Misfire

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squaresteve
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Misfire

Post by squaresteve » 29th January 2013 - 8:10pm

Good Evening all,
I'm getting a misfire especially under load and sometimes at idle, it can be perfect one day and terrible the next. I've checked everything electrical, I have electronic ignition so no points or condenser. I'm starting to think I have carb issues. if I remove the air filters and rev the engine the choke flaps seem to be fluttering in time with the misfire.
I have standard solex carbs. I'm thinking of upgrading/changing the carbs but obviously don't want the same issue afterwards.
Has anyone come across this problem? If so what was the cure?
Car is a 1973 1600 Squareback


Cheers
Steve
1973 Squareback
1969 Fastback
1968 Early bay westfalia

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Editor
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Re: Misfire

Post by Editor » 1st February 2013 - 12:16am

Check the ignition leads carefully. You may have an open circuit or high resistance. They should be about 1000 Ohms end to end (+/- 200 maybe).
Other thing is the rotor arm has a resistance in there - that might be bad. I think that is about 5000 Ohms. A misfire might produce a pulse at the wrong time that might disturb the airflow through the carbs. Sometimes it's visibly burnt. Of course, it might be the electronic ignition. Damp weather can make a marginal ignition system misfire. The different behaviour fromone day to the next suggests to me it's more likely to be ignition - in your case, the unit itself, or the distributor cap/arm/leads/plugs. Plenty of things it could be there. Much checper than new carbs!
Dave.

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scout
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Re: Misfire me too.

Post by scout » 3rd February 2013 - 7:10pm

Excuse the highjack here but I have the same issue.
no power under load.. back fire etc. took it to a garage, had following done..

HT ignition leads set 92600
spark plugs SB91350
Ignition contact set 92360
Distributor Cap 92130
Ignition condensor 92305
Ignition rotor arm 92205
New fuel line where it was leaking.
new hose on balance pipe..left hand side.

Still missfiring... no power under load back fire etc. Someone also recomended I get the distributor changed to electronic ignition..dont know if that would solve the issue but surely be better.

When I bought her I had to drive her all the way back from Leeds to Deal in Kent, she never skipped a beat, however at one point I ran very low on fuel due to not knowing where I was on th M1 and misjudging my next fill up..so wondering if it picked up crap into carbs.
Next day my troubles began, although intermittant.. at first.. now all the time

Any ideas anyone? Might it be a Carb issue.? Any help greatly appreciated...

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Editor
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Re: Misfire

Post by Editor » 4th February 2013 - 2:58am

Yes, typical garage change everything and hope it cures it - certainly helps their cash-flow!

You may easily have got dirt in the carbs, but there's another possibility if you have the external fuel filler flap. Behind there, there's a J-shaped rubber hose that links the filler pipe to part of the tank breather system. That hose cracks every few years. You can get a repair hose from notch1500 on ebay. If you use a piece of 1/2" breather hose, you need to stop it collapsing as it bends though 90 degrees. i used some plastic conduit to keep the hose from collapsing, but there may be other solutions.

If water gets in, that can cause random misfiring - probably wouldn't be all the time.

No need to get electronic ignition.

Try turning the engine over manually - look for lack of compression on any cylinder - could be a valve.

Get acquainted with Jane and Bryan at Elham (01303840374) . They'll sort you out and the charge will be fair!
Dave.

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Marko
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Re: Misfire

Post by Marko » 4th February 2013 - 5:26am

Editor wrote:Yes, typical garage change everything and hope it cures it - certainly helps their cash-flow!

You may easily have got dirt in the carbs, but there's another possibility if you have the external fuel filler flap. Behind there, there's a J-shaped rubber hose that links the filler pipe to part of the tank breather system. That hose cracks every few years. You can get a repair hose from notch1500 on ebay. If you use a piece of 1/2" breather hose, you need to stop it collapsing as it bends though 90 degrees. i used some plastic conduit to keep the hose from collapsing, but there may be other solutions.

If water gets in, that can cause random misfiring - probably wouldn't be all the time.

No need to get electronic ignition.

Try turning the engine over manually - look for lack of compression on any cylinder - could be a valve.

Get acquainted with Jane and Bryan at Elham (01303840374) . They'll sort you out and the charge will be fair!
noticed from your pics that your car was originally a FI model, was it converted or a complete engine swap? just thinking the distributor could be wrong for the carbs but I would expect it to run ok on a run. maybe you just dragged a load of muck from the tank when it ran out of fuel and a carb strip down could fix the problem..
my 1968 Fastback Automatic build thread
viewtopic.php?f=4&t=6896

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scout
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Re: Misfire

Post by scout » 4th February 2013 - 7:30am

Thanks guys for all your help on this and for the ref of people in Elham.
I had also a compression test and all was ok from the test. So ill get that breather tube done and get someone to clean out the carbs. Hopefully that will resolve it.
Ill let you know how it goes...thanks again. 8)
Marko..yes car had a brand new engine in 2006..car also used to be white. But looking at old pics on back of car read VW1600 E..so not sure.

