HIF 38 Tuning

[Declan_Burns]

Are you sure you have it plumbed correctly?
Cross check with the photos below.
Regards
Declan[frame][/frame]
Vacuum advance[frame][/frame]

[MarkyB]

Does it have a metal heat shield?
It needs to be bent back quite a bit or it fouls the exhaust and stops the carb seating on the bottom studs properly.
Offer it up without the carb to check.

Also there need to be gaskets between all the bits that go on the studs.

[moggiegeek]

Plumbed in as per photo.
Gaskets present - assembled dry - do they need sealant?
Will check throttle butterfly
Too wet today - try tomorrow -

Any ideas on checking for an air leaks - with high pressure you can use soap suds but for lower......?

Will persist

[tysonn]

As a matter of interest what would be the result if A and B were not joined or sealed?

[bmcecosse]

Air entry and high idle speed........

[moggiegeek]

I THINK I'VE FOUND THE ANSWER.
When checking if the heat shield was fouling the carb sitting on its studs properly i noticed that the entire inlet manifold rocked up and down giving about one eighth of movement at the air filter end. on close inspection I can see that the inlet and exhaust manifold flanges must differ microscopically in their thickness, maybe a couple of thou, despite being the same manufacturer with excellent reputation.I can see the inlet manifold move slightly whilst the exhaust is fully sealed
Could this be the cause?
Secondly what to do? I thought of using exhaust/gun gum type paste on inlet manifold gasket?
What do you think?

[MarkyB]

Well done for tracking it down.

using exhaust/gun gum type paste on inlet manifold gasket

Bad plan, better to file a little of the exhaust manifold where the nuts and washers bear on it.
Do you have the large washers that where originally used?

[moggiegeek]

Hi - reckon this could be the culprit?
Yes i do have the original large washers - I think a spot of filing is indicated in the morning on the exhaust flanges. Do you think the turbo manifold gasket is contributing due to the hard lining to the port aperture they have?
Will let you all know outcome of saga............

[bmcecosse]

I told you way back on 22 May to check the manifold!!!! That IS the problem -either file the thicker manifold - or file the washers on one half to create a stepped washer - it's then a bl**dy nuisance to line them up correctly of course.......but may be easier than removing the exhaust manifold....

[Roni]

If you file the washers, lining them up is helped with a mark on the top of the washer.

[bmcecosse]

Good tip!

[tysonn]

As a matter of interest when I asked the question last week what the result would be if A and B werent joined together or sealed it was because I was in the process of having a tidy up in the engine bay and my A and B were just sealed(by me yonks ago).I had a handy piece of rubber pipe and decided to join them together.Didnt attempt to test it out as I was doing other things.Decided to pull it out of the garage today as I'm making new door cards.Wouldnt start!Not a cough or a splutter.Removed the pipe and it started immediately.While it was running I put the pipe back on.Engine died.Needless to say I've blanked them off again.

[bmcecosse]

When joined they are an 'economy' device when cruising on low throttle. Maybe your carb is set so finely... although with 'choke' in use for a cold start I can't imagine it will be that sensitive.

[Roni]

The economy device is very dependent on the engine it is attached to. The HIF 38 you have may have originally been attached to a 1 litre Metro.
When I installed the same carb on my 1098 I had to alter this circuit to get proper running. To do this I had a temporary air/fuel meter connected to the exhaust. First, with the circuit blocked off, the correct needle was established. When the car was running correctly, I reconnected the economy circuit and there was an immediate lean misfire. Under light throttle conditions the economy device was leaning the mixture too much. I experimented with different size restrictors in the tube until the correct size was found to enable correct and reliable running. I did this by increasingly drilling out a small hole in a temporary fitting and then making a permanent one. From memory the hole was 0.55mm or 0.6mm but that was right for my engine conditions. (Drill bits for model railroading have other uses too.)

[tysonn]

Interesting.So maybe my carb has a similar history.I haven't got your patience to experiment unfortunately!May just look out for a replacement that doesn't have the economy device.Any recommendations?

[bmcecosse]

Just block the holes... or block the joining tube . That's all there is to it!

[Roni]

If I was going to do it again I would probably just block the tubes and moderate the pressure of my foot on the accelerator pedal. That is probably the best source of better fuel economy.

[bmcecosse]

It was probably a 'wheez' at the time to get good 'Official 56 mph 'fuel economy figures.

[moggiegeek]

Well, after a false dawn of seeing an air leak at the manifold and correcting it as well as screwing in the mixture screw fully and out 2 turns I was disappointed to find things much as before ie running V lean, hot and fast 1500 -2000rpm Until ( underlined) I pressed the throttle butterfly hard to close and revs dropped to a sensible 500/600 - that few thou made a big difference. So......what might this be due to?
I can easily check if throttle cable too tight and put stronger additional spring acting to close butterfly more but do butterfly discs get that worn?
saga continues.......

[bmcecosse]

You were advised 10 days ago to make sure the throttle was fully closed........ There MUST be a little slack in the cable. It shouldn't need a heavy spring - which just makes for a horrible 'drive'.....