cadebytiger
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| posted on 19/5/07 at 02:45 PM |
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Setting up my webers
I have just rebuilt my weber 45 and am having some trouble getting them to idle. I have the type of Webers with the air idle bypass valve.
The book says to leave the idle bypass valve closed to begin with when setting up. Wind the idle mixture skrews out by 11/4 turns and set the idle
speed so it will run. Then balance the carbs after and adjust the idle mix.
I did this but found that I had to have the idle speed very high to get it to run. It was either high or die.
I read dave walkers book on engine management and he talks about this very problem and says it is due to you having to open the butterflies so much
that they uncover the progression holes. At idle no progression holes should be even partially uncovered. I checked this by shining a torch down the
venturi and removing the progression hole cover screw. This indeed seemed to be the case. I could see the edge of the butterfly over the first
progression hole. Dave walker says that to stop this happening you must bleed enough air past the butterfly using the air idle bleed skrew to allow
the car to idle without uncovering the progression holes.
I adjusted the idle speed skrew so that I could no longer see the edge of the butterfly and tried to start the car with the air bleed skrews one turn
out. It started as before but when you come off the throttle it dies. I repeated this turning the skrews out further and further. I am about 6 turns
out and the engine still dies.
Sorry for the long post. Does anyone know what I should try next? How much of the edge of the butterfly should you be able to see through the first
progression hole (if any).
Thanks again
Rupert
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awinter
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| posted on 19/5/07 at 04:12 PM |
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Did you manage to synch the carbs when you had it idling?
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westf27
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| posted on 19/5/07 at 04:21 PM |
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are you sure that your fuel supply is good and that the fuel level is correct,what about ignition timing.I assume your was running ok before the strip
down?Another thought could be large air leak.
555
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flak monkey
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| posted on 19/5/07 at 04:33 PM |
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You should be able to get them running well without the air bleed, or at least enough so the engine runs ok.
Expect an idle between 800 and 1000rpm depending on cam.
Big question is, what jets have you got fitted?
You may be better off starting with the idle screws 2 turns out, if your idle jets are too small then you wont be getting enough fuel through without
the progression holes uncovered.
David
Sera
http://www.motosera.com
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cadebytiger
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| posted on 19/5/07 at 05:05 PM |
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yep managed to get them more or less balanced.
They were running fine before they came off the car and ignition timing should be fine although i will check.
I managed to get them running a little better by winding out 2.5 turns as i read on another setup book.
it is spitting back alot so may be an air leak. it was not coming back down to idle very fast - i think this would poing to an air leak???
Thanks for the help
Rupert
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flak monkey
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| posted on 19/5/07 at 05:10 PM |
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If you get it running and then squirt wd-40 or easy start over the throttle spindles and misab gaskets etc. If it speeds up you have an air leak
somewhere.
David
Sera
http://www.motosera.com
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cadebytiger
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| posted on 19/5/07 at 05:13 PM |
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cool will try it. thanks
do you need to centre the misab plate or should it not be a problem?
Also how much should i compress the rubber washers?
Thanks once again flak monkey
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flak monkey
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| posted on 19/5/07 at 06:22 PM |
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Gap the rubber washer thingies to 2mm. You only need to use one cup under the nut, you dont need one on the carb side. Gap to 2mm between the cup and
the carb body.
Misabs should centre up anyway.
David
Sera
http://www.motosera.com
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cadebytiger
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| posted on 20/5/07 at 01:58 PM |
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Sorry but just to check i understand.
Only use one of the metal cup washers under the nut and not one on the otherside of the rubber bit (between the rubber and the carb body).
Thanks again monkey
quote:
Originally posted by flak monkey
Gap the rubber washer thingies to 2mm. You only need to use one cup under the nut, you dont need one on the carb side. Gap to 2mm between the cup and
the carb body.
Misabs should centre up anyway.
David
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flak monkey
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| posted on 20/5/07 at 02:01 PM |
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Yep thats right. So you have: nut, washer, rubber, carb.
Thats the recommended weber fitment, quite why you get twice as many cups as you need is beyond me.
David
Sera
http://www.motosera.com
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cadebytiger
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| posted on 20/5/07 at 02:06 PM |
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haha. great thanks - goodness you are fast!! 
is this symptom i described with the slow falling revs usually caused by leakage of air then?
i guess that it is the increased vacuum in the manifold pulling air past the misab plates and thus slowing return to normal idle speed - am i right??
Will give it a go today.
Thanks
Rupert
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