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Discussion Starter · #1 ·
Hey All,
I'm stumped. My car is running on 4 cylinders but very intermittently it would run on all 8 for a second or two. I pulled spark plug wires front the distributor one by one to see which cylinder is firing and who's not and replaced 4 spark plugs. The plugs that were not firing is b1 b3 a1 a4 There is spark at the distributor when I hold the wire close but seems not to make it to the spark plug. I ran the engine in the dark and saw not arcing. It's got the original electronic ignition system, rotor and cap @ 75K miles.
Thnx in advance,
Phillip
 

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Are you positive about the specific cylinders not firing?

A-Bank carb supplies cylinders A1, A4, B2, & B3 [1, 4, 6, 7]. B-Bank Carb supplies cylinders A2, A3, B1, & B4 [2.3.5.8]
(Obtained from post Misfire silver shadow2)

Unless that post has an error, and I can't find the reference I thought was in Chapter U about which carb feeds which cylinders, it would appear you might have a carb that's not supplying fuel. But you've got an "odd cylinder out" with B1 if that were the case. I would have suspected B2 based on the above.
 

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I have since confirmed on the Australian Forums (and a thanks to @Wraithman for his post, there) that the above reference about which carb feeds which cylinders is correct. I also updated my firing diagram to include this information.

Font Circle Diagram Line art Pattern
 
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I suspect your spark plug leads are in need of replacement, test them with a multimeter on the K (1000) ohms scale. You should read between 10K and 20K ohms per foot of lead. For instance on a 2 foot lead you should see 20K to 40K ohms. If not within those values they could be the issue and should be renewed. I have also seen this behavior from a weak coil, although it could be a failing Opus ignition module too. If it turns out you have mistaken the cylinders that are not firing, it is likely a fault with one of the carbs or a large vacuum leak influencing one carb's intake tract. I suspect though failed plug leads or a failing coil, especially if the cylinders cut in and out like you have observed. The coil could be marginal in its ability to create a secondary spark, it will not be able to produce enough energy to keep firing all 8 cylinders so it will fire intermittently when it can and will be worse the more load is put upon it.
 

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My money is on a bad Opus ignition module mainly because the problem is intermittent and on more than one cylinder and I have seen this more than once. It has a basic oil filled coil so do a resistance test on that. I don't like to replace parts unless I know they are bad, but an original Opus module is overdue for failure IMO.

It sounds like you have narrowed down the cylinders but to get a "visual" connect an old style timing light to each of plug wires close to the distributor cap. Test one at a time and watch for inconsistent or no flashes from the light to locate the fault cylinders. Do this at varied rpms idle, 1500 and 2000 ranges. Some call this method the "poor man's scope". If its not right, this will confirm ignition problems and not fuel. These two systems when they fail often have similar symptoms.
 

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I bought an S2 from an auction, it ran very badly on the way home , I thought I had been sold a lemon.
Turns out some clown had jumbled just two HTwires on the dizzy to nobble the car for auction
It took me a day to work that one out , relieved but angry at the same time
I eventually found the culprit, a respectable restorer who had done work for a client who wanted to get rid of the car
Nobble it at auction to get it back cheap at the clients expense.
I guess they didn’t expect me to outbid them !
 

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Discussion Starter · #8 ·
Okay.. I've installed a pertronix ignition module, new coil, smoke tested for vac leaks(were none) started her up.. still running on 4 cylinders. Pulled the carbs cleaned em up nice, replaces the 2 small fuel filters and both float needle valves and seats. I'm getting fuel to the carbs but does not seem to be filling the bowls. Car will start and run on all 8 cylinders with starting fluid. I'm stumped
 

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Well, it comes down to lack of air, spark, or fuel, and you've effectively eliminated the first two.

Double check the non-firing cylinders and they are almost certain to be the set fed by one of the two carbs, which means that carb is still a problem.
 

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Discussion Starter · #12 ·
That's what I'm planning on doing tomorrow. I didn't think I'd have to mess with the floats by simply changing out the needle and seat.
 

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Hi Philip - just another couple of things to check:

Are you sure one of the butterfly valves has not come loose on it's spindle and is remaining closed when you press the accelerator.

Have you balanced the carbs.
 

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Discussion Starter · #17 ·
Update. Pulled the carbs to check the floats and sure as can be..They were way out of wack. Now she purrs like a kitten. I had no idea that changing needle and seat would cause the floats to be re-adjusted. Maybe the new ones are shorter or longer?? Anyway, It was a very successful day.
Thank you guys for all the input.. I really needed it.
Cheers,
Phillip
 

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The needle valve fork was set low and allowed fuel to flow over the jet into the engine just with the key on, probably not by much though, but any amount is too much.
Setting the needle valve fork too high should not effect things as all that does is lower the fuel level at the jet, there's plenty of pressure drop at the jet venturi so the fuel vaporizes into the engine if the fuel level is a little lower then normal.


Were the needle valve forks set closer to the float lid or further away, which way did you have to adjust the forks ?
If my theory is correct, you should have had to bend the forks away from the float lid.
This would cause the floats to shut the needle valves off sooner, thus dropping the fuel level at the jets.
 
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