Engine over run question.

[Demon James]

I hope I've termed this right but another issue I seem to have since the new dizzy went on in the dart is the motor not shutting down when I switch off.

Starts fine, hot or cold.

Initial is 17 degrees at 1000 rpm idle.

Max out at 34 degrees at around 2500 rpm.

Plugs are NGK B6S XR5 V power gapped at 36 (on another note, where can I buy replacements/equivalent for future reference?)

Shuts off instantly if temp says less than 170 f but anything over that and it runs on, appears to be worse the hotter it gets (up to 200 ish)

Sometimes it's a small " phutt phutt phutt " and fuel sprays out of the carb.

The worst one was a good 5 to 7 seconds and a little more animated out of the carb.

It's not all the time but more often than not.

Any ideas where to look, what am I missing? Please be gentle with facts and figures as I'm still learning

Cheers guys

[Blue]

Several things can cause running on but I think I'd start with the idle speed, see if you can get it down to 650-700 for a start. Check to see that the primary side transfer slot is only just uncovered, any more than that and you're idling on the main jets. if that doesn't give you sufficient idle speed then you crack the secondaries open a touch to compensate. Reset the idle mixture after that and see what happens. For a race engine you should be using a plug a couple of heat ranges lower than stock, that would be the next thing I'd do if the carb tweaks don't work.

[Pete]

First issue is that 200 is too hot (In my opinion)
I would look into that first.

Then go through the points Blue raises.

[Dave999]

do you need the fancy plugs?

do you need that gap?

if you have a 10+.1 CR and a gap that big, the voltage in the coil is going to have to rise dramatically to jump a gap with 10 time more molecules wedged into it. Loads more electrons to rip from their moorings to make the spark. Try them at 22-26. remember to check timing after change the spark will arrive earlier with a smaller gap *

having recently been through a process of removing total advance to good effect do you need 34 BTDC I'm now at 27 with 14 initial at 900

plug gap and advance are a case of just enough

Do you have wedgey or domey heads dome/semi/poly or hemi heads often need less

do you have a thermostat?

when it is doing this can you check in the dark to see if the exhaust headers are glowing.... they go a cherry red if you are burning fuel in the exhaust and that certainly makes things hot

is the radiator still full and does its top tank sit level with or slightly higher than the water jacket in the heads?

granted none of this has much to do with running on

it really all came from oooh fancy plugs and big gap

remember you only ever use 1 prong on a multi prong plug. it will be favoured until it erodes away and one of the others is then closer. i.e only benefit is they don't need to be swapped and re gapped every service. They have 3 prongs and they therefore need doing every 3rd service works nice for dealers they can charge 4 times as much for the plugs and never need to change them while the car is under warranty


* the higher your static CR the hotter and more powerful spark you need

Hot is a function of power

power is current x voltage
big gap increases voltage dramatically to the detriment of current

big gap does a high voltage lower current spark, its a very quick thing.
smaller gap does a lower voltage higher current spark which starts earlier and it lasts longer.

doesn't matter if its multi spark or single spark smaller gap = longer running spark up to a point.

I think you need more spark staying power so a smaller gap will provide better ignition and leave less unburnt crap about to glow red or burn in the exhaust.

make the gaps too small and you get a high current low voltage spark and diminishing returns, so little of the chamber is exposed to the spark you end up mis firing or not firing at all. or the voltage reached is too low and the plug just doesn't spark the current flows through the mix to earth without firing it off


I have chuntered on sorry

dave

[Demon James]

Chunter away dear boy All good stuff as ever.

I shall attempt to answer your points/questions once I have resized and uploaded a picture of a plug because I dont think they are as fancy as you think

[Demon James]

Single prong plugs Dave

[Demon James]

Replies in upper case, it's not because I'm shouting LOL

do you need the fancy plugs?

do you need that gap?

if you have a 10+.1 CR and a gap that big, the voltage in the coil is going to have to rise dramatically to jump a gap with 10 time more molecules wedged into it. Loads more electrons to rip from their moorings to make the spark. Try them at 22-26. remember to check timing after change the spark will arrive earlier with a smaller gap *

having recently been through a process of removing total advance to good effect do you need 34 BTDC I'm now at 27 with 14 initial at 900

plug gap and advance are a case of just enough

Do you have wedgey or domey heads dome/semi/poly or hemi heads often need less

STOCK IRON HEADS

do you have a thermostat?

