Swapped 4.9 engines in my 1986 F-150

Put in a new oil pump, seals, clutch, timing gears .... while the engine was out.

The carb on the new engine had a bunch of wire (step motor, fast idle, throttle position, ...)

So, I took the carb off my old engine (probably mid 70's) rebuilt it and put it on (needed rebuilding ... leaking .... acc pump had several cracks ....).

Put it on tonight ... started! Set the timing ..... went for a test drive ... when you step on the peddle, the truck almost dies!

If you keep the RPM"S up ...runs fine.

Hit the key ... starts right up.

Just dies when you try to accelerate, Need to feather the acc pedal to get it going.

Any idea what I did wrong?

Mike

 

Take the aircleaner off, and with the engine off, climb up in the engine compartment and look down the carb throat with a flashlight while you push the throttle wide open with your hand. If the engine is cold you might have to pull the choke door open. When you push open the throttle you should see a strong stream of gas squirt into the engine. If it has a delay to it, or it's not very strong, your accelerator pump is not working correctly in the carb.

 

I don't remember all you have under the hood. With the last engine, was the truck converted to Duraspark II? Or are your running a feedback system still without a feedback carburetor?

 

The previous owner stripped almost all the electronics and put on an older (guessing 70's carb).

The ignition failed twice on me as soon as I got the truck.

I bought and installed a GM style ignition ... one hot wire to the distributor (coil in the cap) vacuum advance.

Never a problem since.

I am "guessing" I did something wrong in the acceleration pump or maybe the metering rod or ???? when I rebuilt it.

I do remember being perplexed that when I tried to put air (or carb cleaner) into the small hole with the check ball (in the acc pump cover), nothing came out anywhere.

There was a lot of corrosion in the carb ... maybe the channel is clogged?

2"-3" of new snow .. and still falling! I was hopping it will let off after lunch.

I will put the carb (easy to do the this truck) and see what it going on with the pump / metering rod.

Maybe I put a spacer in the wrong place (there was a plastic washer ... didn't show up in parts diagram .. but there was on on my acc pump rod).

Any idea where it would go? I am thinking right above the big (lower) spring retainer.

Thanks ... Mike

 

Check YouTube and see if Mike's carburetor has a rebuild video on your model. I'd be surprised if they didn't.

 

Did that! I was surprised at the great info he put up.

Actually I followed his instructions ... he had a 4 part series.

I even found one late last night that shows how to check if the accelerator pump works and how to set the meter rod. I will this today.

His does not show this little plastic washer and it is not in the instructions that came with my kit.

Thanks .... Mike

 

I have never rebuilt your particular carb, but a very common thing to happen during a rebuild is the check ball or check needle falls out and gets forgotten about. There is usually at least one check somewhere, the accelerator pump is actually a pump and has to have two checks to work, one of your checks may be built into your pump assembly. The other one is usually downstream in the path to the squirters.

 

Here's a diagram of a electronic carter carb. #10 is the check for the pump.

 

OK ... maybe someone can confirm this for me ....

I looked for a "steady stream" of fuel when the throttle is moved ... got a trickle.

Pulled the carb apart .. I can see fuel move in the hole with the check ball and weight when I push the down then let up an the acc pump ... but not a lot.

Pulled the acc pump off.

I watched several videos but did not see a pump housing that looked exactly like this ... I see the check to take fuel in is on the bottom rather then the top.

OK ... that said, I see the drill hole (plugged) above the ball ... but nothing on the inside of the housing!

This says to me that fuel can not enter into the pump.

I am sure some leaked in around the shaft but it would have been slow to fill and if the fuel drops below the housing, it would get none.

Am I right?

Should there be a hole from the pickup check cavity to the top of the pump?

Could it be this carb has been used for 40 or 50 years and not been working correctly?

Mike


Top of housing ... you can see the drilled hole and the plug (from the side). The check ball is right below the large top plug.

Fuel intake hole with check ball on the right ... no hole inside the pump housing!