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squaresteve
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Re: Misfire

Post by squaresteve » 4th February 2013 - 6:31pm

Mine looks like its the carbs, you can see the choke flaps fluttering when you open the throttle. I also have another noise which is the heads are very slightly loose. So I'm pulling the engine out, going right through it and detailing the engine.
I will then either rebuild the carbs or replace with Dellorto's

Cheers
Steve
1973 Squareback
1969 Fastback
1968 Early bay westfalia

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BarbBee
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Re: Misfire

Post by BarbBee » 4th February 2013 - 11:00pm

idle control whatsit? (the little gold cylinder thing on the carb bottom middle left)
Image

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Editor
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Re: Misfire

Post by Editor » 5th February 2013 - 1:02am

Barrel with electrical connector is the electromagnetic cut-off idle jet. It should click when power is connected (ie turn in ignition and touch the connector to it - or just attach it). When engine is turned off it positively stops the idle fuel and prevents possible running-on. It also stops fuel trickling through the idle circuit into the cylinders if the car has a full tank and is parked uphill, with fuel level in tank higher than carbs.
Dave.

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BarbBee
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Re: Misfire

Post by BarbBee » 5th February 2013 - 11:03am

Just thought I'd offer the idea as I had similar probs on a beetle and was scratching my head till changing that bit :) ( coz I have no idea otherwise :lol: )

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Re: Misfire

Post by Editor » 7th February 2013 - 1:59am

I think if you unscrew it and put 12V on it, you can see the plunger move, but you can feel it do that anyway when fitted. No clunk, no good. Some of them have a small screw in the plastic cover that can over-ride the cut-off (not sure if unscrew or screw in though!
Dave.

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scout
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Re: Misfire

Post by scout » 18th February 2013 - 11:37pm

Thanks Dave for your ref to Jane and Bryan at Volksfarmers , they are lovely people, they cant do enough to help.. :D

Right.. Missfire developed to not starting at all then had to get it recovered to garage at Volksfarmers.

My Carbs were full of fuel and the floater valves had to be changed to older original ones, apparently I had new ones in there malfunctioning..
Engine is running right now however, I'v got a fuel smell coming from the exhaust, Bryan has checked for leaks, no leaks anywhere from fuel lines, Bryan thinks it may be a worn fuel jet overfueling and causing to run rich...so next thing change the jets to less worn ones.. new carbs are a bit expencive...lol Hopefully it may solve it.

Ran the car on tick over, covered the exhaust outlet and engine did not stall..ummm..

Iv also noticed on some threads that some people have pointed to fuel pump issues or fuel pressure regulator, are they same thing or different components? I have a newish fuel pump but it was fitted by previous owner. Also just to note, the engine was replaced by the previous owner to a 1671cc engine and to carbs rather than injection.. still have the wiring and some components for injection set up. Also wondering if the Solex Carbs are wrong for this particular engine size...??

Any thoughts guys?

Thanks & Regards.

Pat. 8)

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Editor
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Re: Misfire

Post by Editor » 19th February 2013 - 1:00am

New needle valves leaking are a common problem.

The fuel pressure regulator is a FI item, though you can get a carb versiom. Carbs need only 3 to 5 psi pressure; our Type 3 injection runs at 28 psi. As mentioned elsewhere, you shouldn't be running the fuel injection pump for your carbs. I would expect that to have been changed already.
Dave.

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Marko
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Re: Misfire

Post by Marko » 19th February 2013 - 5:31am

how do you tell original needle valves from repro? I rebuilt my carbs but I get wet main body gaskets so I assume they are over filling or something.. I acquired a spare pair of carbs at Dubfeeze at the weekend so will have a play later on and see what valves are in those..
my 1968 Fastback Automatic build thread
viewtopic.php?f=4&t=6896

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alex d
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Re: Misfire

Post by alex d » 19th February 2013 - 9:12am

my originals say "Solex"! also Marko, if you have the 316 and 317 carbs like I do make sure you have a 1mm washer under the needle valves and not anything smaller!
P-R-N-D-2-1

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Marko
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Re: Misfire

