Spit seems to run weak at higher revs

[johny]

Could be worth checking the distributor as well. There should be an advance/revs table listed somewhere and then with the vac disconnected and plugged you can use a timing light to check the degrees while an assistant increases the engine revs (ear plugs recommendable)....

[NonMember]

They're always rich at low revs - particularly idle - by design, which makes the plug colour test practically useless unless you do the clean coast trick.

[cliff.b]

8 minutes ago, johny said:

Could be worth checking the distributor as well. There should be an advance/revs table listed somewhere and then with the vac disconnected and plugged you can use a timing light to check the degrees while an assistant increases the engine revs (ear plugs recommendable)....

Yes, I have replaced the distributor over the winter as well so was planning on checking everything again. 

Is there any wisdom out there on the science of how ignition timing could affects combution?

[johny]

1 minute ago, cliff.b said:

Is there any wisdom out there on the science of how ignition timing could affects combution?

uuuf now theres a subject!

[cliff.b]

2 minutes ago, NonMember said:

They're always rich at low revs - particularly idle - by design, which makes the plug colour test practically useless unless you do the clean coast trick.

Ah, interesting. So could leaving the car to tick over for a while actually blacken the plugs?

[cliff.b]

Just now, johny said:

uuuf now theres a subject!

Ok, or any commonly held wisdom (or even opinion) on the matter lol

[johny]

I always thought too advanced gives hotter running (even to melting pistons and sparkplugs) but thats probably over simplification and an expert view is required...

[cliff.b]

47 minutes ago, johny said:

I always thought too advanced gives hotter running (even to melting pistons and sparkplugs) but thats probably over simplification and an expert view is required...

Just been doing some reading about this which suggests that both being too advanced or too retarded can lead to overheating, but in different ways.

Too advanced causing more heat in the combustion chamber due to higher pressures created, even though this may produce more power if not excessive.

Too retarded due to the exhaust valve opening before combustion has fully completed, leading to excessive heating of the valve and manifold.

I've become interested now so will see what else I can find on the subject.

[Pete Lewis]

as the 1500 was devised in the days of emmisions being of interest i dont see how they would be rich at idle that doesnt really stack up

advance is all to do with the time delay it takes for the burn to fully take place with the piston  power stroke 

a low octane burns slower so you retard to allow the bang and down stroke to occur later   higher octane  burns faster so you can optimise the bang and down stroke 

to occur earlier  hence more bang  for your buck 

timing data is included in the WSM as test data  and mostly this is always checked  decelerating  

its no use pointing a strobe a revving at certain speed  its a bit more involved 

as for blocking the vac pipe is a complete  waste of time  the air in here is so small volume it wont affect any running   

pete

 

[daverclasper]

2 hours ago, cliff.b said:

Ah, interesting. So could leaving the car to tick over for a while actually blacken the plugs?

Well, with my Vitesse (bit of spindle play, good jets and and needles, as were replaced a while back, though in hindsight the old ones were probably ok),

I get sooty, with a bit of brown plugs, after half an hour of slow moving/idling. The plug colour after M way driving at say 2500/3000 rpm, is a pale grey. I assume/hope this is ok?. If I go higher rpm, or accelerate quickly to even higher rpm, then doesn't stumble/hesitate, so again hope this ok and not running weak?.

I'm never sure about myself, with the pin lifting technique and also as my spindles have some play and more air, also wondered if correct at idle, then maybe not at higher rpm?   

Have heard that modern fuels give a lighter plug colour?.

Who knows about the intricacies of all this?, not me.

Hope this is useful

[NonMember]

31 minutes ago, Pete Lewis said:

as the 1500 was devised in the days of emmisions being of interest i dont see how they would be rich at idle that doesnt really stack up

The base engine is still a 1940s design. The idle setting is 4%CO even on the late cars, which is about 13:1 AFR, noticeably on the rich side of stoichiometry and definitely richer than the steady cruise condition.

34 minutes ago, Pete Lewis said:

a low octane burns slower so you retard to allow the bang and down stroke to occur later 

No, that's completely wrong. You retard because it is more prone to explosive self-ignition (knock) in the far corners as the flame front compresses the unburnt mixture. If it burnt slower you'd need to advance.

[cliff.b]

11 minutes ago, daverclasper said:

Well, with my Vitesse (bit of spindle play, good jets and and needles, as were replaced a while back, though in hindsight the old ones were probably ok),

I get sooty, with a bit of brown plugs, after half an hour of slow moving/idling. The plug colour after M way driving at say 2500/3000 rpm, is a pale grey. I assume/hope this is ok?. If I go higher rpm, or accelerate quickly to even higher rpm, then doesn't stumble/hesitate, so again hope this ok.

Have heard that modern fuels give a lighter plug colour?

Hope this is useful   

Yes, definitely useful as sounds, perhaps to a lesser  extent, the sort of thing I am seeing. 

Just as a matter of interest, how do you set your ignition timing? By ear, timing light, static with a bulb, meter, fag paper lol

[daverclasper]

Just by low speed/revs in top gear and accelerate, if no pinking then advance timing a bit more until pinks then retard a a bit. Hills can sometimes show the pinking/advance more, even when ok on flats, at least on my car.

