Not 131 but 127

[finnie]

Hi all
My friend has a Fiat 127 with a new carburettor
On it but he's saying that it will idle well and take
full throttle but very erratic in between the two ?
He's also put a new fuel pump on !
Any ideas ?

[Thotos]

It could be any number of things but if the problem started with the new carburettor, then the progression jets are most likely the culprits. They could be the wrong ones for the engine or could be blocked.

[miro-1980]

Few  (key ) questions:

I concur with Totos jets are the most likely suspect  ... but the pump problem is equally likely.

From what say say it is impossible do remotely diagnose the problem

Key element is if change to a new carb as the only change pr other changes were done at the same time.  

It is easy , but requires a very consequent linear analysis, before the reason it can be pinpointed : carbs or something else  

If no changes were made analysis is very simple, id i.e. new camshafts were also put in the matter becomes quite complex.  

If changing the carb was the only change I would think the engine gets wrong mixture between idle and full throttle ( either too much or too little) . Reasons may be from clogged jets, wrong size of jets, fake air from the carb not being air tight (a lose screw, loose jet, insufficient fuel level caused by sticking floater valve, etc , etc ...

I would suggest the following:
 
Put in brand new plugs.

Run it idle for a while and do a CO2 test on the exhaust.

Run the engine until the ventilator switched itself on and off twice (proper engine temp) and see it this changes any.

After running it at variable RPM check if the plugs are proper color ( light beige )

If it looks like fuel starvation - try injecting additional fuel fuel into the carb by hand (with a syringe) to confirm or limit air getting into the barrel by blocking the barrel by hand ...

Some questions that might help your diagnosis ?

Is this the right carb for the engine :(OEM) ?
 - What is the 127 engine ( 900 or  1301)  
 - What carb is he currently using ?
-  What jets are currenty installed
-  Is the carb brand new or rebuild  
- Was the engine modified prior to installation of the new carb .
- Has the new carb been properly cleaned and adjusted:
- Was the carb tuned after physical installation
- What was the previous carb (same or different model) ,
- Did it work well ?

You need to go back to the last well working setup (and or analyze what action produced the curent result.)

Good luck

Miro

PS: It  is a good practice not to make more than one change at the time. If something goes wrong  (which often is the case) you immediately diagnose the source of the problem. If more than one thing is changed at a time the diagnosis becomes exponentially more difficult and cumbersome.   

[finnie]

Thanks guys
Think it`s coming back to workshop for a good clean and check over