ignition timing - the mind of an explosion

[jimbob-mcgrew]

i could use a little help, im trying to get my head round this properly so i know exactly what is going on with my engine.

i understand that TDC is when the piston is at its absolute peak right.
and i understand that the marker on the crank pulley is 10 degrees BEFORE that, which the manufactures state as best right.

when the term RETARDED is used...... would that mean that the spark is delayed and thus shunted CLOSER to the tdc motion... basically in simple terms (a late spark ?)

and when talking about advanced ... would that mean the spark is created EARLIER, and happens BEFORE the 10 degree marker ?

or is it vice-versa ?

also, one thing ive never been sure about with the markers, should they be setup in a vertical line position, i.e = looking from birdseye ? or should they be setup as a diagonal, i.e = closest line from A to B ?

might sound like childs play... like i should know this info all already, but im having alot of problems with my car and i wanna know for sure whats going, rather than guess work from what books only half describe

oppologies for semi-rant. im getting frustrated is all, driving round in a car thats kangaroo'ing.

a breakdown would be :thumb:

[Stuart]

Your initial thoughts are correct. retarding the spark moves it nearer TDC (or even past it if you really goose it up)

[meritlover]

you are right Mr Bob retarding is making the spark later (closer to TDC) and advancing is making it earlier (further before TDC) but you could consider after 0 advance i could be 359 deg BTDC adv.

[chrisd1986]

I would get your self a timing light1st and go over the engine timing mark on the crank with a bit of tipex to make it more visible on the strobe and adjust the ignition timing that way as its more accurate

[marc69]

This might be wrong or patronising but if you use a strobe light, just get the two markings to match. that is it, no need for angles etc, it's all set.

On my 1.4 the cover with the marks is missing. I set it by ear, then experimented by doing a few test drives, it has since been at Knockhill being pushed to the limit almost every month since April. Also when I had it rolling roaded the guy said if it was wrong we would have bent valves testing it up to 7000rpm.

The long shot of this is, if your engine is at least running, if it runs on and is slow, it is retarded, turn the distributor a little ( just a degree or two) in the direction that the engine speed increases, you have gone too far if the engine starts to pink when labouring.

[marc69]

Strobe lights can be bought for about £15, working with old style novas like I do it is a neccesary peice of kit.

[jimbob-mcgrew]

it runs like a bag of turd 15 degrees either side of the marker.

somethings busted somewhere

[jimbob-mcgrew]

its happy as larry when its up in 5/6 grand territory, idles piss poor and upto 3 is pants too

[meritlover]

if you are getting the timing set to the right mark and its not idling properly then its not the distributor, as its obviously doing its job.
when you say its piss poor, what do you mean? missing? stumbling? hunting?
when its bad up to 5/6k is that under load (driving) or just free reving?

sounds like a fuel issue.

On a wild card, have you done a timing belt recently? might be worth checking all the cam timing markings because its so easy to do and you will be chasing your tail for ever if it turns out to be that. if it was out a tooth either direction you would get similar symptoms.

[mowgli]

just annoy you all, most timing information for the carb nova is based on leaded fuel..... so the ign timing marks are actually wrong, usually you need to time it to the haynes, then retard it a couple of degrees

[meritlover]

you are right Mowgli, but it should at least run and fre-rev cleanly. i could understand if it was pinking under load with the book settings and un-leaded fuel, but i think theres more to the issue here.

does the book mention disconnecting and plugging the vacuum line while chiecking the timing?

[burgo]

I have always found the timing marks to be well off in terms of sweet spot. I find the two markers being 10mm apart to the advanced side to be about right. Not sure what that is in terms of degrees

[meritlover]

what do you mean by sweet spot? for sure it will sound sweeter at idle if you give it more advance, but this will not necessarily amount to more power under load and high RPM.
im interested to know what you mean.

