Duncan Mould
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| posted on 19/3/10 at 06:04 PM |
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Zetec flat spot
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?
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r1_pete
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| posted on 19/3/10 at 06:05 PM |
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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.
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fatbaldbloke
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| posted on 19/3/10 at 06:07 PM |
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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]
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Duncan Mould
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| posted on 19/3/10 at 06:09 PM |
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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.
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r1_pete
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| posted on 19/3/10 at 06:17 PM |
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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.
He needs to find out what the tuner has drilled, if he just enlarged the prog holes he's ruined the carbs.
I understand more holes are needed due to the engine being designed to run lean, and the more holes allows it to stay on primaries longer, and give a
longer overlap onto mains.
It is at the changeover from primary to main where the hesitation under load occurs.
[Edited on 19/3/10 by r1_pete]
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austin man
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| posted on 19/3/10 at 07:29 PM |
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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
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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britishtrident
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| posted on 19/3/10 at 07:49 PM |
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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.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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fatbaldbloke
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| posted on 19/3/10 at 11:17 PM |
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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.
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zetec mike
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| posted on 20/3/10 at 12:52 AM |
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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.
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