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SU Throttle response
https://www.ausmini.com/forums/viewtopic.php?f=2&t=81734		 Page 1 of 2
Author:  Ace Radster [ Sun Jun 09, 2013 4:25 pm ]
Post subject:  SU Throttle response
Hi Everybody, finally emerged through the spammers to have an account activated, just in time as my mini is finally back on the streets.

Problem is no throttle response off idle, I've tried different oils in the dashpots, currently has penrite dashpot oil, the only thing I haven't tried is engine oil, but there hasn't been too much difference with any of them.
Have timed it according to the 30* max mechanical advance theory and set mixture using a compromise between colortune and lift pin methods (was a few flats different)
On that though, to get a good mixture, it was closer to 3 full turns from the bridge if that is a clue for anyone.
Details are 1275 + 30, twin hs2, m needles, cam unknown

Will get it over to Matt at Murrarie soon, but just want to try to fix it myself.

Thanks,
Dean
Author:  brett [ Sun Jun 09, 2013 4:39 pm ]
Post subject: 
Try different spark plug leads... That what mine was
Author:  michaelb [ Sun Jun 09, 2013 6:47 pm ]
Post subject: 
What timing advance do you have at idle?
I only have about 1 - 2 deg in my Cooper S
What plugs are you running?
Have you tried to richer up the mixture a little?
Author:  drmini in aust [ Sun Jun 09, 2013 7:09 pm ]
Post subject: 
What carby springs are in it? You want red, not blue.
Author:  Ace Radster [ Sun Jun 09, 2013 7:21 pm ]
Post subject: 
Running about 5 degrees at idle. Plugs are BP5EY and springs are red.
Thanks for the tip on the leads, I hadn't considered that yet.
Author:  drmini in aust [ Sun Jun 09, 2013 7:27 pm ]
Post subject: 
Ace Radster wrote:
Running about 5 degrees at idle. Plugs are BP5EY and springs are red.
Thanks for the tip on the leads, I hadn't considered that yet.

Put a meter on them and check the resistance. If more then 3K ohm I'd bin them.
[I just measured the old ones on a Fiat 500 (1967) I'm fixing for my bro', they came in @ 20K and over 30K. Into the bin...] :lol:

I like Bosch inductive core leads, they don't go hi resistance with age like the common `carbonized string' ones do.
Available off the Bosch rack at Supercrap, Repco etc.
Author:  phillb [ Sun Jun 09, 2013 11:04 pm ]
Post subject: 
I've just fitted twin 1.25 to my car with similar spec. I tried m needles first but they were too lean. I found the same, seemed like I had to screw the mixture way rich to get decent idle.

Although M were standard back in the day I was told the fuels have changed.

Try AH2 needles, they were a big improvement.

Double check while the engine is off that the pistons lift without catching and fall back onto the bridge with a nice metallic 'clunk'
Author:  Ace Radster [ Mon Jun 10, 2013 8:34 am ]
Post subject: 
Thanks for the advise. Leads and plugs check out. Piston drop nicely, but will try the needle suggestion for sure. Will post how I go
Author:  sitnlo62 [ Mon Jun 10, 2013 10:16 am ]
Post subject: 
I would stick with the M needles.
They are not the problem IMO

Having said that I have a pair of good AH2 needles here you are welcome to try if you have your heart set on it..
I am on the southside of Brisbane if you would like to pick them up just PM me and we can arrange it.

Problem could be many things but not knowing the History of the Motor it is hard to say.

Dave
Author:  69k1100 [ Mon Jun 10, 2013 4:59 pm ]
Post subject: 
Might be worth while to borrow a known set or single hs4 for comparison.

Also is it a lack of response or does it feel flat through the rev range?

As for the piston drop there is a method to more accurately gauge the bore of the dashpot and whether it matches the piston well.

http://www.jcna.com/library/tech/tech0006.html

Found here, about 1/3 of the way down the page.

Also throttle shafts wear (Achilles heel of the su) causing a leak after the suction chamber, reducing the piston lift.
Author:  TheMiniMan [ Mon Jun 10, 2013 5:26 pm ]
Post subject: 
has it got a lumpy cam? you say cam is unkown but is it a lumpy fker?

have you made sure of your rocker clearances?

etc?

:-)
Author:  simon k [ Mon Jun 10, 2013 7:02 pm ]
Post subject: 
phillb wrote:
Try AH2 needles, they were a big improvement.


that's what I was gonna say, but it still should drive fine with M needles, just maybe not as dynamic :?
Author:  Ace Radster [ Mon Jun 10, 2013 7:19 pm ]
Post subject: 
I did the piston drop test a heap of times and they both came in pretty close and also did valve clearances recently. Cam doesn't seem too lumpy. it idles pretty smooth at around 900 and drives well, the only issue is if you give it a quick bootfull it doesn't react, kind of feels as though you need to build the revs off idle and then your good to go and the response is there.
I might take Dave up on the offer of trying the Ah2 needles.
Replaced points with Pertronix ignitor from another dissy last night and seems to have changed some of the characteristics.
Just to complicate matters :)
Author:  TheMiniMan [ Mon Jun 10, 2013 7:52 pm ]
Post subject: 
its starting to sound more like a cam-timing issue now,,, but don`t take my word for it cause i`m not there to check anything myself,,, sorry it`s just a guess now... it`s easy to double check tho
Author:  Aussie Brian [ Mon Jun 10, 2013 8:00 pm ]
Post subject: 
I think that michael B was closer to the mark with raising the question re the timing. :idea:
It could be something to do with the amount of advance you have, or are assuming you are getting.....Just a thought.
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