Weber 38 running rich

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Rossouw
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Joined: Sun 26 Aug 2012, 21:18

Weber 38 running rich

Post by Rossouw » Tue 01 Nov 2016, 17:43

Hi,

I have a weber 38 on a skyline 2.8 gtx engine. The engine is running rich (plumes of black smoke from exhaust). It was running fine until I had it overhauled and tuned. I have had two different mechanics have a look at it since, but no avail. I switched to smaller jets, and tuned it countless times, still running rich. What are we missing here? Any advice?

I have also changed the fuel filter and switched to electronic ignition when the carb was off.

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Johann65
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Re: Weber 38 running rich

Post by Johann65 » Wed 02 Nov 2016, 15:34

Cold Plugs?
Member No: 209
Ah! Yes I remember it well! (Only GM's!)
1966 Opel Rekord L CLASSIC SEDAN Current Project

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KSF
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Re: Weber 38 running rich

Post by KSF » Wed 02 Nov 2016, 15:34

It is always difficult to advise this sort of thing from an armchair.. but usually the Weber38 dont have too many problems (did I just hear a chorus of "WHAT??" echoing outside? :D :lol: )

If the black smoke is really a plume as in you cannot see through it, then extra fuel must be pouring down the throats, so I assume it is not that much, but more of the dark haze variety?

Also, if you had two guys look at it, I assume you and them have checked and rechecked the float level (too high or a leaky needle&seat can cause this).

Did you change anything on the fuel supply? Better/newer pump? Any of the supply piping? Webers will start flooding with fuel pressure exceeding about 5-6Psi. They are happier around 3-4Psi.

If you are happy all the jets are in place and snug, just also check the idle jets have not been changed to a different model. Or a shorter model that does not seat the tip properly.

One last thing often overlooked or misunderstood by many is the powervalve arrangement. It has three main parts: The valve itself which screws into the bottom of the float chamber. They don't usually fail, but worth taking out and checking. Depress the centre pin to open, spring pressure returns it to close. Under it in the recess sits the two meter holes. Difficult to see, but must be in place with no obvious damage or lost material due to acid dips. There should also be a copper washer under the valve as it screws in place. Next is the actuator (scarce these days and known to fail). This is that long 'spring' that sits between the two floats and is screwed to the underside of the carb top. it is actuated by vacuum through a port that opens under the throttle butterfly. Check the port is open by blowing through it (the one in the carb base). The hole is located to the one side approx in line with the air correction jets. Then also check the operation of the powervalve by putting vacuum on the matching hole in the carb top. Suck on it, basically. See if the spring loaded part contracts, gets pulled up. Try and hold the vacuum there and see if it stays up.


Something else I should maybe have started with... make sure the choke mechanism is working properly and freely and that they are in fact open when the engine has warm up. If you have any doubts, remove the choke flaps for a test. The choke also has a vacuum diaphragm that can fail, it is supposed to open the flaps a bit during the warm up cycle when you apply throttle. Otherwise it also chokes too much and will cause black smoke.

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Rossouw
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Re: Weber 38 running rich

Post by Rossouw » Wed 02 Nov 2016, 21:05

Thanks for the advice. The plugs are fouling after -+ 50km of normal driving, tips burnt pitch black. I'm on my third set of plugs. There is a major amount of fuel going down the throats.

I will have a look at what you suggested, and keep you posted.

Thanks

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Johann65
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Re: Weber 38 running rich

Post by Johann65 » Thu 03 Nov 2016, 17:49

Take a look at what the output from you coil is. I had fouling due to a coil not giving enough spark! (Voema) +15
Member No: 209
Ah! Yes I remember it well! (Only GM's!)
1966 Opel Rekord L CLASSIC SEDAN Current Project

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