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Symptoms Of A Worn Dizzy


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#1 fenghuang

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Posted 21 July 2016 - 05:24 PM

What are the symptoms of ignition that is too far advanced and too far retarded?

#2 AlexMozza

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Posted 21 July 2016 - 06:51 PM

To far advanced it will struggle to start, and you will get pinking, or pre detonation
To retarded and it will feel very sluggish.

#3 Dusky

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Posted 21 July 2016 - 07:12 PM

Retarded tends to give th eexhaus tmanifold a nice cherry color too. 
Looks great if you have a cherry red mini.  :bah:



#4 KernowCooper

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Posted 21 July 2016 - 07:51 PM

Retarded ignition timing also causes engines to run hotter then normal and under load not only will the exhaust manifold get hotter, it increases the water temperature and fuel vapourization



#5 Spider

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Posted 21 July 2016 - 09:59 PM

Retarded tends to give th eexhaus tmanifold a nice cherry color too. 
Looks great if you have a cherry red mini.  :bah:

 

 

Retarded ignition timing also causes engines to run hotter then normal and under load not only will the exhaust manifold get hotter, it increases the water temperature and fuel vapourization

 

It can also make for light weight exhaust valves

 

BurntValveWM_zpsse4vwl4x.jpg



#6 Spider

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Posted 21 July 2016 - 10:07 PM

Apologise up front if this is over the top and a little long winded, but it's a brief explanation of the whole advance / retard thing, along with the automatic advance mechanisms of the distributor;-

 

The distributors have an automatic advance mechanism that advances the ignition timing with increasing engine speed (although on some non-Mini engines there are a few that require a bit of retard at high speed) and some have vacuum advance.

The burning of the fuel mixture in the cylinders does not happen instantly although it is fast. At some point in that burning process, it will reach it highest or peak pressure.

Ideally, we'd like that peak pressure to happen at about 14 degrees after the piston reaches top dead centre (ATDC)  (that is on it's way down, which makes sense).

So if we had a fixed (no auto advance) distributor, we can easily set the timing so that the peak pressure occurs at just the right moment (14 degrees ATDC) at say 2000 rpm (or at say 60 kmh in top gear).

When the engine speed is increased, the time it takes for the piston to move is also faster. Since it does take time for the fuel mixture to burn, the peak pressure will occur later and the most efficient use of that cycle has not been taken advantage of, ie, efficiency is lost. At even higher speeds the exhaust valve will in fact begin to open while that fuel mixture is still burning so even more efficiency is lost as the pressure that would otherwise be driving the piston down the cylinder is lost out the exhaust! Good for getting the exhaust gases out of the cylinder but doesn't do much for moving the car! Under these circumstances, the ignition timing is said to be retarded.

OK, so now if we set our fixed distributor to suit say 4000 rpm (or say 100 kmh because we all like going away!), then at slower engine speeds the burning cycle will start too early and if it occurs too close to top dead centre and so the piston will tend to drive in to the bearing rather that turn the crankshaft. Again, the best efficiency is lost as the engine is trying to compress the con rods or squash it's bearings. This is said to be over advanced.

Usually, but not always, over advance ignition timing can be heard, it can sound like someone's poured a packet of gravel in to the engine or there is an aluminium can stuck inside it. I think it fair to say most of us here have heard this and is known as pinking, although there are many other causes of this, not just ignition timing.

Who remembers riding their push bike? At what point when pushing the pedals did you get the most out of that push? It wasn't when the pedal was up, it was probably when the pedal was around the 20 to 30 degree mark. What happened when you did try to push to pedal when it's too close to the top? You went red in the face and not much happened, sometimes the pedals would even go backwards and more often than not, you'd hurt yourself. Yeah, I remember that. What happens in an engine is not a lot different.