[jimbob-mcgrew]

meritlover - yeh thats driving under load. piss poor at idle and down low, stutters and misses mildly but continually. seems to not bother it higher up and will start to pull.
the crank and cam marks are spot on, i was going to change the belt and pump as suspected it was out, but the belts healthy, so ill leave it till summer.

mowgli - yeh, i was aiming to go about 8 degrees to compensate for unleaded, but it doesnt run well enough to fine tune it that well at the moment.

burgo - i did some checks on mine and 10mm on the pulley amounts to about 10 degrees (13S engine that was).

when i was adjusting the idle, i noticed fuel vapour round the back of the carb, i dont know if its from the airbox gasket or the float chamber gasket, could an air leak there cause my issues ?

i need to take a look at the fueling too, altho the plugs look good, i think i should play with it to make sure, as ive checked nearly everything else.

i dont think its an issue with leads or plugs, as im getting a constant rhythm of flashes from the gun off each lead. 1 and 4 are flashing on the 10 degrees BTDC pulley marker, and 2 and 3 are flashing about 50 degrees away, at a guess, 320 degrees BTDC (waterpump side of the block)

also out of curiosity, when my cam and crank are inline, my rotor arm points to 2 o clock looking lengthways down at the dizzy, ive got the no.1 lead plugged in there and leads setup 1,3,4,2 going anti clockwise

[meritlover]

an air leak at certain points of the carb would definately cause it to run lean and poorly,similar to how you described.
Check the base gasket between carb and manifold, check the vacuum pipework isnt leaking.

what do you mean 'fuel vapour round the back'?

[jimbob-mcgrew]

difficult to describe, but you know how you can see heat coming off things, like a disturbance in the air, it looked like that, but must have been fuel as thats a cool-ish part of the engine bay. i heard someone say a while back you can test for that by spraying carb cleaner around the suspect area to seal the gap temporarily for diagnotics, does that actually work ?

[burgo]

what do you mean by sweet spot? for sure it will sound sweeter at idle if you give it more advance, but this will not necessarily amount to more power under load and high RPM.
im interested to know what you mean. does 5bhp up on standard confirmed on two occasions help?

[Stuart]

We used to use carb cleaner to detect inlet manifold leaks as we had hyper accurate wideband lambda sensors in the exhaust downpipes. Essentially squirt the cleaner onto the suspect area and see the AFR go nuts, and if its really bad then the engine will increase in revs etc.

[mowgli]

whilst you are checking for poor running on a 1300, make sure the dizzy advance/retard is ok & the coil is up to it.

but definitely look all over for a carb leak too

[jimbob-mcgrew]

how can i check that mowgli, dizzy side AND carb side ?

dizzy size - put my finger over the vacuum unit ?
carb side - sucking on the pipe that goes to the carb ? (i understand it controls some sort of accelerator pump within the carb ?)

theres no way of checking the coil is there ?

[meritlover]

does 5bhp up on standard confirmed on two occasions help?

it does, yes.

thats why i was asking.

[jimbob-mcgrew]

complicated bast4rd carb this is, wish i had a 1b on there, they never give you any crap

[meritlover]

how can i check that mowgli, dizzy side AND carb side ?

dizzy size - put my finger over the vacuum unit ?
carb side - sucking on the pipe that goes to the carb ? (i understand it controls some sort of accelerator pump within the carb ?)

theres no way of checking the coil is there ?

no,
the vacuum in the manifold controls the retard by the sucking the actuator on the side.

disconnect and plug the vac hose, stick the timing light on the pulley mark and let the engine tick over. as you rev it, the timing should smoothly show advance. if it jerks about crazy then the springs are really badly worn.

then suck the vac pipe at idle and it should retard the timing. you should be able to watch this all hapening.

its a clever system that gives primitive 3D timing as its based on load (M.A.P) and RPM.

im starting to think its fuel related by what youre saying now though.

[jimbob-mcgrew]

so while its running both sides suck do they ? and they fight over pressure to control the advance / retard ?

says barely anything in here about the 2e carb, man, this particular haynes is crap

[burgo]

More vac creates more advance being as you need the spark sooner as th revs increase

[jimbob-mcgrew]

right, so the carb controls the dizzy, i always thought it was the other way round.
so when i rev the engine, i should feel a strong suck on that vacuum pipe coming from the carb right ?

and i can simulate that myself by attaching it to the dizzy and sucking on it.
ok this is making a little more sense now

[Stuart]

odds on the vac advance has failed like most tend to.

