HIF 38 Tuning

[moggiegeek]

Installed 12G9400 head with Maniflow inlet and exhaust. HIF 38 carb with K+N pancake air filter on 1098 with standard cam. Nothing else changed since it was running with standard set up. However it won't run below 2000rpm without masses of choke and without choke it simply dies. It sounds very rough - sometimes spitting back through the carb.
I've run two needles I have in it with very little difference - currently ADS in it and have tried ABD.
In the course of this, being unused to HIF carbs, I learned that the tiny loading spring goes above the needle into the carb piston and then the housing is pushed in and retained by grub screw.
However this discovery didn't sort the running.
Can you recommend what to try now?

[MarkyB]

Sounds like an air leak somewhere, how have you plumbed in all the pipes?

[moggiegeek]

Thanks - nothing obvious but, servo take off could be a candidate so I'll block that and see what happens. It normally has servo attached but servo relocated so maybe a fault has arisen.
The other brass vents on carb are connected to:
1) Fuel in - this works
2) What I think is fuel vent/overflow - open ended pipe away from hot bits
3) Vacuum take off - on top of carb next to manifold - smaller pipe typical of vacuum take offs
4) Two other inlets of uncertain purpose - slow running? blanked off.

Carb gaskets put together dry.
I'll try above and keep you posted.

[smithskids]

Have you connected up to the breather system?

[moggiegeek]

Hi - yes its connected to the rocker breather pipe.
A question about the servo having been moved - If the air valve is not horizontal might this lead to the air leak by sucking in air?

[moggiegeek]

HELP>
Have now checked for air leaks, around carb, manifold to head etc, Servo disconnected and blocked off. Rocker cover vent pipe securely plumbed in to carb.
Fuel feed line correct. Overflow/vent correctly open (blocking this resulted in fuel starvation by creating a vacuum) Other vents are blocked.
oil in dashpot
K+N air filter - not oiled
Changing timing has no real effect whatsoever.

Difference between needles above is negligible ( ADS, ABD). Requires some choke to run at all - can run at about 1500/2000 but no lower without stalling. Removing choke results in engine stalling at once Lumpy pick up on using throttle with choke but sounds very much better above 3000.
I'm wondering if this is a question of needle and what might you recommend??

[brucek]

I'm running a BBW needle on a HIF 44 and 1275 with full maniflow exhaust (LCB plus middle and rear silencer) and this works really well. Not sure if it will work with the 1098/12G940/HIF 38 though but it may give you a starting point. Good luck

[smithskids]

I presume you have played with the mixture screw underneath the fuel inlet.

[MarkyB]

How about the float level?
If the needle is too low it would give similar symptoms I think.

[silloyd]

moggiegeek, there's a really good article here on how to do basic set up of a HIF carb.

If, by following that guide, you can get it running albeit not perfectly then you could always try using MintyLamb or WinSU to help you select the optimum needle. The first (free) compares needles, the latter (One off €15 fee for the full version, at the time of writing) having far more variables gives recommendations based on your set up.

Looking on MinyLamb,The ADS and ABD needles you refer to seem to be very similar in profile, which probably explains why you see little difference between them. Both are much richer at the top end than my 'AAU'. [frame][/frame]

BTW HIF44 carbs use different needles from HIF 38 (0.100" for the former, 0.090" for the latter) and the letter codes are different.

I have WinSU and as well as recommending a needle for my set up (1098, standard cam, generic cone air filter, 12G940, 1.5" exhaust, 1.5" alloy inlet, HIF38) it recommended a 'Yellow (Strong)' spring. The standard spring is a weaker 'Red' version (I think). This uprated spring stopped my set up from spitting on overrun.

