Keihin carbs

[SouthhamsChris]

I have been tidying up the engine bay on my 'new' westy and don't know much about these Keihin CVR carbs. The car is fitted with a 2.0 black top zetec engine. Apparently they are bike carbs. What's the advantage over normal carbs? On one end there is a electric cable connection, but this wire is cut off further back so does nothing. Any info would be most welcome, cheers Chris

[Kingster]

They are off a bike which is quite common. 

The wire is for a throttle position sensor usually referred to as a TPS. 

They are considered to be easier to set up than “normal” Weber type carbs, stay in tune better and will drink less fuel as well. 

Bike carbs do not like sitting unused with petrol in for long periods and “gum up” so drain them if you store it for more than say 4-6 months. 

They use a diaphragm under vacuum in each carb to lift the needle when the butterfly opens. If this diaphragm splits it can cause rough running. 

[SouthhamsChris]

Hi Chris, many thanks for the above, as the wire is for a TPS, does this mean the ecu doesn't need this sensor or the ecu is getting the information from somewhere else? My last two westys had crossflows with twin webers.....l guess if the end of the wire is not connected, l might as well just remove it?

[Kingster]

Use of a TPS depends on the ECU I guess. 

A TPS will allow the use of a 3d map instead of a basic 2d map and can help CV type carbs respond better under load by changing the ignition advance in relation to throttle position. 

I don’t think a TPS does much for carbs that have the slides pulled up by a cable.

[SootySport]

If they have never been tuned before then it is worth having them tuned now.  You'll end up with smoother running, more power and more mpg.  If you connect up the Throttle position sensor to the ecu (if there is such connections)   you'll have a little bit more power, not much though, it can allow for finer tuning.     The good thing about bike carbs is they don't leak petrol vapours as much as carb type carbs when stored in a garage and slow speed throttle openings are not as jerky as Webers or Dellortos on a light throttle opening. 

  I have Yamaha R1 carbs since changing over from twin 45 Dellortos I ended up with a few less BHP but the throttle response is a lot more driveable.