Tunning SU's

satancom · Post by **satancom** » Mon Dec 15, 2008 8:12 pm

I have twin HIF SU's on my 3.5 V8. It runs fine with the the crank case breathers off, but struggles with them connected.

I believe its not breathing very well, If I turn the idle up then it will run, and when driving its ok, just idles realy rough. I haven't done anything to the carbs other than changing the bottom seals and believe its running quite rich (sniff test by mechanic mate).

Anyone know of any reference guides to setting the carbs up to basic settings? Im a little out of my depth on carbs but garage can set them if they have the correct specs etc

Any advice welcome.. Its so close to an MOT I can smell it

ChrisJC · Post by **ChrisJC** » Mon Dec 15, 2008 10:03 pm

Haynes do a manual dedicated to SU's.

Chris.

vaultsman · Post by **vaultsman** » Tue Dec 16, 2008 1:23 pm

Pretty good thread on SU tuning on the P6OC site:

SU HIF Tuning

satancom · Post by **satancom** » Tue Dec 16, 2008 2:13 pm

vaultsman wrote:Pretty good thread on SU tuning on the P6OC site:

SU HIF Tuning

Good tips there.. should help me set them up for the MOT anyhow

Cheers

vaultsman · Post by **vaultsman** » Tue Dec 16, 2008 4:46 pm

No problem..good luck with the ticket!

Stan

satancom · Post by **satancom** » Thu Dec 18, 2008 10:37 am

I cheated slightly, old school mechanic twidled the mixture settings mumbling somethin bout it sounding rich... after a few moments the thing was ticking over lovely!

satancom · Post by **satancom** » Thu Dec 18, 2008 3:35 pm

Failed.. co was around 10% bugga

ChrisJC · Post by **ChrisJC** » Thu Dec 18, 2008 4:53 pm

Not an uncommon problem with carb engines. In the old days, one used to lean it right off for the MOT, then richen it back up so it idled properly!

Chris.

RoverP6B · Post by **RoverP6B** » Thu Dec 18, 2008 6:31 pm

If your engine runs better with the crankcase breathers removed, but not so well with them connected, that would then suggest that there is a blockage in them.

Fit new flame traps ensuring that the connecting hoses and attachment pipes on the carbs are all clear. Fit a new engine breather filter too along with new air filters if need be.

If you remove the dashpots, lift out the pistons, you can adjust the jets so that each is essentially the same distance below their respective bridge.
A distance of 2mm should be pretty close, refit parts and trial.

Ron.

satancom · Post by **satancom** » Thu Dec 18, 2008 7:45 pm

I have wound them down a bit and it still runs nicely, also wound the idle so it should help. If not I will pop along when its on the gas analyser and wind it right down to a pass...

RoverP6B · Post by **RoverP6B** » Thu Dec 18, 2008 9:30 pm

"wind it right down to pass".....I assume that you meant to say...wind it up.

Turning the screws on HIF6 carburettors clockwise richens the mixture by lowering the jet.

Winding the screws out..anticlockwise will lean off the mixture.

If you wind out each in turn until the idle speed starts to drop, then wind in one half turn, repeating with the other, then that will be quite acceptable.

Ron.

satancom · Post by **satancom** » Fri Dec 19, 2008 3:53 pm

Got a Pass