Technical Misfire? Backfire?

[TotalnoTito]

Hi, I own a Zastava 128. Since there is no Fiat 128 section, I'm posting this in Uno section because the engine is the same. 1.1 L SOHC 41 kW. I've noticed a problem when climbing hills, especially in low RPM. The engine behaves as if a singular piston doesn't fire, and it stutters for a second. This doesn't happen once the engine reaches a higher RPM. Yesterday, in especially low RPM, it stuttered for longer and made a sound as if it was backfiring. Then resumed working normally. I noticed the carburetor is sooty too.

The mechanics did meddle with the carburetor when it was being serviced, and they lowered the idle throttle. Should I just increase the idle throttle on the carb? Could it be the reason for misfiring? Corroded contacts on the sparkplugs/distributor? Low compression?

Also, I need advice on what to use to clean my carb. Dad says WD40 but I've heard it leaves a film on the carb and messes with it.

Thank you all in advance.

 

[porta]

Don’t use WD40 in the carb, use a decent carb cleaner. However, start with the basics, plugs, leads and coil, points, rotar arm and dizzy cap. If the carbs’ sooty and ‘like backfiring’, it suggests fuel in the carb is being ignited.
If it’s just been serviced, I’d check the fuel filter is the right way round and that fuel is being delivered properly, check the float in the carb and the carb jets. What carb is fitted on it? Oh, and check the flame trap and breather are clear
It doesn’t sound like it’s been serviced very well!

 

[maggellwin]

As previous message (plugs points, valve clearances too) but to me sounds like either the ignition or valve timing, or both, are out

 

[porta]

As previous message (plugs points, valve clearances too) but to me sounds like either the ignition or valve timing, or both, are out

It could have jumped a tooth, it’s not unknown, but I’ve only ever experienced it on the ‘fire’ engines and I’ve had a lot of dealings with the 1100, 1300 and 1500s of 127, 128, X19, stradas etc
It would be useful to know exactly what ‘they’ did or didn’t do on the service