Ignition timing

[c1800]

Originally Posted by packers1712

JFUR4X AND 0 231 163 021

Doug.

That appears to be the correct distributor for ‘71 1800e. Looks like someone has modified/bodged it, I’m guessing in connection with the conversion to SU’s. I don’t know if an unmodified original ‘71 Distributor would work well with the carbs. Seems to me your best bet would be, as suggested, the 123 replacement so you could dial in the most appropriate specs.

You could contact “Amazon Spares”, Rob Henchoz. He’s very knowledgeable and helpful based on what I’ve read on this forum. I can’t seem to find their website, hopefully someone will chime in with contact info.

[c1800]

That’s Amazon Cars,

https://www.amazoncars.co.uk/page.as...&page=About-Us

[packers1712]

Hi C1800, yes my plan is to fit another (hopefully unmolested) distributor of the exact same type that another forum member has one of and see how it performs and base my next move on the outcome of that test!

Doug.

[142 Guy]

Originally Posted by packers1712

142guy do you have a 123 fitted to your car and would you recommend it being the way forward?

If I was to decide to go down the 123 distributor route should I get a unit for a B20E even thought I’m on DCOE carbs or can I choose the one for the B18/B20 carburettors engine?

Doug.

I do not have a 123 distributor. I replaced my D jet controller with a Megasuirt controller which also does ignition control. I went 'full nuclear' and deleted the distributor and the ignition coil and wires running individual coil on plug ignition. It works just fine; but, I don't advocate for this as a convenient solution. It also definitely no longer looks original.

I would be inclined to not purchase the B20E specific distributor because, as I recall, it costs more. If it comes set up with the vacuum retard function that would probably be undesirable. In particular, the B20E distributor is set up to run with a ported vacuum signal which is different than a straight manifold vacuum signal. You probably cannot get a ported vacuum signal off of your DCOE carbs. The B20B variants could work; but, you need to pick your year because by 1971 the B20B was also using vacuum retard which is probably undesirable. Like the B20E, the later B20B distributor may use a ported vacuum signal (I am not super familiar with the SU carb implementation) which will not work for you. The variants of the 123 Volvo distributor that allow you to customize your timing curve would probably be ideal if you have some ideas about what the curve should look like.

A B18A/B or B20A distributor might work; but, the way Volvo specs the B20A distributor timing (I don't know about the B18) is significantly different that the B20B and E. The advance values are specified at much different RPMs so I can't say whether the B20A mechanical curve is at all close to the B20B or E mechanical curve.

The easy way out is probably to call up Amazon Cars and ask them what they would recommend for your particular non original mix of hardware and then purchase their recommended solution. The up side is that if it doesn't work out, at least you have somebody reputable to complain to.

As an observation. With DCOE carbs you may need to completely forgo any thoughts of using a MAP signal to modify the timing. Given the split manifold arrangement and the nature of the carbs, I expect that the vacuum signal would be erratic at best.

[packers1712]

Good afternoon all,

I've took a short video of the mechanical advance weights as they rest to show some free play in them before the spring is engaged but have been unsuccessful at uploading it due to the file size(even after compressing it).

I can't see any way to get rid of this dead band/play as it seems to be inherent in the assembly and no bending of the spring anchor points or even new springs will get rid of it.

My worry is that this is what is causing the unstable idle timing, as in the marks jumping around whilst attempting to measure the timing with a strobe light.

I have sourced an alternative distributor but haven't fitted it yet so it may not present the same unstable timing mark issue experienced with the original distributor, but it has the same free play?

Another one of my thoughts is that this free play is nothing to worry about and that at engine idle speed the weights are already centrifugally extended effectively irradiating any free play prior to the spring being engaged?

Any thoughts or suggestions greatly welcomed!

Doug.

[packers1712]

https://photos.google.com/photo/AF1Q...xpv6UTBI9IHsuc

Try this link for the video!

Doug.

[142 Guy]

Originally Posted by packers1712

I have sourced an alternative distributor but haven't fitted it yet so it may not present the same unstable timing mark issue experienced with the original distributor, but it has the same free play?

Another one of my thoughts is that this free play is nothing to worry about and that at engine idle speed the weights are already centrifugally extended effectively irradiating any free play prior to the spring being engaged?

Any thoughts or suggestions greatly welcomed!

Doug.

Make sure that the unstable timing is being caused by the distributor advance mechanism and not something else. It would not take too much effort to temporarily lock the mechanical advance in place. Do that, install the distributor and using a static method, set the timing to 10 BTDC. Start up the engine and check timing with your timing light. If it is steady you have confirmed that the timing fluctuation is originating in the advance mechanism. If it is not steady with a locked advance then the problem is elsewhere (timing lights with marginal performance can miss ignition events which give the perception that the timing marks are moving). Your back-up distributor may eliminate the need for this particular test if it eliminates the timing fluctuations.

