Hi
has anyone had problems with engine run on? When I turn off the ignition the engine tends to run on a couple of turns and I think that on occasions it is actually running backwards (after releasing the clutch whist running on the car moves backwards when still in first gear.)It is a 1600 single port with a 28pict carb which did not come out with a fuel cutoff valve(68 Kombi). This problem has only started recently and from what I have found out so far could be a build up of carbon or maybe poor quality fuel with too low an octane level. Does anyone have ideas on how to fix this?
Cheers Paul

could be your timing out or maybe even needs a new timing belt

sorry stacy b...

just check ur timing
if thats ok might be the idle jets are a bit big but if its only just started recently then that probably isnt the case
a 28pict is probably a tad on the small on side for a 1600

-Joel

A very common problem with low compression engines. It can't be ignition timing - the key is OFF! It is due to a build up of carbon in the combustion chamber that glow red after the key is off and then the engine "self ignites" like a diesel. Easiest way to try to fix without stripping the engine is to get a cup of water, take the air cleaner off, with the engine running at a fast idle or higher pour the water slowly into the carbi. Not too fast to stall the engine but about a 5 mm stream. Lots of steam will come out the exhuast and hopefully in the process a fair bit of the carbon from th cylinder. You can also do the same with a Wynns product but I think water works almost as well - as long as you dont empty to cup in 2 seconds and hydraulic the engine!

Engines with an electic idle cut off valve also solve the problem as it blocks the idle jet when the key is off.



Ken

a safer way i use of that method is just a spray bottle of water
when the engines nice and hot hold the revs about 3K and spray lightly over the carb throat
less chance of soaking the thing
works wonders on these old carboned up granny putt putt cars

dam thought i was the only person on earth whoes dad told he the secret grasshopper

Stacy b and Dub74L

If the ignition is off, how could it be timing (there would be no spark)

Sometimes it can be using low octane fuel in a relatively high compression engine. It's and old problem from the 1950s and 60s when the petrol was low octane it was necessary to rev the engines of Jaguars and MGs when turning them off. Try reving the engine, turning the ignition off and keeping the throttle open while the engine stops. If that solves the problem your engine is dirty inside the combustion chambers or the fuel is crappy, or both.

A full answer

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Idle Cut-Off Valve


(Also referred to as the "electro pilot jet" and the
"by-pass air cut-off screw.")

The idle cut-off valve is not strictly a "jet," but this is a good place to discuss it. The idle cut-off valve sticks out the left side of the carburetor on H30/31 and 34 sries carbs (but on the right side on 30PICT series) and has an electrical connector on the end. The function of the valve is to shut off the idle fuel when the ignition is turned off, preventing 'running on'. It provides fuel at low medium revs too, so if it's not working you'll get a rough idle and lean mix at lower revs.

The idle cut-off valve receives power from the positive (+) terminal on the coil (#15) -- see the schematic which shows this wiring arrangement. "N" on the schematic is the coil. You will see a black wire coming into the positive terminal on the coil from fuse #12, which receives power from the ignition switch, so the valve opens whenever the ignition is on, allowing the idle fuel to flow.

Note the three black wires leading from the positive terminal on the coil -- one to the backup lights, one to the automatic choke, and one to the idle cut-off jet. That terminal on the coil is just a convenient place to obtain power to these components. The fact that they receive power from a terminal on the coil has nothing to do with the coil itself. The three wires could each go up to fuse #12 individually, but that would be very inconvenient. So VW chose this configuration.

You may have to get creative about how you attach so many wires to the single terminal on the coil. Any auto supply store can sell you a little T-shaped adaptor that will fit on the terminal, with three "wings" (if you will) to which the three black wires can be attached.


Please be sure to use black wire for this purpose -- black means "power when the ignition switch is on" in the VW world.

If the idle cut-off valve fails in the shut position, the car will still run (roughly) on the main jets but will stall as soon as you take your foot off the throttle. If the valve sticks in the open position, the idle fuel circuit will remain open, so if the engine is still turning it will still draw fuel through the idle jet, resulting in running on if there is a hot spot in one or more cylinders. With the idle cut-off valve working correctly, hot spots in the cylinders don't occur as readily, since there is no fuel available to keep the engine running once you turn off the ignition. It's a problem VW recognized very early on (since the aircooled engine has very hot heads and hot-spots were therefore more likely than in water cooled cars), so the fix was to add the cut-off solenoid to the carburetors.

It is very easy to check the idle cut-off valve to make sure it is functioning properly. Turn the ignition on (but do not start the engine). Disconnect the electrical lead from the valve, then touch it to the connector again. If it's working, you'll hear a clicking sound as the relay pulls in. If you do not hear this clicking sound, it's time to replace the idle cut-off valve. They are cheap enough.

When replacing the idle-cut off valve in the carburetor, don't screw it in too hard ... it has fine brass threads and it's screwed into the soft metal of the carburetor. Also check that the valve hasn't worked loose in the carburetor -- they do sometimes, and then work only intermittently. And of course make sure that it's properly connected electrically to the connection on the coil where power is provided (the + connection) -- the lead can break off.


~~~

Thanks for the valuable info Jud I''ll try your suggestions and see how it goes. Will let you know how it goes.
Cheers Paul

ive got a 89 brumby ute that does the same thing and still runs for about 30 seconds to a minute with the key off but only when the engine is hot

There is one problem with revving the engine before you turn it off and that's unburned petrol will be in the cylinders. That will wash away any residual oil and cause huge wear in start up, so it's not recommended.

Problem fixed
I used Kens (Judsons4eva) suggestion of putting water down the Carb. whilst the engine was running and have been driving around for the last few days and hey presto no more engine run on.Thank you for the no cost fix:thumb:thumb:thumb:thumb