A mate of mine has a westfield with a Zetec 1.8 running 40's that has an hurrendous flat spot. the car idles well and emissions are spot on, press the throttle steady/progressivley and it revs clean through. pull off from a junction and floor the thing and it just dies, lift off the throttle and it idles lovely. Any clues or hints?
Sounds like it has the wrong carbs, there are some made specifically for the Zetec with 5 progression holes, its a sure bet his only have 3.
They can be modified. Here's a link to some details.
http://www.alfabb.com/bb/forums/carburetors-fuel-injection/32856-weber-dcoe45-152-45dcoe-progression-circuit-modification.html
[Edited on 19/3/10 by fatbaldbloke]
He has had some engine tuner take £300 off him and he said he had drilled out the carbs which made it a little better. others have said his inlet manifold is to stumpy and needs to be longer. It has mega jolt and a throttle pot on it.
quote:
Originally posted by Duncan Mould
He has had some engine tuner take £300 off him and he said he had drilled out the carbs which made it a little better. others have said his inlet manifold is to stumpy and needs to be longer. It has mega jolt and a throttle pot on it.
I have 40's without 5 progression holes there is a flat spot around 1300 rpm but nothing that isn't manageable.
The Zetec ones do have 5 progression holes though
Check the accelerator pump jets are clear ( they have tiny holes and choke easily) and then take the lids off the carbs and check the accelerator
pump plungers are free and getting pulled down when the throttle butterflies are opened.
Also check the float levels.
What causes the problem is largely related to the ignition abilities even of a simple system like Megajolt. When the Weber DCOE was designed typical
ignition systems were distibutor based with mechanical advance. These meant that the engine ran relatively inefficiently at lower engine speeds so
the primary fuel circuit in the carbs came into use shortly after idle, and the transition period was small enough, maybe only covering 100 or 200
revs, that the relative simple expedient of uncovering some drilled holes through which additional fuel flowed, as the butterfly opened, were
sufficient.
Then, along came 3d ignition maps, which enable engines to run so much more efficiently at low revs, so now the primary circuit doesn't take over
fully until over 2000 rpm in most cases, so a lot of running is done on the transition circuit, which is why the number and size of holes has become
increasingly critical.
Sounds like its not getting any accel enrichment so I'd look at the pump jets 1st. Take the filters off and shine a torch in and open the throttle and you should see a squirt of fuel from the pumpjets, if not unscrew the brass screws above the accell jets, open throttle and there should be a good flow of fuel.