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Splutters/boggy/misfires When Only Turning Right?


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#1 Arthy

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Posted 14 July 2019 - 09:02 PM

This is really weird one. It’s been like this for over a year since my engine rebuild and I’ve learnt to live with it. At first I thought it was the cam going ‘off cam’! Running twin HS4’s with an SW8 cam.

The engine splutters and really bogs down when ONLY turning right. This is mostly on roundabouts in second gear, at around 1-3k rpm when you try and accelerate out. You can hear the engine misfire/change tone as soon as you reach a certain angle.

Now I presume this is carb related, as during the rebuild I thought I’d modify the carbs ‘vizard’ style by cutting the throttle shaft ect...
However I thought I’d see what other people might think it is?

I have used a different coil & plugs and the problem persists. The colour on the plugs seem good and it pulls perfectly fine so I don’t think it’s mixture or timing related, although it has never been set up properly on a rolling road? Using AAA needles in a 1330, with modified head & cam.

Any help would be appreciated!
Arthur :)

#2 cal844

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Posted 14 July 2019 - 09:15 PM

Watch the rev counter, what does it do? If it spikes it's electrical

If it hardly moves it's fuel

#3 ukcooper

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Posted 14 July 2019 - 11:46 PM

my 10p's worth

engine earth strap breaking down but if not and it seems ok fit a second any way wint hurt but may do some good..

 

redo the 12v to the coi..

 

look behind the grill for nicks in the wire where it been rubbing ...



#4 andyapanel

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Posted 15 July 2019 - 11:38 AM

I have had this twice and in both instances it was the coil. 

Did you fit a new one, or try a known good one?

 

If it is definitely not the coil, I might look inside the carb at the fuel bowl.

Good luck



#5 Matpaul

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Posted 16 July 2019 - 03:02 AM

Barring other possible weird causes like a wire touching somewhere when cornering etc.

One cause could be (as I understand it) cornering lowers the fuel level in the jet. In this case a right corner would lower the fuel in the left carb jet (although it would raise the level in the right carb jet at the same time?) on your twin carb setup.

If your left (or both?) carb/s are marginally lean in this area of the needle then cornering may exacerbate the leaness and cause a misfire / bogging down when you try to accelerate? 

I had a similar problem on a single carb setup. It would bog down terribly on left corners (worse when cold). Pulling the choke and waiting or just waiting till it cleared after the corner would see everything back to normal again.

Perhaps a different viscosity oil in the dashpot? although I am running the same dashpot oil as before and now that I have the needle corrected and mixture checked throughout the range I have not had a further problem. 

Good luck.



#6 Arthy

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Posted 16 July 2019 - 03:18 PM

Just an update, I've tried going around the same right hand corners while in neutral and the rev's drop significantly.

 

I've also noticed that the engine doesn't sound just quite right while on part throttle at around 1-3k, although very minor. I'm going to presume this must be carb related so I will have a look at the fuel bowls.

 

Thanks for everyones help so far! :) 



#7 cal844

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Posted 16 July 2019 - 04:20 PM

Id be checking the float valves for junk or wear and then adjusting +.5mm So it doesn't stumble

#8 andyapanel

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Posted 17 July 2019 - 11:40 AM

I don't know how progressive your driving is, but Spitfires (the fighter plane) on SU carbs suffered from fuel starvation on tight turns. This was a fix:

 

https://en.wikipedia...lling's_orifice

 

Good luck solving the problem.


Edited by andyapanel, 17 July 2019 - 11:40 AM.


#9 monkey

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Posted 17 July 2019 - 12:57 PM

I don't know how progressive your driving is, but Spitfires (the fighter plane) on SU carbs suffered from fuel starvation on tight turns. This was a fix:

https://en.wikipedia...lling's_orifice

Good luck solving the problem.


That makes for really interesting reading, but as amazing as minis are I don’t know if they can achieve negative g from inverted flight lol

#10 Arthy

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Posted 17 July 2019 - 02:33 PM

I don't know how progressive your driving is, but Spitfires (the fighter plane) on SU carbs suffered from fuel starvation on tight turns. This was a fix:

 

https://en.wikipedia...lling's_orifice

 

Good luck solving the problem.

 

My driving is definitely 'spirited' to say the least haha, but that is deffo an interesting read!! 



#11 cal844

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Posted 17 July 2019 - 06:45 PM

I'd suggest to try making some small driving style changes to try to see if the issue changes... just to see if your fault stays, gets worse or best case is worked around. Then you can experiment with certain parts... only ever change one part or make one adjustment at a time

#12 Arthy

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Posted 17 July 2019 - 09:17 PM

I'd suggest to try making some small driving style changes to try to see if the issue changes... just to see if your fault stays, gets worse or best case is worked around. Then you can experiment with certain parts... only ever change one part or make one adjustment at a time


I actually have been experimenting with this recently! Even ‘normal’ driving you can still feel the engine spluttering, but it’s no where near as noticeable.

I’ve also noticed on prolonged right hand turns (ie: going round the roundabout multiple times) is when it’s noticeable, but only at certain angles on the steering.

I’m going to mess with the left hand carb float (looking from the front of the car), so it allows more fuel in!

Again, thanks for all the help guys!

#13 MiniMadRacer

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Posted 18 July 2019 - 08:34 AM

Might be worth checking the your fuel pump too. Originally twin carbs were fitted to cars with an electrical fuel pump (Cooper and the Cooper S). If you have a mechanical pump driven by the CAM, it might be worth checking its pumping as it should and ensure the fuel line is "protected" from the heat of the exhaust.



#14 cal844

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Posted 18 July 2019 - 10:25 AM

Might be worth checking the your fuel pump too. Originally twin carbs were fitted to cars with an electrical fuel pump (Cooper and the Cooper S). If you have a mechanical pump driven by the CAM, it might be worth checking its pumping as it should and ensure the fuel line is "protected" from the heat of the exhaust.


I agree this would be another thing to check, it may be that the float is closing off making the engine run lean?

#15 Arthy

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Posted 18 July 2019 - 12:54 PM

 

Might be worth checking the your fuel pump too. Originally twin carbs were fitted to cars with an electrical fuel pump (Cooper and the Cooper S). If you have a mechanical pump driven by the CAM, it might be worth checking its pumping as it should and ensure the fuel line is "protected" from the heat of the exhaust.


I agree this would be another thing to check, it may be that the float is closing off making the engine run lean?

 

 

Thanks for the advice, but I have already converted to a facet pump. It was actually one of the first things I changed since noticing it! 

 

I have just been out for a quick drive after adjusting the float 1mm shorter to allow more fuel in. Also richened the carbs +1 flat too. It has deffo seemed to have improved things, so I will keep adjusting the float, just before it floods! 






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