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Need Very Retarded Engine Timing For Smooth Idle. Is This Normal For My Spec?


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#1 BaronVonchesto

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Posted 22 November 2019 - 08:40 AM

So my (re)rebuilt engine is running (again). Adjusting the timing, Im having to set my idle timing (approx 1krpm) to 20 deg bTDC. trying to retard it further like 18 or 16 causes the rpm to audibly drop and the idle to become rougher the closer i get to 0. at 22 or 24 deg btdc the idle rpm also starts to go down.

 

Here's my engine specs:

998 +40 dished pistons

C-AHT88 minispares head

EVO001 cam timed to 107 degrees (as per spec)

stage 1 kit

CR 9.4 (block and head decked)
minispares forged rockers set to 0.14 thou

fuel mixture set using colourtune.

 

Im running Shell V-Power 97 RON fuel, so was hoping to get the timing closer to TDC. Ive read on the forums that 8-12 is typical for an idle.

 



#2 sonscar

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Posted 22 November 2019 - 09:48 AM

I always was taught that idle timing is variable but all in timing at high revs was the most important as this can quickly cause damage.With the vacuum advance connected my 998 standard mini idles at 24 degrees.If you have fully adjustable timing I would not worry but with a distributor advanced idle timing carries all through the range.Just my thoughts others may vary.Steve..



#3 nicklouse

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Posted 22 November 2019 - 09:53 AM

So my (re)rebuilt engine is running (again). Adjusting the timing, Im having to set my idle timing (approx 1krpm) to 20 deg bTDC. trying to retard it further like 18 or 16 causes the rpm to audibly drop and the idle to become rougher the closer i get to 0. at 22 or 24 deg btdc the idle rpm also starts to go down.

 

Here's my engine specs:

998 +40 dished pistons

C-AHT88 minispares head

EVO001 cam timed to 107 degrees (as per spec)

stage 1 kit

CR 9.4 (block and head decked)
minispares forged rockers set to 0.14 thou

fuel mixture set using colourtune.

 

Im running Shell V-Power 97 RON fuel, so was hoping to get the timing closer to TDC. Ive read on the forums that 8-12 is typical for an idle.

20 at 1k is high

1k is a high idle

 

you don't say what dizzy. if it has a vac advance or not and if it is connected or not when you were setting the timing.



#4 cal844

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Posted 22 November 2019 - 10:43 AM

You want a 850 +-50 rpm idle. As Nicklouse says you'll also need the vacuum advance disconnected and blocked.

#5 mini13

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Posted 22 November 2019 - 10:58 AM

as above, the vac advance needs disconnecting and plugging when checking idle timing. also what carb are you running, or more corrctly where/how is the vac advance being picked up...

 

Some carbs (HIF's ?) have the vac advance hole engine side of the throttle so they pull a lot of vacuum at idle, some have it the other side so they dont start pulling vacuum until the throttle is cracked open. anyway, the long and short is usually you set the advance to about 8-10 degrees without vac and when its connected you'll probably see 15-20 degrees.



#6 BaronVonchesto

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Posted 24 November 2019 - 06:29 AM

aah i guess thats where im going wrong. i have the vac advance connected!

My carb is a HS4 with the hose connected to the carb between the piston and the intake manifold. so i guess the vacuum is always there


Edited by BaronVonchesto, 24 November 2019 - 06:30 AM.


#7 BaronVonchesto

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Posted 24 November 2019 - 06:32 AM

 

So my (re)rebuilt engine is running (again). Adjusting the timing, Im having to set my idle timing (approx 1krpm) to 20 deg bTDC. trying to retard it further like 18 or 16 causes the rpm to audibly drop and the idle to become rougher the closer i get to 0. at 22 or 24 deg btdc the idle rpm also starts to go down.

 

Here's my engine specs:

998 +40 dished pistons

C-AHT88 minispares head

EVO001 cam timed to 107 degrees (as per spec)

stage 1 kit

CR 9.4 (block and head decked)
minispares forged rockers set to 0.14 thou

fuel mixture set using colourtune.

 

Im running Shell V-Power 97 RON fuel, so was hoping to get the timing closer to TDC. Ive read on the forums that 8-12 is typical for an idle.

20 at 1k is high

1k is a high idle

 

you don't say what dizzy. if it has a vac advance or not and if it is connected or not when you were setting the timing.

 

its some japanese electronic dizzy for the 998. not programmable or anything, but it does have a vac advance.

I run an idle at 1k because my cam leads to a really lump idle that sounds like the engine would die at any moment, but realyl its because i need to ensure that the engine runs well enough when the AC is switched on.



#8 cal844

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Posted 24 November 2019 - 10:32 AM

That idle will be ok, you should really get the advance recurved or at least checked

#9 daenesh

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Posted 25 November 2019 - 04:01 PM

 

 

So my (re)rebuilt engine is running (again). Adjusting the timing, Im having to set my idle timing (approx 1krpm) to 20 deg bTDC. trying to retard it further like 18 or 16 causes the rpm to audibly drop and the idle to become rougher the closer i get to 0. at 22 or 24 deg btdc the idle rpm also starts to go down.

 

Here's my engine specs:

998 +40 dished pistons

C-AHT88 minispares head

EVO001 cam timed to 107 degrees (as per spec)

stage 1 kit

CR 9.4 (block and head decked)
minispares forged rockers set to 0.14 thou

fuel mixture set using colourtune.

 

Im running Shell V-Power 97 RON fuel, so was hoping to get the timing closer to TDC. Ive read on the forums that 8-12 is typical for an idle.

20 at 1k is high

1k is a high idle

 

you don't say what dizzy. if it has a vac advance or not and if it is connected or not when you were setting the timing.

 

its some japanese electronic dizzy for the 998. not programmable or anything, but it does have a vac advance.

I run an idle at 1k because my cam leads to a really lump idle that sounds like the engine would die at any moment, but realyl its because i need to ensure that the engine runs well enough when the AC is switched on.

 

You're from kuala lumpur just like me.. maybe we can get in touch and talk more.. PM me..



#10 BaronVonchesto

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Posted 29 November 2019 - 09:47 AM

That idle will be ok, you should really get the advance recurved or at least checked

might just go for a minispares ADU5789MS or C-27H7701 instead. Opinions?

When i have a bit of time ill post an ignition curve of my current dizzy here 






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