I have the vernier adjuster on my dizzy, I normally do 8 full turns at a time, one way or the other for finer tuning (as I understand this is only very fractional?), when it's roughly there anyway.      

[cliff.b]

35 minutes ago, daverclasper said:

Just by low speed/revs in top gear and accelerate, if no pinking then advance timing a bit more until pinks then retard a a bit. Hills can sometimes show the pinking/advance more, even when ok on flats, at least on my car.

I have the vernier adjuster on my dizzy, I normally do 8 full turns at a time, one way or the other for finer tuning (as I understand this is only very fractional?), when it's roughly there anyway.      

Ok, thanks. So presumably, you won't actually know what static advance you are running?

[johny]

Should always check the setting as its just possible, although unlikely, the timing is advanced more than the recommended figure and theres no advantage in this... 

[cliff.b]

6 minutes ago, johny said:

Should always check the setting as its just possible, although unlikely, the timing is advanced more than the recommended figure and theres no advantage in this... 

Yes, I'm planning on checking that tomorrow, along with several other things. But one at a time so I know what, if anything, makes a difference 👍

[cliff.b]

Right, first fault found, and although ignition related I will leave it here for continuity.

The vac advance on my recently replaced distributor was sticking near max (well the plate that the vac unit moves was sticking) which along with a slightly advanced static setting meant my effective static advance at tickover was nearly 20deg BTDC. Interestingly, I had heard no evidence of any pinking.

Anyway, no longer sticking, static advance set to 10deg at tickover and will take out for a test drive shortly. Need to find out what difference this makes before looking at anything else.

[johny]

Good that sounds like progress but just one thing to avoid confusion: the term static timing usually refers to setting it with the engine stopped and turning it manually until the points just open. It sounds like youve been using a strobe to set yours with the engine running which is the more accurate way of doing it👍

[cliff.b]

33 minutes ago, johny said:

Good that sounds like progress but just one thing to avoid confusion: the term static timing usually refers to setting it with the engine stopped and turning it manually until the points just open. It sounds like youve been using a strobe to set yours with the engine running which is the more accurate way of doing it👍

Indeed, yes, I mean the timing without any additional mechanical or vac advance.

[johny]

Well that can still be done either by hand turning of the engine (static timing) or by running the engine at idle with the vac advance disconnected and using a stobe (dynamic timing)...

[cliff.b]

15 minutes ago, johny said:

Well that can still be done either by hand turning of the engine (static timing) or by running the engine at idle with the vac advance disconnected and using a stobe (dynamic timing)...

Yes, that is what I have done. Using the wrong terminology

[cliff.b]

Back for lunch after done road testing, stop every few miles, inspect plugs, adjust mixture, repeat lol.

Now running nicely and seem to have got over the initial issue that started this, a lack of mid range urge. Now pulls strongly from 3000RPM to as far as I am prepared to rev it.

Final test was about 5 miles at "motorway speed", after which the plugs were lighter, but not the white that I was seeing previously. I will fiddle with it further but happy to drive it as is now and have already wasted enough time & petrol today.

[johny]

hey thats not wasting either😁

[Pete Lewis]

as for mixture have you used the piston lifting pin test  ???

has tp be done with filters on or you waste  more time 

when its hot and idles  raise the pin to just touch the air piston

then lift the piston a  1mm ,   and listen to the engine note

you are after a hint of change nothing dramatic

if it picks up 50 rpm for a couple of seconds its rich

if there is no hint of change its correct

if it drops 50 rpm for a second or two its lean 

if you grab the pin and yank it up you just stall the engine  

this is a well proven test but is very light touchy feely   proceedure   

that many cant master ..   be gentle and listen

 

 

[cliff.b]

23 minutes ago, Pete Lewis said:

as for mixture have you used the piston lifting pin test  ???

has tp be done with filters on or you waste  more time 

when its hot and idles  raise the pin to just touch the air piston

then lift the piston a  1mm ,   and listen to the engine note

you are after a hint of change nothing dramatic

if it picks up 50 rpm for a couple of seconds its rich

if there is no hint of change its correct

if it drops 50 rpm for a second or two its lean 

if you grab the pin and yank it up you just stall the engine  

this is a well proven test but is very light touchy feely   proceedure   

that many cant master ..   be gentle and listen

 

 

I will try that but if I drive around town or tickover for any length of time the plugs go much darker, so I assume it is running richer at low engine load. Not saying it should do that but it is, and if I get the mixture correct at tickover I am expecting it will be too weak again when driving faster.

Currently, I am trying to get a compromise of acceptable plug colours over various driving conditions, but still open to any ideas that might give me a more even mixture across the rev range.

What I am getting now sounds the same as Dave Clasper described getting in his Vitesse, yesterday. So is this typical? Is a fixed plug colour at both low and high speed unrealistic? I guess unless you keep stopping and checking it, or use a rolling road, you would never know.

Is it a problem? Interested to know what people think.