Author Topic: Weber DCNF set up?  (Read 3967 times)

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Offline kammtail

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Weber DCNF set up?
« on: July 17, 2010, 12:01:01 PM »
Hello Guy,

I have nearly finished my abarth 1000Tc replica but now I have running problems?

I have fitted a Weber 40 DCNF to my A112 Engined 1000TC replica.
The engine starts well on choke and once warm the engine idles well approx 1000rpm.
When you try to accelerate away in the car the revs drop off and the car slows and will stop.
If you rev the engine quickly the engine also dies, I have adjusted the mixture and checked the float level 50mm
I have also changed the Jets to:
Idle Jet: 50
Main Jet:130
Air Jet:175
Any idea what size Choke Tubes I should have fitted? and any information or ideas would be welcome.

Kind regards
Greg




Offline Abarthfan

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Re: Weber DCNF set up?
« Reply #1 on: July 17, 2010, 04:26:15 PM »
you probably have big diameter of difusor in your carb. (too much air comes in cylinders in that moment if you push more akcelerator) .. it is my idea.



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Offline kammtail

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Re: Weber DCNF set up?
« Reply #2 on: July 18, 2010, 08:03:59 AM »
Hello Abarthfan,

 The size of the Choke Tubes fitted at present are 30 ?

Thanks

Greg

Offline kammtail

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Re: Weber DCNF set up?
« Reply #3 on: July 18, 2010, 09:39:50 AM »
This is what is fitted at present:

Idle Jet: 50
Main Jet:130
Air Jet:175
Ventui: 30
Auxilary Venturi: 2.5

Thanks
Greg

Offline Pantdino

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Re: Weber DCNF set up?
« Reply #4 on: October 26, 2010, 06:07:13 AM »
Greg,
Did you get your car running well?
If so, what did you do?

Offline Paul vander Heyden

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Re: Weber DCNF set up?
« Reply #5 on: September 11, 2011, 06:12:58 PM »
Kammtail,

To make it short, if the float level is correct and the car runs OK once you get it going, then the problem is in the idle circuit.  I would blow out all of the idle jets first.  If it still does it, go one size larger on idle jet.

Basically all Weber carburetors have four circuits.

1.  Idle
2.  Cross-over
3.  Accelerator Pump
4.  High Speed running.

The Idle and Cross-over circuits BOTH draw their fuel from the idle circuit well.  At idle all will be well.  Once you open the throttles slightly, you will uncover the cross-over port(s) which are small drillings in the walll fo the throttle bore (covered by the throttle plate when it is closed).  As you open the throttle intake manifold vacuum will draw fuel out of those drillings to provide additional fuel.  This fuel comes from the "idle circuit fuel well".  If the idle jet is too small, then not enough fuel will be available and the engine goes lean and "bogs".  It may even stall.  Increasing the idle jet should sizesolve this problem.

Paul
Scuderia Topolino