VW Air-cooled mis-fire/ poor running

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Matt74
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VW Air-cooled mis-fire/ poor running

Post by Matt74 »

I'm not on any VW forums so hoping someone here can help. I know Dave999 knows a fair bit about VWs. :help:

Here's the problem I'm having.
My wife's '61 bug running a 1641 twin port engine with twin Weber 34icts developed a severe misfire and would barely run.
On initial investigation I noticed the carbs were leaking fuel and there was also fuel in the sump. The car had only done about 30 miles since the previous oil change so I don't think any harm was done to the engine.

So I rebuilt and tuned the carbs using this guide https://www.wayoutwestie.com/aircooled- ... ed-engine/ and changed the oil. The misfire remained and after a road test the car would barely drive. I've changed the plugs, leads, cap and rotor arm and even bought a new distributor with vacuum advance. Timing is at 7.5° BTDC. Running points and set statically as my strobe light has packed up. I did change to Pertronix electronic ignition and flame thrower coil but changed back to points as the Pertronix was for a 009 dizzy that doesn't have vacuum advance. I left the new coil in place when I changed back to points and vac advanced dizzy.

The fuel pump is new and last time I checked the pushrod moved freely. I do have an electric fuel pump I might try but I don't think that is my problem though I may fit it just to rule it out.

Inlet manifold to cylinder head mating faces are nice and flat with new gaskets and sealant used so I'm 99.9% sure there is no air leak.

Today I went back over the basics and reset the valve clearances, points, timing and tuned the carbs again. The engine ticked over nicely and revved well after warming up on the drive for about 15 minutes with the occasional crackle through the exhaust. After a test drive of about 2 miles it started acting up again to the point it would barely run.

I'm starting to think l might have a cracked cylinder head as the twin ports are prone to cracking but I'm not sure that it would give these symptoms, I don't know what else to try though!

I believe the heads crack between the valves but I'm not sure it would cause the engine to run this bad.

I think I'll end up removing the heads to have a look as I feel I've tried everything else but before I do is there anything obvious I'm missing?

Thanks in advance. :)
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ScottyDave
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Re: VW Air-cooled mis-fire/ poor running

Post by ScottyDave »

Have you tried swapping the coil? Possibly breaking down the hotter it gets. :dontknow:
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Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

ScottyDave wrote: Mon Apr 25, 22 7:09 pm Have you tried swapping the coil? Possibly breaking down the hotter it gets. :dontknow:
Yeah brand new coil.

I thought I'd go back to basics so I checked the fuel pump pushrod again today just to be certain that it isn't dragging at all as that's common. Was nice and free so definitely not that.
Next I pulled a spark plug and it was sooted up so I'm going to re-check the float levels and set the carbs up again as it's definitely over fueling.

I'm pretty sure now that it's a carb issue. I had forgotten that this engine has an Engle 110 cam in it so perhaps the guide I followed is not optimal for this engine but it should still be driveable.

Will probably leave it until the weekend now before having another stab a setting the carbs up.
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Steve
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Re: VW Air-cooled mis-fire/ poor running

Post by Steve »

Just a thought....have you got a heat resistant spacer between the carb and manifold? Could be heat percolating the fuel??
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Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Steve wrote: Mon Apr 25, 22 10:50 pm Just a thought....have you got a heat resistant spacer between the carb and manifold? Could be heat percolating the fuel??
The spacers are aluminium Steve so I'm going to change them. I may have to make them as they are quite thick.
It's had the aluminium spacers for the past 14 yrs though and not been a problem!
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Dom66
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Re: VW Air-cooled mis-fire/ poor running

Post by Dom66 »

If you had it running well for a bit but then it fouled the plugs, check they are the right heat rating / try going one hotter ?
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

fuel in the sump...... its quite hard to get lots of fule in the sump.... it has to travel side ways to get there

[ now ive written this start at the bottom float or needle valve issue]

i'd try a different fuel pump. i think yours has either started to come apart or has a split in a diapgragm. (dpends on type some are rebuildable and the little screws come undone, do em up again and its fixed)

If you have the option change the pedestal and its two gaskets under the pump as well...
a good red/brown orginal is better than the black wonky rubbish from G & S
if the Bore wares it allows the pushrod to offset aganst the pump drive and it intermittently jams

good idea getting rid of the Race only 009.... fasion has a lot to answer for. best dizzy is still the orginal.
if you are running twin carbs connect the vacuum advance to one and use a dellorto pulse smoother from dellorto.co.uk
aftermarcket copy of an old alfa sud part

if its a solex PICT orginal style carb or the twin kadron style i think they have electromagnetic fuel cut off solenoids They need to work
they pull a plunger in and out to cut or open fuel flow check wireing and check for 6 or 12 volts when the igntion is in start and run.

