Webcon UK Ltd

lotus · New user Joined: 17 Feb 2009 Posts: 1

Hi, new on here and looking for some advice. Ive a lotus twin cam with 40s on,and am looking to buy some new carbs,i want to put 45s on it. The head has all been ported ready. What carbs will i nead ie 152, 9s, bleed screws on,Also i know it will need rejetting but can i change over the jets from the old carbs to the new ones or will it be a waste of time,cheers all.

dave999 · Posted: Thu Sep 17, 2009 9:39 am Post subject:

152s have 5 or six progression holes
they work best on multi valve ex fuel injected engines

the old weber performance range had 2 or 3 progression holes

both can work well in either application

but if you choose a 152 and expect to follow the setup for a motor that was done with a series 9 style carb you will find ultimatly that idle setup needs to be different from what you were told would work with the 9 style.

don't get hung up on idle air bypass screws unless you have a modern car and need to achive idle emissions. the performance range never had them. They are a consequence of original equipment supplies to people like fiat and lancia who's car had to pass US emissions

all jets interchange.
the holder and air corrector above the emulsion tubes etc may not, would depend on if your 40s are OEM production car carbs or perfromance range do the jet holders have rubber seals and 1 thread or 2 threads?
if the former they won't swap over

mind why use those jets
if you have had head work done and feel the need for 45s then you will only be doing that bcause you can't fit the appropriate size chokes into your 40s. new bigger chokes usually means at minimum idle and mains.

you could of course purchase a jet reamer......get a decent german one and you can achive nearly the same jet taper that the factory did

pointless getting 45s and setting them up with chokes that could have been fitted to the originals unless right on the boarder. if there is a chance you need a choke that only fits the 45 then 45 is the way to go.
the cross over choke that fits both will flow better in the 45 than in the 40. but only a little bit.

a too small weber is allways a better drive than a too big and lots of people spend out on way too big

Dave