Why Are My Webers Turning Yellow?

[Ren]

Hi All, can any one tell me why my new Webers are turning yellow?

The engine is a 912 block with big bore kit, Nuetex 1 cam, CB straight cut cam gears, CPS push rods and alli pulley, S90 heads with a PM spin on filter and Sebring (Carrera Style) Exhaust. The Webers are new and have the bigger size chokes to match as close to Solex's.

The engine runs great over 3000rpm but bogs down under that which I assume is the cam and heads. Timing and valve gaps are bang on the money but I have a yellow residue on the carbs and get the occasional spit back noise.

Nearly forgot to mention it has an electric pump and regulator set at the pressure for Solex.

Main jet is .140
Air jet is .185
Idle jet is .55
32mm chokes
43mm ram pipes

[richkaz]

Had a similar experience with Webers on my old Alfa Spyder and was told to ignore it as the Millers octane booster was the culprit ?

[Ignatzcatz]

Had the same deal on my old 1580 powered 105E with twin 40's. It was due to fuel standoff from the rampipes which I guess sprayed back over the carbs and the residue from them coloured the carbs. I could'nt afford a pukka rejetting and set-up back then so I suffered a few spits and bangs and about 15 to the gallon, but gas was 5 bob a gallon then so it was no big deal. Ah, days gone by.

[Ren]

Ok for everyone who did not know the answer - it is the main jet that is to big. It is spitting a mist of fuel up out the ram pipes and hitting the air filter and running down the carb body.

A symptom is soot on the body and black exhaust.

I have replaced the .140 for .135 but now it runs like a dog.

So back to the start for me.

[Ren]

Ok so Iput in smaller main jets at .125 and tuned it up. I managed to get three cylinders running sweet but for some reason the last cylinder which I think is number 2 will not tune up. I turn the screw all the way in and no change. I turn the screw out and no change. I think I might have a blocked idle jet or could it be that the other three are so rich that they are covering up the last cylinder? hmmmmm.

[Ren]

Ok so I re-set all the mixture screws 1 and 1/2 turns out and the idle screws 1 turn after just touching the throttle stop parts. I cleaned the plugs off and adjusted the pumps so they chucked a bit less in to the carb. Fired it up and tweaked the idle scews to get the carbs in sync. The idle jet in 2 is not blocked it was the other three covering the mixture of 2. Took it for a blast and it still bogs down at 2500-3000rpm. So wound in the mixture screws each in turn till the engine falls then back out 1 turn. Took it for a spin and its the same. I suppose Dave it could be the air jets. Yes Dave it could them. Worth a try. Better get some then. Ok Dave I will.

Any Weber experts near Southampton?

[cubist]

Well done Dave...

[Ren]

So Dave which air jet would you recommend? hmm....