There seems to be so many posts on here about fitting bigger carbs to K series motors. In the majority of cases a bigger carb is not needed, especially on stock motors. Here is a simple test you can do to see if you really NEED a bigger carb....

 

1. Fit a vacuum gauge to your inlet manifold.

2. Floor it through the gears and take a note of the lowest vacuum readings.

 

If you get a reading of between 0 to 1.5" of vacuum you don't need a bigger carb.

If you get a reading of 1.5" of vacuum or higher, remove the aircleaner and try again... If it drops under 1.5" of vacuum, all you need is a sports aircleaner or maybe just replace stock one if it is dirty.

If you get a reading of over 1.5" of vacuum (even without filter) you really could benefit from going to a bigger carb.

 

It is as simple as that.

Edited July 27, 200917 yr by Felix

camshaft, camshaft camshaft!!!!!

 

I keep telling people, before you go putting a bigger carburettor and exhaust on your corolla, pull the engine out, rebuild it (new rings bearings balance etc) and put a different profile cam in it, pay some attention to detail when you assemble it, and you will never look back!!

 

If you just whack a big carburettor on a standard engine you will be disappointed. If I had have upgraded the carburettor first, I would have stuck with it for a little while and then bought a faster car.

 

The camshaft would be one of the components that changes the engine's characteristics the most. I'm told a light flywheel makes a huge difference too, but can't vouch for that YET!!

 

Robert.

I agree with you totally Robert with fitting a warmer camshaft before a carb upgrade. NOT a hot cam but something warm up to 270 degrees duration (ie. 25/65 65/25) will wake up an otherwise totally stock motor.

 

The above mentioned cam will give very good gains with future mods such as more compression (10:1), extractors, exhaust (no bigger than 2"), bigger carb, some headwork, dizzy regraphing and shorter diff gears.

Is this test only for N/A motors ?

 

Cheers Ben

Yep, unless you remove your boost pipework to your carb in a blowthru setup.

if your car isnt na you will go out of vac to boost so i would say test for na

ok cheers Guy