DCOE’s with brake servo

[packers1712]

Compared to the SU’s it is very drivable so from that side of things I’m happy, if I can sort the brake servo thing and the “dropping onto one carb during tight right handers” then I’ll stick with the Weber’s because as sad as it sounds the main reason for switching was to get the induction noise but if that’s at the cost of day to day drive ability then back to the SU’s it is!

Doug.

[Rustinmotion]

Originally Posted by packers1712

Compared to the SU’s it is very drivable so from that side of things I’m happy, if I can sort the brake servo thing and the “dropping onto one carb during tight right handers” then I’ll stick with the Weber’s because as sad as it sounds the main reason for switching was to get the induction noise but if that’s at the cost of day to day drive ability then back to the SU’s it is!

Doug.

No problem but if you ever want to try a 30 or 32 choke drop me a line I’m just across the M1 in MK and I think I still have a set of 30 and 32 chokes for a set of 40 DCOE I have
Why do you think it’s throttle linkage causing the issue on RH bends?

[packers1712]

I was thinking maybe because it’s all rods and when the engine moves slightly during cornering loads that maybe the spring loaded link between the two carbs is allowing one carb to be pulled into a more closed position, the symptom is exactly like when one carb pair of butterflies are closed.
I’m going to experiment with setting the idle speed screw on the second carb so that it is a back stop and see if it makes any difference , it’s currently disengaged so that the idle speed is controlled from just one carb and the spring loaded synchronised link deals with the rest, it’s s bit of a long shot but I can’t really understand what else it could be especially as it only happens when turning tight right handers!

Doug

[Rustinmotion]

Originally Posted by packers1712

I was thinking maybe because it’s all rods and when the engine moves slightly during cornering loads that maybe the spring loaded link between the two carbs is allowing one carb to be pulled into a more closed position, the symptom is exactly like when one carb pair of butterflies are closed.
I’m going to experiment with setting the idle speed screw on the second carb so that it is a back stop and see if it makes any difference , it’s currently disengaged so that the idle speed is controlled from just one carb and the spring loaded synchronised link deals with the rest, it’s s bit of a long shot but I can’t really understand what else it could be especially as it only happens when turning tight right handers!

Doug

How close are the carbs to the body or the steering shaft, any chance they hit something when hard cornering forcing one carb up ?
It also could be float chamber level or incorrect emulsion tubes
Check float level setting and check there is no fuel in the floats
Do you know what jets you have?

[packers1712]

Good theory on the carbs touching the steering column, I’ll check but I would think they’d move away from the column when turning right if anything and they are not really close to the body, I’ve reset the floats so the needle valve is open for even longer by closing the gap by a millimetre, if the floats where taking in fuel it would be flooding at idle wouldn’t it?
The jets are 50F9 idle F16 emulsion tubes with 130 mains and 180 air correctors.

Doug.

[Rustinmotion]

Float level is critical as it sets the level the fuel sits in the emulsion tubes and dictates which of the holes are in play, I’m just thinking out loud but sharp right turn may effect fuel level differently due to the float hinge position, I’d think you would have to be only borderline on emulsion tube and fuel level for this to happen

[packers1712]

Oh right ok, I'm not sure I follow what you mean but I'm assuming your saying something could be happening that isn't desirable?

Doug.

[Rustinmotion]

Originally Posted by packers1712

Oh right ok, I'm not sure I follow what you mean but I'm assuming your saying something could be happening that isn't desirable?

Doug.

If you look at the image you can see the fuel (yellow) is sitting at the emulsion tube so increasing the fuel level covers more holes and lowering exposes more
The holes help promote aeriation of fuel (marked in green) making it easier for the vacuum created in the choke area to pull fuel into the carb
Changing F numbers on the emulsion tubes alters position number and size of holes all of which impact the transition from idle jet to main, lifting or lowering the fuel level does the same, it’s for this reason Webber prefer to rubber mount the carb to dampen engine vibration which causes the fuel to froth
In your case if the level is not correct and your car leans into a corner the fuel could rise up or drop down making it perform poor for a few seconds, just a thought

[packers1712]

Ok thanks but how on earth do I investigate if this is what is happening or not?

Trial and error I guess swapping out bits until the symptom goes!

Re-fitting the SU’s is sounding more tempting by the day!

Doug.

[Rustinmotion]

Originally Posted by packers1712

Ok thanks but how on earth do I investigate if this is what is happening or not?

Trial and error I guess swapping out bits until the symptom goes!

Re-fitting the SU’s is sounding more tempting by the day!

Doug.

Start by setting float height, I think it should be 8mm from gasket to underside of float when holding the lid vertically, float hinge at the top, at least that’s ruled out, then go over your linkage to see if engine movement could cause one carb to be closed. Do you have a go pro or old phone you can mount under the bonnet to film what’s happening ?
Out of interest how did you get to the jetting solution you have?
If you can afford it an hour at Northampton motorsport on the dyno and they can set it up perfect for your car