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Aussie Greg
Samba Member
Joined: March 19, 2004
Posts: 253
Location: Blue Mountains N.S.W. Australia
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 Posted: Tue Sep 23, 2008 1:57 am Post subject: mystery flat spot/misfiring |
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Hi guys,
Ok I have a 65 1200 bug (stock standard) I have been trying to find the cause of a flat spot / misfiring when driving. It seems to get worse as the car warms up.
So far I have swapped the distributor, coil, condensor, it has new ignition leads, new spark plugs (checked the gaps), I have cleaned and re-assembled the carburettor and I have re-set the timing and triple checked it. I have also adjusted the tappet clearances and all seems to be ok 
I cannot see or hear any exhaust or manifold leaks but, I have noticed the manifold directly under the carburettor ices up and stays quite cold! Could it be as simple as the heat risers being clogged up with carbon? Would this cause the engine to miss or have a flat spot under acceleration? Hope someone can shed some light 
Greg
_________________
If it's not in a Volkswagen I'm not going!
My email - [email protected]
1963 Beetle
1965 Beetle
1982 Type 25 Transporter/Vanagon
1985 Type 25 Caravelle/Vanagon
2001 Golf |
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Slow 1200
Samba Member
Joined: July 02, 2004
Posts: 2105
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| Posted: Tue Sep 23, 2008 4:36 am Post subject: |
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| yes, manifold icing causes flat spots and hesitation, do you have the stock air cleaner with all the hoses hooked up? |
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Aussie Greg
Samba Member
Joined: March 19, 2004
Posts: 253
Location: Blue Mountains N.S.W. Australia
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| Posted: Tue Sep 23, 2008 5:49 am Post subject: |
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Hi slow 1200,
Yes I have the hoses all connected up and the stock oil bath set-up. One other thing I did notice was white oily sludge in the breather tube from the oil filler to the oil bath. Obviously moisture mixed with oil Don't know what to make of that!
I did clean the sludge out but, if the manifold is icing up... Could that be causing the sludge as well?
I'll take the manifold off if I can get time tomorrow and inspect and clean out the heat risers... Hopefully that will solve the problem.
Thanks heaps for your help and I'll let you know how I go.
Greg
_________________
If it's not in a Volkswagen I'm not going!
My email - [email protected]
1963 Beetle
1965 Beetle
1982 Type 25 Transporter/Vanagon
1985 Type 25 Caravelle/Vanagon
2001 Golf |
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bill may
Samba Member
Joined: August 27, 2003
Posts: 14160
Location: san diego,ca
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vicsvw
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Joined: February 27, 2003
Posts: 1001
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blackhorse
Samba Member
Joined: September 09, 2006
Posts: 229
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| Posted: Tue Sep 23, 2008 6:53 pm Post subject: |
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| Aussie Greg - I had the same problem and it was the heat riser tubes. Not as easy to clean as it sounds. I just finished the job on Saturday after a week of soaking it with carb cleaner and drilling. I was told to use a piece of clutch cable in the drill and fray the end of it. I found the best results when I used a thicker piece of cable - cut at various lengths - and a hammer drill. Make sure you run the drill in reverse. Learn from my mistakes and it will save you time and headaches. Cheers! |
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MTIguy
Samba Member
Joined: October 19, 2006
Posts: 182
Location: West Chester, PA
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| Posted: Tue Sep 23, 2008 8:12 pm Post subject: |
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Possible split or crack in a spark plug wire. I had a car when it warmed up and I took off around 3,000rpm the car would buck like it was out of gas or spark, come to find out I waited till night, warmed up and jacked the throttle sure enough spark plug wire was arc(ing) onto a metal source nearby.
F.Y.I. the plug wires were brand new!
Good luck.
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I know who I am! I'm the dude playing the dude disguised as another dude! |
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Aussie Greg
Samba Member
Joined: March 19, 2004
Posts: 253
Location: Blue Mountains N.S.W. Australia
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| Posted: Wed Sep 24, 2008 12:56 am Post subject: |
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A big thankyou to you all ! 
It looks like I'm going to need a day or so to work on fixing this problem!
Bill May, thankyou what you tell me makes perfect sense! I was starting to think the two problems were somehow related.
vicsvw, thanks for the helpful links.
blackhorse, thanks for the advice, I will try what you have said... From memory when I last had the manifold off I saw quite a bit of carbon inside the heatrisers but, unfortunately I did not think it was going to be a problem  Oh well another mistake I have learnt from 
MTIguy, I was thinking the same thing as I have had a new sparkplug lead crack and arc before but, I had a spare and tried it on each plug to make sure  Thankyou
I did not get to check today too many other home duties to attend to but, will get time over the weekend.
Greg
_________________
If it's not in a Volkswagen I'm not going!
My email - [email protected]
1963 Beetle
1965 Beetle
1982 Type 25 Transporter/Vanagon
1985 Type 25 Caravelle/Vanagon
2001 Golf |
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carln
Samba Member
Joined: February 26, 2008
Posts: 66
Location: Indianapolis
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| Posted: Wed Sep 24, 2008 3:46 am Post subject: |
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| Is the vent pipe hooked up between the air cleaner and the oil filler? That helps keep the humidity down. Check your manifold for tightness/leaks at the heads. |
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Aussie Greg
Samba Member
Joined: March 19, 2004
Posts: 253
Location: Blue Mountains N.S.W. Australia
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| Posted: Thu Oct 02, 2008 3:09 am Post subject: |
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Ok I have made some progress... Could'nt find and old clutch cable so I bought a short length of cable wire (same thing anyway) I attached it to my drill and was able to clean alot of the carbon build-up out. I am unsure of one thing though. On the 1200 manifold it has a cast aluminium section which covers the centre section of the manifold I can only push the cable through as far as the casting on each end of the manifold. Does the heat riser tube continue right across the manifold? Or Only as far as the casting on each side? Ok I have probably confused everyone  If I were to blow compressed air into one end of the heat riser... should it come out the other end? Cheers
Greg
_________________
If it's not in a Volkswagen I'm not going!
My email - [email protected]
1963 Beetle
1965 Beetle
1982 Type 25 Transporter/Vanagon
1985 Type 25 Caravelle/Vanagon
2001 Golf |
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vicsvw
Samba Member
Joined: February 27, 2003
Posts: 1001
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| Posted: Thu Oct 02, 2008 8:56 am Post subject: Yes |
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Yes it is open all the way through. Try the (Acetylene turned off and using oxygen only) Not to much oxygen as the burning carbon really gets hot and to much oxygen can melt the runners.
This way is so easy and fast it is worth taking the manifold to some one who has a Acetylene torch. Vic
http://www.1800vw.bizhosting.com/qa_heatrisers.htm |
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Aussie Greg
Samba Member
Joined: March 19, 2004
Posts: 253
Location: Blue Mountains N.S.W. Australia
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| Posted: Tue Oct 07, 2008 6:38 pm Post subject: |
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Thanks vicsvw,
I'll have to find someone who can help me out with an acetylene then.
Cheers
Greg
_________________
If it's not in a Volkswagen I'm not going!
My email - [email protected]
1963 Beetle
1965 Beetle
1982 Type 25 Transporter/Vanagon
1985 Type 25 Caravelle/Vanagon
2001 Golf |
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