20 replies to this topic

[__Alex__]

Dear Mini Lovers,

 

I am contacting you because I am unhappy with my current engine setup. 

 

I had a stage 1 kit fitted on my 1000cc HS4 1988 Mini by a professional (K&N filter in the factory airbox, stage 1 intake manifold, AAU needle, LCB Freeflow exhaust manifold, Maniflow exhaust line with double silencer). Out of the shop, I suspected the engine was running rich. However, as it ran good and pulled strong through the rev range, I left in at that. I didn’t notice any increase in fuel consumption. 

 

I ended up failing MOT with a CO level of around 15% at idle so I decided to tacle the problem. I checked the timing, which was around 20° of advance, so I set it to the specified 8°. This drop the mixture to around 5% CO at idle and the engine still ran good. 

 

I then dropped the mixture to the specified 2.5% CO at idle and the engine doesn’t pull as strong as before. In particular, there is a weak point between 2500 and 3500 rpm. When the engine is cold, it completely chokes in this rpm range and produces absolutely no power (I have to pull the starter cable, though it runs fine without up to 2500rpm). Except for lack of power, the engine runs at starts good. 

 

So here are my questions:

 

- Can I / should I run richer? Any recommended value?

- Is it possible that the engine is lean at higher rpm though it is good idle due to carburettor fault?

- Is 8° of advance still right with a stage 1 kit (I’m still running the standard camshaft)?

 

Chears,

Alex.

 

by the way: The distributor was recently rebuilt, HT leads are new, stark plugs are recent, valve clearance was just checked. 

 

[cal844]

Set timing to 10°BTDC(Vac advance blocked) at 1000 rpm

Take a 7/16th spannerr so you can adjust as neccessar whilst on the road

Edited by cal844, 04 August 2015 - 03:27 PM.

[carbon]

Alex,

 

Sounds like you're running slightly weak between idle and mid-range.One option would be to take it to rolling road and get the needle changed or reprofiled.

 

In meantime here are a couple of things to check which may help:

- if you're running thin oil in dashpot go up to 20W50 grade

- check the dashpot spring against a good red spring, if in doubt replace with new red spring

 

Are there any other modifications to the carb?

[mini stephen]

Hi my 92 city e 1000 with brand new stage one kit was running the same when first fitted cal responded to my post and I followed his advice with just under 3% CO the car drove a dream on private lane I have weakened it slightly for test and its the same as urse I will just limp to test centre then richen mixture after test thanks again cal

[Mini Manannán]

I've only been mucking about in earnest with SUs for that last 2 years but this is how I see it now.  

 

This is not directed at you personally: People think it's a matter of pop a new 'recommended' needle in and all will be fine and dandy.  The SU is more 'organic' than that, you twiddle with one thing, it affects another which affects another etc.  You have to chase round in ever decreasing circles to get to optimum.  We don't have a RR here on this island so I'm having to 'make do' with a wide-band AFR meter which will get there in the end just slower than an RR session would.

 

 Did the 'professional' consider the advance curve when he upgraded you?  Did he service the carb, check the dashpot spring, check the jet needle for wear?  Even if all is new and shiny the needle will, very probably (some will say definitely) need customising to suit YOUR engine set-up so a rolling road session with someone who is 'old school' is the best way forward.

 

 

I imagine there will be some 'old school' tuner/mechanics near to Paris, have a chat and see what they say.

[cal844]

Hi my 92 city e 1000 with brand new stage one kit was running the same when first fitted cal responded to my post and I followed his advice with just under 3% CO the car drove a dream on private lane I have weakened it slightly for test and its the same as urse I will just limp to test centre then richen mixture after test thanks again cal

No problem! 

 

 

To the OP

 

3% CO and 10° btdc timing should be close, i run 20w50 oil in my carb dashpot, on both our road going minis, they run spot on!

 

With the SU carbs, i adjust the carb so the engine holds back at 80 mph(runs lean at 80 mph) i then richen one flat of the nut until it stops leaning off(car will go flat out) it should now be about right.

