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weber DCOE 40 carbs - pump jets

wonkey eyed barmaid

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They meter the fuel to the accelerator pump circuits, these provide instantaneous enrichment when the accelerator is suddenly opened, this extra fuel covers the weak spot which occurs when the air in the induction system accelerates into the engine faster than the fuel through the main jet, without the acclerator pumps the engine would stumble and die. There is also a bleed back system which prevents too much fuel being modulated. Too large a pump jet will flood the engine when the throttle is opened and will cause a slight misfire coupled with much black smoke.



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Interesting...am rejetting my carbs after a Blydenstein conversion on my 1600vx.


Current jets are


Mains 115

Emulsion F7

Airs 195

Idle 60F6

Chokes 30

Pump 45


On advice i am changing only


Idles 45 F9

Pumps 35


It is running rich with black smoke being blown out on quick pulses of the throttle.Its floods when hot.And tick over surges. are these symptoms cause by the pump jets? Am i going to lose performance by going to 35? Or Is it the Idles which control this?


Thanks Ian

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i think my idle jets are 50's - and I am also planning to change down to 45. just waiting to fit the jets next time im at home.


my pump jets are 50, and I have been advised by redline to change them down to a 35.


my main jets are 115. *thumbup*



oilyhands. thanks for the informed response. it may explain when my car stutters and farts a bit when I open the throttle quickly. I always assumed it was overfuelly, but thought it was down to general setup etc. I now suspect that the pump jets are overly large.


will let you know the results of the change.

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60F6 idles are the act of desperate man.. 45F9 or 50f9 should be fine. A 35 or 40 pump jet is probably about right. The rest of the calibration looks reasonable, the mains may be marginally lean and the airs a little on the large side.



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Hi Chas,


I bought 8 jets and a couple of gaskets from Southern Carbs for about £25 and did the set up myself using a carb vacuum guage and a color tune plug. They are worth owning to keep your carbs in a good state of tune. It is easier than you think to tune them aslong as you have the correct jet sizes.


After the Blydenstein conversion and rejetting the car tick over is much better,smoother,loads more power and torque. Its is like having a bigger engine. Better fuel economy also even though i tend to stick my foot down more than ever!


A standard engine will benefit from rejetting though as i think the standard jetting is way off.





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I have put on about 2000 miles since the conversion - goes very well but wont tick over and I will need to get it tuned to get it through the mot. I was wondering if anyone knows what Southern Carbs would charge to set it up for me and if they are experts. I have had poor experiences in the past with some of the so called tuning companies so would welcome any recommendations in the west london area



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