Ebgine run on caused by advanced timing?

[rebuilder86]

What is the theory behind this fellas.

When the key is turned off the coil is off. 

i call bullshit on the whole thing and say retarded timing = hotter hot spots which ignite fuel without a spark, so retarded timing causes run-on, not advanced timing. Where do these people (it seems everyone on the net) get this scenario and how can it be?

[rebuilder86]

oh and before someone sais detonation causes hotspots and preignition. no.  nonono. 

preignition can cause detonation

detonation occurs after the spark and is a result of the spark starting the fire too early and then the flame front accelerating past the speed of sound due to the continually compressing mixture.

but detonation doesnt cause hot spots, it just puts a holes in things or snaps things.

is there any other reasons i havent thought of?

[7000rpm]

Run on can be the carby shut off solenoid not working, typically 

[rebuilder86]

well, no believe it or not, run on shouldnt happen. and the anti dieseling valve kinda hides the problem. but i was asking if anyone could explain where this idea of advanced timing causing miraculous magic combustion with no spark, comes from.

[ke70dave]

Becareful coming all guns blazing.....I am all for good discussions, but you might put people off:)

I've never heard of anyone say engine run on is because of advanced timing, like you say the second you turn off the key the spark plugs stop. 

The most obvious cause of engine run on is when the engine is so full of burnt carbon that the carbon stays hot enough to ignite the fuel mixture that is still being drawn through the carby. And this is either caused by residual fuel between the carby and engine, or that fuel solenoid valve sticking on. 

Running a heap of "seafoam" or "subaru upper cylidner head cleaner" through the engine will take care of this carbon and put an end to the running-on issue. All my engines have always had the head off and cleaned early in my ownership and ive never had any dieseling issues. In fact all the years playing with carby engines ive never had dieseling issues. The only time ive ever seen it is on engines that are completely stuffed and is a miracle they run at all. 

Maybe prolonged used of overly advanced timing causes excessive carbon build up? Maybe that's where the myth comes from. Never ever heard of it myself though.

 

 

[rebuilder86]

haha dave i get excited when i see ur avatar pop up that uve replied to one of my posts. sometime i think, maybe he really looks like timoen. :p

u havent run into the garbage i come across. ive just read it so many times in forums while trying to so research on peoples 4 cylinder NA timing setups. I read it so many times that i started to believe it. but with a clear head, i wanted to make sure my pals here, couldnt give me a reason as to why these people may be correct.

but yeh it appears there are more people who say "advance timing has nothing to do with run on" than the uninformed. ive been googling this morning and it seema for every incorrect poat, there are a few others who correct the person.

[rebuilder86]

your point on advancing perhaps causing carbon deposits is pretty understandable...

Mind you, the old trick of taking the car for a hard thrash to remove carbon takes advantage of braking carbon loose by subjecting it to sonic bangs from mild detonation. so id say detonation might, help the situation haha. maybe not extreme detonation, but no one would run their car like that..... or would they.

[ke70dave]

On a K motor you can have the head off in 30mins, spend a few hrs with degreaser on all the valves and the top of the pistson, a $50 head gasket put it back together and it will probably run better than ever.

[rebuilder86]

I'm only asking out of interest because of all the nonsense my research into timing is finding.

My motor is running frikn sweet these days. touch wood.

but yeh damn, i did a head gasket change out on the farm on the bush basher corolla and recorded it. took about 45 minutes with a quick dirty valve cleanup. This engine is the best engine ever designed.

[LittleRedSpirit]

I see a few shades of grey here.  Dieseling on is caused by a false ignition from the extra compression and heat held by carbon deposits around the chamber.  As David says it still cant happen without access to fuel so you either have fuel pooled in the manifold and a very rich car generally to create this or you have a carby that doesn't cut the fuel with ignition properly.  I've only ever had one car that did it, an ae71 with 500000klm.  The 4ac went in the bin shortly after.

I've never heard an argument for timing causing the issues with carbon that cause dieseling.  This idea of advanced timing causes carbon deposits must be from retarded people, because you need advanced timing to make an engine run, quite a lot at low load, and far less at high load, but advanced timing it all is.  I guess maybe they mean over-advanced and pinging.  To me this means your talking to some real kooks that probably dont set their base timing, inspect plugs, use a wideband or tune the timing on a dyno.  So I would disregard what they say unless they can explain the science.  I assume if you advance the timing correctly, you ignite all the fuel and it is swept from the cylinder most efficiently.  If you over advance it, you simply send a shockwave back against the rising piston and hurt the inertia of the engine, but you dont lack the ingredients for full combustion of the fuel and air, you might actually fractionally extend the window of time the explosion has, so incomplete combustion causing soot is not going to be associated with this over advancement, more likely under advanced and rich reading would be logically more likely to leave semi combusted particulates behind.  The carbon may signify worn rings allowing the engine to burn oil also.  I think if someone says they can pin the ills of any dieseling engine on timing alone they might be tripping.

Toclean it out and stop the dieseling, you can get a water sprayer that sprays a fine as possible mist, then put very slowly about a litre of decriminalised water vapour through the engine while at low to middle revs.  This will de carbon the head and ports.  You dont need any special products.  If you dont want to stand there doing it you can rig up a very simple water injection system and spray it in while driving for a while.  If the motor stumbles, too much water, a fine mist of water is ideal, but dont be in a rush cause a teaspoon of water added at once could ruin the motor.

 

[rebuilder86]

little red, exactly. i can't write a readable paragraph like u, so thank u for giving me the words to describe the stupidness of these suggestions.

i actually also came across this crap it was listed as a list of symptoms and their causes.

under the heading "engine deisels / runs on" it had all the normal causes but then seperately listed "timing too far advanced" and "vacuum advance broken"

vac advance broken i completely understand. but "advanced timing" - my left testicle.

buggered if i can actually find this stuff now. Its just had me stressed for so long and its good to see we all here agree that its nonsense.

[rebuilder86]

hey a couple of sources i have read have stated that fine mist spray isnt actually good enough and that u should drop a vacuum tube into a glass of water and let it do its thing.

i am not game on that idea, the vac advance tube sticks pretty damn hard to my hand. I'm fearfull of locking it up. 

have u been able to confirm carbon removal using the process? no one ever has any proof of concept so i tread with caution.

Edited November 17, 2017 by rebuilder86

[LittleRedSpirit]

Its an old trick an experienced mechanic has taught me.  He used to buy cars off off the old ladies n gents at the nursing home in his suburb and do this, service fix any issues and resell them running properly for a few extra quid when he was younger.  Just read about any water injection system pro and cons and they will always talk about how it keeps the ports and chambers far cleaner, near perfect.  I've heard of people doing it to an old motor pre pull down to make the cleanup and disassembly of gunky rings easier.

 

It seems counter intuitive to say the problem of dieseling is caused by any ignition source if the key condition of dieseling on is an off ignition.  Its also not sensibe to say its caused by lack of vac advance or too much vac advance, that will just run like shit.  Pick a lane is it cause by more or less unicorn ignition events?

[LittleRedSpirit]

I actually typed decriminalised water vapour.  lols.

[rebuilder86]

i thought u did that on purpose. i like it and I'm using it from now on. i see calcium and lime as criminal. i have a real problem here in the jungle with lime and calcium in the water. people have their radiators pulled apart, rodded and aoldered back together HALF YEARLY here. its cheaper to do that than use decriminalised water.