Thread: 2.25 petrol - poor running with Zenith

Thanks once more for the input guys. I really appreciate it.

Firstly, the good news - I was able to spot the "EP" mark with the endoscope, so I set up a dial indicator on exhaust valve #1 to check valve timing. It's not quite dead on, but it's close - right as the EP mark goes past, the exhaust valve drops a tiny bit more (about 10 thousandths of an inch) and then starts coming back up. In my mind, this is enough for the engine to run properly - any confirmation/denial here would be great.

The capacitor (or condenser, whichever you choose to call it) had the right amount of capacitance according to my multimeter, although I didn't test leakage resistance - not sure how to do that, advice here is also welcome. I decided to convert it to electronic ignition at some later date after it's running, since the amount of rewiring needed for a positive earth system was higher than I'd expected. It seems better to change just one thing at a time.

My coil looks OK (3.7 Ohms across the SW and CB terminals), which makes sense since I've previously had that coil running fine (and the spark looked good with the plug out). A general question here, though - how old is too old? I don't know if it's the original coil from 1959, but it's definitely period-correct, and almost certainly over thirty years old. How long do those old-school oil-filled Lucas units last?

The bad news is that I'm really starting to suspect a vacuum leak after ruling out the above. Instead of a smoke machine I'm just going to apply ~3psi of air pressure and start spraying with soapy water - I've got an air regulator coming in the post, I'll be ready to go as soon as it arrives.

Thanks to everyone who's suggested things, and keep the ideas coming :-)

- Will

Originally Posted by WhatIsClocks

Thanks once more for the input guys. I really appreciate it.

Firstly, the good news - I was able to spot the "EP" mark with the endoscope, so I set up a dial indicator on exhaust valve #1 to check valve timing. It's not quite dead on, but it's close - right as the EP mark goes past, the exhaust valve drops a tiny bit more (about 10 thousandths of an inch) and then starts coming back up. In my mind, this is enough for the engine to run properly - any confirmation/denial here would be great.

The capacitor (or condenser, whichever you choose to call it) had the right amount of capacitance according to my multimeter, although I didn't test leakage resistance - not sure how to do that, advice here is also welcome. I decided to convert it to electronic ignition at some later date after it's running, since the amount of rewiring needed for a positive earth system was higher than I'd expected. It seems better to change just one thing at a time.

My coil looks OK (3.7 Ohms across the SW and CB terminals), which makes sense since I've previously had that coil running fine (and the spark looked good with the plug out). A general question here, though - how old is too old? I don't know if it's the original coil from 1959, but it's definitely period-correct, and almost certainly over thirty years old. How long do those old-school oil-filled Lucas units last?

The bad news is that I'm really starting to suspect a vacuum leak after ruling out the above. Instead of a smoke machine I'm just going to apply ~3psi of air pressure and start spraying with soapy water - I've got an air regulator coming in the post, I'll be ready to go as soon as it arrives.

Thanks to everyone who's suggested things, and keep the ideas coming :-)

- Will

Seems you are doing this quite comprehensively & trust you can come up with some good answers however, you mentioned in one of your initial posts that "it fails as soon as you give it some herbs" or words to that effect, & the first thing that entered my head was "Fuel Starvation" & the fact at that point you didn't know if the Carby Float level was even correct. I don't see any mention of it.


How thoroughly has this been explored? I may be totally out of place here & my depth, but if it was mine I would be checking this aspect further, after all it is only a stock standard Rover 21/4 donk which usually has a fair bit of operating tolerance & I would doubt that there are too many Donks that are set up finely by the Manual.. Maybe you are looking for things that may not even exist? I would also delay fitting the Electronics until you get this sorted once & for all. I could just about guarantee that my '66 2A would not come anywhere near the tolerances you are seeking but she starts & runs extremely well.

So I toss this into the mix (possibly just to confuse matters) but it was my initial reaction based on my own experiences & which doesn't appear to have been mentioned..

Regardless, I wish you well with you investigative Tests.

EDIT. Just rechecked the posts & Post #3 by Gippslander really touched on the above, but my water is telling me more actual detail is needed.

Originally Posted by 4bee

Seems you are doing this quite comprehensively & trust you can come up with some good answers however, you mentioned in one of your initial posts that "it fails as soon as you give it some herbs" or words to that effect, & the first thing that entered my head was "Fuel Starvation" & the fact at that point you didn't know if the Carby Float level was even correct. I don't see any mention of it.


How thoroughly has this been explored?

Sorry, I might've neglected to mention it in a previous post - that was one of the things Roger and I went through. The float height was a tiny bit off, but only 2mm out from the 33mm (from memory) that it was meant to be. We tweaked it back anyway, and it tested fine (blocked air flow and held a vacuum). Unfortunately that didn't make a difference to how it was running.

