Your AFR gauge could provide the answer to the mixture question.

At light throttle the vacuum chamber will adds extra advance to the actual advance value.
If the engine is stumbling around 2000 RPM with constant & (very)light throttle on the road (in 2nd gear),
that's also a sign of too much advance.
If you disable the vacuum advance by disconnecting the vacuum hose from the chamber (and seal the
hose towards the carb), and the detonation / stumbling remains, then the advance is too much.

 

vacuum advance is already disconnected:thumbs:
no stumble before or after disconnection.

Only detonates on sudden throttle opening, very fast acceleration.

any further retard then it is less than 7 degrees static and that has an effect of horrible take off and fats heating when idling.
its just under 8 degrees static now.

Thats normal detonation dont worry ......

hope so.

well I's still like to try as slightly stonger spring.
As I have a new assortment set coming. new ones with different tensions.
Maybe the old ones in there have just lost some of their tension.

I would prefer a higher static advance (9 degrees or so) and slower advance curve to its max at 4500 rpm. I know it doesn't feel quite right.

 

Thats normal detonation dont worry ......

 

Well, with weak springs the max advance will be reached sooner.

 

yep that's what I think is happening.

 

Look , there will be always some detonation especially on sudden acceleration due to old school electronics. Since your performance is good , your carbs are tuned and your current is strong then this is normal especially if you dont have performance issues or high consumption.

 

Do you know at what rpm the secondary spring comes into play on the Bosch?

If the detonation is occurring mainly at 2500-3200 rpm is the secondary spring starting to come into action here or just the primary?

There is a small amount of slack in the second, which I think comes into play after about 6-7 degrees of advance.
But what revs? Not sure.
maybe just try a stiffer primary spring first. I know it never pings at full revs (max advance around 34 degrees)

Trial and error is tricky here because they are difficult to change.

Says below the 2nd one comes in at a much higher rpm.

Mechanical Advance - Inside the distributor are a set of springs and weights. The weights are held in place by springs and swing outward as the shaft rotates with the engine. As the weights move the plate that holds the points twists counter clockwise relative to the shaft. This has the effect of advancing the timing because the points are now closing earlier than before (the shaft rotates clockwise with the engine). This is called mechanical (or centrifugal) advance and the reason we need more advance as the engine spins faster is that the piston is travelling faster but the chemical reaction in the combustion chamber still has a relatively fixed reaction time. If the advance comes in too soon the pressure from combustion might try to force the piston down during it's up travel. If it comes too late, less torque will be produced as the pressure will be wasted as heat absorbed by the cylinder walls.
dizzy curves

Most Bosch distributors (except for the 009) have two types of springs inside. The first is fully extended and reacts as soon as the engine speed increases from idle. The second spring is elongated so that it begins to stretch at a much higher rpm. Not only different in length but this spring is also stiffer and the overall effect is an advance curve that has two slopes: at first a quick advance then it tapers off. The maximum advance is limited by two stops inside the body that prevent the weights from moving further outward at higher rpms. The required amount of advance depends on the combustion chamber design and the camshaft selection. 20-24 degrees is typically required by 3500rpm. After that the turbulence of the intake mixture is enough to promote combustion at the maximum advance.

 

For the 305.50 engine the max centrifugal advance is reached between 3400-3500 crankshaft RPM
[Marelli and Bosch 0237601017(?)] these are providing at least three slopes in the advance curve.
The engine 305.58 was equipped with a differently calibrated dizzy, which provided higher centrifugal
advance values (probably it has 0237601014 Bosch number) also with more than two slopes.

 

thks. As mine is the 30550 engine your first figure helps a lot. (but I did think that the 2 final marks on the flywheel were for advance curves at 3500 and 4500 rpm so max comes in at 4500)
It seems to ping more at around 3000 rpm if I hit the pedal hard.
So maybe the secondary spring is a little weak.
What do you think?

Yep seen pics of the Sun 600. not sure if any exist here.
:thumbs:

 

A nice tool to tune the centrifugal advance (called Sun 600), only a few left since
the ignition advance is determined by digitally stored ignition maps.

