VW Air-cooled mis-fire/ poor running

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

Post by Matt74 »

Thanks Dave you know your stuff. Yes I'm using F6 emulsion tubes!

I'll read through your post a couple more times and have another go.

I'd better order some more plugs!
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Steve
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Re: VW Air-cooled mis-fire/ poor running

Post by Steve »

Dave, I'm pretty sure you forget more in a day than I will ever know! :thumbright:
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Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Steve wrote: Tue Apr 26, 22 4:50 pm Dave, I'm pretty sure you forget more in a day than I will ever know! :thumbright:
He's a clever chap isn't he? And he always gives great advice which is very much appreciated by myself and I'm sure many others.

It's good to know these carbs should work as I was having my doubts. Hopefully I just need to follow Dave's tuning guide and the jobs a good'n. :study:
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

lets hope i haven't made matters worse :)
Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

A little update on this. I didn't get around to having another go at setting the carbs up as planned last weekend but managed to find some time this afternoon.

Machine 7 don't seem to be selling the Bosch plugs for the Mexican cylinder heads anymore, or at least I couldn't find them on their website so I googled the Bosch plugs to try and find some and came across a classic BMW forum and someone had mentioned that they have problems with the Bosch plugs if the fuel mixture is even slightly off so they changed over to NGK BP6ES plugs and haven't had a problem since. They didn't mention what problem they were having but I thought why not try some NGKs.

I know Dom suggested trying a hotter plug but as I always buy the plugs from Machine 7 I assumed l had always used the Bosch plugs, now thinking about it l really don't remember if they were Bosch or not that I had always used.

Anyway I gapped the new NGKs and bunged them in. I was short on time so didn't disconnect the linkage as you should as every time I disconnected them the things need adjusting again. I was confident the throttle on both carbs were opening and closing at the same time so I wound the mixture screws in then back out 2 1/2 times and fired her up.

Straight away l needed to wind the the mixture screws in so wound them in a 1/4 turn at a time whilst also adjusting the idle and making sure the carbs were balanced. There was no crackle or popping from the exhaust like before and it was much easier to make adjustments this time where as with the Bosch plugs it didn't seem to make any difference what I did.
The carbs ended up with the mixture screws out only 1/4 turn. Idle seems a tad high but any lower and it feels that it may start to stumble so left it on the high side and went for a 15 minute drive staying close to home just in case.
I took it nice and easy at first. Feels like it could do with a bit more timing. Either that or its the 110 cam but I need to fix or replace my timing light first. The car is much happier at higher RPMS which is a bit of pain really and I think that is due to cam but maybe more timing will improve things.
Towards the end of the drive l gave it some welly and it goes really well. Spun the wheels pulling out of a side road which Mel complained gave her whiplash but she's happy the problem seems to be sorted.

Made it home without any stumbling, missing or backfiring so I'm feeling fairly confident it's finally sorted. My money is on the plugs being the issue. Have to say it really had me stumped and had me second guessing myself and in the end getting pretty frustrated.

Gonna take it for a longer drive tomorrow and fingers crossed it will drive as well as it did today.

Thanks all for your suggestions and taking the time to share your knowledge and help me out. :thumbright:
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

super news

idle screws out 1/4 is prbably the 1 size fits all idle jet

small idle jet might help on that front..

but i'm inclinded to think if it aint bust......etc

Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Did I say idle screw? Sorry Dave I meant mixture screw. I think it may still be a tad rich but will leave as is until my new timing light arrives.
Went for another good run yesterday 20 minutes or so then Mel went to get some ethanol free fuel and went for another drive without any issues.

