...

Compression test is next on the list.

pcf_mark said:

I would try to narrow it down a bit before you change anything else and lose your way. Fancy name is cylinder balance test but take one spark plug wire off at a time while the engine is running and observe the drop in rpm. Put wire back on and go to the next one. See what this tells you.

If each cylinder has about the same drop in rpm then you have a carb that is probably set up wrong or your distributor is not timed correctly.

If one or two cylinders do not make an rpm drop you found your culprit(s). Change the plug and wire to a "good" cylinder to see if the problem moves with it. If so the parts are bad. If not dig deeper into that cylinder - check valve adjustment, is there a big vacuum port on a shared runner that is leaking, leaking intake gasket, etc. Let us know what you find.

Click to expand...

Will do.
I appreciate the advice. I will look at those items mentioned and report back.

I doubt the symptoms are related.
Pull the belts off and try wiggling the fan. If there is any movement at all, the water pump bearings are shot.