Originally Posted by WhatIsClocks

Sorry, I might've neglected to mention it in a previous post - that was one of the things Roger and I went through. The float height was a tiny bit off, but only 2mm out from the 33mm (from memory) that it was meant to be. We tweaked it back anyway, and it tested fine (blocked air flow and held a vacuum). Unfortunately that didn't make a difference to how it was running.

No dramas WIC, but it was worth a mention recalling the problem I had when I first got her which threw me a curved ball back then.


Hope you find a remedy very soon as these things can take the gloss of a new pet.

G'day Will,

You are making good progress and note waiting for parts. Good that you found the EP. As I expected the EP is retarded by a few degrees and is not causing your poor running. Only loss of torque. The effect is, the opposite happens on the Inlet Peak. That is advanced and so less fuel mixture enters the engine. Valve timing is still critical and I set the valve clearance using a dial gauge noting that I had the rocker tips ground to remove the wear so the feeler gauge is actually measuring the gap.(Keep an eye on the EP over time because it is an indicator of timing component/chain wear.)

To measure the leakage of a capacitor you need to use a megger that applies voltage at working voltage of cap. A quick check is using meg-ohm range on your multimeter and see if any resistance. (Your Capacitor looks OK if resistance is infinity.)

Coil resistance for a 12 volt coil without needing a ballast resistor is 3.8 to 4 ohms. The secondary winding (7 to 8Kohm)usually goes open circuit over time. I would check the polarity is correct. Your vehicle is positive earth so the + terminal goes to the contact breaker.

I agree that there is probably a vacuum leak somewhere apart from the vacuum advance. The gasket on the inlet/exhaust manifold would be suspect. Over time the exhaust manifold flanges distort and crack the gasket and don't seal properly and the hot spot flapper seizes up. (A series 3 manifold flows better and has a permanent hot spot.) I would firstly check the manifold nuts and the 2 bolts under the inlet manifold are tight and see how it goes. A vacuum gauge would show an inlet manifold leak straight away.

I agree don't change more than one thing at a time. Good decision not to fit the electronic ignition as you cannot static time it. Timing has to be done dynamically and need a timing light and degree wheel setup to do it properly. (I fitted a MSD 6T ignition system
to my engine and use points to trigger because static timing can still be set to get it running then time the ignition.)

Once the ignition is setup and distributor advances working and static timing set any poor running is pointing to carburetor and/or a vacuum leak on inlet manifold.

You're getting close to fixing the poor running. Let us know how you go.

Chris

Originally Posted by Busted Syncro

To measure the leakage of a capacitor you need to use a megger that applies voltage at working voltage of cap. A quick check is using meg-ohm range on your multimeter and see if any resistance. (Your Capacitor looks OK if resistance is infinity.)

Coil resistance for a 12 volt coil without needing a ballast resistor is 3.8 to 4 ohms. The secondary winding (7 to 8Kohm)usually goes open circuit over time. I would check the polarity is correct. Your vehicle is positive earth so the + terminal goes to the contact breaker.

Thanks for the tips Chris. I went and measured it again, the capacitor looks healthy with the tests you mentioned - I have a 12V power supply I put across it, and it sat at zero amps after the initial spike.

Regarding coil polarity, my terminals are labelled "SW" and "CB", so it's pretty clear which way around it needs to be. I double-checked anyway and "SW" definitely goes to the ignition switch, and "CB" definitely went to the distributor (before I removed it).

Coil polarity will make an undetectable difference in running. In theory at least, it affect plug life.

Quick update on this: Supercrap Auto managed to mess up the air regulator order so badly that, after a week of enquiries, they called me to say they don't have it at all and can't source one. I've bought a similar-looking model off ebay, which I should probably have done in the first place. All this for a $40 air regulator! (I'm aware my local paint shop probably has one, but I wanted digital on the theory that it'd be more accurate at the ~3psi I'll be working at).

Anyway, I got the replacement vacuum unit this week and installed it. I inspected the centrifugal advance while I was at it. The centrifugal advance seems fine, they swing out when I hold the rotor arm still but wind the input shaft backwards. They don't retract 100% of the way just under their own springiness, but if I apply any sort of friction to the rotor arm while turning the input, they retract. Can anyone confirm that this is reasonable?

The other issue I'm chasing is that one of the screws (holding the plate with the capacitor and points to the distributor body) had the head stripped off it, thankfully the thread is fine. I'm aiming to get a replacement, it seems to be some sort of BA? If anyone here knows, please give me a yell. (Otherwise if I can't match the thread, I'll just put a straight cut in the head of the existing screw. Not the end of the world.)