Correct needle for HS4 carburettor?

[miniseven_man]

Hi,
I've recently got my wife's 1960 Mk1 Austin Seven Mini back on the road after being layed up for 13 years. After an earlier restoration when it was ground up restored, it was fitted with a A+ 998 low compression engine from a 1980 mini. The engine had seized whilst stored about 8 or 9 years ago due to a rusted piston in one bore. I've had the 998 engine rebored & relined & fitted +0.040 flat-top pistons. I've fitted a 12G295 Cooper head after having hardened valve seats, new valves & slight shaving to raise the compression & also fitted a MiniSport CA2 cam (same specification as ST948 997 Cooper cam). I've also added duplex timing gears, a 3 branch exhaust manifold, a sports exhaust system & a SU HS4 carburettor. This has H6 needle fitted.

Most of these old "Cooper" parts came from the original MG 1100 engine that was installed in the car when my wife bought it in 1969. It was a pretty fast little car back then. This engine was considered to be beyond repair when the car was restored in 1998 & was scrapped although I kept some of the "Cooper" parts for future use.
It now runs quite nicely with the A+ "Cooper" engine but lacks power/torque above 3000rpm (especially under load when going uphill), which I think maybe due to fueling or timing. I've tried several different needles & the H6 (as fitted to the HS4 when originally installed on the MG 1100 engine) seems to give the best results, although it runs a bit rich; the plugs quite black. As Mk1 Coopers were fitted with twin HS2 carbs, I've not been able to find any information or quidance on other more suitable needles.

Any help & suggestions would be appreciated.

Also I think I may need to replace the Lucas 59D distributor as this may also be contributing to the reduced performance, as it from the low compression A+ engine & may have the wrong advance timing curve. I've been told I can get a modified replacement 59D with electronic ignition put together, to give the MK1 997 Cooper advance timing curve. I've yet to look into this.

[carbon]

Retarded ignition timing at 3000rpm could give flat performance. Any idea how much advance you're running at this engine speed?

Getting the right advance curve with a modified engine is not a trivial exercise, unless you have one of the mappable systems.

[ianh1968]

Needle first, timing second...
(... and welcome to the forum!).

I agree totally with Carbon...

BUT

Firstly you determin the mixture that you want/need to run,
then you select a curve that will ignite this mixture to give the
optimum results.

Mr Vizard suggests H6, E3, or No7 for various states of 998cc tune.
That said, H6 and E3 also appear in his listings for single 1&1/4" carbs
on anything from 850 to 1098.

No7 and AAA were popular needles for single HS4 carbs and these are
quite a bit richer than H6 and E3. I'm having a problem believing that
the plugs would be "black" due to a rich mixture although it is of course
possible. Maybe the idle mixture is just set way too rich?

Are the plugs running too cold? This can black the plugs to the point
where there is an electrical short and they no longer function. I had this problem
when I was running an engine in once with some RA4HCX plugs that were too
cold - Putting some "sixes" in cured the problem.

NO-ONE HERE WILL BE ABLE TO CHOOSE A NEEDLE FOR YOU.
The usual advice of "use a dyno" will apply for both the needle selection
and subsequent timing calibration...

Here's a chart with some needles on it - For reference, DL is for a bog-standard
1098cc engine with an automatic box... This is richer than H6.

NeedlesFor998cc.png

See here:- http://mk1-performance-conversions.co.u ... l_carb.htm
Ian

[miniseven_man]

Retarded ignition timing at 3000rpm could give flat performance. Any idea how much advance you're running at this engine speed?

Getting the right advance curve with a modified engine is not a trivial exercise, unless you have one of the mappable systems.

Thanks for your advice, carbon. I'll check the advance at the weekend & I'll let you know what I find.

[miniseven_man]

Needle first, timing second...
(... and welcome to the forum!).

I agree totally with Carbon...

BUT

Firstly you determin the mixture that you want/need to run,
then you select a curve that will ignite this mixture to give the
optimum results.

Mr Vizard suggests H6, E3, or No7 for various states of 998cc tune.
That said, H6 and E3 also appear in his listings for single 1&1/4" carbs
on anything from 850 to 1098.

No7 and AAA were popular needles for single HS4 carbs and these are
quite a bit richer than H6 and E3. I'm having a problem believing that
the plugs would be "black" due to a rich mixture although it is of course
possible. Maybe the idle mixture is just set way too rich?

Are the plugs running too cold? This can black the plugs to the point
where there is an electrical short and they no longer function. I had this problem
when I was running an engine in once with some RA4HCX plugs that were too
cold - Putting some "sixes" in cured the problem.

NO-ONE HERE WILL BE ABLE TO CHOOSE A NEEDLE FOR YOU.
The usual advice of "use a dyno" will apply for both the needle selection
and subsequent timing calibration...

Here's a chart with some needles on it - For reference, DL is for a bog-standard
1098cc engine with an automatic box... This is richer than H6.

NeedlesFor998cc.png

See here:- http://mk1-performance-conversions.co.u ... l_carb.htm
Ian

Thanks for your welcome ianh1968, your suggestions & your needles chart.

I'll check the idle mixture at the weekend. I'll also try to download your needles spreadsheet.

I'm definately going to have to get it on a rolling road to sort this engine performance problem, but I hoped to sort out some basic faults before I do this, so as to make best use of the dyno session.

[carbon]

Would suggest a couple of additional checks on the carb before doing any tuning:
- make sure the float needle is sealing properly, this can give very rich idle and black plugs...
- check spring type fitted in dashpot, should be red type for single HS4
- if needles are not new check for any signs of wear (this only really applies to swing needles)

Most common cause of float needle not sealing is dirt/rust from petrol tank, can be quite bad if car has been laid up for length of time. I recommend fitting one of the cheap clear plastic in-line fuel filters just before the carb, keep an eye on it and change once it gets really mucky.