I'd also try opening the tank immedialtly after it splutters to a stop

if the tank goes BONG or there is a massive inrush of air. Your cap or on tank breather is blocked and its vacuum thats causing the problem

i had a 67 that used to do this, well my sister did but she never drove it...
hell for leather and then put put put fart.... open tank close tank good for aother 15 minutes horrible car SelecTaDrop lowerd done before sway away adjusters were invented. no suspension and eventually no floor and no fillings in my teeth, but boy was I cooooool.... grinding the frame head over speed bumps


i got a vented cap.

2 or 3 types one for early tanks with a vent in
one for later tanks that were vented via an on tank pipe to charcole filter type set up or via a pipe from the side of the tank up to the filler neck that had a vent in it but used a non vented cap....

sounds like fuel issue rather than electrical to me


[START HERE]
last thing
carb stuff

floats if metal do they have a hole? i.e have they sunk. heat them in the oven dump into water look for bubbles. mark where the hole is
heat in oven to dry and solder up hole with a tiny bit of solder, you will need plumbers flux
reset flaots

if plastic have hey gone soggy and sunk due to the move to ethanol E10 fuel.?

and while you are in there

are the needle valves in the carbs ok i.e not worn out... or has the rubber tip fallen off due to E10....i think they have or had rubber tips... if you have ever run an electric pump the needle valves get hammerd and their ability to control fuel into the bowl again similar issues to if the floats sink if the carbs are flooding the bowles are just pooring fuel into the motor once full.

additional missed ICT reference

ICTs don't have the fuel cut off but parts are easy transits used ICT ICH and webcon and dellorto.co.uk has lots of bits
i used to raid the breakers yards for ICTs ICH from tranists and 36 MM weber IDF and dellorto DRLA off the alfa sud and related itallian rust.

i.e if its float or needle valve related you can get bits and not have to dick a bout with a soldering iron.

ICT floats plastic as far as i can tell.... i have had 2 DCOE plastic floats go spongy and sink in the last ten years wonder if one of your ICT ones has


Dave
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

cracked heads

they run ok with cracked heads well they run not ok but better than you describe. i think most run about for 1/2 the life of their motor with craked heads :)

you can avoid it a bit by running 1300 TP heads which have been fly cut out to the 1600/1641 cylinder size
what you loose in top end rpm you gain in torque



smaller valves means more space between them and the spark plug hole...

most only realise they have a cracked head when it gets so bad it spits the spark plug out
you really need to overheat it which you on't do if all the flap and bellows shennanigans is still in the shroud and under tins and you havethe correct wider twinport fan don't be running the 1200 1500 fan....


Dave
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Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Dave999 wrote: Tue Apr 26, 22 9:28 am fuel in the sump...... its quite hard to get lots of fule in the sump.... it has to travel side ways to get there

[ now ive written this start at the bottom float or needle valve issue]

i'd try a different fuel pump. i think yours has either started to come apart or has a split in a diapgragm. (dpends on type some are rebuildable and the little screws come undone, do em up again and its fixed)

If you have the option change the pedestal and its two gaskets under the pump as well...
a good red/brown orginal is better than the black wonky rubbish from G & S
if the Bore wares it allows the pushrod to offset aganst the pump drive and it intermittently jams

good idea getting rid of the Race only 009.... fasion has a lot to answer for. best dizzy is still the orginal.
if you are running twin carbs connect the vacuum advance to one and use a dellorto pulse smoother from dellorto.co.uk
aftermarcket copy of an old alfa sud part

if its a solex PICT orginal style carb or the twin kadron style i think they have electromagnetic fuel cut off solenoids They need to work
they pull a plunger in and out to cut or open fuel flow check wireing and check for 6 or 12 volts when the igntion is in start and run.