Only problem I have now is an oil leak from the oil pump cover thanks to my engine builder either stripping a thread or not bothering to fix it. This was several years back but is now leaking a bit more than it used to. I'll try and degrease around the cover and try and seal it up with some instant gasket or tiger seal for now and come back to it later!
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

no probs i knew what you meant :)

oil pump cover has a gasket
oil pump cover is held on by studs and nuts
and the nuts are special half the thread of the nut is steel but the other half of the nut has a plastic insert. a kind of red top-hat plastic insert
the flat red end of the nut goes to the cover and the plastic bit seals any leak around the stud or across the face of the cover.

you can take cover off replace gasket and put cover back on..
pulley and rear engine tin out
followed by the filler piece that sits behind pulley
to access the pump

whats really hard is taking the pump out without dismantling the case halves. you can get a puller but it can still bust the pump....
and you need the correct pump for you cam...

but maybe you won't need to do that...could just be cover gasket rather than a leak from around the pump or its flange to case face gasket

Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Hmm. I bet it ain't the right pump but it's been in there for long time now and nothing bad has happened. Yet!
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

don't worry it must be

its all in the depeth of the pump or the length of the drive

US performance cams all follow a pump set up that was used in 1 verion of the engine
hence when fitting a US 3 bolt cam the pump or maybe just the drive needs to match..... its so long agao i can't remeber
if it didn't match you'd already have a very big problem

Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

I see. Thanks Dave :)
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Well it's been running great all week until yesterday afternoon. Sitting at the traffic lights about a mile or so into the journey and Mel said it felt like the engine was going to die. Brought the revs up and almighty loud bang and large plume of black smoke out the back.

Car started again but wasn't happy. I drove out to meet her on the way back. Turned the idle mixture screws in a tad and drove it home myself. Was on a hill and it drove up it fine even under hard throttle. Turned out of the junction at the top of the hill and it was really angry popping, banging and kangerooing.

Plugs indicate it is still too rich. Was 21° in the shade so maybe the higher temps were enough that it wasn't going behave. Either that or something in the ignition system is breaking down but I think more likely it's too rich at idle.

Checked points gap and timing again and its spot on. Runs fine again on the drive after cleaning the plugs. Idle mixture screws now out just 1/8th of a turn. Didn't take it for a test run as while it I had it running on the drive it decided to spew a lot of oil out of the pump cover (at least thats what it looks like).

I'm going buy some mains and airs as you suggested Dave and and try again after I've fixed the oil leak.
Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

I might also try some hotter NGK BP5ES
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Dave999
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Re: VW Air-cooled mis-fire/ poor running

Post by Dave999 »

not sure how the idle set up works on a ICT

on a DCOE its a 3 pronged pain in the ass

the jet has a hole in the end.. which is the jet size
the jet has a hollow centre which dicates how much fuel is availble in the hole it sits in
the jet has a hole in the side that dicates how much air is mixed

obviosly with 3 factors that can be changed it becomes a bit of a juggling nightmare
as the numbering is linked to the second 2 aspects, when they were invented and for who, and nothing to do with the main cause of leaness or richness cuased by the jet size

looks like you don't need to worry abou that thank goodness

https://www.dellorto.co.uk/shop/weber-c ... -dgas-ich/
https://www.webcon.co.uk/products/15141 ... et-ichdgf/

the options are all about just the jet hole in the end 55 beinbg .55 mm i think.... :)

if you have 55s and you are on 1/4 of a turn out on the mixture screws i think a 50 or a 47 might do the job hard to say without seeing/hearing it and well bugs sound funny anyway so no guarantee it would help.....

do the idle jets first

a motor under load and at high rpm, well high for a VW, can stomach a rich condition on the mains for much longer
if fact yoy tune slightly rich anyway for higher rpm

idleing pig rich does tend to have much more impact on plugs and running

get the idle set up right first

get a gunson colour tune. you are looking for a pale blue flame at idle with the idle screws out about 1.5 turns


sounds like it needs a tad more advance at ilde, and you are rich i guess it gummed up the plugs and back fired


new gasket for pump cover and see how you go, replace it with the correct sealed nuts, not just some 13 mm nuts you have lying about from an exhaust or manfold swap like everyone else does... :)


Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
Matt74
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Re: VW Air-cooled mis-fire/ poor running

Post by Matt74 »

Cheers Dave,
Will order some new jets and a colour tune and try again.
Will order the correct oil pump cover nuts as well. They are just regular full nuts on there at the moment. One stud has pulled the threads though. Should have been fixed when the engine was rebuilt several years ago.

Thanks for the advice. Much appreciated!
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