No Power and Backfiring

[Kiloengineer]

Hi all, I am still stumped on this problem. I have summarized below, would appreciate any ideas.

Symptoms:
Car starts pretty easily and when warmed up idles very nicely. It can drive downhill ok and can accelerate a little. Going up any kind of a slight incline there is no power whatsoever, and if I keep trying to go uphill it just dies. Sometimes it also backfires. When I check the spark plugs they are black with soot.

What I have done to try to fix the problem:
Compression test – all 125-140psi, a little higher when oil is added
Adjusted tappets
Entirely new ignition system.
New genuine Lucas 45D distributor to replace the old 25D
Replaced condenser in this new distributor 3 times
Thoroughly filed, cleaned and gapped points
New plugs (2 sets), new wires
New coil, and then replaced that one with a known good coil from my Jaguar
Replaced old wiring from fuse box to coil and from coil to distributor
Adjusted ignition timing
Right on 6deg BTDC at idle, advances (mark moves counterclockwise) when idle speed is increased
New vacuum line from carb to distributor
Entirely new fuel system
I rebuilt the Zenith 36IV with a genuine rebuild kit. Flattened all of the housings.
Replaced Zenith with brand new Weber
New fuel line from pump to carb and new filter (the filter does not fill up all the way, only a little less than half)
New fuel pump, inspected the old one which looked fine.
Removed fuel pickup line to check for clogs, all clear
Added 5 gallons of gas to tank to make sure I was not low
Fuel in glass sediment bowl is full and clean
New exhaust manifold (the old one was cracked by the down-pipe attachment)
New intake manifold gaskets and all new attachment hardware
Engine runs 50psi oil pressure
Dynamo output seems fine, lights are bright and the battery does not run down.
Tightened fan belt.

[Whiterabbit]

Back firing is unburnt fuel in the exhaust. Black sooty plugs is an indicator of too much fuel. You are not on the throttle at start up or going down hill but on it going up. Sounds like the idle mixture is ok but the main circuit in the carb is too rich. Dont know these carbs well but know what the symtoms are. An air jet is pluged or something in the main circuit is giving you too much fuel. Too much fuel pressure from an electric pump or fuel level too high will also cause those symtoms.
Brain storming.

[1971Series88]

clogged jets in the carb? - or - Spark Plugs?
looks like you have replaced nearly everything else

[milhouse]

How is the air filter and air hose/tube from the filter to the carb? Too much fuel can also be caused by too little air mixing in. Perhaps something is blocking the air intake or filter?

[Kiloengineer]

I disconnected the air cleaner hose completely to see if the filter was blocked (I recently serviced the air cleaner with oil) - no improvement. Also to whiterabbit's ideas, I get the same symtoms with the rebuilt Zenith and the brand new Weber. I guess it could be that both carbs are set up wrong but it could only really be the float level I would think. Not getting enough air does seem to support the symptoms.

[SafeAirOne]

I've had the flexible air intake hose delamnate on the inside before, causing a flap of cloth on the inside of the hose to block the air passage when I increase the throttle.


Black plumes of diesel smoke and no power...

[albersj51]

Perhaps the carbs have the wrong size jets? Also, did you check/redo your timing after installing the new exhaust manifold?

[Kiloengineer]

Both of the carbs (Zenith and Weber) have new, stock jets so I think that should be ok. And I did check the timing after the new manifolds were installed. I sure like SafeAirOne's idea about the intake hose being blocked, I wish I could check that now but I am stuck at work!

[LR Max]

Both of the carbs (Zenith and Weber) have new, stock jets so I think that should be ok. And I did check the timing after the new manifolds were installed. I sure like SafeAirOne's idea about the intake hose being blocked, I wish I could check that now but I am stuck at work!

I don't buy that. I bought a brand new weber 1 barrel from a rover parts place (forgot where, bought it eons ago) and it came with a #175 jet. I needed a #150.

If you were close by, I would lend you my colortune, then you would know EXACTLY what is going on inside the engine under different loads.

But yeah, I'm willing to bet a very good sammich from the sammich shop up the road from the office that you have too big of a jet inside that weber.

[Kiloengineer]

I will take the Weber apart and find the jet size.

I have not heard of a colortune, I will look that up.

[stomper]

Are you sure you have the plug wires on the dizzy cap correct? I have seen them mixed up, and the truck would idle great, but would backfire and sputter as soon as you press the gas. That was with a 6 cyl. ford ranger, but since you have tried everything else, you might want to check this.

[Jeff Aronson]

Colortunes are helpful mixture determination devices; British sports car companies still carry them.

Reading through your post and the responses, I'm a little skeptical about a carburetion problem. I run a Weber also and there's very little adjustment that would result in a stoppage of the car as you've described.

I do note that you "replaced the coil from one in a Jaguar." The coil serves a critical function in the ignition; the wrong one would let the car start but would not provide the right charge under load. Series Rovers coils do need to be the right one for the car; just because Jag used a Lucas coil, too, does not make them right for a Series Land Rover.

Similarly, your points may be gapped and cleaned properly but they may not be opening properly. I'd certainly install a new set of points, along with changing out the coil, so you know the high tension side of the ignition system is working correctly.

As to the fuel side, when the car stops and, I assume, sputters to the side of the road, what happens when you disconnect the fuel line to the carb? Do you still get a healthy squirt of fuel when you try and start the car? That would let you know if the fuel pump has an issue.

Lastly, and no offense taken, but can you try to run the car without the fuel filter? That way you could eliminate it as a source of the problem.

Keep us informed as to what you find.

Jeff

[Kiloengineer]

Problem fixed! Replaced the new 45D with the old 25D distributor, now runs great. I will have to find out what is wrong in the new one. Certain it was not the condensor. As Jeff suggested it may have been the points. I also think it could be the rotor. Maybe I will try an electronic ignition.

The reason I bought the new distributor was that I was having trouble with running the car but at that time I had issues with the Zenith and the PCV valve. I noticed that my old 25D had some radial play in the shaft so I thought it would be a good idea to replace the entire thing. After I replaced the carb and removed the PCV, solving those problems, I was still left with the dizzy that was faulty.

Lesson learned - change one thing at a time whenever possible.


Thanks very much for the ideas guys! Cheers.
Jason.