YES (HAS BEEN DRILLED BY OTHERS - STARTS TO OPEN IN A PAN OF WATER AT 190 DEG F)


when it is doing this can you check in the dark to see if the exhaust headers are glowing.... they go a cherry red if you are burning fuel in the exhaust and that certainly makes things hot

EXHAUSTS DONT GLOW

is the radiator still full and does its top tank sit level with or slightly higher than the water jacket in the heads?

RAD IS FULL AND LEVEL IS SLIGHTLY ABOVE WATER JACKET.

granted none of this has much to do with running on

it really all came from oooh fancy plugs and big gap

remember you only ever use 1 prong on a multi prong plug. it will be favoured until it erodes away and one of the others is then closer. i.e only benefit is they don't need to be swapped and re gapped every service. They have 3 prongs and they therefore need doing every 3rd service works nice for dealers they can charge 4 times as much for the plugs and never need to change them while the car is under warranty

SINGLE PRONG PLUGS


* the higher your static CR the hotter and more powerful spark you need

Hot is a function of power

power is current x voltage
big gap increases voltage dramatically to the detriment of current

big gap does a high voltage lower current spark, its a very quick thing.
smaller gap does a lower voltage higher current spark which starts earlier and it lasts longer.

doesn't matter if its multi spark or single spark smaller gap = longer running spark up to a point.

I think you need more spark staying power so a smaller gap will provide better ignition and leave less unburnt crap about to glow red or burn in the exhaust.


make the gaps too small and you get a high current low voltage spark and diminishing returns, so little of the chamber is exposed to the spark you end up mis firing or not firing at all. or the voltage reached is too low and the plug just doesn't spark the current flows through the mix to earth without firing it off


I have chuntered on sorry

dave

[Dave999]

ah so normal plugs...I should have just looked em up

ok

fine

gap? 36 seems big...... suppose it depends on coil and ignition but it still seems big...

something is making it hot

suspicious that its is likely to be mixture or something to do with ignition timing if everything else is alright

i.e no. gasket problems
no obvious cooling problems (bellt pump radiator issues)
standard heads


odd

is the TDC on your balancer TDC?

Dave

[Demon James]

Managed an hour on the car tonight, Dave.

Rightly or wrongly I swapped out the stat for an old one with no valve just to see if it was flow restriction or opening late.

The stat I took out was opening at 190 Degrees F which seems high to me?

I didnt want unrestricted flow, hence using an old stat body with just the middle bit missing.

Aaaanyhoo, now running at 175-180 after 15 mins idle so I can now at least run longer whilst checking things over.

The transfer slots where far too visible upon removing the carb (clearly got myself in a muddle when I last fiddled with idle oops, silly billy)

Now set so they are just visible, looks like a tiny square instead of a slot

So, she fired right up but a bit lumpy until the temp climbed, to be expected?

Once the temp settled at 175 the idle was better but not brilliant.

Checked initial timing, 17 Degrees.

I had already set the idle mixture screws in and back out 1 1/2 turns but it was quite stinky and the AFR meter said 12.3. So I turned each screw (this carb has 4) in by a quarter turn. AFR sat at 12.6 (still stinks) so I turned in again a quarter turn, AFR said 12.4.

It appears that they are not having any affect in mixture though

Anyway, time ran out, car was at 175 to 180, turned her off and no overrun, stopped instantly.

I will remove plugs again maybe tomorrow night or sat morning and see what they look like, also try a slightly smaller gap but I guess I need to figure out the idle mixture issue?

Cheers guys, your help is much appreciated as ever, I'm determined to get there and understand how I got there

[Blue]

Ok progress! I have found fuel pressure and float bowl level both have an effect on idle quality. I set the level so that it just weeps out when you rock the car side to side, no more than 5 psi fuel pressure. What is your idle vacuum and what size power valve?

[Demon James]

Fuel pressure is bang on 5

Level is nearly half way up sight glass. I must admit I have always run it as you say, just trickling out of the float level plug.

This carb has clear level glass inserts. It's a brand new carb by the way.