[meritlover]

More vac creates more advance being as you need the spark sooner as th revs increase

i disagree. its not as simple as i made out in my original post. Advance is controled by the bob weights, as the centrifugal force flings them out with increase in cam speed.
technically the vac advances the timing too. im trying to remember how the nova works, but i think its

zero vac+zero speed = base timing (hence why the tube is disconnected when setting the timing)
high vac+idle speed = slightly advanced timing to help the burn and compensate for poor cylinder filling
low vac+low RPM (accellerating)= returns timing closer to base timing. (better cylinder filling but low RPM)
low vac+high RPM (high load high speed)= increases advance above base timing.

its never really retards the timing, it just reduces the amount of advance to base timing.

[meritlover]

right, so the carb controls the dizzy, i always thought it was the other way round.
so when i rev the engine, i should feel a strong suck on that vacuum pipe coming from the carb right ?

and i can simulate that myself by attaching it to the dizzy and sucking on it.
ok this is making a little more sense now

thats right. its not so much the 'carb controlling it', but the change in manifold vacuum caused by the position of the butterfly within the carb.

[meritlover]

odds on the vac advance has failed like most tend to.

its possible... The ign timing wouldnt really cause the symptoms described. it would affect performance, but not to that extent.
more likely because the rubber diaphragm has ruptured causing enleanment of the mixture.

[jimbob-mcgrew]

ok, so i ran the checks.
all the hoses appear to be good.
the timing marks pull when the carbside hose is plugged and revved.
the dizzy side however didnt move, i sucked and sucked, and got no resistance, i think i just got a few lungs full of asbestos in the process and no timing movement.

i tightened up the 4 float chamber screws abit more, and tightened the 3 main securing nuts a fair bit, in a bid to pinch down tighter on both gaskets.
timing seems about most acceptable at about 6 degrees BTDC, pinched the dizzy down at that.

adjusted the idle screw abit better, so its neater with the choke pull but not touching it.
and richened the mixture about 1 and a half turns. (will check the plugs after its next run to see if i went overboard)

i need to adjust the choke flap i think, it closes slightly tighter than it looks in the haynes, the guy has a 2mm drill bit in there by the looks of it, i think it can be adjusted by an allen key somewhere on the backside of the carb ?

apart from that, its about as good as i can get it, its a tad better but not great still.

i have a clear plastic inline fuel filter between the pump and carb and i noticed it was full to the top, should it be like that, i dont think so, im wondering whether the fuels not going thru quickly enough ?

[jimbob-mcgrew]

^ and ontop of that i still cant get my head around the timing, as turning the dizzy clockwise to the bulkhead is supposed to advance it right ? but it moves the mark closer to TDC, which in theory is a LATER spark no ?

and i guess i need to replace that vacuum thingy on the dizzy

[meritlover]

when you sucked the hose, was it sucking air straight thru or did you suck up against resistance?

my understanding was the engine rotates clockwise (looking on the crank pulley), the cam turns the same direction albeit 1/2 crank speed. therefore moving the dizzy towards the bulk head would mean the rotor would trigger the coil earlier and advance the timing.
all i can think of is that if you already have your timing set too far retarded (firing after the timing marks), advancing the timing would appear to move the timing towards the mark.

if you line up the timing so that the strobe is fiting when the 2 marks meet. and rotate the dizzy towards the bulkhead, the firing mark on the pulley will appear to move towards the bulkhead and away from the casing pointer.

how do you know you have it set at 6 deg BTDC unless you have a TDC mark on your pulley?
Am i not right in saying the notch on the pulley is a timing mark, and the mark on the pump casing and timing belt pulley is a TDC mark?