 

IMHO both springs are weak or one of them is broken.
The weaker spring (and it's counterweight) would be responsible for the 1degree/100 RPM advance steepness,
in the ~950 to ~1500 RPM range.
Around 1500 RPM the stronger spring is start to kick in, changing the advance steepness
about 1degree/200 RPM. This steepness remain constant until the crankshaft reaches 3400-3500 RPM,
after that the (centrifugal)advance will not increases further.

I think the max advance is reached before 3400 RPM, and the rich mixture starts to detonate
during hard accelerations and high engine loads.

 

Great info thanks lonewolf.

Yes the carbs are set up with a richer mixture now. 55 idles and 145 mains.
This was to eliminate a flat spot. Maybe the mains need to be 142 again but I am running with MSD 6A so it does burn well.

Maybe the detonation was less evident with the leaner mixture as it burns faster but had a horrible flat spot.

 

Has anyone tried the vacuum advance from the manifold instead of ported?

I could have a higher idle advance and lower overall advance once the throttle is opened.
Just curious of how much it advances the timing at idle as I don't have the vacuum canister attached right now.

 

a neat trick could be to use the vacuum port from below the throttle plate for the advance.

This is adjustable. So I can retard the idle advance to about 6 degrees or enough to compensate for the weak springs and open this vacuum port just a little to raise the static idle advance to about 9 degrees.
= good advance at idle which will drop to zero once throttle is opened.
Not sure how it will respond but an easy trick to try.

 

:rant:

new dizzy springs never arrived! 5 weeks now and i bet they are lost foreever! (also had a box of Christmas presents go missing!!)

Anyway the company has offered to send me another pack. Will get them sent to my office this time (international free trade zone!).

But so much time waiting to get my timing working as it should. I miss being able to floor it WOT while overtaking etc.

(even if I sell it and change it for the 33 ie series 3 I'd like to get it working properly first of course)

 

I changed the filters back to the original airbox with an extra big cold air intake tube to rule out the detonation occurring due to hot air soak.

No improvement!

It doesn't occur under load at any other rpms in any gears other than the range between 3200 ish to 3600 WOT.
Mostly in 3rd, a little in 2nd but none in any other gears.

So next variable could be the secondary dizzy spring? (hasn't arrived yet!)

It has also been suggested my compression maybe a touch high if I have tried all other possibilities!!
A thicker head gasket would be needed!!

 

I also get some detonation from my 1.4 ie Imola around 2500 RPMs on 2nd & 3d gear. It doesn't do it always, mainly detonation occurs after the engine get warm, but differently from brit01's 33, mine does it even at higher revs (when accelerating hard or floor the pedal). It is not very loud but I still can hear it.
I'm afraid it is running a bit lean, but WHY? Could this be a sign of a worn fuel pump? Car also takes a while to fire up (not the first start in the morning)

Is it normal for the fuel injected 33 to run a bit lean, as my spark plugs are more whitish then brownish?
Could detonation also be caused by a slightly bigger gap than normal, in the spark plugs?


No oil consumption, no lack of power...

 

MON!!

MON=83

Extremely low grade octane rating here (and I'm using the best available on the street)

Should be at least 87 for an engine with my compression!

Have to look into this further.

 

What is your knowledge on adding toluene?

 

May have found a source of the race/aviation fuel with 99.6 MON and 100 RON.
Just costs 10-15% more I believe.

add maybe 30% of this to each tank?
Detonation problem solved with this for sure!

btw only E10 is available here. Introduced a couple of years ago.

Look at this link
E10 should not be used! Great.

http://www.ahmf.org.au/PDF_Docs/Ethanol%20in%20Petrol%20final.pdf

 

I will reduce my plug gap I think
Maybe the powerful MSD and 1.1mm gap is not working at higher revs on my engine - I mean its just igniting the fuel too soon.

1. The small area of fire around the spark is called the 'kernel' by automotive engineers. A bigger sparkplug gap inherently creates a bigger kernel. This bigger kernel not only starts bigger but grows 8 times faster, because of what is known as the 'Volume Power Law'. The Volume Power Law is a fancy way of saying "If you make a ball shaped thing twice the diameter it will contain 2x2x2=8 times the volume inside.
What this means in practical terms is that making the sparkgap bigger is like slightly advancing the ignition timing. More ignition timing increases the chance of detonation/pinging.

