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Mon Jun 30, 2025 6:43 am

Hey guys! First time posting here I've had a search about on the forum but can't find exactly what I'm after.

So got the 1600 DP on Solex P-40 (Scat carbs) with a 009 & electronic ignition and coil to match, got it idling perfectly timed to 30° BTDC revving up the engine until then distributor advances no more (don't have a rev gauge)

Here is where the problem lies as it idles lovely revs up lovely but on load when driving it stumbles and backfires, so advancing the distributor more until it drives perfectly, got plenty of power no more backfire which then puts the timing wayyyy out according to my strobe light with the advancing dial on the back is passed 60°…

I've seen somewhere that you should max out the accelerator pump and upsize the main jet to compensate but I'm not sure if that's my issue?

Any help is appreciated! :D

Mon Jun 30, 2025 9:44 am

Chinese 009?

Mon Jun 30, 2025 10:22 am

No its stamped bosch so definitely original

Mon Jun 30, 2025 10:39 am

im not familiar with those carbs . here is the article about accelerator pumps but its for the stock 34 pict3

http://www.vw-resource.com/accelerator_pump.html

Mon Jun 30, 2025 10:45 am

Yes this is the website I saw that you need to enrich the fuel to use a 009 to get rid of the flat spot and hesistantion I believe, annoyingly this is a friends beetle so I'm unable to work on it often but we are trying to get it running as perfect as it could be

Mon Jun 30, 2025 10:58 am

thats inherent to the 34 pict 3 with the 09 , with dual carbs i dont think thats your problem . you have 2 carbs squirting now .

Mon Jun 30, 2025 11:23 am

I wanna say that the problem lies in the timing? As I said we have it timed to 30° and it didn't like to run under load so we turned the distributor anti-clockwise in small increments after each drive until it ran perfectly, according to my strobe light it was over 60° or so it says but coming to think of it maybe I need to mark the pulley at 28° and 32° and use 0° on the light to see where the timing lands :lol:

Mon Jun 30, 2025 11:55 am

Backfires? (Loud bang), or missfires? If you dip the clutch and rev it a few times, does it pick up and go

Mon Jun 30, 2025 12:13 pm

Howdy ... and welcome !

Get back to basics :

Valves
Points
Timing
Carb adjustment

Also :
Choke
Fuel delivery
Spark wires quadruple checked
Spin rotor by hand - does it snap back fully & quickly
Check for any vacuum leaks

Dual carbs synced & linkage same at idle AND full open

Generally popping on acceleration is lean & on deceleration is exhaust leak

Cover all bases ... stay safe

jinx

Mon Jun 30, 2025 2:13 pm

Underside of the distributor body should state country of manufacture.

Mon Jun 30, 2025 2:26 pm

Cusser wrote: Underside of the distributor body should state country of manufacture.
Not always

Mon Jun 30, 2025 10:50 pm

Who.Me? wrote: Backfires? (Loud bang), or missfires? If you dip the clutch and rev it a few times, does it pick up and go

Yeah so backfire out of the exhaust when revving up, it just stumbles and barely moves under its own power timed at 30°

Tue Jul 01, 2025 2:13 am

Are you sure you are checking cylinder #1?

Tue Jul 01, 2025 3:44 am

I suspect there's something wrong with your timing light or the way you're using it.

Tue Jul 01, 2025 4:59 am

Slow 1200 wrote: Are you sure you are checking cylinder #1?

Yes 100% at TDC with a 009 it points to the rear right (around 4’oclock) matched the rotor with the notch in the distributor casing, it starts and idles perfectly it just doesn't move under its own power as it sputters/hesitates and sometimes backfires but rotating the distributor CCW until it drives perfectly, I'm gonna 3d print a 7 inch degree wheel to place on the pulley to mark the correct locations of 28° to 32° and use the gun at 0° rather then using the dial on the back to see how I get on

Tue Jul 01, 2025 12:16 pm

VWLeroy wrote: Slow 1200 wrote: Are you sure you are checking cylinder #1?

Yes 100% at TDC with a 009 it points to the rear right (around 4’oclock) matched the rotor with the notch in the distributor casing, it starts and idles perfectly it just doesn't move under its own power as it sputters/hesitates and sometimes backfires but rotating the distributor CCW until it drives perfectly, I'm gonna 3d print a 7 inch degree wheel to place on the pulley to mark the correct locations of 28° to 32° and use the gun at 0° rather then using the dial on the back to see how I get on

You need to make sure the correct notch (there may be as many as three) in the pulley is actually pointing at TDC, the rotor in the distributor just points somewhere near the right place.

You cannot do timing off the distributor rotor..

Locate TDC with a probe down the number 1 spark plug hole, then look at what mark on the rear pulley points upwards at the joint in the case.

Then measure round the pulley to get the timing angles, and mark it up with Tippex or white paint. .

It still sounds like your timing is extremely badly off.

Fri Jul 04, 2025 6:40 am

mikedjames wrote: VWLeroy wrote: Slow 1200 wrote: Are you sure you are checking cylinder #1?

Yes 100% at TDC with a 009 it points to the rear right (around 4’oclock) matched the rotor with the notch in the distributor casing, it starts and idles perfectly it just doesn't move under its own power as it sputters/hesitates and sometimes backfires but rotating the distributor CCW until it drives perfectly, I'm gonna 3d print a 7 inch degree wheel to place on the pulley to mark the correct locations of 28° to 32° and use the gun at 0° rather then using the dial on the back to see how I get on

You need to make sure the correct notch (there may be as many as three) in the pulley is actually pointing at TDC, the rotor in the distributor just points somewhere near the right place.

You cannot do timing off the distributor rotor..

Locate TDC with a probe down the number 1 spark plug hole, then look at what mark on the rear pulley points upwards at the joint in the case.

Then measure round the pulley to get the timing angles, and mark it up with Tippex or white paint. .

It still sounds like your timing is extremely badly off.

So on this particular pulley there's a big dip that indicates TDC and I have confirmed this by taken off the valve cover and checked that both valves on cylinder #1 are closed which then points the rotor arm at approximately 4 o'clock basically pointing at the pulley I then line up the notch in the distributor with the rotor arm.
It then fires up I rev it up to it stops advancing and time it to 30°BTDC, as I said it runs and idles great but when a load is applied it starts to stumble and backfire, so I retarded it until it ran brilliant but I think it then puts the timing lower the 28° but I've 3d printed a degree wheel that will slot over the stock pulley so I can then mark the relevant marks onto the pulley and see how I get on

Thanks for the help so far! :D