I'd also try opening the tank immedialtly after it splutters to a stop

if the tank goes BONG or there is a massive inrush of air. Your cap or on tank breather is blocked and its vacuum thats causing the problem

i had a 67 that used to do this, well my sister did but she never drove it...
hell for leather and then put put put fart.... open tank close tank good for aother 15 minutes horrible car SelecTaDrop lowerd done before sway away adjusters were invented. no suspension and eventually no floor and no fillings in my teeth, but boy was I cooooool.... grinding the frame head over speed bumps


i got a vented cap.

2 or 3 types one for early tanks with a vent in
one for later tanks that were vented via an on tank pipe to charcole filter type set up or via a pipe from the side of the tank up to the filler neck that had a vent in it but used a non vented cap....

sounds like fuel issue rather than electrical to me


[START HERE]
last thing
carb stuff

floats if metal do they have a hole? i.e have they sunk. heat them in the oven dump into water look for bubbles. mark where the hole is
heat in oven to dry and solder up hole with a tiny bit of solder, you will need plumbers flux
reset flaots

if plastic have hey gone soggy and sunk due to the move to ethanol E10 fuel.?

and while you are in there

are the needle valves in the carbs ok i.e not worn out... or has the rubber tip fallen off due to E10....i think they have or had rubber tips... if you have ever run an electric pump the needle valves get hammerd and their ability to control fuel into the bowl again similar issues to if the floats sink if the carbs are flooding the bowles are just pooring fuel into the motor once full.

additional missed ICT reference

ICTs don't have the fuel cut off but parts are easy transits used ICT ICH and webcon and dellorto.co.uk has lots of bits
i used to raid the breakers yards for ICTs ICH from tranists and 36 MM weber IDF and dellorto DRLA off the alfa sud and related itallian rust.

i.e if its float or needle valve related you can get bits and not have to dick a bout with a soldering iron.

ICT floats plastic as far as i can tell.... i have had 2 DCOE plastic floats go spongy and sink in the last ten years wonder if one of your ICT ones has


Dave
Dave999 wrote: Tue Apr 26, 22 9:28 am fuel in the sump...... its quite hard to get lots of fule in the sump.... it has to travel side ways to get there

Car is always parked facing up hill so figured the carbs were being gravity fed and getting past the needle valves. Needle valves did have some wear. Apparently the new ones are not as good quality these days and floats (plastic) need to be set lower to shut them off.

Pretty sure floats are good. I read you can submerge the plastic ones in hot water to check for holes. Will try that. I think I'll set the floats to 6mm and set everything up again from there.

Already changed the pump for a better quality one. I don't think the old one was leaking into the sump but it could have been. I'm now running a fuel pressure regulator but may switch to a huco electric as I have one already just to be sure fuel pressure is not too high.

I'll post my jet set sizes later to see what you think. 👍
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

i'd be wary of adjusting float height too much on a weber

higher will cause it to tip in more off idle and into transition
lower will tend to make it lean at idle and trsnasition and continue leanish all the way throigh to an RPM whch is just sucking fuel direct from the jet

i.e you have a jet that meters fuel into the emulsion tube well from the bowl
you have a drilling with a tube in it that has airholes through it, air comes down its middle and bubbles with the fuel in the emulsion tube well and the mixture is drawn out of the bore into the venturi this tube screwed into a bore air gets in via a hole inthe air corrector part of the top of the tube
the height of the fuel in the bowl dictates how much of the tube is submerged at different rpms

low RPM all of it, every hole in it is bubbling away into the fuel that surrounds the tube in the emulsion tube bore it comes down the middle forces fuel in the middle out and bubbles in the slightly higher fuel outsidethe tube between it and its bore
High rpm that tube well will be almost empty. fuel comes in via the jet and mixes with a full tube bore of air before being wipped out into the venturi



better off withfloat height correct by bending tabs or using the thicker washers under the needle valve
but the aim should be to get the level correct so that it covers all the right parts of the emulsion tubes at idle and just off

YES parking on a hill will allow fuel to perculate into the carb and into the engine
you end up with the fuel in the bowl tipping into the venturi, this allows the floats to droop, the needle valve to open and fuel from the tank which is a car length higher up hill to gravity feed the bowl and into the motor

park it the other way round. save fuel :)
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Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Thanks Dave,

I set the float height to 8mm after following wayoutwestys guide which says the following.

