Any Weber 40 DCNF experts out there?

[NTEL]

Hi, Hope you can help. With the promise of extra horse power and torque I have recently has three Weber 40 DCNF carbs fitted to my Ford 2.9 V6 cologne engine to replace a single Weber 40 DFI 5. I took it out last weekend to Brands Hatch and noticed the following:

1. The water temperature was much higher to the point that I had to keep the fan running throughout the race in order to keep it at about 90 degrees. Previously I had to blank off the radiator and keep the fan off.

2. The car was a lot slower off the line and seemed to get to about 5500rpm a lot slower than before.

3. Over 5500rpm it did seem to be better than before and seemed torquier and more powerfull.

4. Previously the ignition timing was set to 38 Deg BTDC. Don't know what it is now but it looks as if it has been further advanced judging by the original mark I put on the dissy base. This would have been done by the tuner following the carb installation (on the rolling road).

5. Only one of the carbs pump jets seem to be working.

6. The spark plugs seem "pale" and have a very thin light brown coating on them (especially on the back 4 whos pump jets don't seem to be working.

7. When I blip the throttle on the change down there is a slight delay before engine revs rise. ( could that be a result of the pump jets not working ?)

8. Two of the three carbs seemed to be fitted with odd gaskets between the main body and the body top (float chamber cover). There are two triangular shaped holes (air ways?) at the opposite side to the float chamber, these were partially blocked by the gaskets. I opened the holes in the gasket out and this seemed to help in the second race.

9. Fuel consumption seemed to be the same, if not, less than before.

Would I be correct in thinking the engine is running very lean?

I'm not sure of the jet sizes at the moment but will know when it goes back to the rolling road in the morning.

Could anybody suggest any jet / emulsion tube sizes as a starting point please so I can compare? The carbs are fitted with 35mm chokes and 3.5 aux venturis.

Thanks in advance

Dave

Edited by NTEL on Tuesday 16th June 13:48

Edited by NTEL on Tuesday 16th June 14:02

[rev-erend]

Dave

Sounds like overall you are running lean .. although really you should put a gas analyser on to see the afr reading through out the rev range at a set statis throttle .. and only after that is correct with main jets / correction tubes move on to acceleration enrichment.

Running over lean is going to give high temps, it's slower to burn and ignite.

The total advance is not really dependant on the carbs - it's dependant on the piston / squish area causing knock etc.. 38 degrees sounds around about right .. although as your max revs are not that high 2 degrees less might actually give you a faster burn if you are not using fully mapped igntion.

Edited by rev-erend on Tuesday 16th June 14:25

[NTEL]

Thanks for that Alan. For reference the engine revs to 7300rpm.

[rev-erend]

Dave - I've not had carbs for many years now but can recommend the webber carb tuning book .. if you can borrow a copy it's pretty good.

[Pigeon]

NTEL said:

Could anybody suggest any jet / emulsion tube sizes as a starting point please so I can compare? The carbs are fitted with 35mm chokes and 3.5 aux venturis.

I don't think you've got to that stage yet.

Accelerator pump jets not working suggests that something is actually buggered, not just mis-sized. And you say two of them had odd gaskets which didn't fit properly... so I'm guessing these carbs have some history.

First thing is to completely strip them and thoroughly clean them and make sure nothing is blocked... the accelerator pump jets obviously, but all the other little holes and passages too.

Also those odd gaskets may be affecting the float height.