Need help from you turbo gods

[advinnie]

Hi all I have a 1600 draw through turbo set up on my bug using a T 3 turbo and a Weber 40 DCOE carb and a CB performance black box to control the ignition. Now she starts fine, cruises fine and accelerates great and produces 10psi of boost but there is just one problem and it’s a big one. She will idle all day long at 1000rpm and when in neutral if you rev it up and then suddenly come of the accelerator the rpm’s will fall nicely back down to the idle speed of 1000rpm BUT on the road it’s a different story, like I say she drives amazingly but when coming up to a junction or roundabout or any other situation where you have to dip the clutch the engine will stall. You have to control the rpm for a few seconds using the pedal. I have tried everything I know of but I can’t stop her from stalling when I dip the clutch. Do you lot have any ideas?
Cheers

[buguy]

Could it be something in the clutch that's causing it?

[Buggsy]

If it is a fuel problem: VW, along with most OEM manufacturers solved this carb problem with what was called a decel dash pot. This was a little diaphragm pot that made the throttle plate close slowly those last few degrees when you let off the throttle. This keeps the suddenly closed throttle form causing high vacuum and pulling a slug of raw fuel into the motor causing a stall. You can likely pull one off an old VW carb, or any old carb from the 70s and retrofit it to have the stem bear against the throttle arm about a quarter inch before it closes at idle.
If it is an ignition problem: on the timing table, shift all the numbers to the right so you have an empty row below the idle speed. Set this row for 850 RPM. Fill in the empty boxes with ignition numbers 3 or 4 degrees higher than what you use at idle. This way, if you dip below 1000 RPM, the higher ignition timing will "catch" the engine before it dies, and stabilize it back at 1000 RPM idle speed. This is what Megasquirt recommends with fuel and ignition timing. It has worked well for me, it should work for you.

[Buggsy]

Here are some examples, some mechanical, some electric, but I would just go to a junkyard that has older cars and pluck one off a carb. Good luck.
http://www.jegs.com/p/Holley/Holley-Thr ... 5/10002/-1

[Chip Birks]

Sounds like something you could fix by adding timing in the map above typical idle map and rpm, and then down a few hundred rpm so that when you release throttle it adds timing to essentially catch the idle and get it back to happy.

[advinnie]

Thanks for the help people. Here’s a little more information. I was wrong about it stalling when cold and hot, after some more testing I’ve noticed that after starting (cold) it will take about 30 seconds using the throttle before it will idle on its own THEN I have around 3-5 minuets of the engine working correctly with out any stalling, its after this time when it starts to play around and it will stall if I rev it up and come if the throttle sharply when in neutral but not that often.
Here is my first map I wrote but with this map I was getting a massive flat spot around 96-98Kpa @ 1750 rpm as long as I stayed out of this area all was good but hit this area and the engine would stop accelerating and start coughing and banging so spoke to CB performance and they told me to up the timing to what’s in the second map and this will remove the flat spot witch it most definitely did( I have no idea why this fixed the flat spot)
Both these maps have the same stalling issues
My first map

[advinnie]

My first map

[advinnie]

Second map witch sorted out the flat spot

[Chip Birks]

Where does it idle on that map? You said 1000rpm, what kpa?

[advinnie]

71 Kpa

[Chip Birks]

If you look at that map, you'll see that your timing gets lower and lower once the engine starts stalling out. As the engine dies, the active cells on the table move up and to the right, i would change the curve so that the cells above 1000rpm and to the right of 71 kpa increase timing. Raise those numbers till it doesn't stall anymore.

[advinnie]

Good tip will sort that out tomorrow and see how it goes cheers