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Discussion Starter #1
Hi guys
My 1977 SWII LRF32027, failed smog check due to high Nox.
I found out the following after extensive troubleshooting:

The engine idles very smoothly. But, whenever I pull the following plug wires individually, A2, A3, B1 and B4, while the engine is running the engine continues to idle without stumbling whatsoever, not even a tiny bit, none, zip, nay.

If I remove the plug wire for either B2, B3, A1 and A4 individually while the engine is idling, there’s an obvious stumble or rough idle.

I’ve swapped out the plugs and wires from the “good” cylinders with the “bad” cylinders and same results as explained above.

I even removed a plug from one of the “bad” cylinders and connected the plug wire to it and started the engine. The plug fired with a healthy, bright spark.

The plugs from the “bad” cylinders are as dry as the Sahara Desert.

I also did a compression check. The “good” and “bad” cylinder readings were 130 psi.

The car normally sits for up to six months between drives.

It has a fresh tank of gas

The car idles and also accelerates smartly on the highway as if it’s running on all 8 cylinders. As I mentioned above, the engine idles very smoothly

Considering the plug wires are new and that the plugs are also good as evidenced by them firing when removed from the cylinders, it appears no fuel is getting to the aforementioned “bad” cylinders above.

My question is this: what anomaly would cause the carburetors to port petrol to only some cylinders and not others?

Since 4 of the 8 cylinders are not producing energy by a lack of rough idle or stumble when their plug wires are removed, how come the engine idles and accelerates so smoothly and smartly??

It’s like the car has a V-4 engine but idles and runs like an 8 cylinder engine.

I would greatly appreciate any help from the forum.

Patrick
 

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It's interesting that the two groups of cylinders you give are serviced by each carb i.e. A2, A3, B1 B4, by the B carb and B2, B3, A1 A4 by the A carb.

In answer to your question "what anomaly would cause the carburetors to port petrol to only some cylinders and not others? " I would say the carbs need balancing.

Geoff
 

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Discussion Starter #4
It's interesting that the two groups of cylinders you give are serviced by each carb i.e. A2, A3, B1 B4, by the B carb and B2, B3, A1 A4 by the A carb.

In answer to your question "what anomaly would cause the carburetors to port petrol to only some cylinders and not others? " I would say the carbs need balancing.

Geoff
Geoff

I just thoroughly analyzed your response. Looks like the B carb has an issue, since those are the “dead” cylinders.
Thanks for your input
 

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I have had a similar problem. What had happened with the HIF7 carburettor was the jet tube had moved up towards the piston. It had come loose from the plastic suction nozzle in the bottom of the carb. A quick way to check that is to remove piston dampers then the suction chambers and then lift out the pistons, keeping the parts for each carb on the carb they came from. Looking into the tops of the carburettors the jet tubes, centre where the needle fits, see if the level of the tubes is the same on both carbs.
The other thing to check is that the pistons are nice and free to move in there chambers, especially the B bank carb,
These carburettors are very simple and rarely give any trouble but if you have to dismantle it, put a new float lid seal in and make sure the float lid is in the correct position before tightening screws.
Personally, I doubt if the carburettors have gone out of balance that much.

Jake.
 

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Hi guys
My 1977 SWII LRF32027, failed smog check due to high Nox.
I found out the following after extensive troubleshooting:

The engine idles very smoothly. But, whenever I pull the following plug wires individually, A2, A3, B1 and B4, while the engine is running the engine continues to idle without stumbling whatsoever, not even a tiny bit, none, zip, nay.

If I remove the plug wire for either B2, B3, A1 and A4 individually while the engine is idling, there’s an obvious stumble or rough idle.

I’ve swapped out the plugs and wires from the “good” cylinders with the “bad” cylinders and same results as explained above.

I even removed a plug from one of the “bad” cylinders and connected the plug wire to it and started the engine. The plug fired with a healthy, bright spark.

The plugs from the “bad” cylinders are as dry as the Sahara Desert.

I also did a compression check. The “good” and “bad” cylinder readings were 130 psi.

The car normally sits for up to six months between drives.

