Too rich?

[Phil Bishop]

There was a recent thread about balancing idle jet settings on Webers. (I run a Classic with a 1600 Vauxhall valve.) While I think I have the four jets as equally balanced as I can get them (given the limitations of the little 'plug it in the hole' type flowmeter I possess) how do you know if the whole set are running collectively too rich or too lean? I had a long run round the M25 yesterday (cold!) to Brooklands and I had so much fuel coming through the air filters that it was getting up on the screen and all over the rear wheel arch. Instinct tells me that if there is so much fuel sloshing around that it can do this, then it must be running rich, yet I have read that if the carbs spit back then they must be too weak. I'm confused.

[oilyhands]

The idle volume screws only adjust the mixture *at idle* there is a technique you can use to get the mixture correct at idle here, the fuel slope for the rest of the engine range is determined by its calibration, I.E. the jets, chokes and emulsions tubes in use. It is entirely possible to be weak at idke and rich elsewhere or vice versa. If you have fuel sloshing around it is probably not because the jets are incorrect, it's more likely to be caused caused by standoff, or by the float jets not functioning correctly and flooding the carb.

 

Oily

[AndreK]

I have same car. I hope the following is not too patronising. Accepting that due to the inlet manifold design on this car, the standard jetting is a little strange, try:

 

1. Check inlet manifold is adequately tight

2. Check carbs are tight enough to the manifold to prevent leaks but not so tight that there is no movement at the rubber bobbin mounting bushes

3. Remove plugs and soft wire brush clean, refit. This is easier if the alloy tubes are removed first, bolster chisel is useful for unscrewing them

3. Set idle to around 1000 rpm

4. Set balence with your flowmeter, also check still balenced at 2000rpm at least

5. Re set idle to 1000rpm

6. Using a gunsons colourtune, adjust the 4 mixture screws to be just (I mean only just) on the rich side of the blue flame

7. Re fit K & N air filters after cleaning an re-oiling

 

This should cure the petrol spilling out of the air filters, and you should find that your car idles and runs smoothly. Failing the above you may like to try a visit to a good rolling road to thoroughly sort the Webers!

[acbateman]

We have a 1700 XF on twin Webers and the front carb always seems to run rich at low speed - as assessed by dark plugs in cylinders 1 and 2. The car has been rolling road - tested and runs v well and I have checked the float heights, replaced the needle valves and cleaned the K&Ns. This seems to me to be a Weber trait! Has anyone else experienced this phenomenon?

 

 

[Foxy Smith]

Just to add my two pennorth, I had a serious problem of petrol overflowing the float bowls, meesing around with float heights and new needle valves was no help. The problem was traced to an over specced fuel pump which was powerful enough to overcome the needle valves/floats. Replaced with lesser fuel pump, problem solved. Webers only need 3.5-4.5 psi or less, could have used pressure regulator I suppose.

 

Alan

[dmc]

If you have fuel coming out of the air filters

two possibilities are :flooding or stand off

flooding would normally be accompanied by bad running & black smoke

stand off isn't unusual in race cammed engines but milder tuned

engines cam timing can be the cause!(and other mechanical valve train problems)