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Misfire/stumble/flat Spot Between 3-4Krpm


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#31 brivinci

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Posted 28 April 2025 - 05:28 PM

UPDATE: I am not 100% sure how for why, by this flat spot/missfire has now been corrected. Could be one thing, or a series of little things. I hate not knowing but I will list out what I did, and what I found. Not one thing "fixed" this straight away. Durning a 500 mile trip, we noticed it was improving...

Motor was out to replace ring gear on flywheel. Flywheel, crank, Cooper S pulley were all balanced (confirmed balanced) 
Cam timing was set to Calver ST's specific degree.
Distributor was installed and clocked correctly. 
Rotor replaced: The one in there had a burn spot just off the edge of the metal piece. This piece also wiggled around. Junk

Found my new fuel trap was leaking from seam. Glued/siliconed to get me on the road. Replaced with original Rover unit I had once home. (2nd replacement trap to fail)
Noticed throttle body bolts were not as tight as I would have thought. Removed sandwich plate, replaced gaskets and refit with blue loc-tite.

Reset roller rockers and gapped plugs.

Any one of the above, if wrong/loose/worn/leaking could have caused from issues. Not sure which is was (or if its something else entirely) that got rid of the issue. I have a feeling it will come back, with my luck. Fingers crossed and thanks for coming along for the ride!



#32 ultimax5

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Posted 02 May 2025 - 03:50 AM

UPDATE: I am not 100% sure how for why, by this flat spot/missfire has now been corrected. Could be one thing, or a series of little things. I hate not knowing but I will list out what I did, and what I found. Not one thing "fixed" this straight away. Durning a 500 mile trip, we noticed it was improving...

Motor was out to replace ring gear on flywheel. Flywheel, crank, Cooper S pulley were all balanced (confirmed balanced) 
Cam timing was set to Calver ST's specific degree.
Distributor was installed and clocked correctly. 
Rotor replaced: The one in there had a burn spot just off the edge of the metal piece. This piece also wiggled around. Junk

Found my new fuel trap was leaking from seam. Glued/siliconed to get me on the road. Replaced with original Rover unit I had once home. (2nd replacement trap to fail)
Noticed throttle body bolts were not as tight as I would have thought. Removed sandwich plate, replaced gaskets and refit with blue loc-tite.

Reset roller rockers and gapped plugs.

Any one of the above, if wrong/loose/worn/leaking could have caused from issues. Not sure which is was (or if its something else entirely) that got rid of the issue. I have a feeling it will come back, with my luck. Fingers crossed and thanks for coming along for the ride!

 

Hi brivinci, glad to know your car is running well now.  Just curious, did you end up changing your fuel pump? 



#33 brivinci

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Posted 02 May 2025 - 05:57 PM

I never did end up changing it. I have had so many issues with new parts failing that I will hold off (for once) just replacing things "just in case". 

I have put a few more miles on the car and the problem still seems sorted. Very excited to have this ripping for a fresh season. About to sign up for an AutoX event. What are these called in the UK? Where you race around cones against the clock?



#34 ultimax5

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Posted 03 May 2025 - 05:56 AM

I never did end up changing it. I have had so many issues with new parts failing that I will hold off (for once) just replacing things "just in case". 

I have put a few more miles on the car and the problem still seems sorted. Very excited to have this ripping for a fresh season. About to sign up for an AutoX event. What are these called in the UK? Where you race around cones against the clock?

 

I see, thanks for your reply and really good to know your Mini is still behaving itself.  I think it's called the same thing, Autocross.  I live in Malaysia though.






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