1600 twin port poor running

[fordescort1]

Can anyone help???
My 71 twin port runs like a pig.
When purchased it ran fine but cut out at every stop.
So after a few tweeks of the carb I got it to idle but when driving it had a really bad flat spot and no power.
Carb off and a good clean out and check over, choke set up and both adjustment screws set to standard settings.
Now idles better but after about a minute revs start to die down slowly, blip throttle and picks up again but still starts to die.
The rubbers on the manifold are a bit perished so I have got new ones to fit and new points and condenser. These are on the to do list.
I am new to air cooled so don't know whether its a fuel issue or something more serious and don't get much chance to mess around with it.
It is running 34 Pict 3 carb, standard oil bath air box but no air intake pipe as no hole in tin ware for it. And no heat exchangers but has j tubes and the small pipes to inlet manifold (pre heat tubes??) are cut off half way between manifold and tin wear. Do these need blanking off??
All tin wear in engine bay looks OK but I don't think I have a thermostat or flaps fitted. Is this going to be a problem.
I had a Hillman imp once and this had the same problem which turned out to be a faulty coil.
Its a bit embarrassing as I am a mechanic but only work on more modern stuff and air cooled can be a problem so I have heard.
If any fellow bay owners can give me some pointers I would be greatful as at the moment it is just an expensive garden ornament, but a nice looking one

 

[creationblue]

Sounds like it's sucking in to much air from that perished seal, until u make sure everything is airtight you will be fighting a loosing battle

 

[bigdaz]

The carbs can suffer from worn spindle bushes giving air leaks.
When you cleaned out the carb did you blow out all the airways the idle circuit is prone to blocking.
Also when you set the carb up did you check that the screw on the throttle arm is not wound in to keep the tickover up (it shouldnt touch the cam once the choke is off)

This might be helpful http://www.vw-resource.com/34pict3.html" onclick="window.open(this.href);return false;

 

[Trikky2]

Can anyone help???
My 71 twin port runs like a pig.
When purchased it ran fine but cut out at every stop.
So after a few tweeks of the carb I got it to idle but when driving it had a really bad flat spot and no power.
Carb off and a good clean out and check over, choke set up and both adjustment screws set to standard settings.

Standard settings are the start point so that the engine will start. Once warm these settings have to be adjusted to make it run right.

Once your sure the throttle stop screw is only stopping the butterfly jamming in the carb and that the butterfly is fully closed, you can set the big air screw and the small mixture screw when the engine has warmed up.

Turn the small mixture screw in each direction to get the fastest idle speed. If the idle speed is now too high, turn the big air screw inwards to slow the idle speed down. Then turn the small screw each way again to ensure you still have the highest idle speed.

 

[Trikky2]

Also when you set the carb up did you check that the screw on the throttle arm is not wound in to keep the tickover up (it shouldnt touch the cam once the choke is off)

This might be helpful http://www.vw-resource.com/34pict3.html" onclick="window.open(this.href);return false;

It Should touch the cam. That's why it's called a Throttle Stop screw :lol:

 

[bigdaz]

Also when you set the carb up did you check that the screw on the throttle arm is not wound in to keep the tickover up (it shouldnt touch the cam once the choke is off)

This might be helpful http://www.vw-resource.com/34pict3.html" onclick="window.open(this.href);return false;

It Should touch the cam. That's why it's called a Throttle Stop screw :lol:

Ahh but its only there to open the throttle when the choke is on ?

 

[cyberdyne systems]

Also when you set the carb up did you check that the screw on the throttle arm is not wound in to keep the tickover up (it shouldnt touch the cam once the choke is off)

This might be helpful http://www.vw-resource.com/34pict3.html" onclick="window.open(this.href);return false;

It Should touch the cam. That's why it's called a Throttle Stop screw :lol:

Ahh but its only there to open the throttle when the choke is on ?

Agreed, I tend to wind it to almost come in contact (imagining the is some fag paper in between)

 

[Trikky2]

Also when you set the carb up did you check that the screw on the throttle arm is not wound in to keep the tickover up (it shouldnt touch the cam once the choke is off)

This might be helpful http://www.vw-resource.com/34pict3.html" onclick="window.open(this.href);return false;

It Should touch the cam. That's why it's called a Throttle Stop screw :lol:

Ahh but its only there to open the throttle when the choke is on ?

It has to touch the cam because otherwise the throttle butterfly jams into the carb throat which will chew away at the soft metal making a ridge.

This wear ridge upsets the flow on small throttle openings which will also change the vac signal to the vac advance and can cause the throttle to be stick when opening.

The way to set the stop screw is to adjust it until, without touching the throttle arm, it just grips a thin piece of paper like a fag paper. Then give it an extra quarter turn inwards.

It's easy to see its a delicate adjustment by the very fine thread used on the screw.

 

[fordescort1]

Throttle stop screw is set as you have said.
The carb looks like a copy, should I get a genuine and rebuild it???
Does anyone have any views on the thermostat and flaps that are missing

 

[Trikky2]

Well yes your right. The problems your having relate to a previous owner deciding random parts of the engine were put there by VW merely for decoration and to give their workers something to do.

Air intake :- the air cleaner has two inlets, one for cool and one for warm air. Like many other vehicles, the air flow into the carb is varied between warm and cold to prevent icing in the carb and manifold.

Manifold :- like many cars, the manifold is heated to prevent icing and to prevent fuel condensing onto the internal metal surface.

Thermostat :- the thermostat and its flaps does exactly the same job as the thermostat on water cooled engines in that it regulates the engines operating temperature when running and speeds up the warm up phase (which is when most engine wear occurs).

If you fix these problems then not only will your engine run better, use less fuel, produce more power but there's a good chance your carb problems will be solved as well.

 

[fordescort1]

So does this mean that I have to put heat exchangers on and a new manifold.
What the hell is that going to cost?????????
What do other people do with the pre heat tubes when no heat exchangers fitted.
The thing that has always puzzled me is that if engine tin wear is so important then what happens when an air cooled engine is in a beach buggy. No tin wear fitted to them.

 

[Trikky2]

So does this mean that I have to put heat exchangers on and a new manifold.
What the hell is that going to cost?????????
What do other people do with the pre heat tubes when no heat exchangers fitted.
The thing that has always puzzled me is that if engine tin wear is so important then what happens when an air cooled engine is in a beach buggy. No tin wear fitted to them.

If you don't have heat exchangers then block off the holes both on the fan shroud and in the tinware. There are many threads on the net about this.

A beach buggy engine is open to air flow on all sides and hence the hot air will blow away rather than get sucked back in.