Carb needle for HIF38 on a 1098?

linearaudio · Post by **linearaudio** » Thu Oct 15, 2009 6:12 pm

A bit cheeky as this is a question about the boys' Austin 1100 (or Morris if it makes it any more acceptable!)
This suffers the same strangled exhaust system type as the Minor, so I have cobbled a Metro "cast lcb" manifold and HIF38 onto a free flowing system for him. Question is- what is the "recommended" needle for this set-up? I haven't (yet) gone as far as the 940 head, maybe he'll get that for Christmas!

Post by **bmcecosse** » Thu Oct 15, 2009 6:15 pm

AAA !

linearaudio · Post by **linearaudio** » Thu Oct 15, 2009 7:36 pm

So you recommend the good ole AAA for standard head as well as 940 use? I'll go with that, just surprised you don't need a different profile!

Post by **mike.perry** » Thu Oct 15, 2009 8:51 pm

If you are not happy with an AAA needle, get yourself a copy of the SU Reference Catalogue and SU Needle Charts and study that.

Post by **bmcecosse** » Thu Oct 15, 2009 9:25 pm

AAA is just a standard 'starter' needle for the carb - it doesn't know what head is upstream - it just meters fuel according to air flow. With a standard head - the carb may never get to full air flow (ie piston lifted right up) - but it still needs ~ the same fuel/air mixture at the lower flows to run the engine.

linearaudio · Post by **linearaudio** » Thu Oct 15, 2009 9:54 pm

Thanks for the clarification, it certainly runs like a bag of bones on the 998 needle! Three screws to swap the piston assembly for my Moggy one should give a quick check!

PS I also had huge problems trying to start the engine with the HIF carb, wouldn't even fire, then I spotted the servo takeoff tapping in the top of the manifold- Dohh!

Post by **bmcecosse** » Thu Oct 15, 2009 9:55 pm

Good for economy!

Post by **Stig** » Fri Oct 16, 2009 8:48 am

Thanks for the clarification, it certainly runs like a bag of bones on the 998 needle!

Hmm. My 1098 runs pretty well on an untouched 1.0L Metro carb. I'd have to check the Metro manual to see what the standard needle was, maybe it's pretty close to AAA. What model Metro was your carb from?

You could try http://www.mintylamb.co.uk/suneedle/ to compare needles.

Post by **bmcecosse** » Fri Oct 16, 2009 9:07 am

Any idea what needle that is 28 ?

linearaudio · Post by **linearaudio** » Fri Oct 16, 2009 9:43 pm

Stig, mintylamb is excellent, been on it several times in the past! My "new" 998 carb has an ADS, coupled to the part throttle economy bypass. The previous HIF which I got for my Moggy had an ADP, without the bypass function. Comparing them, the ADS is a tad richer all through the range than the ADP, both are way leaner than the AAA, very visibly so! My Moggy wouldn't run on the ADP without filing lumps off it, so maybe you have a richer 998 needle? Don't know the Metro model, that end of the car was too far into the nettles!!

Post by **mike.perry** » Fri Oct 16, 2009 10:46 pm

That looks like a very useful website

Post by **pskipper** » Sat Oct 17, 2009 8:12 am

linearaudio wrote:I also had huge problems trying to start the engine with the HIF carb, wouldn't even fire, then I spotted the servo takeoff tapping in the top of the manifold- Dohh!

Any chance to learn... Why would this cause problems? I'm pretty sure that there is a similar arrangement on Lynda's police car's 1275 midget engine attached to the crank case to reduce pressure!

linearaudio · Post by **linearaudio** » Sat Oct 17, 2009 8:56 pm

This was an uncontrolled vent to fresh air of about 1/2" diameter on my manifold as I hadn't sealed it off! Hence a rather weak mixture, in fact at cranking speed probably sucking ALL its' air through that instead of the carb!

Post by **pskipper** » Sun Oct 18, 2009 8:20 am

Ah, we also have a problem engine in another car, everything looks okay but it just won't fire!

Post by **wiglaf** » Sun Oct 18, 2009 5:53 pm

How much difference does the needle make? I ask as my carb's now really rather worn, and sticking although it seems to center properly...

I'm thinking that a cheap mini-needled or similar carb that works properly could be better than a "correct" one that doesn't, as a stop-gap while I sort the current one. Thoughts?

Post by **bmcecosse** » Sun Oct 18, 2009 7:36 pm

The dashpot needs to be able to slide up and down easily - not a lot else to go wrong! If it's 'sticking' - take it off (3 screws) and clean eveyrthing very carefully. If still sticking - a very little brasso can be used to polish up the inside of the 'bell' and the piston that runs in it.

Post by **mike.perry** » Sun Oct 18, 2009 8:38 pm

The engine should run well enough on whatever needle is in the carb. You just need to get the correct needle for the best economy / performance for your engine.

Post by **wiglaf** » Sun Oct 18, 2009 8:46 pm

Thanks for the advice - so you'd confirm as reasonable a broad plan of:

* cheapo mini carb for a "spare", fitted in the meantime - imperfect economy/power, but smoother running at least
* strip and clean up the current one at leisure, and see if that sorts it
* if, as garage-given advice suggested, some internal parts need replacing due to excessive wear, do so - again, at leisure

Now the summer reenactment season's over, I've the time to move back towards doing-it-myself rather than relying on professionals - except where Rule #1 kicks in. (Rule #1 - know your limits, and get help before you break it; not after!)

Post by **bmcecosse** » Sun Oct 18, 2009 8:52 pm

This is the same garage that 'recommended' an unleaded cylinder head ..........? Mini carb should fit ok - if the float bowl is at the correct angle. What can 'wear' in the early SUs - is the hole where the throttle spindle sticks through each side. This only affects idling and has no ill effect whatsoever on running (since the possible in-flow of air is tiny!) - so as long as you adjust the idle satisfactorily - it doesn't matter a hoot! Since most engines spend less than 1% of their running time 'idling' - it's hardly worth worrying about it.

Post by **wiglaf** » Sun Oct 18, 2009 9:47 pm

I don't think it helps that jet is loose and the screw that secures it won't stay secured - I'm not sure whether it's that one of the threads has somehow gone (and if so, if I need to replace jet screw, bearing, or what??), or I need to renew one or more of the *stack* of washers there are.

There's also some scoring on the edge of the piston, suggesting something isn't as straight as it should be?

I'm having to keep her running rich and on quite a fast tickover for the engine to keep going - though so long as I do so, it's fine - except when the piston decides to stay open or shut.