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Rough Idle Still !


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#1 Ol timer

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Posted 05 August 2018 - 12:56 PM

I still seem to be having idle problems with my 1974 998 mini

 

I have recently replaced/Fitted the following, not just because of the Idle issue, things needed sorting 

 

Stage 1 Kit

Rebuilt HS4 Carb, Fitted new Stage 1 Needle

Electronic ignition

Lucas Gold Coil

New Sparks set .025 

New Leads.

New Rad and stat, heater matrix and heater hoses

Oil change

 

Apart from happy with the way things came out. I was also hoping one of the things above may have cured the issue however None have made any difference to the idle, it still fluctuates engine shake

It acts like its going  to stall and there is fluctuation on the Tacho between 750 - 1000 rpm

Drives find when I put my foot down no issues at all.

Am stumped where else to look

 

 

 

 



#2 unburntfuelinthemorning

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Posted 05 August 2018 - 02:13 PM

Is it better if you raise the idle speed?

 

Have you checked the ignition timing?

 

Have you checked the fuel mixture at idle?



#3 Ol timer

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Posted 05 August 2018 - 02:23 PM

ignition timing has been checked and done when I installed the Electronic Dizzy parts. Also checked colour of Sparks and they are a nice golden brown as well as lifting carb piston to check fuel/air mix. when I increase the Idle speed to about 1100 it settles down, could it be vacuum unit leak or dead on the Dizzy? or Vac tube?

 

Just unplugged the vac lead of the Dizzy, makes no difference on or off...


Edited by Ol timer, 05 August 2018 - 02:57 PM.


#4 unburntfuelinthemorning

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Posted 05 August 2018 - 04:36 PM

What sort of tacho are you using?



#5 Ol timer

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Posted 05 August 2018 - 04:44 PM

Got a Smiths, like the one in the link below,

 

http://minispares.co...mg.aspx|Back to



#6 carbon

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Posted 05 August 2018 - 05:03 PM

ignition timing has been checked and done when I installed the Electronic Dizzy parts. Also checked colour of Sparks and they are a nice golden brown as well as lifting carb piston to check fuel/air mix. when I increase the Idle speed to about 1100 it settles down, could it be vacuum unit leak or dead on the Dizzy? or Vac tube?

 

Just unplugged the vac lead of the Dizzy, makes no difference on or off...

A few checks worth doing here:

- check that the vacuum canister on the dizzy is not leaking, as the rubber diaphragm inside can split

- check that the dizzy baseplate moves when you apply vacuum to the can, the cans can stick

- check there are no splits in the black nylon tube between carb and dizzy, they do get brittle with time



#7 Ol timer

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Posted 05 August 2018 - 05:10 PM

cheers mate.. will do that, SO the Vacuum from the Dizzy to the Carb can affect Idle?



#8 unburntfuelinthemorning

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Posted 05 August 2018 - 05:28 PM

 

Got a Smiths, like the one in the link below,

 

http://minispares.co...mg.aspx|Back to

 

Probably a silly question but does it have a switch on the back for 4,6 and 8 cylinders and is it set to 4?

 

Edit:  Scrap that idea - it'd read low, not high if it was set wrong, duh.


Edited by unburntfuelinthemorning, 05 August 2018 - 05:42 PM.


#9 Ol timer

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Posted 05 August 2018 - 05:54 PM

 

 

Got a Smiths, like the one in the link below,

 

http://minispares.co...mg.aspx|Back to

 

Probably a silly question but does it have a switch on the back for 4,6 and 8 cylinders and is it set to 4?

 

Edit:  Scrap that idea - it'd read low, not high if it was set wrong, duh.

 

The gauge is working correctly. the engine is fluctuating causing the gauge to do the same



#10 Moke Spider

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Posted 05 August 2018 - 07:47 PM

When the Carb was overhauled, what was replaced?



#11 cal844

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Posted 05 August 2018 - 09:59 PM

Just thinking here, air leaks, also you say the spark plugs are a tan colour, richen it up a little, 1/8th turn will suffice

#12 Bat

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Posted 06 August 2018 - 06:26 AM

Hi,

I was thinking air leak too.

Vac can should be doing nothing at idle if the butterfly is set right, it should cover the vac port to the dizzy.

Cheers  :proud:



#13 harrythehat

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Posted 06 August 2018 - 06:30 AM

Vac lead off the dizzy makes no difference

 

It should affect the tickover run higher, theres a problem in that area, don't change any mixture till air leak is sorted



#14 harrythehat

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Posted 06 August 2018 - 06:35 AM

check vacuum on dizzy suck on little pipe

advance moves, then you should not be able to suck any more air through it should be solid.

 

check the rubber connecting pipes with your own sucking while its connected to thin plastic pipe just a tiny leak is enough to upset the system



#15 carbon

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Posted 06 August 2018 - 04:45 PM

check vacuum on dizzy suck on little pipe

advance moves, then you should not be able to suck any more air through it should be solid.

 

check the rubber connecting pipes with your own sucking while its connected to thin plastic pipe just a tiny leak is enough to upset the system

+1. My experience with a split vacuum can diaphragm is that it significantly the idle quality.

 

I have also had the black plastic advance pipe develop small splits which had same effect






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