Just rebuilt my 2 barrel motorcraft carb and its still hard to start meaning takes long time for it to finally start. Then it won't idle till it's at operating temp. It revs up nice and smooth however it falls flat on its face with a hesitation then catches on and is fine right after idle. When warm choke is fully open mixture screws are both 1 1/2 turns out. Timing is at 6 BTDC does at times spit back through carb.

Smells a little rich, its on old 1973 360 in my F250 4x4 no valve train noise at all actually sounds really good mechanically. After sitting a day or so big white puff of smoke when it first starts , valve seals. Hard to replace in truck?

Any ideas how to make this run better it drives fair after taking off from start above idle and starts really hard cold or specially if its been sitting a couple days.

Thoughts?
Thanks Tim

 

When you rebuilt the carb, did you get the coil spring on the correct side of the diafram? Remove the air cleaner, and with the engine dead, move the throttle linkage, look inside for two small streams of gas, if none, it will start hard.

 

Several things come to mind. Is the choke system sit up properly? Vacuum break adjusted and working correctly? Does the fuel bowl have fuel in it or is it draining so you have to pump fuel up to the carb and refill it before it will start. Power valve is a very good place to loose the fuel out of the bowl. Was the reason for rebuilding the carb the hard start problem and if so did the carb rebuild change anything?

 

Carb rebuild did not change anything, vacuum break?
I put a new power valve in it.
I will check my float bowl before start up

Is it tough to change valve seal in track?

 

The choke system will have some sort of vacuum diaphram to open the choke to keep it from flooding until the choke gets enough heat to open the thermostate. As I recall that carb had a couple of variations to that system. If the diaphram leaks or if the system is not adjusted correctly it will flood until the choke warms enough to open. Just because it has a new power valve does not mean that it holds gas. I just finished up a Holley 4160. Let it sit for a day and the bowl was dry. Power valve gasket did not seal up. Put another new one in and now it holds fuel. One way to check for leaks is to get four 5/16 by say 3 inch bolts to make a stand to hold the carb up off the bench. Run one nut down on the bolt, insert bolt through carb base and put the other bolt on top. Makes a very nice stand to work on a carb. Fill the fuel bowl and watch under the carb for leaks. Since a rebuild did not change anything you may have other issues. You mention big puff of smoke. What is your compression like in this engine? What condition are the spark plugs in? With the right tools changing the valve seals is not to bad a job. A lot depends on how much room you have. Power brakes and heater boxes have a way of getting in your way.

 

Brand new plugs have not done a compression check but a good idea
So the power valve keeps the gas in the float bowl from running back to the tank?

Need a valve spring compressor and a way to keep valve closed

 

That is not quite correct on the power valve. It is actually a vacuum operated valve that opens to deliver more fuel to the engine depending on the load conditions hince the name power valve. What happens though is if they leak either due to a hole in the diaphram or the gasket leaking they will allow the fuel to drain off into the vacuum chamber of the carb which finds its way into the engine. It will also cause the engine to run rich as the engine now has another source of fuel that is uncontrolled. The symptons can be hard start after sitting a day or so (no fuel in bowl) hard start after a few hours engine still warm (flooded from excess fuel draining into motor) rich running engine due to uncontrolled fuel leak. The holley 4160 that I mentioned had the issue of an idle of 900 rpm. Could not get it any slower. I than discovered a major vacuum leak. Carb base gasket was leaking at the PCV valve. It all made sense at that point as fuel and air both were being added at points they should not have been. When I put the carb on the bench and filled the fuel bowl in about a minute fuel starting dripping out of the vacuum passage that supplied the power valve.

As to your comment about a way to keep the valves closed. Take an old spark plug and screw an air nipple into it. Hook that up to an air compressor and the air pressure will hold the valve in place. I let the piston go to bottom dead center, usually the air will turn the motor over anyway. Just be carefull not to loose air pressure once the keepers are off the valve.

Keep in mind it takes 3 things to make a gas engine run. Good compression, good spark at the right time, and the correct amount of fuel. Any one of those taken out of the picture and you have a no run or poor run engine.