5 replies to this topic

[rab-butler]

Hi all, before anyone asks, YES I HAVE READ all the other forums but i am looking for THE DEFINITIVE ANSWER!!

I have a HIF44 carb which has overfueled and after adjusting the screw anticlockwidse to make it abit lean, she blew the head gasket on the M5 this afternoon. Now my questions are:

Q1: if there's a standard setting for the fuel mixure screw, not the idle screw? as in fully close then say complete 2 full turns??

Q2: I read that a breather hole on the HIF44 Card is meant to be blocked, which one is this?

Q3: I have the following, MG Metro block, head, cam, HIFF44 Carb with K+N cone filter, standard rockers, lcb manifold and minisport inlet one, I downloaded the winsu piece of kit., and the needle shoulg be B?D. any ideas peeps?

also if anyone has anything to contribute to helping will be greatly appreciated

Regards

Rich .

[Pigeonto]

ssshhh no need to shout !!How do you mean it overfuelled,flooded?? Sadly there isnt a definitive answer once you get away from standard equipment. Its nice if you can have the adjustment at 1/2 way point so as theres plenty to go in each direction but its rare. Your engine may sit at a different angle due to the top steady,anything can cause a variation. People like to start with the top of the jet level with the bridge.Something is wrong if you need the jet all the way one way. I would start with setting the float level correctly,checking the 4 hole mounting flange of the carb for flatness-sanding flat if not-,all the obvious potential air leak areas- vacc advance pipe,engine breather connections.Dont know which breather hole you refer to,the normal one to block is the one which links to the timing cover breather or drop gears case breather or both with a Y piece if yours has been changed to the little filters on those breathers to take the place of the pipework.
The mixture screw doesnt really have much effect other than at idle so after that its all about the needle,oil in dashpot and spring.Your engine is just MG spec and they used a BDL which is most definately the one to get. I'd be very surprised if it wasnt ok,it fuelled my 1380 without any re-profiling of the needle shape.

[Ethel]

The mixture screw has equal effect at all times, but you do need to alter the needle if you want to increase or decrease the mixture at a specific engine load.

A good starting point with all SU's is to put the top of jet level with the top of the bearing (brass tube), viewed from above with the dashpot & piston removed.

Hif's have a separate choke jet, it's worth investigating it isn't leaking if you're having difficulty getting the mixture leaned down. It's the little hole on the engine side of the jet "bridge". Block the main jet with a finger and blow down the float breather, to see that it doesn't flow petrol with the choke closed.

You shouldn't have to block off any vents, some people disable the part throttle weakening device (presumably because they like wasting fuel), but not all SU's have it.

[jaydee]

Hi all, before anyone asks, YES I HAVE READ all the other forums but i am looking for THE DEFINITIVE ANSWER!!

I have a HIF44 carb which has overfueled and after adjusting the screw anticlockwidse to make it abit lean, she blew the head gasket on the M5 this afternoon. Now my questions are:

Q1: if there's a standard setting for the fuel mixure screw, not the idle screw? as in fully close then say complete 2 full turns??

Q2: I read that a breather hole on the HIF44 Card is meant to be blocked, which one is this?

Q3: I have the following, MG Metro block, head, cam, HIFF44 Carb with K+N cone filter, standard rockers, lcb manifold and minisport inlet one, I downloaded the winsu piece of kit., and the needle shoulg be B?D. any ideas peeps?

also if anyone has anything to contribute to helping will be greatly appreciated

Regards

Rich .

That needle is supposed to be BCD.

Though MG metro engines were fitted with BDL needle IIRC.

[rab-butler]

The needle is BDL so least thats correct, looking at the float chamber, etc etc, it looks all ok, another theory for what happened was maybe the thermostat failed?? but got an uprated head gasket and new 88deg thermostat on order. My main issue was that mixture screw, if there was a standard way of setting it? I may try that halfway in/out like Pigeonto said (sorry for shout )

On the lookout for a BCD needle aswel ;)

[jaydee]

The mixture screw has to be set with a gas tester, with engine warm, set it until the tester reads about 2,5 CO.
The overfueling can be caused by the jet holder, as DILLIGAF already pointed out, cant see how a faulty thermostat can cause overfuelling..

Edited by jaydee, 29 March 2012 - 10:39 AM.