Interesting observation Dodgeman. Most low manifold vac problems I've run into were cam/valvetrain related and long runners or high rise manifolds or both cam and manifold. 265 Hemis are a good example actually with that huge intake manifold where the carb sits a metre or two away from the head. I can say with complete confidence that the all to common Webers go out of tune complaint is 9 times out of 10 due to crap linkage setup...cant stress that enough. You dont have a chance in hell tuning and balancing with dodgy linkage. Unfortunately there are a lot of twin setups out there with disgusting linkange setups and the carbs get blamed. I used to tell customers I cant tune your car with that linkage on and they would walk out and go find someone who would do it...only to come back again.

Rallytwit...never thought of that. I know who I'll be having a chat with if I ever went that way.

A couple of things to consider with bike carbs.........if you use the CV style you will likely be playing with springs to get them right. For ones like the FCR type yes they are sweet but they will be more money than webers. Finally having run a bike engined race car you need to keep in mind the carbs are not set up to deal with lateral G loads, remember the bike leans over so any G force pushes the fuel down................no side to side sloshing. Under heavy breaking on a bike your mostly off the gas so the fuel sloshing forward won't be an issue............but in a car right handers could be an issue??? We had to do some pretty extensive work with the float bowl to cure all the carb problems.................just food for thought.

Tom

Quote:
When I wrote my post I was thinking of a local 1200 coupe with bike carbs & these are of the diaphragm type which seem to have much in common with automotive CD carbs when it comes to principals of operation.

With these, the fuel flow is regulated by demand & a measure of vacuum is retained in the manifold.

With sidedraughts [which are frequently feeding a 'big cam' engine] there is little between the atmospheric pressure outside & the manifold pressure inside.

My own limited experience with a vacuum gauge & various one-cylinder-one-throat systems has resulted in my view on the subject.

Has anybody noticed that the Valiant Charger models with the triple Weber induction did not come with a brake booster from new?
The reason?
Vacuum signal too low to be of any use in this application.

LOL :)) I do prefer a sinister and smart black straight haired
pub owner myself with a tat in the right place.
http://www.mytattoodesignslive.com/wp ... /02/tattoo4.thumbnail.jpg

i wonder if a single 48mm version of a flatslide could be used
as a suck through turbo setup?

i think i just blew my load... they look hot as... almost as hot as a blonde nympho who owns a pub

I like simplicity that requires little room and reduces weight significantly.
Therefore bike carbs all the way whether low or high rpm.

they also still have a needle and seat to govern fuel flow into the fuel bowl

with webbers you generally dont have much vacuum as you have a bigger cam to suit. but with a stock cam i would think that you would still have a normal amount of vacuum...till you opened the throttle

aren't most bike carbs gravity feed? when you are sitting at a set of lights don't they over fuel??

I understand that you dont get ported vacuum but if you're fitting twin sidedraughts I dont think you're gonna be too worried about no vac advance. Vac advance works soley on cruze/light throttle for better fuel economy. I thought Dodgeman was saying you have less manifold vac with webers than with bike carbs.