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?

put a stronger dash-pot spring in the carb

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

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.

What oilz is in the dashpot, maybe try something a little thicker?

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

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.

Well done, from your armchair

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.

ha ha, way cool, thanks for that

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

_________________
No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.