Weber carb upgrade

[BSCR 914]

Have a rebuilt 1975 2.7 and I want to add Weber carbs. The carbs are from a 1966. Will I need to replace any parts to suit this 2.7 as I don't believe there would have been anything close to a 2.7 in 1966.

[larrym]

replace the venturis with 32 or 34's; rejet them per Bruce Anderson's book - it's pretty well covered there

- or do a google search for weber 40 jetting or similar - that will lead you to many forums

best source for the parts is Pierce Manifolds - put that in google as well

you should also do the well-modification and the venting mod - get the tool from PMO,

and you need to get the base insulators too

for the CIS heads on your 2.7 - you must either get-or-make base gaskets/seals that cover the injector dimple or - get PMO manifolds which are made to cover that problem - else you will have a vacuum leak problem

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[advtracing]

have done this just last year , weber 40's on a 2.7 . these webers were on a 2.8ltr so changed the jets / ventures . Had to redo the curve on the distributor . used pmo heat shield spacers to cover the indent dimples left from injectors .

just finished tuning and in a 980kg car goes like hell



Porsche cis to carb swap - YouTube

[jakz]

That looks great!!

[BSCR 914]

Interesting. The carbs came off a racing car. If I take the carb apart will I be able to see what sizes are there? Also, if I'm not racing is it a must to change these parts? Will the motor be harmed or just performance?

[larrym]

yes- open them up, & remove all the jets, etc - the numbers are embossed or inscribed on every single part

the parts work interactively, so you can't just change one jet size without it affecting sizing of other pieces - see any of the manuals listed below for detail on that

just to help ya out with your adventure - -

webers run on the idle circuit up to about 3000 rpm before they go fully onto the main circuit - race cars don't operate under 3000 so ... no telling what ya got until ya look

for my 2.7 ( RS p&c's, solex cams) - my weber 40's have 34mm venturis, 185 air correction, 55 idle, 135 main, F3 emulsion tubes, PMO tall manifiolds, percolation fix and base insulators

- i tuned it to these settings over many hours of roadtesting & track driving using dual 02 sensors in the exhaust with a Halmeter - at one time i had a testing inventory of over $1000 in jets & stuff - all purchased from Pierce Manifolds - and i had the dizzy recurved by Rennsport Systems who know what works for what cams & CR & displacement & intended use

for a 2.7 Bruce Anderson recommended 145 air, 60 - 65 idle, 135 mains, 34 vv, F3

Jerry Woods recommended - for same carbs on my 2.8 with e-cams; 180 air, 70 idle, 165-170 main, 34 vv, F3

Kevin Redman recommended for 2.7 with CIS or e-cams: 180 air, 60 idle, 145 min, 34 vv, F3

there are several good books on Weber tuning you can buy -

Pierce manifolds used to sell a really good Weber Tuning Manual and it has lotsd of detail on jets & combinations of what does waht when mixed-matched (dunno if still available)

definitely buy Tomlinson's Weber Tech Manual

- also go look for this article - Weber Music from an old Kit Car magazine -

read everything on the PMO website

- and buy yourself relevant copies of PCA's Upfix'n series as well as Excellence's Technical Notes,

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