finally tackling the fuel system on the 76 f150 I just picked up. Truck runs good, but appears to be running quite rich. When I pulled the plugs to do a compression test, all 6 were black. I have noticed that if I hit the throttle quickly, it will belch black smoke real quick and then go back to clean exhaust.

I knew the carb needed rebuilt, so I figured this would fix it. Rebuilt the carb last night, installed new needle and seat and adjusted the float to 3/8 from the top of the float to the bottom side of the top of the carb. Tuned with a vacuum gauge and was pleasantly surprised to have 18-19 in of vacuum with a steady needle. Truck still belches black smoke when you smack the throttle.

Gonna double check the metering rod adjustment today, as I didn't have the throttle stop screw backed off when I adjusted it initially.

choke is opening properly as well.

Any advise?

 

Check your idle needle valve screws, not sure what Carb you are referencing but on an Eddy 2 turns out is a good start point

 

Could also be sucking oil past the valve guides.

 

Is your vacuum gauge jumping very quickly or is it steady? If the needle is jumping/vibrating HIO Silver hit it on the head

 

Black smoke is certainly indicative of Excess fuel. If it were burning oil it would be blue in color.

 

When I tested vacuum last night , the Guage was very steady at 18-19 ". I do have what sounds like a noisy lifter. I kinda attributed it to sitting for several years . I pulled the valve cover and checked for excessively loose push rods. All were able to be spun , none seemed excessive .

hopefully it doesn't need a Valve job. I called a local machine shop that I have used in the past and they quoted me $475 .(worst case )

 

When I tested vacuum last night , the Guage was very steady at 18-19 ". I do have what sounds like a noisy lifter. I kinda attributed it to sitting for several years . I pulled the valve cover and checked for excessively loose push rods. All were able to be spun , none seemed excessive .

hopefully it doesn't need a Valve job. I called a local machine shop that I have used in the past and they quoted me $475 .(worst case )

 

You need to be sure you have a filter before the carb. If there's junk in the tank or lines it will just clog up the carb again.

 

Truck has a fuel filter before the pump. I opended up the carb two weeks ago and cleaned it out. Wednesday the accelerator pump ruptured, so I took it apart for a rebuild. still good and clean .

 

Messing with it further , the smoke is blue. a quick rev will net a cloud of blue smoke. With the idle at 650, the Guage is relatively steady , but will drop 2-3 " here and there. I have a definite valve train noise. For the moment I'm going to leave the motor alone and start on the body , In cab electrical , and interior. After the first of the year , I will pull the motor and trans. My favorite machine shop says they will hot tank and inspect it for $40.

I will likely do a full rebuild and paint at that time. Already have a full gasket set and seals for the np-435

 

Clairvoyance....

 

Hopefully your oil burning is a valve stem seal or two or 8 that are compromised..... There are ways to change them without removing the heads.... Although some would suggest to go ahead and take the heads off also and knock out a new head gasket...... ......... Good luck, there are a Ga-jillion posts and threads on the web about both processes...........

 

Stem seals had crossed my mind, only issue I saw with that was that it smokes on throttle even after running for a bit. Ill yank it out sometime after the new year. Goal is to have it semi road worthy by mid march.

 

Revisiting this post one more time. It does appear to be burning a little bit of oil. Was worn out guides common on this engine? I am planning to pull the motor in the next couple weeks to paint the cab. I'll likely pull the head same day and get it to my machine shop. In the mean time though, It definitely does belch black smoke when the throttle is smashed. Enough to leave black soot on the wall in my carport.

I wouldn't think the float being set wrong would cause this, as it should overflow out the top of the carb, Correct??

Should I be trying to adjust the primary metering rod?

 

Seems like have tuned the carb all out so I'd retune the engine after the heads have been rebuilt.

If still belching smoke afterwards, then it might be a matter of piston rings. One way to gauge that is to do a before and after compression test upon putting a lil bit of oil in the cylinders (one at a time) to see if the compression markedly increases.