Twin side-draft help

[Browneye]

Greetings watercooled wizards out there,

I'm looking for advice in regard to setting up some twin dellortos for my mk1 golf.

They are already installed on a vw AFT engine (1595cc) and I'm looking for some jetting/tuning tips or even solutions to help get her running.

The carbs are Dellorto DHLA40H
Engine is running a 280 degree cam

Here is a video of it running (just) mainly using the choke circuit.
The carbs are also backfiring through the intake on some occasions.
https://www.facebook.com/#!/jordan.b...5/?pnref=story

Has anyone set up carbs like this on a similar engine size? I will take on any advise that people will offer.

TIA

[sports racer]

If it's any help I can get the jet sizes off the twin 40's running on the old KR 16v motor. Won't be perfect but it might put you closer to driving the car to a proper tuning place.

Cheers

Paul

[Browneye]

If it's any help I can get the jet sizes off my twin 40's running on the old KR 16v motor. Won't be perfect but it might put you closer to driving the car to a proper tuning place.

Cheers

Paul

I've had a read through online and my jet sizes are what is recommended. The problem is, I believe the DHLA40H is an emissions carburettor, and the idle jets require a different size.

That being said, I'd love to know what others are running in their twin carb set-ups, particularly on the idle circuit

[sports racer]

Have you tried the trick of cutting a piece of cardboard so it has 4 holes matching your throttle bodies. Get the car started and slowly slide the cardboard so it starts to restrict airflow into the carbies. If it idles ok with some of the intake blocked off then the idle jets aren't big enough. If it just makes things worse then the idle jets are too big.

[Browneye]

Have you tried the trick of cutting a piece of cardboard so it has 4 holes matching your throttle bodies. Get the car started and slowly slide the cardboard so it starts to restrict airflow into the carbies. If it idles ok with some of the intake blocked off then the idle jets aren't big enough. If it just makes things worse then the idle jets are too big.

That sounds like an interesting test actually. I assume this is because the restrictions makes the air move faster and creates a larger vacuum.

Just out or curiosity, what size chokes (venturi) are you running? I believe mine are 34mm although I haven't checked in a long while. Might be worth sizing them down a bit, possibly down to a 30 or 31mm?

Also, what would cause a backfire through the intake (as seen in the video on piston 3)? Running too rich or too lean?

[sports racer]

The restriction allows less air in so alters the fuel/air mix slightly. I don't know how accurate the test is, just something I remember someone doing years ago.

Backfire is usually caused by incorrect timing. It can be caused by a high duration camshaft which opens the intake valves earlier than a standard cam. Because the valve is starting to open on the exhaust cycle some exhaust gas can ignite the incoming air when it's idling. It doesn't happen at normal running rpm because the incoming airflow is faster and everything is being sucked into the engine.

[sports racer]

DHLA 40
Throats 39mm
Emulsion tubes 7772.5
Mains 135
Idle 05