2. Bigger sparkplug gaps are harder for the ignition system to get a spark to jump across. This is especially true at high rpm, (like above 3500 rpm) and at wide open throttle. So a too-big sparkplug gap can cause a missfire at high rpm and wide open throttle. This missfire will show up first as very slight and intermittant, and gets worse as the rpm goes up. Unfortunately at high rpm there is already more noise and vibration naturally, and it is sometimes hard to detect the slightly greater vibration that the truck driver normally uses to spot missfires.
A slight missfire can cause a ping. What happens is this: after a missfire the next filling of the cylinder is much greater because there is not the normal left over exhaust gas that is normally there. Instead of getting 80% fresh mixture in like a normal filling of the cylinder - that cylinder now gets 100%. Normally the 20% left over exhaust gas slows down burning ( like EGR pollution valve schemes) but now the burning is even faster with 100% pure mixture. This 'supercharged' situation results in detonation pinging that the truck driver hears as an intermittant ping.

 

Very interesting...

I'm experiencing detonation, @ high revs it's getting worse. I haven't check my plugs from 1 year or more. Maybe the gap has got bigger as the electrode gets consumed. I'm using NGK (iridium). What should be the gap for the 1.4 ie. Maybe worth checking the plugs. It is getting worse as it needs oil change also.

Tell me something, would a worn fuel pump give this pinging @ high revs if it's not delivering enough fuel?

 

Detonation (knocking or pre-ignition) can be caused by so many things. That's the nightmare I'm having.

you have injection right? (injection is a different case - could be a bad air flow sensor or anything like that creating a lean mixture)

Can be a change in fuel (Normal premium to E10 for example)
Worn fuel pump yes, so its going very lean when fuel is needed
worn dizzy, worn dizzy springs (or broken) (carb models)
dirty combustion chambers full of carbon creating hot spots that ignite the fuel
bad plugs, or too hot a plug
list goes on...

Try checking your plugs first and also the pressure of the fuel if you can.
Could be an air leak that under revs it sucks in air and creates a very lean mixture causing detonation.

If you Google it there is a lot of advice (for ie and carb models).

Probably in your case its one of the sensors for the ie management system (maybe air flow?) lambda's tend to go rich when malfunctioning I believe, could be wrong


Last night I set some more pre-load on the secondary dizzy spring.
I will also change the plugs back to normal non-projected (B8ES) and reduce the gap down to 0.7mm.



let me know how you get on

 

Well I seem to be getting somewhere now at last.
I had no knocking today!!!

I adjusted the slack/pre-load on the second spring last night.

The first spring is under tension normally and is good up to 1500 rpm.
The second one has about 6/7 degrees of slack and comes into play after 1500 rpm, Then the sum of both control the total advance after that.

I modified the second spring(I have a spare), and took out this slack to pre-load the total more. I knew this would have an effect on the off idle acceleration though.

When fitted and started her up she was very retarded. I adjust this round to 8 degrees static, factory mark on flywheel.
With the vacuum pipe disconnected and revved she advanced visibly slower which was the idea.

With vacuum attached she advanced nicely above 36 degrees fast. Good.

Warmed her up and took her out.
Gave her a thrashing and NO PINGING!!

Advanced a little more, 5mm or so ( 1 degree more approx). and pinging came back, backed it off to 8 and all good so far.

What I would like though is to have this slack back in the second spring but a stronger spring. (H&H have failed to deliver again - maybe they are addressing it incorrectly - very unusual).

I also notice one of the spark plugs ground electrodes looked a bit hot. You know the change in colour around the ground electrode can indicate the heat rating, well this change in colour was more near the thread on one of them.
maybe go to a colder plug.

Also maybe just because I was thrashing her about the coolant was a few degrees hotter which was strange and a bit disturbing. Thought without the detonation she would have been cooler. ??

