1600 Twinport Tune up question

[Raggles]

Has anybody any thoughts/ideas/comments on the following:-

I have set up my motor as follows....

set valves at .15mm cold.

with engine fully warmed up ... 123 ignition unit set to 7.5 degree advanced on the built in test light then checked at 30 degree advance at 3,500 rpm.

Set the carb (34pict 3) fuel mixture set to 4 full turns out .... idle screw to 2.5turns out. Fired the engine up again. Then set the idle at 900rpm. Following this turned fuel mixture out until max revs achieved (half turn), then back in until it started to slow and set it just before this point (roughly back in a quarter turn). re set the idle to 900 rpm.

The engine seems to run smoothly and idles smoothly when stationary .... so far so good. Over a long journey it runs pretty cool (can handle the dip stick)

However ... when starting from cold .... it fires almost immediately and idles on the automatic choke. As soon as the choke closes the revs immediately drop and the motor stalls without a little foot on the throttle. I then have to wait until fully warm before the idle picks up and then it runs smoothly at 900 rpm.

If I then switch off the engine and try and re-start in a couple of minutes time I have to turn it over 5 to 7 times before it fires ... and then it is fine.

If I am on a long drive and stop the van for a period of say 10mins (for a sandwich etc). the engine is still pretty warm. When starting up again I have to turn it over 5 to 7 times before it fires. Then it won't idle but stalls for the first couple of minutes until fully back up to running temp ... then everything sweet again.

There must be something going on here, but I can't think what.

Would be interested if anyone has come across this.

Tim

 

[Trikky2]

These carbs were tetchy back in the day. One trick we used to find worked well was to change the idle jet for the one out of a 1303s beetle which was one size larger.

Before doing this you could try giving the mixture screw another eighth to quarter turn anti clockwise (out) to richen it a tad more. Also, if you look at the auto choke cover, you will see the setting marks. Slacken the screws and turn it about five mm more, to increase the tension closing of the choke flap.

 

[Raggles]

These carbs were tetchy back in the day. One trick we used to find worked well was to change the idle jet for the one out of a 1303s beetle which was one size larger.

Before doing this you could try giving the mixture screw another eighth to quarter turn anti clockwise (out) to richen it a tad more. Also, if you look at the auto choke cover, you will see the setting marks. Slacken the screws and turn it about five mm more, to increase the tension closing of the choke flap.

Just realised I wrote 30 pict 34 instead of 34 pict 3. I assume you realised this.

Will try some of the things you suggest to see what happens.
Any ideas why it would not fire immediately when warm?

Tim

 

[Moseley]

I hope your valve gap is a typo, should be 0.15mm!

 

[Raggles]

I hope your valve gap is a typo, should be 0.15mm!

Now edited ... not doing well on the typos!

 

[Raggles]

Thought people might be interested in this reply I got from Tim at Volkzbitz who provided me with my refurbished 34 pict 3 ...

It sounds like the carb flooding either too much pressure, debris in the float valve, or it could be the fuel line getting too hot. When the fuel line gets hot, the gas expands causing excess pressure that floods the carburettor, it’s a common problem especially with the ethanol fuels. Here is a video I made showing what happens when gas get hot.

https://www.youtube.com/watch?v=Qok1bCxcQkk" onclick="window.open(this.href);return false;

This is why it starts well when cold, but when left for a few minutes when its warm the engine is flooded. I have the same problem on my Karmann Ghia. Try holding the pedal to the floor whilst cranking, this will allow more air through.
So move any fuel lines that are near anything that gets hot.

Its probably chugging a little after it starts, this is probably because the plugs are a little wet. Before driving, try holding it at a fast idle for 10 seconds, not racing, just enough to clear it.

If its not running great when its cold and the choke has come off, then you can adjust the choke to stay on a little longer by loosening the 3 screws and turning the choke anti-clockwise a little, try 1/4 inch.

My fuel line is currently quite close to the pre heat pipe (though tagged away from and not touching it). I have also recently moved the fuel filter from the engine compartment to below the van which might also be effecting the heat build up.

I will try moving the lines and adjusting the choke to see what happens.