I have fixed the stumble in my Cooper. I put in a new intake. I would think that this would not fix the S stumble because people are still complaining about it after putting in an aftermarket intake, but it worked on my Cooper.

I wish I could have gotten in on the Twister group buy but I had already purchased the Mini Mania intake, which uses the stock air box but replaces the intake "snorkel".

I don't get the hesistation why starting off from a stoplight, and there seems to be more power at low end. This may not be real, but it certainly is a smoother acceleration. It is noticeably louder, which could be fooling me that I am getting more power.

The reason it works is apparent when you look at the stock intake:



The new intake "snorkel" eliminates the large box and tube on the left side. That box acts as kind of a buffer and, combined with the tube on the far left which goes into some further box in the wheel well, helps quieten the intake. It also robs the intake of air. Eliminating this forces air directly into the airbox, and I feel smoother power delivery from a start. It also has lessened the rough idle when the air conditioning is on. Not eliminate, but considerably lessen.

I think Cooper owners could benefit from any of the aftermarket intakes, all of which eliminate the cursed intake "muffler."

 

I wonder if the stumble is due to excessively rich mixtures? Seems like more than a few people have noted reduced stumbling with intakes or pulleys. Maybe that's why the car I test drove in SoCal didn't stumble but when my S arrived in the half-mile high city of Tucson, it bucked like a bronco. Hmm... Maybe a clothespin on the fuel line will fix it.

 

>>I wonder if the stumble is due to excessively rich mixtures? ... [snip] ...

Graham (host of the Dallas pulley party) still has the stumble, even after installing Randy's ECU upgrade (which leans out the mixture to a more reasonable A/F ratio). Perhaps he might comment here on his experience and whether any other participants in the pulley party commented on the stumble...

 

I have added the intake, exhaust, pulley and ECU, all of which have had no effect on the stumble, nor would I expect it too. The stumble is caused by the software, not hardware.

 

>>I have added the intake, exhaust, pulley and ECU, all of which have had no effect on the stumble, nor would I expect it too. The stumble is caused by the software, not hardware.

Yeah, S-owners seem to have a whole other problem. Re-reading what I wrote I think I was pretty clear I was talking about Coopers not about the S. You folks still have a problem that these modifications haven't fixed. Odd, though, that the ECU fix still has not made a difference. That IS a software fix, innit?

 

You know, it just occurred to me.

Advancing the spark timing results in:

Now, I'm no expert. These are just obervations I've obtained from tuning cars by feel. My technique was always to slowly advance the timing (for power) until the car began to stumble in 1st, stumble when floored in any gear, and/or had excessively sluggish throttle response. Any takers in my new (MCS) theory? Not that we could do anything about it.