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I am having trouble with my truck. It has been getting significantly more terrible gas mileage than usual. I just went to the store and back and used half a tank. The truck also has black wet specks coming out of the tailpipe. The truck also had a hard time starting and did not have power on the upper end. I have recently rebuilt the carburetor and so this was my starting point. I checked and rechecked the float adjustment and it is correct. I also have referenced my Haynes manual with not a whole lot of luck.
I do know that when it starts to get cold like it is now here in NC there must be some proper carb and choke adjustments. I have the stock 2bbl Motor craft 2150 carb and the stock automatic thermostatic choke. The heat riser tube had been broken off so I installed a new one and it seems to do better on startup. The down shift bar and choke vacuum piston to the transmission were also disconnected so I properly reconnected those things.
I believe that my carb and choke are out of adjustment and I am not sure how to fix it for this issue? Or does this sound like something else is going on? The Haynes manual says for proper choke placement reference the VECRI sticker in the engine bay...which is conveniently still not in place. Also I have just learned that there is a fast idle screw and am not sure how to adjust that properly either?
As for the carb I have read that the fuel and air mixture screws should be at about 1.5 turns out of the carb, can anyone check the validity of this?
Get the Shop manual for your truck. There is a bunch of things to look at in a 50 year old truck. Everything from sticky brakes to underinflated tires... I don't know how away far your store is but...
1.5 turns on carb mixture needles is just a ballpark baseline setting to get it to start and idle, it will need to be dialed in. Carb tuning and engine timing makes a huge difference.
Start with a compression check, check plugs, learn jetting, distributor curving, and carb adjustment. Very rewarding but you'll have to do your homework as it's pretty involved. Get the manual!
Practically guaranteed, given how you describe the symptoms. The plugs condition are the windows inside to the overall engine health, and tune.
You'll have to be methodical and thorough to get a handle on this if you want to solve it. You'll see how one problem affects something else, and that in turn, affects two or three other things down the line. All of the carburetor gurus I read emphasize on the importance of making sure the ignition and engine timing is squared away before adjusting or condemning a carburetor. "90% of carb problems are ignition related" they say. And they're right.
Modern computer controlled cars are built around this observation, they monitor and even count the number of times a plug misfires, monitor the exhaust gas O2 level, engine timing, air flow, everything. Emissions requirement were part of it, the recognition that a proper tuned and adjusted engine makes the most power and produces the least pollution with the best fuel economy.
2100 and 2150 are some of the best carburetors made, all the documents and manuals are available for download online, and lots of websites go over them. Study them, and the general carb setup guidelines and you'll get it figured out. It's important to maximize the state of tune if for no other reason to prevent fuel from diluting the oil and fouling plugs. It will wash out piston rings and build up sludge and piston scuffing.
Yesterday I adjusted the choke accordingly I believe I was running too rich. I pulled and checked all the plugs and they were all fouled. They are new plugs only about 6 months old. I cleaned them well and regapped them. I drove to the store and back and noticed a little improvement but not much. (still in the 4mpg range.) I removed the plugs today and checked them again to see if they were still clean. They looked just as bad as when I cleaned them yesterday! It appears that there is massive and quick amounts of carbon build up which makes me think that the mixture is still running too rich. I am thinking next step from here is more research, check timing, and maybe check fuel and air mixture screws on backside of carb. I have posted pictures below of the plugs after I cleaned them, drove, and removed again. Any and all advice is helpful! Thank you
Did your carb still have the tag on it by chance so you know what carb your actually working on? Sounds to me like the choke pull off is not adjusted or working correctly. That is where I would at least start. How did it run before you did the carb work? Was the running rich the reason you did the carb work? Another area where they can get lots of fuel is the power valve if the gasket is leaking or the diaphragm is leaking.
I agree, the idle mixture screws are important but there's somethings else(s) going on. I knew the plugs would look bad, they have to. This needs fixed or the carbon and sludge will score pistons, rings start to stick etc.
How old is the fuel pump? It's crucial that the pump provides proper pressure, and volume, at all times, under all conditions. New manufacture pumps on the other hand, are notorious for excessive pressure. About 5 psi is plenty. The tank and lines have to be clear. The needle and seat have to shut off supply when float rises. These things have to be done in order, starting at the fuel tank itself.
The next area to focus on is the float height and consequently the fuel level in the bowl. They are not the same thing. The "dry float" height set on the bench is just a ballpark setting. It is wise to check the actual fuel height in the bowl after it has idled for a few minutes. On the 2100 series it is very easy, just four screws and the air horn can be removed. A US quarter can be used for this, though some trucks have different fuel heights. Adjust the float height wherever it needs to be to end up at the right fuel height, that's what counts. Fuel height in the bowl affects idle mixture settings and even jetting to some degree.
Once the fuel delivery and carburetor bowl fuel height is verified to be within specification, ignition (wires, cap, rotor etc) squared away, and ignition timing set correctly, THEN the carb can be tuned accurately.
A vacuum gauge is SUPER useful here, they are a great aid to verifying proper ignition timing, diagnosing vacuum leaks, valve adjustments, determining power valve (economiser) selection, and setting idle mixture. If you want to maximize engine tune and power as well as mileage, the gauge is practically essential. A wideband O2 sensor is even better, still need a gauge tho.
The hot setup is to install a long hose to monitor engine vacuum in the cabin at steady highway cruise speeds. A power valve number selected at about 2" below the minimum vacuum at cruise is optimum. Elevation also determines or factors into the power valve selection. Denver or Leadville trucks can't use stock value power valves. A quick way to determine if the power valve itself is bad, turn the idle mixture screws all the way in. The engine should stall. If not, the power valve should be replaced.
Sounds like mine when I forgot to reattach a plug wire after some maintenance. Pull 1 wire at a time while it's running (carefully) and listen for the healthy snap-snap-snap of the spark as it arcs. No snap = no fire = wet fuel in the cylinder = all kinds of nastiness.
Though for the plugs to foul like that, I'm surprised it's running at all, and it's got to be bucking like a sonuvagun...
12-17-2016, 01:09 PM
