27 replies to this topic

[bajean]

So recently my mini started experiencing a high rpm miss at around 5000 - 5500. This happened after changing the inlet manifold from the cast aluminum one to the maniflow steel inlet, this is on a set of twin HS4. The spec of thr engine is as follows

1293 / 11:0:1 CR / Med - piper xt cam with 1.5 ratio rockers / MED rally spec head 36/30 / Aldon yellow dizzy with msd 6AL 2 box and Blaster 2 coil and NGK BP7ES plugs / Twin SU HS4 carbs on manifflow steel inlet / STG 2 LCB into a 2 inch exhaust. Thats a quick summary of the engine. Im thinking its fuel related but what do you guys think.

[PoolGuy]

I’d check for air leaks before anything else.

[bajean]

Just fitted all new gaskets and checked everything multiple times as it had blown the inlet gasket. I sprayed brake cleaner to check if the engine note changes and nothing. So i dont think thats at fault. Thanks for the suggestion

[imack]

Had to change the needles in my twin hs4's when swapping between a modified leyland manifold a large bore maniflow twin hs4 manifold, no other mods had been carried out.
Was a good few years ago now, can't remember what needles I changed from and to.
Have a completely different engine spec now so needles have changed again.

[bajean]

I see. It flows much better then the standard manifold so could be it needs a different set of needles. I believe it has a set of aam in it at the moment. If you happen to remember or find the needles you had installed please message me.

[imack]

Currently going through rolling Road sessions with my car trying to get the fueling right. AAM are far too rich for mine in the mid range causing misfiring.
1380, 11.5:1 cr, MED 37/31 offset clubman head, MED fia15 historic race cam, 1.5 LDX rockers, maniflow large bore long 3 into 1 manifold, maniflow race RCM, Maniflow large bore twin hs4 steel intake, MED stubstacks & ITG filter, Aldon red dizzy.
Currently struggling to find needles to get it rich enough below 3500 but don't get excessively rich in the 3500 -6500 range. 6500 - 8500 isn't a problem.

Edited by imack, 28 May 2023 - 12:41 PM.

[bajean]

If you dont mind me asking, what needles have your tried so far and with which did it perform the best.

[imack]

Peter Baldwin set it up a few years ago although the engine spec was slightly different, he fitted AAU needles, but it drove like it was lean at lower rpm.
Initially used same needles in current engine but it drove worse than previous engine at low rpm. Rolling Road proved it to be very lean below 3500 and to rich in the mid range then a touch lean between 6500 and 8500
I already had AAM and ABY needles but these were found to be too lean at low rpm and massively rich everywhere else (misfire rich)
Have tried aac with the intention of modifying them but they were way too lean everywhere.
ADF are richer at bottom end leaner at mid and top end than AAU but still not suitable for modification. They do drive a bit better below 3000 rpm though.
Have now converted the carbs from biased needles to fixed needles which opens up a load more needle profile options.
Rolling Road sessions are on going to try and get it right.

[ACDodd]

A decent pair of custom needles will have this right in 30mins.

Ac

[cal844]

A decent pair of custom needles will have this right in 30mins.

Ac

I agree, a good check over and optimisation will get the car singing properly again

[bajean]

A decent pair of custom needles will have this right in 30mins.

Ac

You dont happen to have a set lying around i can buy…… In the meantime i’m gonna give the AAU needles a go. I also have an AEM afr gauge ive been planning to install for the past year and still haven’t done it, so this would be the perfect time for it.

[PoolGuy]

That made me chuckle, sorry. Anyway, yes the afr gauge would be a great help.

[bajean]

That made me chuckle, sorry. Anyway, yes the afr gauge would be a great help.

Hahhaha that’s why i put the fullstops. Il get the gauge installed and start fettling with needles then.

[timmy850]

It’s impossible to make a custom needle without knowing what the engine actually needs. It could be rich or lean, or even an unrelated ignition issue that has just become a problem

If you measure the afr you’ll know

[bajean]

It’s impossible to make a custom needle without knowing what the engine actually needs. It could be rich or lean, or even an unrelated ignition issue that has just become a problem

If you measure the afr you’ll know

It was a joke. Thats the plan get the afr hooked up and go from their. I hope its not ignition related as i have just installed a MSD 6al box and blaster 2 coil ( and the aldon dizzy is brand new ). That reminded me im running some vp unleaded octane booster and it seams to coke up the plugs with this brown coating sort of.