5 replies to this topic

[min ritz ryan]

Hi all, as the title states, I need advice on what carb to run on my 1275 engine. Currently im running a hs4 but it needs a new jet as the tube keeps getting blocked somehow, and ive been told that hif 44's are practically bulletproof if built properly.
Can any one give me a direction to turn, either stick with my hs4 or go to the hif 44?

Any advice would be great, thanks

[KernowCooper]

The HS4 is 1 1/2" the HIF 44 is 44mm  so a bigger carb and depending on the state of tune your engines in may be over carbed its used on the MG Metro 72bhp standard so has more air flow than the HS4

 

The HIF38 is the same size as the HS4

Edited by KernowCooper, 25 May 2013 - 11:52 PM.

[Leics1275]

I have the 44 on my 1275 and it it's fine, now for the silly question, Kernow can you simplify 'over carbed' , should i drop down to a smaller carb ,and how would it change the performance ?

 

Dave

[Tommyboy12]

A matched carb will provide the correct airflow at a given engine speed. Too large will mean airflow is too low, which means your airflow isnt high enough at high rpm and you lose hp. A carb that is too small will reach max airflow too soon and you will loose top end hp, but on the flipside you will get max torque sooner.

[Ethel]

That's pretty much it,

 

Of course the throttle controls how much air goes in to the engine and, all other things being equal, it will take the same amount of air to drive the same Mini at the same speed, whatever the carb & engine. What will alter with the carb's diameter is velocity of the air, and that's what creates the depression that sucks the fuel out of the jet, and the pressure differential that raises the piston to meter the fuel. A carb that "maxses out" as the engine does will have the full range of piston lift available to meter the fuel.

[Captain Mainwaring]

More important than just carb size is to use a radius plate at the carb mouth. It makes a huge difference to potential maximum airflow and stability through the carb.