2.8 bogs and won't go over 58 MPH

[Jim Oaks]

I rebuilt the carb on the 2.8L in my girlfriend's son's 1984 Bronco II and had the thing running pretty good.

Now it starts hard and occasionally backfires through the carb when starting, stalls when coming to a stop, and bogs down and doesn't want to go over 58 MPH.

I re-set the idle mixture screws and adjusted the fast idle screw so it doesn't stall when I stop, but it still bogs down while I'm driving it. It doesn't drop off when I give it gas, it just doesn't seem to have any power like something is holding it back. It does run a little better if I let off the gas a little.

Someone swapped a Duraspark ignition on this thing before we got it.

Any suggestions?

 

[alwaysFlOoReD]

Timing?

 

[Jim Oaks]

Thought about that. Having trouble getting to the bolt to loosen the distributor. There isn't much room back there.

I forgot to add that I noticed the vacuum line from the distributor run to the vacuum-T on the back of the manifold, not the carb.

 

[rusty ol ranger]

Thought about that. Having trouble getting to the bolt to loosen the distributor. There isn't much room back there.

I forgot to add that I noticed the vacuum line from the distributor run to the vacuum-T on the back of the manifold, not the carb.

The vacuum advance normally runs to the manifold.

If its backfiring out the carb that sounds like timing to me. Unless its more of a cough then a backfire, if thats the case that generally means its starving for fuel.

 

[AndyB.]

How did it run before you fixed it?

 

[Jim Oaks]

May

The vacuum advance normally runs to the manifold.

If its backfiring out the carb that sounds like timing to me. Unless its more of a cough then a backfire, if thats the case that generally means its starving for fuel.

Be more of a cough and not that often. I thought about timing, but I don't understand how the timing was ok and now it's not. Also considered plugs and wires.

 

[fastpakr]

I'd definitely want to put a light on it and see what the timing is doing.

 

[rusty ol ranger]

May
Be more of a cough and not that often. I thought about timing, but I don't understand how the timing was ok and now it's not. Also considered plugs and wires.

Hows the float level? Any vacuum leaks at the carb base?

 

[alwaysFlOoReD]

Hows the float level? Any vacuum leaks at the carb base?

Yes, a lean condition will poop out the carb.

 

[Jim Oaks]

Finally got around to doing a compression test on this thing. Did it with the engine cold and all of the plugs removed.

Didn't try to figure out exact psi. Just note the closest reading in 5 psi incriments.

Results:

#1. 75
#2. 75
#3. 90
#4. 75
#5. 90
#6. 85

It's been my understanding that a healthy engine should be a minimum of 100 psi on each cylinder.

Haven't tried adding oil to the cylinders and retesting yet.

 

[PetroleumJunkie412]

Finally got around to doing a compression test on this thing. Did it with the engine cold and all of the plugs removed.

Didn't try to figure out exact psi. Just note the closest reading in 5 psi incriments.

Results:

#1. 75
#2. 75
#3. 90
#4. 75
#5. 90
#6. 85

It's been my understanding that a healthy engine should be a minimum of 100 psi on each cylinder.

Haven't tried adding oil to the cylinders and retesting yet.

RIP

 

[AndyB.]

Time for a leak down test to find out if you’re doing rings or valves.

Wide open throttle during compression test, right?

 

[Uncle Gump]

Was cranking speed good...

Did each cylinder get the same revolutions...

You sure you had a good seal on the tester...

Was the throttle blocked wide open...

 

[Jim Oaks]

Ok, used an oil can to squirt some oil in the cylinders. Can't say that they all got the same amount, and I couldn't get any into the #3 cylinder because there wasn't enough space.

Results:

#1. 125 (originally 75)
#2. 100 (originally 75)
#3. No oil - couldn't re-test
#4. 110 (originally 80)
#5. 135 (originally 90)
#6. 115 (originally 85)

 

[Jim Oaks]

Fawk.

Throttle wasn't wide open.

Turned it over 8 revolutions for each test.