Weber 44IDF poor running question

[euroauto]

Hi all.
I have a 1980 Fiat 131 Racing with a newish engine bored .6mm over, 8mm dome pistons, 40/80 cams and my biggest issue: IDF 44

The carbs idle poorly and rich.
idle 52 with bleeds out 1 full turn ( 50 tried with bleeds closed and carbs are too lean and pop up, un-drivable)
tube f11
main 135
choke 34
mixture screws out 1.5 turns

Any thoughts appreciated.

[Guy Croft]

Check the following;

1. Fuel pump delivery pressure at the feed at the carbs must not exceed 3.5-4 psi. Too much will lift the float needles off their seats.

2. Run the engine at idle and look into the barrels (wear safety glasses in case the engine spits back). See if the pump jets are dripping onto the throttle plates. If they first check that the pump jet actuating lever under the carbs is not fouling the inlet manifold and holding the diaphrams open. If it is the manifold needs to be relieved a bit. If that's OK then it might be float level (s). Take off the top covers of the carbs and check the float setting. If they are OK then it will be a fault in the pump jet circuit - maybe blocked non-return valve in the pump jet assembly, fitted in the carb upper body with two sprays - one per barrel. It may simply be that the daiphrams have gone hard in which case you need IDF service kits, which I can supply.
If the jets have been dripping you may be able to balance the carbs and set the idle mixtures effectively. You should get a 'Colortune' device to do this.

2. Carbs out of balance can also cause dripping on the pump jets and has a major influence on whether the idle mixture screws will give the right response. With the above checks out of the way I suggest you start by removing the carbs, unscrewing the idle speed screw (s) and holding them up to the light to make sure the throttle plates close fully (without much more applied force than the carb springs themselves.) Obviously the system might need a bit of help to close when the cable or linkage is fitted up and so apart from the torsion springs on the carbs themselves there should always be reasonably strong spring on the linkage. It is very common on old carbs for the throttle plates to worn or to be out of alignment and not close properly, thus allowing an imbalance of airflow one carb to another.

3. Before setting up, remove the 4 brass idle jets (2 piece, with O ring), located in the upper part of the carbs on the outside near the top flange, and make sure they are claen. They are notorious for blcoking, especially with foam filters, because the float bowl is exposed to any debris falling into it. As far as idle setting and balance is concerned the two have to be done in 'tandem'. One of each of the 2 air bleed adjustment screws located on each carb mounting flange (with locknut) on one carb must be closed, the barrel that flows more air on one carb should have its bleed closed, the other is opened to compensate. This is set up at idle - 750-850 rpm. You have to keep resetting the idle speed on the master (front) carb because as the balance is improved the engine speed will climb. The idle mixtures must be set only when the balance is correct, and again, Gunson (Colortune makers) offer an inexpensive balance gauge which is essential when doing IDF tuning.

4. If after going through all that the engine still runs badly there may be a compression problem, or something else like ignition fault, but the Colortune will help trace that. See:

http://gunson.co.uk/tools.aspx?cat=486

GC