Fuel Cut Off Solenoid

[mrbodly]

Hi all

I have a 2L Aircooled T25.

What is the purpose of the fuel cut off solenoid on the left carb? A previous owner has cut the plunger off the end of mine.

The van idles poorly once warm and stalls when stopping at junctions/traffic lights, could the bodged solenoid be responsible?


Cheers
Myles

[CovKid]

generally stops the engine running on but they can leak and that never helps with idling.

[BOXY]

The fuel-cut off solenoid helps stop the engine running on when the ignition is switched off. It shouldn't effect the engine when running.
Check the rubber tee and elbow on each end of the balance pipe that runs across the bulkhead between the carbs. If either are split or disconnected the engine will stall at low revs. Check the spade connectors on both the fuel solenoids if they're not getting +12v with the ignition switched on, that could cause low rev issues as well.

[mrbodly]

Thanks for the replies. Sorry, looking at the Haynes it is actually the 'bypass idle cut off valve'.

[kevtherev]

sometimes called an anti dieseling valve too.

[CovKid]

Very symptomatic of an air leak - damaged gasket (any from carbs downwards), ill-fitting hose, wear in throttle flaps (thats the lowest ones), inlet gaskets or anywhere air can get in. At full throttle openings the engine is less fussy but at low revs and idle the engine needs a predictable and accurately metered does of fuel and air in the correct ratio to stop it cutting out or running rough. Thats presuming leads and plugs are in good order ofcourse. With that in mind I'd look for leaks. Certainly not uncommon on an engine that may have been poorly maintained.

Also vaccum pipes (ie one to dizzy) - check that fits snugly both ends. Check that distributor plate moves smoothly if you suck on that pipe and that it will stay in that position if you stick your tongue over pipe end while sucking.

The van idles poorly once warm and stalls when stopping at junctions/traffic lights

[mrbodly]

Thanks all, plugs and leads recently replaced.

There is a tiny hole in the rubber elbow, where it slides over the carb outlet, which in turn is held in place with a jubilee clip. Don't think any air is escaping here but will replace anyway.

Also have an intermittent starter issue as well, this van is really testing my patience at the moment!!

Cheers
Myles

[mrbodly]

Also recently replaced the vaccum hoses but will test the distributor plate.

[CovKid]

Starter may be brushes that only make contact some of the time. You can replace brushes on their own but you need a whopping soldering iron.

[BOXY]

There is a tiny hole in the rubber elbow, where it slides over the carb outlet, which in turn is held in place with a jubilee clip. Don't think any air is escaping here but will replace anyway.

The air won't be escaping, the engine will be sucking too much air in weakening the mixture. If you've recently changed the vac hoses have you connected them back up correctly?

[CovKid]

As Boxy has underlined it is incoming air that has to be predictable at idle. Too much and the mixture leans out. From the top of the carburettor or carburettors down, everything should be sealed with no opportunity for air to work its way in other than where its meant to, as far as cyclinder heads. Carb settings are set when the above is correct. Invariably people 'tweak' in an attempt to compensate but it rarely works.

Check that the accelerator flap spindles are not letting in air from outside. Unless yours have been rebushed since new, chances are they have up and down play in them, and if there is movement, air can get in. You can sometimes find leaks by spraying WD40 or similar around potential leak areas when the engine is running. If theres a leak you'll hear the engine revs rise as the leak is momentairiy blocked. It only takes one loose or porous hose to create similar problems.

[mrbodly]

Thanks chaps

Vac hoses definitely reconnected correctly, I photograph everything as I dismantle as a safety net. Matches yours Boxy, thanks for the pic.

Not that it'll solve my issue but I have a new bypass idle valve to fit and will be helicoiling the carb where the threads were previously stripped.

I've bought a new rubber elbow and t-piece for the balance pipe. After fitting these I'll systematically check for leaks and report back.

As always, thanks for all the advice.

Cheers
Myles

[mrbodly]

I've just noticed on Boxy's pic, the outlet on the back (towards cab) of the air filter housing has a pipe connected to it, mine does not, it is just open. Should I have a pipe connected?

[Ralf85]

Thanks for the replies. Sorry, looking at the Haynes it is actually the 'bypass idle cut off valve'.

The problem might be electrical. I had a similar problem with my old 1600 T2 (not sure yours will have the same wiring, but I'm sure there is not that much difference). It turned out to be a faulty electrical connection. When properly connected the power from the lead keeps the valve open. With the lead broken the valve wants to close. At higher revs there was enough pressure to keep the valve open. Every time I stopped the valve closed cutting off the fuel. I replaced the lead and the problem was solved.

To check this out, I unscrewed the bypass valve, took it out then reconnected the lead and held the valve against the engine to earth it. I got somebody just to switch the ignition on (not the engine). The electrical pulse should cause the valve to open (move inwards). If it does not move, then the lead is probably the problem. An easy and quick check. Let us know how you get on.

[mrbodly]

Hi Ralf

Thanks for the reply. I'm pretty sure in my case the bypass valve isn't the culprit because at some point someone has cut off the plunger off, so it wouldn't be able to restrict the flow of fuel.