Post by Marko » 19th February 2013 - 10:07am

I'll have a look at my spare carbs, they look like they haven't been touched so will compare..
my 1968 Fastback Automatic build thread
viewtopic.php?f=4&t=6896

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scout
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Re: Misfire

Post by scout » 20th February 2013 - 4:16am

Thanks Guys, Ill get it checked when she goes back into Volksfarmers. 8)

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Marko
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Re: Misfire

Post by Marko » 23rd February 2013 - 11:40am

I Just had a play with my spare pair of carbs, they look original and untouched which is good to compare to my rebuilt ones on the Fastback. the cut off valves are different to the ones in the Fastback carbs, they have a ball bearing in them and a metal washer spacer.. I'm tempted to fit these in my good carbs and see if they weep fuel out the gaskets. just looked in my engine bay and the gaskets are still wet despite not been turned over for a few days!

I need to invest in an ultrasonic bath to clean stuff like this in, with a bit of work I can have a nice pair of spare carbs. only thing missing is the right hand side choke and small con-rods to operate choke butterfly's.

Mark.
my 1968 Fastback Automatic build thread
viewtopic.php?f=4&t=6896

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Editor
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Re: Misfire

Post by Editor » 24th February 2013 - 2:31am

You should have a metal spacer washer under the needle valve. For '71 to '73 it should be 1 mm thick, and for 12V up to 1970 it's 0.5mm, though it's listed by carb part number, so non-original carbs might differ. You definitely need one anyway!

Really, the fuel shouldn't leak out from the gasket anyway. That implies the surfaces aren't flat - which is not that uncommon. If the carb is overfilling it runs out the overflow pipe into the carb throat.

I've seen someone say that to test the needle valves hold the carb top upside down and try to blow gently through the fuel pipe. The weight of the metal slug is enough to prevent anything flowing. It sounds possible, but a quick calculation suggests it would need to weigh a couple of grams - I reckon the moving slug would be quite a bit less than a gram, thinking of the chemical balance weights we had in a box. Maybe you get an idea if it leaks readily.
Dave.

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Marko
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Re: Misfire

Post by Marko » 24th February 2013 - 10:40am

Editor wrote:Really, the fuel shouldn't leak out from the gasket anyway. That implies the surfaces aren't flat - which is not that uncommon. If the carb is overfilling it runs out the overflow pipe into the carb throat.
that's what I thought really but did wonder.. I made the mating surfaces as flat as I could and thought I got it perfect but obviously not!

my engine is a 71 so not sure on carbs! it has a metal washer but after-market cut off valves that have a bad reputation apparently so will check fuel level in carbs 1st.

right now it's starting and running the best it ever has and not even set timing!

apologies to Steve for hijacking this thread little :oops:

Mark.
my 1968 Fastback Automatic build thread
viewtopic.php?f=4&t=6896

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squaresteve
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Re: Misfire

Post by squaresteve » 27th February 2013 - 10:10pm

Marko wrote:
apologies to Steve for hijacking this thread little :oops:

Mark.
No problems Mark I'm taking it all in. :-)
1973 Squareback
1969 Fastback
1968 Early bay westfalia

Houghmeister
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Re: Misfire

Post by Houghmeister » 28th February 2013 - 10:55am

I had exactly this issue - it turned out to be a filthy fuel tank. If the car has been stored for ages and then driven and run low on fuel it can dislodge all of the treacle at the bottom of the tank. Check the fuel filter to see if it is dirty - if it is then replace it. If it gets dirty again very quickly then the problem is with the tank. There is an easy fix for this ( easy once you know how!!! ) James Wooton sorted it for me 02083172973

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Marko
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Re: Misfire

Post by Marko » 3rd March 2013 - 6:28pm

I took the tops of the carbs off today and the fuel level seams OK (about 12-13mm from top of lower carb body). the gaskets I used from MEGABUG seem very thick compared with the originals so I find it strange they seep fuel. floats are not stuck and valves seem to be OK too.

Image

below is a comparison between the rebuilt carb on the right and the spare I have on the left, the spares seem in good condition actually and I might rebuild them..

Image
my 1968 Fastback Automatic build thread
viewtopic.php?f=4&t=6896

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Re: Misfire

Post by Editor » 7th March 2013 - 3:14am

Just had a thought - I think I recall a plastic spacer that fits on the carb float arm pivot. It's possible to get that the wrong sde of the hinge pin. My memory is a bit vague as I've not had my carbs apart for ages. It's a sort of plastic piece with two 'legs' and a curved joiner. it's probably put in there correct, but I remember reading something a long time ago about getting it wrong, and not closing the needle valves fully.
Dave.

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