weber problem?

Dicko4 · Post by **Dicko4** » Fri Feb 13, 2015 9:45 am

My series 1 3.8 having just had an engine rebuild was on a rolling road for tuning with its new to me webers (Italian) and Megajolt (Ray Livingston) when lots of black smoke eminated from the exhaust from the front three cylinders.
So front three very black and rear three OK therefore problem was across the middle carb. Jets and chokes all seemed the same as was compression.Plugs changed and OK. Megajolt comfirmed timing OK and swapping leads from 3 and 4 made no difference so not electronic. I am new to webers but dont see how they can fuel their pair of cylinders so differently. During the running in engine ran OK but no large throttle openings.
Any thoughts, comments or solutions most welcome
Dicko4

Post by **Heuer** » Fri Feb 13, 2015 10:23 am

Weber Set up Guide 1: http://dl.dropbox.com/u/8496016/Weber%2045DCOE.pdf
Weber Set up Guide 2: http://dl.dropbox.com/u/8496016/Weber%20Wisdom.pdf
Tuning DCOE Carburettors by Kimble & Trindal: http://dl.dropbox.com/u/8496016/Tuning% ... uretor.pdf

PeterCrespin · Post by **PeterCrespin** » Fri Feb 13, 2015 3:16 pm

Dicko4 wrote:My series 1 3.8 having just had an engine rebuild was on a rolling road for tuning with its new to me webers...when lots of black smoke eminated from the exhaust from the front three cylinders.
So front three very black and rear three OK therefore problem was across the middle carb.

Don't follow your logic. With Webers you have six carbs served by three float chambers. If the exhaust from the back three cylinders 1,2 & 3 are OK then it's not the middle carb it's the front carb (as that is the only one unique to that exhaust pipe).

Was the engine pulling hard when the smoke started? Was there any mechanical noise? How many miles on your just rebuilt engine? Did you measure compression before or after the incident?

JEP41 · Post by **JEP41** » Sat Feb 14, 2015 7:09 am

I had a similar problem after an engine rebuild and it turned out to be one piston oil ring installed incorrectly allowing oil blow by, especially under hard acceleration

jag68 · Post by **jag68** » Sun Feb 15, 2015 5:23 am

The obvious choice for this would be too much fuel through the front carb. If the enriching mechanism (it's not a choke) is stuck on that might be it. Disconnect whatever set up you have for the "chokes" and make sure they are completely off. My experience with Webers suggests that you don't actually need to use these devices at temperatures above freezing - you can get enough enrichment by pumping the gas pedal before starting.

More likely it's a fuel level problem in the float chamber. What are you using for a fuel pump/regulator? Weber's - unlike SU's are incredibly sensitive to fuel pressure and fuel level. Take the air filter off the carb, and without starting it, turn the fuel pump on, wait a few minutes - up to five. Watch to see if you get fuel leaking from the carb intake tubes - that's where it comes from when the pressure overwhelms the needle. and the fuel level rises. In other words you get raw fuel leaking into the intake, which will leak out the front of the carb. Two point five psi is all they can handle safely. An SU fuel pump generates momentarily way more than this when the diaphram is first released by the magnet. My experience is that you can't get Webers to work on a SU fuel pump - you need a 3 - 4 psi rotary style and a good pressure regulator. An alternate explanation is that the fuel level is set too high or the needle and seat are defective. It's common that one carb will relieve the excess pressure and leak as opposed to all three doing it at the same time .

Take a look at these things and let me know if it's not fixed.

Dicko4 · Post by **Dicko4** » Mon Feb 16, 2015 9:45 am

Many thanks for replies but not yet had a chance to sort things out. However there are no enriching devices or air filters.I feel fuel level the most likely problem but not heard of the SU pump problem. I have two switchable SU's and it could be that they were both on during the test so might be an influence.
Weber info very helpful thanks David.
Will post the solution when it becomes clear

Dicko4 · Post by **Dicko4** » Mon Feb 16, 2015 5:23 pm

Car will be with local expert tomorrow so hopefully problem will be revealed. I just tried Jag68 suggestion of running the fuel pump and looking for fuel flow but nothing to be seen. I am not sure what the opening in the front of the carbs is for--overflow? but in each case there is a small amount of oil. Is this normal.From what I see on the web there are two floats connected to the fuel inlet so maybe scope for each cylinder to be treated differently

jag68 · Post by **jag68** » Mon Feb 16, 2015 8:20 pm

The big hole in the front of the float chamber is to ensure that the chamber is at atmospheric pressure. I suppose you could get fuel flowing out of it if it rose high enough. To get that high it has to overflow the passages going to the carb throats, so that's usually where the excess fuel goes. There is no oil in the carbs. You may be seeing fuel with most of the light ends evaporated. It can get thick enough to look like light oil, before it turns to sludge.

The problem with SU fuel pumps and modern Webers comes from the spring loaded needle in the check valve where the fuel enters the carb. The pulsations from the pump diaphragm can easily overwhelm the spring. If you don't have the spring loaded needle (you have old stock or aftermarket stuff) you may be okay. If it works ---- you know the old saying: if it ain't busted don't fix it.

When you turned your fuel pump on and let it sit did it stop ticking shortly after turning on or did it continue to tick slowly?

There are two floats per carb but they are connected together.

Dicko4 · Post by **Dicko4** » Mon Feb 16, 2015 9:24 pm

Yes got spring loaded needle.Pump did stop ticking soon and no fuel showing. You are right about evaporated fuel on closer examination.Looking at the schematics I see the two floats joined together but if they were at different heights then I guess only the higher one would work for both cylinders. I am optimistic that all will be revealed tomorrow.Canadian input much appreciated .

Dicko4 · Post by **Dicko4** » Mon Mar 16, 2015 7:14 pm

turns out my webers had been set up fora race car and it seems that were only Woking well at top revs. Also the throttle linkage was not properly synchronised . Adjustment of the linkage and a reduction in choke size has made a massive improvement and I plan to get to another rolling road as soon as I can.I appreciate all the input and will let you know how the curves look
Dick

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