[jimbob-mcgrew]

lol i get what your saying lol
its confusing as the marker moves closer to zero degrees when advanced, and in the haynes it says RETARD it to 7 degrees

yeh felt like air was just pulling thru to me

[meritlover]

lol i get what your saying lol
its confusing as the marker moves closer to zero degrees when advanced, and in the haynes it says RETARD it to 7 degrees

yeh felt like air was just pulling thru to me

sounds like the actuator is burst/perrished. plug the hose at the distributor end so that no air is being drawn into the manifold and affecting your mixture. you should hear the engine note change and the idle drop slightly as you plug it.

i would like to clarify the marks on the pulley being ign timing marks. Someone like Mowgli would know. They really have to be. if it was a TDC mark, then the base timing would be on TDC. i dont know how the book can say retard to 7 deg if there isnt a graduated mark on the pulley. you would need a timing disc to do that. or rotate the dizzy by 3.5 deg lol

[meritlover]

you kind of need to stop playing with the ign and the carb at the same time. plug the vac hose with a nail or something, get the ign set bang on the 2 marks with a strobe and leave it as said, it wont be 100% for the unleaded fuel, but it should run better than you are describing.

then play with the carb in a methodical fashion.

does it run any better if you pull the choke out by any amount? if it improves, this may verify the lean running..

can you borrow a carb off anyone?

[garyc]

The vac advance is an economy device, if its broke all it will do is make you use more petrol. To test it disconnect from the carb end and suck it while the engine is ticking over, if its working the ignition will advance and the rpm's will increase.

[jimbob-mcgrew]

plug it you reckon ? ok ill do that before it leaves the drive.

the choke... the chokes really funny, as it requires nothing less than maximum to start the car, but 5 mins later, i have to kill it off completely before the engines half warmed up, as it stutters hard when you want anymore than 2000 rpm, as soon as you flick it off it goes.

nah, cant borrow one. theres only one of my mates left thats daring enough to drive a carburettor, and its not a vauxhall.

i might just have to fork out loads of money and replace everything

garyc - it doesnt do anything, the unit must be dead

[Stuart]

Given on most of the T40 builds they dont hook up the vac advance, it kinda proves its not vital for a decent running setup.

[marc69]

I run my `.4 track car with no vacuum advance, so long as the weights in the distributor work, I have had no ignition problems from 850-over 7000 rpm, sso forget wirrying about that.

My advice is get the ignition timing set right, then tackle the carb. Check all gaskets and the two things (enrichment valve and something else) are not leaking, if there is any tiny leak the ar will not idle and will not run until high revs.

Is there no-one near you who can actually see and help you? Once it is running, the ohc ignition and 2e3 carb work really well .

Oh, I don't think you can actually adjust the mixture, as far as I know that's just a screw to adjust the idle speed on the throttle, I couod be wrong, have never looked for mixture adjustment on these.

[meritlover]

this might help:
http://onemanspanner.wordpress.com/2011/06/13/pierburg-2e3-on-a-vw-vanagon/

http://www.gowerlee.dircon.co.uk/2E3type.html

im sure you will have the manual choke but its the same principle

[jimbob-mcgrew]

:thumb:

[jimbob-mcgrew]

is there anyway i can test the secondary throttle diaphragm/actuator ?

ive basically come to the conclusion that its being starved of fuel.
adjusting the mixture screw does nothing, i can wind it all the way in and cut the supply, and it doesnt effect anything, so it must be running on fumes.
the problem must be before that. maybe the accelerator pump or the enrichment valve ? i'll try adjusting the pump delivery tomorrow, see what happens, and i'll pull the casing of the pump and valve covers to see if any blockages underneath.
if that doesnt work ill have to bite the bullet and spend an obscene £50 on a gasket kit and give it an overhaul, altho i have a funny feeling that might not fix it, it might be a dead secondary throttle diaphragm ?
ppftt this is hard work for someone with minimal knowledge, learning as i go.

[meritlover]

you can test vacuum secondary by sucking the tube like you did with the distributor or use a syringe, its up to you.

[jimbob-mcgrew]

has got bloody cold outside all of a sudden, not keen to work. ill have to brave it tho, and sort this out, cars b0rked.

i think i might just drive it to your house meritlover, and crash it thru the wall, right into your front room. leave it there, walk off, offer some passer-by a ridiculous amount of money for his bicycle and ride back home

[marc69]

The second throttle body just gives a wee boost at 3500rpm [plus, the car will drive fine without it if the proper throttle body is all correct,

[jimbob-mcgrew]

ok im getting somewhere now. the secondary throttle diaphragm tests good with suction, but theres no vacuum from its source end of the carb, the hoses are ok, no vacuum there !

marc - i kinda did a half way bodge for now, and adjusted the primary throttle pump to its maximum so the cars got as much fuel as it can get on the single port, whilst i try and get the other port working, its better like it, but wants more juice and air from the secondary.

so close now - whats controlling the vacuum there ?