So to reduce those effects and gain the best efficiency from the engine, the ignition timing advances automatically with increasing engine speed. There are many factors, mostly inside the combustion chamber of the engine that affect the speed that the fuel burns at and of course the actual mixture ratio (weak or rich) will have a big bearing on this too. Engines are very sensitive to this and it is for this and so the amount of advance is rarely linear or a straight line but more of a curve. It is for this reason that a certain distributor that suits one type of engine will not suit another. Also, to further complicate this, different Octane fuels burn at different rate, high octane burning slower (no that is not a typo) hence why you need more advance with higher octane fuels. Compression ratio too has a bearing on ignition timing requirements.

Here is the advance curve numbers for most 998 engines

998distadvtcurve.jpg

and for most 1275's

1275distadvtcurve.jpg

So, for example, if we put a 998 distributor in a 1275 engine, it would over advance and likely ruin the pistons (seen that more than once).

 

And just for a graphical example, here's a 998 vs 1100 distributor;-

 

DistributorCurvesAYG1056vs41417_zpsacede


So far, this has been about the Automatic or Centrifugal Advance in the Distributor.

Some also have a Vacuum Advance as well. When you accelerate the cylinders fill reasonably, but when cruising down the road, they don't. Under these conditions, there is little mixture in the cylinders and again, it take even longer to burn. Also on cruise or part throttle, the manifold has a high vacuum. This vacuum is used to operate another mechanism on these distributors to further advance the ignition timing although this has little to do with avoiding engine damage, it is more about getting even better efficiency from the engine. In most cases, it could be disconnected and won't do any harm, other than use a little bit more fuel.

Some problems that can occur if the ignition timing gets too far outside the sweet spot - other than lost efficiency - are;-

Over Advanced;-
Damaged Engine Bearings,
Damaged Pistons - the top of the piston can squash down on the top piston ring and jam it,
Burnt holes through pistons (though, this is extreme),
Engine overheating

Retarded;-
Burnt Exhaust Valves (very common),
Cracked Cylinder Head (it will crack between the inlet and exhaust valve seats),
Cracked Exhaust Manifold,
Engine overheating


Edited by Moke Spider, 21 July 2016 - 10:49 PM.


#7 fenghuang

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Posted 21 July 2016 - 10:56 PM

Thanks all. (Espciay Spoder. I've never understood vacuum advance until now!)

So am I right in thinking that if I'm struggling to get the combustion to not be yellow (with a Colortune), even with the carb jet at its highest, there is a chance that the ignition is too advanced?

#8 fenghuang

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Posted 21 July 2016 - 10:58 PM

Assuming all the other ignition components are in good condition and adjusted properly, what would be the symptoms of a worn dizzy?

#9 KernowCooper

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Posted 21 July 2016 - 11:34 PM

If you have the Carb jet wound up to its highest point then your setting is incorrect, winding the jet up is weak and down is rich



#10 Spider

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Posted 21 July 2016 - 11:34 PM

Thanks all. (Espciay Spoder. I've never understood vacuum advance until now!)

So am I right in thinking that if I'm struggling to get the combustion to not be yellow (with a Colortune), even with the carb jet at its highest, there is a chance that the ignition is too advanced?

 

A Yellow flame as viewed in with the ColourTune generally shows a rich mixture (and I think you already know that). Ignition timing will have little effect on this.

 

A few things here. At idle with Carbs, the mixture tends to be on the rich side and that's normal. If this is occurring even at around 1500 RPMs or higher, then I'd be looking at the float bowl level and / or the fuel pump pressure, on that the suspicion being that one or the other (or both) are too high.

 

Also, check the needle and the the jet are not worn. The Spring Bias types do wear and can be very hard to see. At Idle and low throttle opening, the very slightest change to either of these has a fairly big effect, they are VERY sensitive.

 

Just on that, check that the Jet size is correct, ie, you maybe running with needle(s) for 0.090" Jets, but have a 0.100" jet in there, though I'm sure it would flood, but a simple check all the same.

 

<Edit for my crappy spelling >


Edited by Moke Spider, 22 July 2016 - 10:22 AM.


