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[munro]

Since refitting my 1.7 8V twin carb engine (out for gearbox overhaul) I have had a misfire on what appears to be number 3 cylinder. It varies a bit, but on lukewarm to hot idle number 3 cylinder does nothing. I can hear a kind of puff-puff noise which suggests the cylinder is cycling over but not firing at all. If I pull number 3 plug, no change at all in idle. The puff-puff noise corresponds exactly to the intake vacuum pulsations for the associated carb barrel as measured on brake servo vac take off.

I have changed plugs twice (Golden Lodge), renewed plug leads, checked for spark using a high energy 25Kv spark tester - good healthy repeated spark. Distributor cap and rotor appear fine...I doubt I'd get a 25Kv spark if any problems there. So I suspect not an ignition problem.

I thought vacuum leak so i have pulled the carb and the intake manifold and rejointed these. If i spray carb spray around the base of the carb/intake whilst idling it makes no difference. Also do not seem to get any change in idle if I spary carb spray direct into the #3 carb barrel, which normally increases idle if vac leak or decreases if rich...made nil change.

I disconnected brake vac servo to ensure no leak from there. No change.

I have fuel to the carbs, and can see a squirt from accelerator pump. Little inlet fuel filter is clean/clear to this carb.

i have checked valve operation with exhaust manifold and intake manifold removed...all valves appear to be opening and closing fine. I have also checked compression...all around 75-80 psig which i thought seemed a bit low but all four cylinders are the same so this must be OK.

Next step for me is to pull the carb off again and see if there is a blockage to the rear main jet or something. Presumable this requires a carb overhaul kit.

Whare do i get a Weber carb kit from in the UK??
Any other suggestions welcome.

Thankfully the weather is fair so I can drive my Spitfire....but I want my Alfa back!!!

Munro.

[boxertricks]

nothing like a good mystery eh... could try asking the carburettor hospital - the guy who runs it (eric) is really helpful and theres nothing he doesnt know about them. carb overhaul kits are pretty cheap i think:

http://www.carburettorspecialists.com/default.htm

[munro]

Thanks Boxer.

I've ordered a carb overhaul kit from Eurocarb (www.dellorto.co.uk... they also do Weber kits for 40 IDFs). £29 including VAT post and packing...hopefully arriving tomorrow.

I've had a look on the web for some guidance on IDF o'haul and cannot find much that's downloadable...one item from a Texa Porsche 912 site but it doesn't go into much detail. Will keep searching - there's bound to be something as these carbs are pretty popular with the Veedub community.

Fingers crossed.
Munro.

[munro]

Well, stripping, cleaning, refitting th ecarb didn't work - still just as bad. Have also fitted a new dist cap, tried a spare coil. Still no improvement. Took it along to my local Alfa service specialist - he cannot solve either!!!!

Any help out there? I'm getting desparate. Anyone in UK got a used 40IDF carb they can sell cheap? Prefereably to suit the offside bank?

Any other (polite) suggestions welcomed.
Thanks.

Munro.

[paulhide]

Wow!. not many options left. Dave Peters might have one or a pair of dellortos, though they tend to go for 50-70 quid a pair. 07860861898. Who last tuned/ balanced your carbs? Compressions sound very low, but it depends how you measured them. (If the misfire had disappeared above 3000rpm then it would probably be something to do with the idle jet.)
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Owner's Club 33 Registrar. Now from P4 & S2 1.7 QV
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