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Tuning Auto Carb


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#1 Chappie


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Posted 16 August 2020 - 09:41 AM

Hi all

I've got a 1989 Auto 998

After getting it MOT ready a few months back I handed over the keys to the tester and it just kept stalling and they aborted the test.

I managed to tune the carb and get it running fine and rebook the MOT.
A few months later it started stalling again in reverse. So I managed to tune it again.

Last night every time I came to a complete stop at traffic lights the engine would stall and when I start it I have to hold the revs above 1000 or pull the choke to get her going.

I know how to basic tune the carb but wondering if anyone knows why I have to do this so often?

I know the idle revs should be sitting at around 800 but mine prefers 1000-1100 otherwise it'll stall.

Any help appreciated.

Side note the auto engine is temporary, I'm planning on swapping it for a manual when I have the time.

Chappie ^_^

#2 cal844


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Posted 16 August 2020 - 10:56 AM

Is there enough oil in the dashpot? Use half a cap of engine oil

#3 RustyAutoCityE


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Posted 16 August 2020 - 12:33 PM

Make sure there is no rubbish floating around the needle/seat.


A dirty carb will cause all kinds of running problems.

#4 Chris1275gt


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Posted 16 August 2020 - 02:05 PM

I'd check the piston is moving freely in the pot I had the same problem and found very light scoring on the piston and pot, polished them out and it's been fine.

#5 johnR


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Posted 16 August 2020 - 06:36 PM

Is the throttle spindle worn?

#6 jime17


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Posted 16 August 2020 - 07:25 PM

Have you altered or checked the timing?

#7 Algordo1100


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Posted 17 August 2020 - 05:34 AM

Do you perhaps have a slight, but steadily worsening air leak?

Might also explain the reluctance to idle correctly.

#8 Pigeonto


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Posted 17 August 2020 - 07:23 AM

Sounds like inconsistent fuel level. I'd fit a new float valve and also a new oil filler cap if it hasn't had one recently. Vacc tube to the dizzy needs checking at the rubber ends. Breather hose. Remove dizzy cap, suck on vacc tube to see if the assembly moves and stays there ' til you release. + All service areas have been attended to obviously

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