Having trouble getting recon DF engine to run smoothly

[AlanR25]

Here’s the background. After overheating problems damaged the old engine, I fitted a recon DF engine in my 1983 T25. Now back running, but big problems when the engine comes under load (accelerating and gradients). Anything other than the MOST GENTLE use of the throttle results in backfiring and complete loss of power.
I have been trying to adjust the carb (Solex 34 pict 5) without much success (plenty of info on pict 3 but not much on pict 5).
Is the adjustment process the same for both?
Info on vw-resource.com for the 34 pict 3 tells how to adjust the “Fast Idle Adjuster” / “Throttle screw” by screwing it in until it just touches the bottom of the stepped cam and then screwing in ¼ turn. Haynes says put it on the 3rd step and adjust to get 1900rpm. Maybe they are both right.
I have been setting the Fast Idle first, then the Bypass Screw, then the Volume Control Screw.
I would be grateful if anyone can direct me to instructions that apply for 34 pict 5?
Also if anyone recognises the loss of power symptoms and can propose which way to go?
Thanks.

T25 (1983) DF Engine - Leisuredrive conversion – a charmingly retro nightmare.

[kevtherev]

Is there an accelerater pump on the pict 5?
Or some sort of transfer jet?

[DevonAid]

General misfire and power issues on DF's (amongst others) can relate back to air intake and exhaust system leakage issues. If it's a rebuilt DF, are you 100% certain intakes and exhaust went back on properly and are leak-free?
Was the carb swapped from the original engine and generally running ok prior to overheating-in which case big carb adjustments may not be necessary at this stage.
I would check the basics first, particularly those things that have been touched on engine swap: air-intake & exhaust leaks, ignition timing and system etc

[AlanR25]

Is there an accelerater pump on the pict 5?

Yes the pict 5 has an accelerator pump.
I have checked the quantity of fuel being delivered and it is about right.

Was the carb swapped from the original engine?

Yes, but it is a long time since it was running OK.

I would check the basics first

I may have some air intake leaks (inlet manifold/carb)(carb/inlet duct)(throttle damper diaphragm) - Didn't think any of them were bad, but I will keep checking and try to eliminate them.
The idle-speed adjuster screw seems to make very little difference to the idle speed - does that suggest an air intake leak?

T25 (1983) DF Engine - Leisuredrive conversion – a charmingly retro nightmare.

[bigbadbob76]

Sounds more like an ignition timing issue to me, maybe a vacuum leak?
Worth checking anyway.
Just my 2p for what it's worth.

[itchyfeet]

Did you set the timing on the new engine, you can't just swap the dizzy becuase the drive cog may be fitted incorrectly on old or new engine