#11 KernowCooper

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Posted 21 July 2016 - 11:42 PM

Answering post 8 - Pretty much answered in your other post on ignition timing, and in extreme cases the shaft bushing can be so worn it makes setting the dwell almost impossible, Lucas distributors are no where near as bad as Delco though.

 

I'll merge the two posts


Edited by KernowCooper, 21 July 2016 - 11:46 PM.


#12 fenghuang

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Posted 22 July 2016 - 09:25 AM

If you have the Carb jet wound up to its highest point then your setting is incorrect, winding the jet up is weak and down is rich

I know that, but if I can still get a yellow burn with the jet would all the way to the top, then presumably there's something else wrong. Possibly the wrong needle / jet combination. But ...

The jet is new, and correct for the carb. (It came diect from Burlen SU and they were given the code from the ID tag on the carb.)

The needle came as part of a Stage 1 kit, from Minispares, and was specified for a standard 998.

So if they don't match, so unless the ID tag was for the wrong carb body, I don't understand why.

 

Answering post 8 - Pretty much answered in your other post on ignition timing, and in extreme cases the shaft bushing can be so worn it makes setting the dwell almost impossible [...]

Without wanting to be churlish, is it answered? If it is I can't make the connection.

Early / late timing - I'm starting to understand that. But I don't understand what difference a worn dizzy would make.

I'm assuming the shaft bearings would be the things that wear, which would make the shaft loose, which could(?)mean the ignition timing continuously varied from early to late, making the ignition timing inconsitent (and therfore the dwell angle, as you say), but what symptoms would that lead to?

One thing I'm wondeing about is that I can't seem to get a steady reading on a digital tacho.

(I'm assuming there isn't a problem with the meter - it's pretty new - and I've got the tacho connected correctly: -ve probe to (cleaned) coil bracket. +ve probe to +ve terminal on the coil.

https://www.youtube....bed/v4prkGorI_k

 

And the brun colour is not consistent. (Each cylinder constantly varies colour, and no two cylinders seem to burn with the same colour.) But Spider says the burn colour shouldn't be related to timing issues. So maybe not.
https://www.youtube....bed/gVrXbPpJuAM

 

(Sorry - I can't figure out how to embed the videos - only link to them.)

 

 

A Yellow flame [...] generally shows a rich mixture [...] Ignition timing will have little effect on this.

 

A few things here. At idle with Carbs, the mixture tends to be on the rich side and that's normal. If this is occurring even at around 1500 RPMs or higher, then I'd be looking at the float bowl level and / or the fuel pump pressure, on that the suspicion being that one or the other (or both) are too high.

 

Also, check the needle and the the jet are not worn. [...]

 

[...] you maybe running with needle(s) for 0.090" Jets, but have a 0.100" jet in there, [...] a simple check all the same.

The float bowl and float have been replaced, and I'm pretty sure I adjusted the float correctly. But I can check. If the float is working ok, my guess is that that should rule out the possibility of excessive pressure from the fuel pump. Yes/no?

(As above) the needle and jet are both new.

How would I tell what size the jets and needle are?



#13 Spider

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Posted 22 July 2016 - 09:30 AM

What Carb, Manifold and Fuel Pump are you running?



#14 fenghuang

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Posted 22 July 2016 - 09:57 AM

Carb - HS4 (FZX1146 ... assuming it's the right tag on the carb)

Manifold - Minispares Stage 1

Fuel pump - standard (old) mechanical (but more than that I don't know)


Edited by fenghuang, 22 July 2016 - 10:01 AM.


#15 sonikk4

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Posted 22 July 2016 - 11:40 AM

I take it you have done a Stage 1 conversion judging by what you are saying?? if so take it to a rolling road and they will sort this out for you. You can spend a lot of time messing around whereas they will have all of the equipment needed to hand. 

 

Even if you have not done a conversion its still worth taking it.






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