Holley 850 track warrior. I will have to check my notes that I took before I installed. I noted PV size, jets etc but can't remember off hand. Will look up tomorrow.

Going back to levels, the instructions with this carb say set it to half way up the sight glass. When I first installed it I had the levels as I would normally. The motor would nearly die when you slowed heavy or stopped quick. So thinking this may be primary float bowl washing forward, I raised the levels. Seems to have stopped that issue.

[Dave999]

a 195 stat should be ok for the UK on a standard motor
I wonder if it was sticking.... or in the wrong way round, have done that before. they don't work very well.


what do your idle mixture screws meter? usually fuel..... but they can be just a simple air bypass or they can meter pre mixed air fuel (usually weber style carbs)

if the screws are doing nothing

you have the throttle too far open or if you have such a thing, your idle jet is too big.

or occasionally a big air leak that you have compensated for elsswhere by accident

if you run too rich for too long while fiddling, your plugs will get fouled and often they never recover leading you into a case of ever decreasing returns and frustration as you make bigger and bigger adjustments that have less and less impact for rougher and rougher running. it can be hard to tell if you just have it set up bad or if its misbehaving due to plug issues

I have found a Gunson Colour tune to be exceedingly useful fo getting idle just right, it can highlight a difference as smaller than an 1/8th of a turn on an idle mixture screw very effective for port on port set up (webers) might be less so when you have 4 barrels all dumping into the same big hole but ultimately a blue ish flame for each cylinder should still be achievable


if you try to tune everything to 14.7 on the AFR meter with anything other the Fuel injection it will be lean when you stamp on it, carb delivery is all over the place you want to be a little bit rich so it doesn't do a big lean bog down when you pull away with haste . tune it so it feels right then set about cleaning it up checking the AFR with no detriment to the feel.

I tried to tune to the meter from the begining, much frustration later eventually went to a rolling road where he said you have been trying to tune to that bloody meter from the get go haven't you,....don't do that, give it what it wants based on feel and what you intend to do (performance or economy) and tidy up the idle and any too rich points using the meter or other tools later on.

if you run way too rich and bog it down to a near stall your sensor gets swamped and shows a lean or error which then takes you in the wrong direction.

if you run way too lean and you bog it down into a stall immediately after recovery the exhaust is full weak mixture that has fuel in it at a level that can be measured and it shows a massive rich 11- 10 on the meter which of course takes you in the wrong direction.


his opinion was meter is great for a running car you are improving
but its only 1 side of the story for initial set up, for that you need the seat of your pants or a dyno, and use the meter as a second confirmation that you were moving in right direction on a running and driving motor .

meter alone from first start up can lead you away from where you want to be

anyway

got it to about 12.5 - 13 and tidied it up from there..... a bit......still a bit stinky but Jings it goes better. doubt it goes much faster but it is certainly more enjoyable.


Dave

[MilesnMiles]

Bit of an echo chamber here, but..
Tuning my carb with MMA chaps at Shakey a while back and reducing float level really helped with idle.

AFR, not much good for non EFI cars at idle in my experience. Had all issues Dave identified. Used vacuum and drivability as my measure.

Mine occasionally runs on, no pattern. I turn the motor off in gear and no issue. Modern fuels don't like our cars and provide various wobbles, I find.

[drewcrane]

Bit of an echo chamber here, but..
Tuning my carb with MMA chaps at Shakey a while back and reducing float level really helped with idle.

AFR, not much good for non EFI cars at idle in my experience. Had all issues Dave identified. Used vacuum and drivability as my measure.

Mine occasionally runs on, no pattern. I turn the motor off in gear and no issue. Modern fuels don't like our cars and provide various wobbles, I find.

Same here todays fuel if you want to call it that is always an issue here , since we live here in high elevation the bring down the octane to 91,so carb cars well soon enough efi is in the works, sorry to hack the thread,carry on

I do however use a pyrometor in the exhaust so it is not to lean or to rich,and use a vacuum gauge to get the most vacuum

[Demon James]

Cheers chaps, definitely setting up with my vac gauge next then.

To be fair, that's how I set the latest double pumper on the Demon as there is no AFR.

It's only because there is one fitted to the Dart already. I did a calibration in free air etc but I can appreciate your points on trying to set up a carb by hand vs EFI