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[RBL]

My 1.7 8V uses a pair of 40 IDFs. After rebuilding it, I've now got the timing right at idle and the carbs are just set at the basic preliminary settings, however it's popping and backfiring a bit and over-runs when I let off the thottle. Any simple tips as to what I can try before I get a specialist out to tune them properly?

Also - what do the accelerator pumps do? When I reconditioned the carbs I lost the settings on the adjustment rods - roughly where should the nut be on the rod to get a basic setting??

Thanks
Rich

[Chris Notsis]

THe over-run is normal, but it depends on the pitch/note of this popping. Certainly, the carbs would need to be synchronised by someone who has a 4-tube manometer. A scope can never help in this area. Ear is useless. Have this done by someone accustomed to this type of car / carb. A good non-dealer Alfa mechanic can help here.

An accelerator pump enriches the intake fuel charge when throttling up. If this does not happen, then the engine would stall because the air-fuel balance would be wrong. BY injecting a solid stream of fuel into the throat as soon as the throttles are opened, it gives time for the other parts of the carb to 'catch up' with the demands of the engine. It is essential, also, that float levels are correct for the IDFs, both for maximum rise and drop.
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Chris Notsis

[RBL]

Thanks Chris

[Sprintervention]

Just been and checked a set in the workshop. From memory the nut should be adjusted so that 5mm of the pump rod is visible past the nut. That appears to match the carbs I have which measured at 4.9mm and 5.1mm of rod that was visible.

Hope that helps. I can post a picture if you need.

[RBL]

Thanks Spintervention!

I wasn't far off with 7mm but 5mm sounds more llike it. It's difficult to find the best setting at the moment 'cos although it's running fine, it's not on the road yet.

Thanks for that
Rich