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Missing under part throttle/constant speed
https://www.ausmini.com/forums/viewtopic.php?f=2&t=77027		 Page 1 of 1
Author:  smac [ Sat Jun 02, 2012 1:02 pm ]
Post subject:  Missing under part throttle/constant speed
Got a stock 998 engine I finally want to sort out. Had an issue with it missing every few seconds at constant speed. Feels ok accelerating, idles just fine, but sitting at constant speed it misses. Very noticeable at 50kph, less so at 100kph but still there.

Got as far as checking over ignition system a while back, but ran out of time. Leads are good, condenser good, points good, vac system good. Needle is stock 998 (ADE), cam stock, dashpot and all it's workings seem ok.

Now here's the thing: cranking the mixture up makes the issue go away. So I figure I'm either chasing a leak on the intake side, or I thought maybe too advanced for some reason (rich mixture burns slower so too much advance less of a problem). I thought I'd checked that, but maybe my memory is failing....I forget....

Any other thoughts?
Author:  TheMiniMan [ Sat Jun 02, 2012 2:28 pm ]
Post subject: 
put a stronger dash-pot spring in the carb
Author:  smac [ Sat Jun 02, 2012 2:38 pm ]
Post subject: 
Hmmm...so thinking the plunger is settling too high at constant speed?

No way of knowing what spring is in there, stock I imagine, as everything else about the car is original.
Author:  drmini in aust [ Sat Jun 02, 2012 2:44 pm ]
Post subject: 
What oilz is in the dashpot, maybe try something a little thicker?
Author:  smac [ Sat Jun 02, 2012 5:57 pm ]
Post subject: 
ATF in there now, but I think it was 3-1 when I started chasing this. OK under acceleration and no stumble when I step on the go pedal so was kinda assuming oil is ok. Spring would make sense though, more so than the leak idea cause leak would bugger up the idle as well I would think.
Author:  smac [ Sun Jun 03, 2012 1:22 pm ]
Post subject: 
TheMiniMan wrote:
put a stronger dash-pot spring in the carb


Well done, from your armchair :lol:

Had a ferret through the cupboard and found 3 HS springs. Using the calibrated weight on my patented smac-o-spring-o-measurer (otherwise known as the lid on a coffee plunger) I measured comparative heights of my four springs as 104mm (existing spring), 111mm, 123mm and 124mm.

Tried the 111mm, definite improvement, but still a slight miss. Tried the 123mm and no miss. Runs better through the whole range too. Sensitive wee buggers aren't they?

Ta' very muchly, the beer is in the mail.
Author:  TheMiniMan [ Sun Jun 03, 2012 2:25 pm ]
Post subject: 
ha ha, way cool, thanks for that 8)

I really am awesome aren`t i ???? 8)
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