I figured while my camper is getting welded painted I would get my head around advance curves and MAP settings.(see motor spec in signature) I was advised on buying a 123 programmable distributor by JPM. Does this look like a good start?
Why don’t you ask JPM? Your non-standard engine will require a different advance curve to any other engine.
No. I want to keep it more simple. I have carbs and will keep them,i just want a more precise dizzy...over complicating things is not the smartest,imagine sitting somewhere thousands of miles from home with FI that has stopped working. So.....back to the question. Would it run ok with this curve? I do intend to play around and try different adjustments.
The vacuum advance looks quite heavy - I looked at a lot of distributor curves I scanned from a VW engine service manual just now and mostly VW would have maybe 5-7 degrees off ported vacuum :/ https://www.hamble.online/vowo14/curves Of course you are using MAP which has a different characteristic to the ported (venturi flow related) vaccum - the peak advance will be for a highish manifold vacuum corresponding to a cracked open throttle, dropping to zero at max vacuum and zero at zero vacuum.
The reason I bought a 123 with selectable curves was that I knew nobody could tell me how to programme the curve. Some info here. http://thelatebay.com/index.php?threads/123-ignition-from-vintage-speed-for-a-type4.54108/
Seems odd that your engine builder hasn’t told you what curve it needs and what vents to run .. I would have thought it all needs to match his cam and engine specs
He said 28mm vents and recommended the 123 Ignition so ive contacted him and awaiting his response. So many have said i should have 30 vents so i will try them.
why not ask the manufacturer, they should be able to answer your technical questions. the topic has been raised before on the forum so a search may turn up something.
Trying to understand tuning and all the conflicting advice made my head hurt so I went for the standard 123 and selected the curve they recommended
What distributor do you have on the engine currently? Here are the curves for a few Bosch distributors but obviously none of them will be optimised for your engine. Wait for JPM to tell you what the engine needs, nobody else will know.
Mine is the stock dizzy with accufire module..bit worn so getting timing scatter. Ive seen that graph... What motor specs you have?
The problem with the old Bosch distributors is that the springs on the centrifugal advance weights are clipped over little plastic pieces that hold them straight. When the pieces get hard and crack off, either by themselves or when big fingers fiddle with them, they do two things : cause a lot of timing scatter at idle as the springs are loose at zero advance. allow slightly faster advance with rpm. I was lucky at the Slough Swapmeet to find an original Bosch for £5 where the springs were still clipped over the plastic pieces, but the follower on the points had actually flattened the lobes on the shaft in the distributor, and the vacuum canister was bent. It did not matter as I fitted a magnet ring for an Accuspark, and gently hit it with a hammer until the vacuum canister straightened up, The timing jitter went away that I used to have. But now I have another effect : that a slight flat spot just off closed throttle has become more noticeable because the timing is consistent on all four cylinders. With a lot of timing scatter, it covered up the flat spot because each cylinder fired with a slightly different advance .. oh well. Like dither in an analog to digital converter that gets rid of distortion by adding noise ... The timing jitter on mine was about 4 or 5 degrees. I thought the timing light was broken (which it had been). But with the 'new distributor' suddenly the mark on the pulley sat absolutely still.
I think one thing with tuning a stock engine which is closing in on being a 100 year old design is that it is made to be insensitive to tuning by being restricted in different ways, so you can tune it quite badly and it still runs almost the same. So you can do something wrong and nothing much happens. I still find it strange that on a motorway, for instance, the engine really does not seem to 'notice' a change from 15:1 Air fuel ratio to 11:1 in terms of power, while in a more highly tuned engine it would probably start to stumble or backfire. We get 50 HP from 1600 cc. In supercars today you would get almost 300 HP from 1600 cc.