[moggiegeek]

Thanks to all for such a rich supply of resources. I'm still really struggling.
Looking at the graphs of richness/leaness at various needle stations it seems they are pretty similar for the first 5/6 increments. This is where my set up really struggles. Looking at it now I wonder whether:
a) there is an adjustment I haven't seen on the carb for richness/leaness - I will check again
b) whether there is spring in dashpot at all ( silly I know but I got to doubt it!)
c) whether the jet size is smaller and needles suit the bigger size - hence extreme leaness at lowe end. How ould I recognise the difference anyway?

Continued help required.
Thanks

[silloyd]

The diagram here shows where the idle screw is and what the various connectors are (the rest of that thread is also worth a read).

Needles should be stamped with their code - AFAIK 'A[XX]' needles are for the HIF38 and 'B[XX]' are for the HIF44.

[win]

Hi
I bought a HIF 38 carb,from a forum member, reported removed from a running car.
After much head banging, the damper spring was missing, worth a look.
Regards Win

[daveyl]

Worth checking that the jet moves up or down, (and isn't seized) when adjusting the mixture.

You can confirm this by removing the dash-pot/piston, and as you turn the mixture screw, you'll notice the the jet tube should rise or fall according to which way the screw is turned.

As for jet and needle sizes. The hif44 has a slightly bigger hole in the jet tube and so will accept the needles that have a prefix letter 'B', e.g. 'BDL' The hif38 has the prefix 'A', e.g. 'AAA'.

[smithskids]

check that the rocker cover/oil filler cap has a small vent hole in it(about 1 mm) some of the bmc engines didn't have a hole in them.

[bmcecosse]

Obviously there is an air leak - I suspect the manifold is not fully seating on the head - check carefully. Is it definitely clear of the exhaust manifold?? And are the manifold flanges equal thickness? You need an AAA needle - but this is not the problem at the moment - because all needles are virtually the same in the 'idle' range. As others have also suggested - the piston must rise easily and fall back with a clunk. Use the lightest spring possible in the carb....madness to use a heavy spring if you want snappy throttle response! But don't worry about that now = provided there is a spring in there........

[moggiegeek]

Hi - checked out all your suggestions:
1) Re air leaks - Yes - discovered air leaks to servo and rectified
2) Re spring in dash pot - its a sealed unit but falls with a clunk when slightly raised.
3) Mixture screw siezed at first giving only one rotation now cleaned and fully adjustable - Jet rises and falls in response to screwing in/out of mixture screw
4) some muddle over numerous brass inlets - hopefully resolved using final version of HIF38 diagram on MMOC
5) Float level OK, chamber clean, fuel inlet needle valve OK.
6) Ignition timing fine etc.
7) Have AAA needle available
all gaskets sealed

So - hoping all will be well at weekend when re-fitting

Two Questions:
1) Does screwing mixture screw in weaken or richen?
2)Using a turbo exhaust manifold gasekt ( cos it was hanging around) - any prob with this? Air leak wise

[silloyd]

In answer to the first question, see this article, which has the following under diagram 12: "On HIF carbs the jet height adjustment is made by turning this screw. Screwing it in lowers the jet (richens mixture), screwing it out raises the jet (leans the mixture off). To get the jet at the correct starting height, wind the screw in until the jet is flush with the bridge, then wind the screw in two turns. This again sets the jet at around 0.060-inch (1.5mm) down from the bridge."

The bit in blue helps you get a reasonable start point for the idle mixture.

[moggiegeek]

Hi - just been trying to get it to run at a reasonable idle.
Current position is:
1) It has AAA needle in it
2) Will idle at 2000 - no choke
3) If I lift the piston it stumbles
4) If I restrict the airflow somewhat it picks up.
5) It overheats.

However if I run it at higher revs on accelerator it picks up fine and sounds good at medium and higher revs.
I have some other needles available = AAU, ABT and ABD, but probably at low revs it doesn't make any difference.
Should I return to it on another day and start from screwing in the the jet and then out 2 turns as recommended to get a starting point?????

[bmcecosse]

It needs to idle at 500 revs....no point fiddling with it at 2000 revs! There MUST be air getting in....are you SURE the throttle plate is closing right down ?