Restoring a 1989 air cooled 126p. Engine runs ok with choke but when pressing the accelerator I get a backfire and then the engine stalls. The spark plugs and contacts are new, refurbished carburettor has been fitted and I had the timing checked. Fuel filter looks ok (doesnt look blocked). Any suggestions to check and solve the backfire and stall?
Technical Fiat 126 Air Cooled Engine Backfire &Stall
- Thread starter DMack1967
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Technical Fiat 126 Air Cooled Engine Backfire &Stall
If popping back through the carb, is there any clues on the colour of the spark plugs indicating one cylinder running bad?
Changing the carb made no difference?
Have the valve clearances been checked?
Is it possible you have a burnt out or sticking valve?
Air leaks on the exhaust will cause popping but wouldn't account for stalling/cutting out.
A bad air leak on the inlet side may, usually warped carb base through over tightening.
If you suspect engine valves etc. a compression test may be a start, possibly followed a a "leak test" to confirm which valve etc. if able to do that.
Thanks BugsyMike,
I took the spark plugs out. They were sooty but that's because I've been starting on choke. I compression tested both cylinders and both seem ok, giving 120 psi. I did notice that there is a really small amount of fuel seeping into the carburettor base (see photo attached). The carburettor is a reconditioned unit with fresh gaskets and a brand new carburettor base plate. Do you know if this seep is normal and if no, where is the seep coming from?
I took the spark plugs out. They were sooty but that's because I've been starting on choke. I compression tested both cylinders and both seem ok, giving 120 psi. I did notice that there is a really small amount of fuel seeping into the carburettor base (see photo attached). The carburettor is a reconditioned unit with fresh gaskets and a brand new carburettor base plate. Do you know if this seep is normal and if no, where is the seep coming from?
Attachments
Ideally no seep of petrol around carb.
120psi sounds good compression or at least OK.
Did engine have the same problem before the new carb, as some cheap copy carbs are not perfect.
Is there a good clean fuel supply to the carb.
Do you know if the carb needle jet and float height are good?
If any dirt is coming through fuel it can easily block jets in carb causing problems.
If timing is wrong engine can backfire.
There are many things that can cause issues , but any old school mechanic should be able to fix it as is no more complicated than an old petrol lawn mower. I know that is easy for me to say as have repaired all sorts of mechanical objects since the 1960s, the difference with modern stuff is it usually needs specialist diagnostic equipment and expensive parts.
There are many on Forum who have specific knowledge on the 500s and 126 engines, they may be able to pinpoint the problem.
