Carb set-up

[Beanderb4]

Guys,

I'm just in the process of setting up the carbs on my 2.0l series II spider but I cannot find the air bypass screw on the carbs. Have I gone mad, or is there an early version of these carbs that does not have an air bypass screw??

Cheers,

Paul.

[Dinoswede]

Hi. Yes, you are absolutely right! The first version of 40 DCNF has no air by-pass screws, and I think the same also apply for 40 DCNF 6. On 40 DCNF 12, you will find
extra air by-pass adjustment screws. (On the early 40 DCN 14 carburettor, you will not find these, either.)
Dinoswede

[Beanderb4]

Thanks Dinoswede. So am I right in thinking the only way to balance these carbs is by adjusting the idle across all three carbs then.

Paul.

[ThomasK]

Adjusting the carbs is more than just adjusting idle speed:
- beneath idle speed there is to adjust:
- idle mixture with the idle mixture screw (influence up to apprx. 2.500 rpm)
- synchronisation at the gas linkage and with a flow meter that measures the capacity of air being "breathed in" (influence on the whole rpm range)
- float bowl level: don`t underestimate this as it has big influence on how the carbs works (influence on the whole rpm range)
- and of course you can change the needles, but you should know what you do as this can also improve but also worsen the character of the carbs (with the different needles you influence different rpm ranges).

KR, Thomas

[Beanderb4]

Thanks Thomask

I am looking at all these 'Influencers',
I've adjusted the timing, now I'm looking to balance the air volume before I go on to the linkages and idle mixture. However, when I went looking for the air bypass screw there was none! So I just want to check that my only option for balancing tbe air file across the carbs us to use the idle speed?

Thanks,

Paul.

[Dinoswede]

Beanderb4; I feel we have a small missunderstanding here - If you have the 40 DCNF carburettor versions WITH air flow adjustment needles on your car, you are able
to balance the air flow between the two different venturis in the same carburettor. This is to be done with all three carburettors, obviously, one at a time. After that,
you are able to adjust the three different carburettors against each other, working at the linkage rod nuts between the carbs, using the same kind of "vacuum meter"
as in the first step, making them sucking air into the engine at the same level.
If you have the 40 DCNF carburettors WITHOUT air flow adjustment needles, you just have to accept the fixed vacuum value between the two venturis in each of the
carburettors, that is you can go directly to next step - balancing the three carburettors against each other working at the linkage rod nuts, as above.
Next step will be adjusting the idle mixture, cylinder by cylinder. During this step, you will have to compensate the idle speed now and then, to keep it on desired
rpm:s, using only one of the carburettors idle stop screw - don´t tamper with the linkage rod nuts, as that would mean the balance between the carbs would be lost!
My experience is, you have to rev the engine a second or two, after each idle mixture adjustment, to get a better understanding of what the last adjustment did to
your engine.
Hoping this answered your questions!

Dinoswede

[Beanderb4]

Thanks Dinoswede. I am WITHOUT.

You have provided me with the clarification I was looking for. There is no misunderstanding!!

I will be out in the garage tomorrow evening and hopefully out on the road by Saturday!!! The sun is shining over here in Ireland. It's a rare occurrence and I have to make the most of it!!

Paul.

[2dinos]

I went thru this exercise recently. After years of living with it being kind of goofy, I got it so I'd say it's pretty reasonable.
What was making me crazy was :

(Well of course for starters - the no balance screws).

1. The float height. I had the float ht set too low, and it had the most ridiculous flat spot, and I was chasing this forever.

2. Mixture setting. Trying to set mixture by ear didn't work for me. I would up with the stinkiest overly rich running engine. I have inspection tubes welded to each header pipe, and I used a gas analyer and made multiple passes down all the cylinders checking the out put at each individual one. She starts soooo much better, doesn't smoke out the whole street, and runs quite strong.

[Stefan2000]

Been reading on my issue for a while and it seems to be that i'm not the only person but could not find an answer to the question yet.
I have a slight dead spot while accelerating around 3000 rpm. It's a 2000 with the 40DCN 14's. I'm quite sure it's taking place at the transition point between idle and main circuit. It's only while accelerating with slight throttle response.
Ignition is spot on, advance mechanism and advance curve is 100%, valve clearance is good, compression good, carburettors are clean and all jets are the Original size, float level is correct etc.etc.
Who has the same problem or more important, who had the same problem and knows how to fix it?
I have some slightly larger idle and main jets but i'm a bit reluctant to switch them as long as i can't measure my AFR while driving.

Thanks in advance!

[robmurray]

Hi Stefan
A flat spot can be caused by stuck advance retard bob weights in the distributor - a common fault. Just a thought.
Regards
Rob