Assuming that you determine that the advance mechanism is the source of the problem, if the idle speed is stable and the timing marks are moving, that indicates a problem for the following reasons.

• If having a stable idle speed is important to you, a fluctuating advance at idle means that you will never have a stable idle speed because ignition advance has a very big effect on idle speed.
• If the advance is bouncing around at idle that could be an indication that the advance may also be moving at other engine operating points. The engine will generally not detonate at at the idle operating point; but, at different RPMs and mass flow rates the timing fluctuations may initiate detonation. To avoid any risk of detonation you may need to grossly retard base timing which is not consistent with good performance. This would seem to be a a strategy inconsistent with the effort associated with fitting DCOE carbs

"Another one of my thoughts is that this free play is nothing to worry about and that at engine idle speed the weights are already centrifugally extended effectively irradiating any free play prior to the spring being engaged?"

This implies that you are considering allowing the distributor to operate with high mechanical advance at idle. This becomes close to operating with fixed advance over the complete operating range. With fixed advance, if you set the distributor to give you 10 BTDC at idle you are going to have ~10 deg BTDC at 3000 RPM which will result in poor performance. If you set the timing to give you 32-35 deg at 3500 RPM you will have too much advance in the 2000 - 3000 RPM band and may initiate a detonation fest unless you hold off on applying throttle until the engine speed is above 3000 RPM. Running high advance at low RPM will also make the engine very hard to start.

[packers1712]

Originally Posted by 142 Guy

Make sure that the unstable timing is being caused by the distributor advance mechanism and not something else. It would not take too much effort to temporarily lock the mechanical advance in place. Do that, install the distributor and using a static method, set the timing to 10 BTDC. Start up the engine and check timing with your timing light. If it is steady you have confirmed that the timing fluctuation is originating in the advance mechanism. If it is not steady with a locked advance then the problem is elsewhere (timing lights with marginal performance can miss ignition events which give the perception that the timing marks are moving). Your back-up distributor may eliminate the need for this particular test if it eliminates the timing fluctuations.

Assuming that you determine that the advance mechanism is the source of the problem, if the idle speed is stable and the timing marks are moving, that indicates a problem for the following reasons.

• If having a stable idle speed is important to you, a fluctuating advance at idle means that you will never have a stable idle speed because ignition advance has a very big effect on idle speed.
• If the advance is bouncing around at idle that could be an indication that the advance may also be moving at other engine operating points. The engine will generally not detonate at at the idle operating point; but, at different RPMs and mass flow rates the timing fluctuations may initiate detonation. To avoid any risk of detonation you may need to grossly retard base timing which is not consistent with good performance. This would seem to be a a strategy inconsistent with the effort associated with fitting DCOE carbs

"Another one of my thoughts is that this free play is nothing to worry about and that at engine idle speed the weights are already centrifugally extended effectively irradiating any free play prior to the spring being engaged?"

This implies that you are considering allowing the distributor to operate with high mechanical advance at idle. This becomes close to operating with fixed advance over the complete operating range. With fixed advance, if you set the distributor to give you 10 BTDC at idle you are going to have ~10 deg BTDC at 3000 RPM which will result in poor performance. If you set the timing to give you 32-35 deg at 3500 RPM you will have too much advance in the 2000 - 3000 RPM band and may initiate a detonation fest unless you hold off on applying throttle until the engine speed is above 3000 RPM. Running high advance at low RPM will also make the engine very hard to start.

I may have mislead you with my explanation, did you view the video clip, all I'm trying to say is, could the free play prior to the weight engaging the spring be feature of the CA and perhaps its nothing to attempt to try and rectify, I'm not suggesting having a fixed advance my intention is to set the static timing, check it with a strobe light at engine idle speed, go onto check the max advance and adjust the distributor to achieve what I desire then go back and re-check the idle timing setting to confirm it isn't drastically high so as not to induce "difficult to start" symptom.

Doug.

[Rustinmotion]

There is a cheaper option than a 123, Accuspark offer an electronic box that controls timing advance you just mechanically lock the distributor and the box delays the spark to match the curve programmed

[Burdekin]

A friend had his refurbished by H and H Ignition Solutions. He is fussy with the detail and was very happy with the job they did. I did a megajolt conversion for the estate like 142 Guy but for a standard engine I wouldn't bother. You're running carbs, me personally I'd just get a 123 dizzy with the standard curves, put it on the B18B curve and set it at 17 to 19deg at 1500rpm and it should run spot on for you with the dual SUs.