Discharge holes


The float was high on the carb so I bent it to be a bit lower

 

Is the carb in this video sort of like yours?
I watched him put the accelerator pump assembly together, but I still could not tell exactly how the input check works. I can tell when he mounted it, that the accel pump is submerged in fuel in the fuel bowl. Also you can see him put the accel pump linkage together. Do you have lots of stroke when you move the throttle? The trickle is your problem, just keep trying to figure out what's wrong.

Basically what is going to happen, if the accel pump cavity is empty from just being used, the diaphragm is going to go back down, sucking in fuel from the bowl. But it can't suck fuel if it can suck air from the discharge. So that is why there is a check ball or needle up high near the discharge. You can see in the video he talks about it being either a ball and weight, or in his case he just had a pointed needle. When the diaphragm is sucking in fuel from the bowl, the discharge check will be closed to block air from being sucked in. It fills up with fuel in that chamber and then sits there waiting for the next time you hit the pedal.

When you hit the pedal to open the throttle, the diaphragm is going to start expelling the fuel it has stored. But there has to be another check in the system or it will just push the fuel back into the bowl where it came from. On the 2150 carbs this is the little rubber check right in the accel pump well. On your carb I can't tell how the other check works. But however it works, it shuts when the accel pump is expelling fuel, so that forces the fuel to the discharge. The fuel runs up the discharge passage, pushes the check ball or needle off it's seat, and squirts out of the discharge nozzle.

When you get off the pedal the whole thing starts over again, the discharge will close and this forces fuel by the intake check and fills the accel pump well again.

You will get a really strong continuous stream from the discharge nozzle till you run out of stroke on the pump if it's working correctly. Then your stumble will go away.

 

Well I figured I had nothing to loose ..... in my mind, I came to the conclusion that the pump was not getting fuel.

I punched out the plug and cap.

I was right ... the hole had not been completely drilled through from the fuel inlet check to the upper cavity of the pump.

There was no way of fuel getting in except in the clearance around the pump shaft.

I drilled it through (actually you can see two holes, I drilled the first one at an angel down but the through hold did not go far enough to hit it).

I used a nail for the pin (pushed it in using a vice) ... had an extra ball laying around (.015 smaller but don't think that will matter) ... and reused the top plug.

Just bolted it in ... filled it with mineral spirits ... PUMPS GREAT!

Nice strong steady stream.

Wow ... a 45 year old defect!

I will bolt the carb on in the a.m. and see what happens ....

Thanks ... Mike

 

Found a video from Mikes Carburetor showing my exact pump body. At 1:37 in the video he shows how the check goes through to the inside of the body to fill the pump.

My hole was never drilled through !!!!!!!!!!!!

A 45 year old defect!

Amazing the truck ran all these years.


I am putting the carb now and see how it works.

Mike

 

Nice find, but your discovery has me scratching my head. Whatever vehicle had this carb would have barely been able to accelerate. It would have run like that from day one off the assembly line. It's hard to imagine anybody would have thought that was acceptable.

But I guess anything is possible. I have a 1948 Jeep, and back then a throttle restrictor was installed at the factory. It was just a plate below the carb, designed to limit power during the break-in period. After several hundred miles, the dealer was supposed to remove it. I know several instances of guys finding the restrictor still installed, 70+ years later.

 

My best guess is that with the float level high, there would be enough clearance around the shaft that gas would be drawn under vacuum (plunger going down) through that crack into the pump.

I may have never noticed it but the float was set very high plus the spring was missing from the float (small pin that goes into the bottom of the needle with a spring between them0.

By fixing this I probably "made" the problem appear.

Any who knows where this carb came from ... may have been sitting on a shelf for years (my truck was owned at one to by a auto repair shop and used to plow their yard), taken off a car just for that reason ... because it would not accelerate right.

Interesting about the restrictor .... could not figure out why my RV was not cooling from the A/C ... found one of the pipes plugged ... gasket had not been punched out so it was solid in the duct.

Just put the carb back together ... running outside (in the snow, almost a blizzard here) to put it on and try it.

Mike