It has a fresh tank of gas

The car idles and also accelerates smartly on the highway as if it’s running on all 8 cylinders. As I mentioned above, the engine idles very smoothly

Considering the plug wires are new and that the plugs are also good as evidenced by them firing when removed from the cylinders, it appears no fuel is getting to the aforementioned “bad” cylinders above.

My question is this: what anomaly would cause the carburetors to port petrol to only some cylinders and not others?

Since 4 of the 8 cylinders are not producing energy by a lack of rough idle or stumble when their plug wires are removed, how come the engine idles and accelerates so smoothly and smartly??

It’s like the car has a V-4 engine but idles and runs like an 8 cylinder engine.

I would greatly appreciate any help from the forum.

Patrick
Looks like one carb is not delivering fuel. Each carb has a separate small filter in a cylindrical housing where the fuel line enters the float chamber. Remove the 2 screws from the top of each filter housing and pop off the lids, it's spring loaded inside so use a cloth to catch anything that might pop out. I normally insert a small bolt into the centre of the filter housing lid to get a grip when lifting it off, one of the bolts from the air intake scuttle should fit. Clean out the filter housing with some carb cleaner and blow it with an air gun, replace the filters and hopefully you will be good to go. If the filters are dirty the chances are that the main filter underneath the car also needs to be replaced. If you have electronic ignition it might not be a good idea to test for spark with a plug wire or plug removed as I believe this can damage the ignition module.
 

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There is no damage to the module when testing for a spark due to the nature of the design. The module simply interprets the on-off signal from the hall-effect sensor and triggers the coil. No harm.
 

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Discussion Starter #8
I have had a similar problem. What had happened with the HIF7 carburettor was the jet tube had moved up towards the piston. It had come loose from the plastic suction nozzle in the bottom of the carb. A quick way to check that is to remove piston dampers then the suction chambers and then lift out the pistons, keeping the parts for each carb on the carb they came from. Looking into the tops of the carburettors the jet tubes, centre where the needle fits, see if the level of the tubes is the same on both carbs.
The other thing to check is that the pistons are nice and free to move in there chambers, especially the B bank carb,
These carburettors are very simple and rarely give any trouble but if you have to dismantle it, put a new float lid seal in and make sure the float lid is in the correct position before tightening screws.
Personally, I doubt if the carburettors have gone out of balance that much.

Jake.
Thanks, Jake
I will do as you suggest and report back to the forum.
Patrick
 

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Discussion Starter #9
Looks like one carb is not delivering fuel. Each carb has a separate small filter in a cylindrical housing where the fuel line enters the float chamber. Remove the 2 screws from the top of each filter housing and pop off the lids, it's spring loaded inside so use a cloth to catch anything that might pop out. I normally insert a small bolt into the centre of the filter housing lid to get a grip when lifting it off, one of the bolts from the air intake scuttle should fit. Clean out the filter housing with some carb cleaner and blow it with an air gun, replace the filters and hopefully you will be good to go. If the filters are dirty the chances are that the main filter underneath the car also needs to be replaced. If you have electronic ignition it might not be a good idea to test for spark with a plug wire or plug removed as I believe this can damage the ignition module.
Thanks for your suggestions. I know where both filters are. I will definitely check them first since that’s fairly simple to do before I go about removing the carbs.

Patrick
 

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It's not going to be the filters, if the filters were clogged and causing fuel starvation it would not be evident at idle but at higher revs. You most likely have a vacuum leak that is affecting the carb associated with the misfiring cylinders.
 

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I agree with Jim, most likely would be vacuum. I would chech every hose coming off the intake manifold for cracks and poor fit.
 

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It's not going to be the filters, if the filters were clogged and causing fuel starvation it would not be evident at idle but at higher revs. You most likely have a vacuum leak that is affecting the carb associated with the misfiring cylinders.
Yep, Jim makes a good obervation and if there's a vacuum leak the spark plugs affected would likely be grey/white in appearance as a result of lean burning. However, in my experience a vacuum leak usually causes erratic running for a while when the engine is started from cold, the revs tend to automatically rise and fall and some misfiring is usually evident, the performance then gradually stabilizes as the engine warms up.
 
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