[Dave A]

If you are having idle issues the secondary choke is not part of the issue at all. It could be as simple as some crud in the idle jet or fuel filter. On top of the carb there are some brass fittings, one has a slot for a screwdriver, thats the idle jet. Unscrew it and spray some carb cleaner threw it. The pipe that the rubber fuel hose connects too has a small filter inside it, hook it out and see if its blocked up. If it is throw it away and fit an inline filter in your fuel hose somewhere.

[meritlover]

the vacuum is 'controlled' from the manifold. its what's used for load sensing. how have you adjusted the throttle pump? that doesnt do anything for steady fueling, it just rides up the cam on the butterfly and gives a squirt to enrich the mixture as the air speed drops across the venturi.

it wont use the secondary until its in a high load (accellerating) situation. so that should be pretty much shut until the vacuum and throttle position requires it to open.

did you ever get your timing set? how did you do it, and what is it set to?

[meritlover]

On top of the carb there are some brass fittings, one has a slot for a screwdriver, thats the idle jet. Unscrew it and spray some carb cleaner threw it..

part no. 6 on the diagram http://www.gowerlee.dircon.co.uk/2E3type.html


The pipe that the rubber fuel hose connects too has a small filter inside it, hook it out and see if its blocked up. If it is throw it away and fit an inline filter in your fuel hose somewhere.

Part no. 2 on the diagram http://www.gowerlee.dircon.co.uk/2E3type.html

[jimbob-mcgrew]

If you are having idle issues the secondary choke is not part of the issue at all. It could be as simple as some crud in the idle jet or fuel filter. On top of the carb there are some brass fittings, one has a slot for a screwdriver, thats the idle jet. Unscrew it and spray some carb cleaner threw it. The pipe that the rubber fuel hose connects too has a small filter inside it, hook it out and see if its blocked up. If it is throw it away and fit an inline filter in your fuel hose somewhere.

idles better now that ive fiddled, its ready for secondary.
ive stripped the carb and blown it all out, and pulled that filter out.


the vacuum is 'controlled' from the manifold. its what's used for load sensing. how have you adjusted the throttle pump? that doesnt do anything for steady fueling, it just rides up the cam on the butterfly and gives a squirt to enrich the mixture as the air speed drops across the venturi.

it wont use the secondary until its in a high load (accellerating) situation. so that should be pretty much shut until the vacuum and throttle position requires it to open.

did you ever get your timing set? how did you do it, and what is it set to?

i adjusted the little cam lobe on the backside of the butterfly shaft, so theres earlier engagement of the pump, it actually idles steadily for once now, and ive got the mixture screw exactly 3 full turns out.
timings set at zero degree's (the gun says) - a cm from the pin toward the waterpump side, seems happiest there, so im leaving it.

the only manifold connected pipe goes to the choke diaphragm.
the secondary throttle connects to the lower half of the carb

[meritlover]

ignore the gun if its one of those adjustable ones. they are only any use if you have a TDC mark or you know what youre doing. The notch on the pulley should line up with the mark on the casing at idle speed and with the vac hose plugged. job done.

if the timing isnt right to start with then you wont know where you are with the carb. for instance. if you were running too far retarded then you would have to open the idle screw so far out to make the idle speed up that the mixture screw wouldnt be doing anything and it would start trying to fuel from the main jet.

youl end up fudging the carburation to get it to run right and you wont know where you are.

[jimbob-mcgrew]

ive got a TDC mark, 1cm away from the factory 10 degrees BTDC mark.
it takes alot of skill to drive the car without stalling it, set anywhere else.
its running almost good at the moment. i need secondary throttle tho.
ive ordered a gasket kit, hopefully it brings the vacuum back ?

[meritlover]

well, sounds like you've got it sorted anyway