 

 

 

On a side note:: have you ruled out the coil(we had one fail, the car was flat and struggled at the revs your issues are at)

 

 Hope im of some help!

Edited by cal844, 04 August 2015 - 08:46 PM.

[Mini Manannán]

 

Hi my 92 city e 1000 with brand new stage one kit was running the same when first fitted cal responded to my post and I followed his advice with just under 3% CO the car drove a dream on private lane I have weakened it slightly for test and its the same as urse I will just limp to test centre then richen mixture after test thanks again cal

No problem! 

 

 

To the OP

 

3% CO and 10° btdc timing should be close, i run 20w50 oil in my carb dashpot, on both our road going minis, they run spot on!

 

 Hope im of some help!

 

 

Whereas I put 20/50W in mine; it wasn't right.  60% 20/50W and 40% 12W fork oil made it much better but not perfect, more experimentation needed...

[cal844]

 

 

Hi my 92 city e 1000 with brand new stage one kit was running the same when first fitted cal responded to my post and I followed his advice with just under 3% CO the car drove a dream on private lane I have weakened it slightly for test and its the same as urse I will just limp to test centre then richen mixture after test thanks again cal

No problem! 

 

 

To the OP

 

3% CO and 10° btdc timing should be close, i run 20w50 oil in my carb dashpot, on both our road going minis, they run spot on!

 

 Hope im of some help!

 

 

Whereas I put 20/50W in mine; it wasn't right.  60% 20/50W and 40% 12W fork oil made it much better but not perfect, more experimentation needed...

 

Its trial and error, all setups are different id now Try some 15w40, ask a local garage for a very small amout(you only need 50 ml)

[Dusky]

I use ATF, I think dashpot oils can be easily related to teh camshaft. With 20W50 my 998 with a 544 cam just wouldn't do anything below 2.5K but stutter. Changed to atf and I had atleast a clean ' pull' untill it came on cam.

Cheers

[cal844]

I use ATF, I think dashpot oils can be easily related to teh camshaft. With 20W50 my 998 with a 544 cam just wouldn't do anything below 2.5K but stutter. Changed to atf and I had atleast a clean ' pull' untill it came on cam.
Cheers

As i say, engine spec, carb spring weight etc etc make a difference

[KernowCooper]

What does the engine do if you lift the lifting pin (if you have one, or small screw driver to lift the slide) ? engine dies = to weak, your year car can go to 3.5% CO for the MOT

[__Alex__]

Thank you all for your answers, they're very helpfull!

I will try with a bit more advance and a bit richer at idle. 

 

Cal, I take from your response that you recommend setting the timing on the road rather than to a specified value? 

 

Carbon, I'm surprised by your answer: the car runs fine until mid range and then powers off a little. I would have guessed the mixture is right until mid range and then lean, not the opposite. Am I missing something?

Concerning questions that were brought up:

- the carb is stock apart from the AAU needle. It was not serviced. I considered rebuilding it, be it seems quite tricky...

- as for dashpot oil, I'm running a mix of 20w50 and what ever was in it when I got the car 2 years ago. The car doesn't pull in 4th gear when starting from a stabilised mid range rev (when it used to when it was richer), so I don't suspect the dashpot damping to be the problem. 
- the advance curve is stock

- I don't think there are are moving parts (pins or screws) on the carb except for the idle adjustment and starter assembly.

 

[ACDodd]

This engine very likely needs a custom carb needle to fuel the engine properly. I would suggest a few tenths of a thou off the needle diameter between stations 3 and 5 would sort the problem. This work must b e carried out in conjunction with a gas analyser to ensure that it does not cause the fuelling to go too rich. The best place to get this work done is on a rolling road.

AC

Edited by ACDodd, 06 August 2015 - 10:31 AM.

[cal844]

Well said Mr Dodd, I agree, but before tuning the carb, I'd always suggest cheapest and check everything else first

[ACDodd]

Maybe I need to run a needle mods class. This one would not be free though!

AC