Backfire

[g4zur]

Hi all and happy new year.
I have just rebuilt the twin SU's on my wedge.
1980 2.0l FHC
I replaced waxstat jets with the conversion kit, I now have a problem I hope someone can assist me with.
Starts on slight choke ok, take choke off after a while runs fairly well but far from right, above about 2000 revs. It seems good, below it's what I would call fluffy. If I slowly press accelerator All seems ok, If I press accelerator firmer it misses and Is slow to pick Up and once stalled.
Also after starting and stopping engine, Every time after engine stopped about two seconds It backfires ONCE out of exhaust.
Is it Mixture Balance or a combination of the two.
Many thanks as always
Gareth.

G.P.Albrighton

[saabfast]

Have you checked the timing? Sounds as if it may need a tweak.

PS Happy New Year to all from a very soggy Kent!

Alan
Saab 9000 Stg 1 (now passed to son for his family car)
Saab 9000 2.3 FPT Auto (now gone that others might live)
Saab 9000 2.3 LPT Auto
'81 TR7 DHC

[Workshop Help]

Just a wild guess here.

Are you leaving the choke engaged for a prolonged period of time? If so, the misfire could be from fouling spark plugs. The purpose of any choke device, be it automatic or manual, is to aid in starting a cold engine. It is supposed to be disengaged as soon as possible once the engine has started. Leaving the choke on too long over enriches the mixture.

Please pull the spark plugs. If they are sooty black, disengage the choke much sooner than you have been. Take the car out for a decent run and recheck the plugs. Also, confirm the choke cable is fully disengaging when pushed all the way in.

Mildred Hargis

[Hasbeen]

That sounds like 2 things to me,

1. you haven't got the SUs tuned well. Poor idle is usually down to carb balance[suck], poor mixture on one or both carbs, sucking air somewhere after the carb. These faults become less effective at higher revs.

How was it before the carb job. If bad, it could be the same fault as before, ignition timing, valve clearance or air leak.

2. you are sucking air into the inlet system, somewhere after the carb, or have a leak in the exhaust system.

Hasbeen