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I had a hs6 on my mini to start with but they are quite finiky and innacurate carbs so i decided to change to a later and better HIF44, only problem is i dont have a clue where to start with it. The engine will start and run but the throttle response is aweful even with no load on the engine, ive tried the choke that seems to help which i should immagine means it is running too lean, but if i take the choke off and up the fueling it just dies. I realy dont have a clue where to start with HIF's, so has anyone got any ideas?
How do i set up my SU HIF44 carb?
- Thread starter [huzeeee]
- Start date
ahhh memories 
You can get generic needles that will make it run ok but you need a custom needle for best results.
Mine was like that too when i had a HIF38, make sure you have the correct carb oil in. I used some fork oil and it was sweet.
You can get generic needles that will make it run ok but you need a custom needle for best results.
Mine was like that too when i had a HIF38, make sure you have the correct carb oil in. I used some fork oil and it was sweet.
This is what you need http://www.winsu.co.uk/ That will tell you the needle you need depending on the engine and state of tune.
Soldato
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Maybe a stupid question but have you checked the oil in the top of the SU. It uses something like 3 in 1 but causes havoc if it runs dry.
First check the O rings in the fuel enrichment assembly (AKA choke, though it isn't a choke). These can perish/break and it really screws up the mixture. Also check that the piston smoothly rises and falls over it's entire working stroke, and dirt or corrosion in the dashpot will screw things up.
Note that the mixture adjustment screw (cross head on back of carb) works in the opposite direction the the brass nut on the HS style carbs. Turning it anti-clockwise weakens the mixture, clockwise richens it.
Assuming the needle is correct for your application, then with a warm engine you adjust the the idle mixture to get the highest RPM. As the RPM goes up, adjust the idle screw to bring it back to whatever the standard idle speed is (~800-900 RPM). This should get you in the right ballpark.
Use the lifting pin to raise the height of the piston slightly, and note the engine speed. If the engine speed rises, it's running too rich. If the engine bogs down and stalls, it's running too lean. Ideally you engine speed should just rise briefly and then drop back to around normal idle speed. Don't push the pin all the way in, you only need to lift the piston by around 1mm.
BTW, what size engine do you have in the mini? If it's a fairly standard 998 then you will never get an HIF44 running correctly on it, they are simply too big. The HIF38 is far more suitable for these engines.
As mentioned by someone else, ensure the damper is topped up with oil. This damper does the job of the accelerator pump in fixed jet carbs, if the oil is low you will find the engine will bog down quite badly if you snap the throttle open.
Note that the mixture adjustment screw (cross head on back of carb) works in the opposite direction the the brass nut on the HS style carbs. Turning it anti-clockwise weakens the mixture, clockwise richens it.
Assuming the needle is correct for your application, then with a warm engine you adjust the the idle mixture to get the highest RPM. As the RPM goes up, adjust the idle screw to bring it back to whatever the standard idle speed is (~800-900 RPM). This should get you in the right ballpark.
Use the lifting pin to raise the height of the piston slightly, and note the engine speed. If the engine speed rises, it's running too rich. If the engine bogs down and stalls, it's running too lean. Ideally you engine speed should just rise briefly and then drop back to around normal idle speed. Don't push the pin all the way in, you only need to lift the piston by around 1mm.
BTW, what size engine do you have in the mini? If it's a fairly standard 998 then you will never get an HIF44 running correctly on it, they are simply too big. The HIF38 is far more suitable for these engines.
As mentioned by someone else, ensure the damper is topped up with oil. This damper does the job of the accelerator pump in fixed jet carbs, if the oil is low you will find the engine will bog down quite badly if you snap the throttle open.
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I don't think he's online so I'll answer for him - It's a fairly extensively modified 998 which has been bored out to just over 1000 now, it's had porting and polishing work, bits have been balanced, lightened and he's got some fairly aggressive cams in there too. It should be circa 70bhp according to him.
My brother had a very simmilar spec engine, with a ported, big valve 12G295, powermax pistons, LCB etc. and the HIF44 on it never worked very well despite being set up on a rolling road. It will need a very rich needle (or a very filed down one!) to stop it running weak at the midrange and top end.