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Hesitation At 2.5K Revs When Cold


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#1 Chew

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Posted 07 December 2017 - 08:52 PM

Hi everyone, just a quick issue regarding my mini,

 

The car appears to hesitate upon acceleration (50%+ throttle) when reaching about 2500rpm and hesitates to 'go' , but the issue is sorted when the car reaches operating temperature and revs freely through the range. I can't really find a definitive solution. Just to note, the car is running particularly rich and needs to be sorted, plugs are frequently fouled making start up a bit of a pain. HS4 carb Mini 30, 998 A+. I'd just like to know whether the issue can be sorted or is it something to expect with the car being recently started (Always give about 5 minutes for the car to warm up when cold before setting off).

 

Cheers.


Edited by Chew, 07 December 2017 - 08:56 PM.


#2 cal844

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Posted 07 December 2017 - 10:56 PM

It sounds like it's too rich, a few questions::

once started do you push the choke in slightly?

Is the dashpot oil correctly filled?

#3 Chew

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Posted 12 December 2017 - 06:26 PM

It sounds like it's too rich, a few questions::

once started do you push the choke in slightly?

Is the dashpot oil correctly filled?

Yeah, depending on where it's sitting (rpm wise) I'll usually push the choke in so it sits at just over 1K revs. Dashpot is filled (I think with 10w40).


Edited by Chew, 12 December 2017 - 06:27 PM.


#4 cal844

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Posted 12 December 2017 - 11:23 PM


It sounds like it's too rich, a few questions::

once started do you push the choke in slightly?

Is the dashpot oil correctly filled?

Yeah, depending on where it's sitting (rpm wise) I'll usually push the choke in so it sits at just over 1K revs. Dashpot is filled (I think with 10w40).


When the car hesitates pull the choke out maybe one inch, does it improve or get worse? If the engine hesitates then pulls like a train, try a 20/50 engine oil... our minis hate anything thinner (or thicker) than 20/50 engine oil all year round. They run well, so, why not try a heavier oil, to see if that's the issue?

#5 dyshipfakta

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Posted 13 December 2017 - 07:12 AM

interestingly mine is ike this if I run 20w50 in the dash pot its deffo an easy and cheap place to start.

#6 Chew

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Posted 14 December 2017 - 11:21 PM

 

 

It sounds like it's too rich, a few questions::

once started do you push the choke in slightly?

Is the dashpot oil correctly filled?

Yeah, depending on where it's sitting (rpm wise) I'll usually push the choke in so it sits at just over 1K revs. Dashpot is filled (I think with 10w40).


When the car hesitates pull the choke out maybe one inch, does it improve or get worse? If the engine hesitates then pulls like a train, try a 20/50 engine oil... our minis hate anything thinner (or thicker) than 20/50 engine oil all year round. They run well, so, why not try a heavier oil, to see if that's the issue?

 

The choke doesn't seem to have any effect really. One thing to note is that when i do hit 2K rpm and the engine hesitates the exhaust appears to 'pop' until the car stops hesitating. I'll try and get a video at some point.


Edited by Chew, 14 December 2017 - 11:42 PM.


#7 GraemeC

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Posted 15 December 2017 - 08:56 AM

Get the (known) fuelling issue sorted before trying to find a fix to something that may not be a problem



#8 cal844

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Posted 15 December 2017 - 10:43 AM

Does sound like it's going lean at that point

#9 Chew

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Posted 15 December 2017 - 01:58 PM

Does sound like it's going lean at that point


This is what confuses me. The sparkplugs when checked are fouled/near fouled. The only sign of a lean mixture would be cylinder 2 which has a slightly white residue whereas the other 3 sparkplugs are fairly black. I've adjusted the mixture slightly and I'll check again soon.

#10 cal844

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Posted 15 December 2017 - 04:17 PM

Does sound like it's going lean at that point

This is what confuses me. The sparkplugs when checked are fouled/near fouled. The only sign of a lean mixture would be cylinder 2 which has a slightly white residue whereas the other 3 sparkplugs are fairly black. I've adjusted the mixture slightly and I'll check again soon.

One of my 1275s was lean but plugs were black haha

#11 hhhh

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Posted 15 December 2017 - 05:15 PM

Reading the plugs is only going to show you what the last several seconds of running are burning like. It sounds like a momentary lean spot due to the pop with the hesitation. If it were rich, it would probably just bog and feel "heavy". I'm usually happy to put up with a little rough running when cold that clears up when warm because it tells me my mixture is close to spot on. 

 

As far as warming up goes, it's best done by gentle driving rather than idling because cold running is what causes the most wear and nothing warms it up more quickly than putting it under load.






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