Regards

 

mine does it mostly when really hot (engine). If i drive at normal temp she wont ping, detonate (@ all or just a little @ around 5500-6000 RPM).
Today I'll change oil + filters, taking out the plugs also for a check (will fix the gap) and let you know how is gone and if there is still problems or not...

 

just took out the plugs and they were kind of whitish more than brown, but this might be normal for fuel injected engines, but I don't think is normal the code on the plugs itself BKR7EIX.

I'm running the NGK BKR7EIX which I think are not the right ones for my 1.4 boxer. The ''7'' stands for the heat rating right? Boxers need a 6 heat rating right, so I'm running the 7 (1 step colder)...!

So apart the gap that might have increase by using the plugs for about 45000 km, also the plug itself is not the right one for my engine.

Could all this lead to detonation or pinging at high revs??????
I have a feeling that this might have been the detail that made the difference in my car.

Any opinion?

 

under load or sustained high revs the ground electrodes will get hot. if too hot they will glow red hot and cause pre-ignition (knocking/pinging sound).

Going a step hotter(7 to 6) will make the plug even hotter and the condition worse.
I am using B8ES. (7 is normal). 6 maybe if you only use it for short trips around town.
I use 8 because I push mine hard and use it for motorway runs at the weekends plus I have an MSD running (high voltage).

Maybe you want to go for normal copper plugs. BP7ES or BP8ES.

Did you say you have carbs or fuel injection?
Not to familiar with why detonation is caused with engine management systems.

But the plugs are the same. If the plugs are too hot you will get pinging.
(if yours are white it means to mixture is going to lean which can cause pinging - bad news)

:thumbs:

 

I have fuel injection.
From what I see from the plugs, I would say it tends to run a bit lean, but this might be due to mixture being calculated more accurately from the ECU in the fuel injected 33, and maybe is just normal for the i.e.
I also push hard mine whenever I have the chance, I like to rev her to the limits and is mostly there when I get pinging...
I drive mostly in town with a lot of stop & go.
So as the plugs are not black and sooty (they are very clean), should I go again for the 7 heat range or 6 heat range. Summer will come soon...

thanks,
Elvis

 

There shouldn't be pinging on a ie I believe due to knock sensors.

To see if the heat range is too hot you can inspect the ground electrode.
There will be a colour change somewhere along it. Should be around the middle (bend).
If its closer to the threaded part then it's too hot, if it's near the end of the tip then it's cold.
Always safer to be on the cold side as long as it doesn't foul up (not self cleaning).

The colour of the ceramic part should be a brownish colour, not white(too lean).
How is the colour on the top of the thread part of the body?

You don't want lean and hot plugs.

But if you're doing a lot of city driving the plugs would tend to be blacker rather than whiter(lean).
They tend to clean up on long motorway runs not stop/start driving.

Maybe Lonewolf can jump in here as he's more familiar with all of the sensors on injection models. Might be your air flow monitor or temp sensor.
But the plugs are basic to read as I mentioned.

NGK website will also recommend what plug you need. Have a look for your model.

 

Hi,

The injected 33 models weren't equipped with knock sensor.
Light electrode colour of the plugs is normal, even in city driving,
if the closed loop control is working correctly. The plugs are operating at
somewhat higher temperatures compared to the carb models.

The IAW ECU switches to open-loop mode above 4500 RPM (the lambda control will be disabled),
so if the mixture becomes too rich (more likely) or too lean, it won't be corrected. This may results detonation.

 

knew you were watching:thumbs:
so no knock sensors? suprising. Even the later 1995 1.7 16v models? (there is one beautiful one for sale here now - friend of mine.
certainly am tempted - look at those seats!! and the colour burgundy!

Alfa Romeo 33 16v - Año 1995 - 183000 km - en MercadoLibre

 

:lol:

Yep, no knock sensor. The 16V model was marketed with the same Bosch Motronic ML4.1 engine management
during it's whole production period.
But the 145/146 models with the 1.7 16V engine (and the upgraded Bosch Motronic M2.10.3
engine management) aren't equipped with this sensor either.

That's a very nice 33 16V. Someone was kicked the power window relay out of it's place.
The relay just hanging there.

 

power window relay hanging? where I can't see that?

I can see one of the front headlight water squirters missing though.