"Recently there has been a change in the needle valves recently which has caused them to leak at the standard height of 6mm. Even with new 150 sized valves and the correct fuel pressure they would not shut off.

Since the valves have changed I now set all weber Ict’s to 8mm."

Is it worth trying them at 6mm? I'm wondering if they are lean at 8mm which means having to wind out the mixture screw more to compensate meaning too much fuel at idle causing the plugs to foul up at low RPMS?
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Ok here is a list of the jets I fitted as per the guide I followed. Engine runs a 110 cam which makes driveability a bit poor at low RPMS so maybe these jets aren't perfect for the set up.

F6 emulsion
145 mains
55 idle
165 air corrector
150 needle valve (smallest available these days as far as I know)
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Dom66 wrote: Tue Apr 26, 22 8:47 am If you had it running well for a bit but then it fouled the plugs, check they are the right heat rating / try going one hotter ?
Pretty sure I've always used the same plugs as they're the only ones supplied by machine 7 for the Mexican cylinder heads. Doesn't mean they are right though so I'll look into it. 👍
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

OK

sounds like you have it right
that fella on the link you list has his head screwed on

do you have the suggested emulsion tubes F6? if not it will never work....i promise i went through this with mine.......
i'm trying to feed a 700CC cylinder with a cvarb designed for 400cc to 500cc Cylinders on a 2 litre 4 or 2.5 litre 6 and mine is a 4.4 litre 6

do you have the 120 140 or 150 needle jets


set the float height with an 8 mm drill bit between the lid and the float. its the easiest way, ideally you set float height with 1 tab and you need a setting for float droop and get that right as well.

8 mm from the lid rather than 6 alters how hard the needle jets will be pushed when closed. sounds like a bodge, but presume he caters for it with his jetting and emulsion tube suggestions

the rest of what he says makes sense to me when i think about my own weber DCOEs i think following his lead makes sense

you will not get anywhere if the BOLT IN configuration is not right

emulsion tube tailors the delivery across the range from about 1200 rpm up to redline and the main jet makes it rich or lean to a certain extent across that range, this is your fuel air profile across the range

idle set up
new set of cheap plugs get 2 sets
and a decent set for REAL you don't need to spend lots just get branded plugs don't need no daft platimum multi contact shennaingans
NGK or bosch or champion if buying in a box rather than a plastic bubble pack... there is a reason most sell em in boxes, they don't get busted when they are thrown from the delivery truck someone tell champion.


it needs to idle well but the mixture needs to be "fat" enough to get you over transition from idle onto the main circuit
he seems to cater for that with a 1 size fits all....if you can get away with that no issue. when i stuck dells on mine idle jet was the onlything i changed.... horses for courses.
best way to tune the idle is initially with a timing gun so you can see rpm increases as they happen, rpm will labour up an down, note the peak if it swings 900 rpm to 915 rpm, and you make a change that consistently sees apeak 920 rpm even though it still stumbles back to 900 thats your rpm increase.
you are edging slowly towards "nice" the path there won't be smooth.
get it running
get them balanced, same opening per carb, linkage off, use feelers use airflow meter whatever
turn idle mixture screws in to zero than out exactly 1.5
get it running 1.75 turns if necessary.
once balanced REMEBER wind in or out each throttle stop screw the same on both carbs to get it ildeing away just a tad faster than normal if normal is 850 run it at 900 rpm to help keep plugs clean while tuning

tweak side to side till it stops wobbling about
then get the timing gun or rev counter on it. wind out 1 mixture screw 1/4 of a turn. if the rpms increase good. if they don't turn it back
turn the other the same if they increase leave alone and return to the other side
try again this time the rpms will probably stay the same but it should smooth out i.e the max rpm you see stays the same but the lumpering up and down range gets smaller

if no use
try turning them in
try 1/8 of a turn
you want to hear/see the idle speed increase that you get when the idle mix is right this is like a shallow hill with a steep peak for the top

no good, no good, no good, excellent no good, no good ,no good. we don't know which side the hill you are on and it will be within 1/2 a turn on the ilde mixture screw

wait till it settles each time
and give it a big rev every few minutes and let it settle to clean off the plugs pull both carbs equally to avoid popping and farting and gumming up only 2 of the plugs


