James Rogers Posted May 23, 2002 Share Posted May 23, 2002 My Zetec with 45s and a Dunnell EMS experiences a significant flat spot when accelerating below 3000 RPMs. Also the engine burbles when cruising on light throttle in this range. Above 3000 performance is fine. I’ve tried running both 55F8 & 55F9 jets with no difference. Is this possibly a progressive hole issue with the Webers manufactured in Spain? If so, what modifications are required and who can perform this service. Thanks in advance for the help. James F. Rogers Link to comment Share on other sites More sharing options...
R2D2 Posted May 23, 2002 Share Posted May 23, 2002 I think that it is quite common to richen the idle so much that you "flood" around the flatspot but this gives a crappy idle. I had a similar problem with 45DCOE152s fitted to a 1700cc Twin Cam and had an extra progression hole drilled by Roger King, which has solved the problem. I believe that it's worse with 16V engines such as VXs and Zetecs and the soultion is to drill two extra holes. Webcon have the correct jig but since the take over by Intermotor the switchboard seems a nightmare. Alan Collins on 01932 750252 which is a direct line, is the carb progression hole drilling man and it may be worth speaking to him. Link to comment Share on other sites More sharing options...
Martin S. Posted May 23, 2002 Share Posted May 23, 2002 James, Mine is a 2Ltr Zetec on Spanish 45's/Dunnel 3D/standard cams/165BHP and runs nice and smooth throughout the range. I have 4 progression drillings, the 2 nearest the flaps being slightly bigger than the 2 furthest away. My carbs have definately been drilled 'cos whoever did it put a hole through one of the butterfies at the same time, not ideal for smooth running! (now soldered up) Chokes are 36mm Main jets are 148 (I think though the stamping's not clear, could be 140!) Emulsion tubes F16 Idle Jets 55F9 My idle mixture screws are all around 2.5 turns from fully in. Hope this helps. BRG Dedion 2Ltr Zetec - Warrington Link to comment Share on other sites More sharing options...
BlueShark Posted May 24, 2002 Share Posted May 24, 2002 My Vx 16v has exactly the same problem. Standing starts are a nightmare, pulling away from junctions a hazardous game of throttle control. Once over 3000 rpm, it flies. 2 rolling road sessions have failed to resolve the problem, but as it was running very rich, the idle jets were changed fromm 55F9 to F6, which leaned it out a bit, but didn't affect the flat-spot. Mr Shaw in Daventry did however comment on the size of the choke-it is a 40 as opposed to a 36, which seems to be more common, and he theorised that this might be the problem. I don't know, and am a bit reluctant to spend money on four new chokes at the moment. Came across a friendly Subaru driver the other day, and saw it take off like a champagne cork, whilst mine was coughing, spitting and bogging down... Andreas. Link to comment Share on other sites More sharing options...
oilyhands Posted May 24, 2002 Share Posted May 24, 2002 Err.. changing to 55F6 from 55F9 will *richen* the progression.. F6s are desperately rich. An F8 or F2 will weaken the progression by emulsifying more air with the fuel stream. Does sound to me like the progression drillings dont suit the engine airflow requirements, it's quite common with 16v engines. This can lead to oversizing of the idel jets to compensate, causing a cycling from rich to weak on progression.. its worth having the progression drillings sorted out.. The choke size can influence the main jet 'signal' and hence where the main circuit starts, but the progression should cover the transition from idle to main cicuit Oily Link to comment Share on other sites More sharing options...
BlueShark Posted May 24, 2002 Share Posted May 24, 2002 Oilyhands, I may have gotten that one wrong, by the sound of it. I am not particularly technically minded, so forgive my stupidity. The idle jet that was put in had a smaller fuel outlet and a bigger air hole in it than the F9. Andreas. Link to comment Share on other sites More sharing options...
oilyhands Posted May 24, 2002 Share Posted May 24, 2002 Sorry.. didnt mean to imply anything about you personally, just didn't want anyone lead up the garden path unintentionally, it's likely that a 50f8 was used.. Oily Link to comment Share on other sites More sharing options...
BlueShark Posted May 25, 2002 Share Posted May 25, 2002 No worries, pal. All I went on was what Mr Shaw told me and showed me, but by the sound of it you are probably right. I've got to check that one out! Cheers! Andreas Link to comment Share on other sites More sharing options...
Klaus Loske Posted May 28, 2002 Share Posted May 28, 2002 Hi, probably check if all progression holes are there! Bought some brand new Weber 45´s and there was one progression hole missing on one barrel. Probably the Spanish went on siesta.... The problem was that one spark plug got blocked at idle and then it would not accelerate smoothly until the plug was burnt free again. Probably worth checking (take some nylon fishing line) and see if you can poke through all progression drillings). Klaus Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now