hi
i have the newer designed 151 dcoe carbs on my engine and was wondering if i could use the vac take off port for my map sensor on these carbs as they have 1 per port runner which would mean i could smooth it using the reservoir then straight into the mjlj. My only problem would be having to drill out the port hole where it opens into the port runner of the carb,do oyu think this could bea realistic option for my instal or would drillig my manifold be the best way to go??
p.s. these hole are behind the butterflies between the carbs and the head
thnaks in advance
weber dcoe 151 vac take off port
Moderators: JeffC, rdoherty, stieg, brentp
The vacuum takeoffs may be too small. I have weber 44 idf x2 on my type1. Admittedly there is only one port per carb so two total but the vac signal wasn't smooth enough or strong enough to use for MAP. I ended up building a TPS MJLJ. Hook all 4 up with tees to a vac gauge and take a reading at idle, part throttle, etc. Others here can tell you the values you are looking for, I forgot 
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!thanks for that danny p, i think i will look into drilling the holes out a bit, the covers on them are large enough to accept at least a 4mm thread so would just be a case of drilling out the material below the cover's thread, i hope
failing that what is the optimum size for the vac take off if i was to tap into each manifold runner?
failing that what is the optimum size for the vac take off if i was to tap into each manifold runner?
Standard vac pipes are normally 3-4mm diameter so that should be adequate for tapping into a port.
I'm not an expert in vacuum engineering, but I would have thought that smaller is probably better as there's less air between the measurement point and the sensor to expand as the vacuum increases - I don't think I've ever heard of a vacuum that "wasn't strong enough". But too small can bring it's own problems and that's why people put empty fuel filters and the like into the pipe to smooth out the vacuum seen by the sensor
You should be looking for numbers in the order of 20-30kPa at idle and 90-100kPa at full throttle...
Martin
I'm not an expert in vacuum engineering, but I would have thought that smaller is probably better as there's less air between the measurement point and the sensor to expand as the vacuum increases - I don't think I've ever heard of a vacuum that "wasn't strong enough". But too small can bring it's own problems and that's why people put empty fuel filters and the like into the pipe to smooth out the vacuum seen by the sensor
You should be looking for numbers in the order of 20-30kPa at idle and 90-100kPa at full throttle...
Martin