youare looking for the highest RPM with the samllest throttle opening and the least amount of idle mixture for smooth running
if the motor is rocking carb balance and or idle mixture between sides could be better....
or you need to up the idle speed

you should be able to get it to idle at 800-900 rpm with any sane road cam

if all else fails use a gunson colour tune £20 well invested, but on a bug you will need a makeup mirror to see what you are doing with your new glass bodied spark plug

connect up linkage
you should hear no chage to idle
likange should be attached and adjusted so it is loose at the drop links with the throttles on their stops
and JUST tight enough to activate both the instance the centre pull pulls.
Alternative
by all means use 1 carb throttle stop to adjust both letting the linkage take the strain of conrolling idle position of the second carbs throttle plate, balance them up by adjusting linkage length on the side that is the dependent carb
just a different way to achive the same outcome

BUT only do this with a CB performance style hex bar that mounts between air filters, you can't do it with an empi swivel set up and i'm not a fan of a fan shroud mount set up becasue the shroud can move indepently of the carbs if things are not done right.

Once happy adjust idle speed back to normal from your slighty elevated 900 rpm remeber depending on how you set up the linkage this may involve just 1 throttle stop screw or both...


this is his ball park, if you are not working with this you have probably answered your own question

1600/1641cc
145 mains, 165 airs, 55 idles, f6 emulsions, 150 needle jets. although he recons 120 or 140 are better needle jets in this application

id buy 2 145 mains 2 150 mains and 2 160 mains
F6 Emulsions

i usually aim for + 50 on the air corrector but my carbs feed 1 cylinder per carb barrel, yours have to cater with pulses from both the cylinders they feed, disruptiong their "day job" rather than just one.

there must be a reason for him going only 20 up and its probably this id buy 155 165 175 air corrector jets
they richen or weaken mixtre across the range but a bigger air corrector will make it leaner at high rpm and cause the main circuit to start earlier at low rpm bigger airs make it easier to drag fuel in from the emulsion tube well at lower RPM.

think of them scewing or pushing a fule air profile vs rpm graph 1 way or the other, tweking 1 end leaner and the other end richer without too much change to the overall shape

think about it the air corrector has a bigger hole so the fuel under it is exposed to a greater weight of air above it (to the edge of space) pushes the fuel in the emulsion tube centre down more when its under vacuum from the running engine than the fuel outside of the tube sitting in the bore, you get a greater mismatch betwen fuel levels IN the emulsion tube and OUTside of it when its all sealed up down its hole. so it alters the bubbling/mixing charcteristic, tuning your emulsion tube fuel air mix profile dependent on vacuum


Its a pig to do
you only know you can do it once you try
once you get it right you can't understand how you could get it wrong so much before hand :)

Look up David Vizzard Emulsion tube comparison to holley meetering blockset up. explians how they work and why the two companies just did the same thing but with different parts acting on different mixtures of fuel and air


They might be leaner at 8 mm in theory the level in the bowl is lower BUT not if modern needle jets are leaky old junk.... he is catering for the drip drip drip... or weber spain in their infinit wisdom did something daft with the float size/mass/dimensions LIKE they did on the DCOE. i.e he doesn't know why he has to do this but there may be an easy answer, It might not be the needle jet quality. It might be modern floats differeing from the Transit and bedford van floats of yore which will have been soldered spun brass hemispears.

8mm could be the new way you can try Webcon and ask is 8 mm the setting on NEW ICTs when 6MM used to be the setting for OEM ICTs

i.e. have your spanish minions made a another change for the hell of it (don't say that)

if they are in a good mood they will tell you, if you spend some money they may well become quite chatty

if you buy stuff off ebay get it all from the same place, genuine weber is best but eastern European copy stuff aint bad just don't mix and match
infact the ENTEK EMPI JINLIN FAJS stuff from china isn't THAT bad you just have no comeback, if you get some rubbish friday afternoon "after lunch in the pub" jets or stuff that went out the backdoor of the factory.

Dave
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

Plugs

if you use an NGK 5 currently try a 6 or 7

i went from 5 - 7 but had to cater for a move from a CR of 8:1 to a CR of 12:1 and a silly old cam

i get lost with bosch but the internt will know via a comparison table

Dave

Jings that was big post above apologies all.... :)
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