Technical Uneven slow running & Lumpy

[ClassicFiat500]

For some reason the tickover on my 650cc has gone very erratic, when I take my foot off the accelerator the revs are not dropping as they used to the engine speed takes a while to drop down, I am also getting quite a lot of popping through the trumpets (Webber 40 dco which I know is too big for the car but it has run nice & smooth and even in the past ). The engine stalls at under 1000rpm Any suggestions welcome I have checked the accelerator return spring , would an air leak on the inlet manifold cause the problem? and is it worth cleaning the float chamber in the carb? When the car is running at around 65 MPH its great but under 2000 rpm” The car has recently in terms of miles %0 miles ago had a full service including a carb rebuild. The car starts with no problem.

 

[ClassicFiat500]

Just one other thing re my uneven running, I have re-connected my electric fuel pump due to the fact the carb needs to fill up when the engine has not been started for a week or so, I found that the petrol is pumped into the carb before you turn the engine over on the electric pump, whereas with the mechanical pump i had to turn the engine over for ages to fill the float chamber.

 

[ClassicFiat500]

Little bit of a late update regarding very rough & lumpy running,. I have driven 38 miles since a major service £5K at a supposed to be very reputable Classic Fiat 500 Garage, of which included an engine out job to sort out engine leaks also a recon steering box (which still leaks) & brake overhaul. Took the car for a 2 mile run of which it started popping, backfiring and running like a dogs dinner. I thought the head gasket was blowing but no! the carburettor (weber 40 dco) was almost hanging off with one bolt missing & three VERY loose letting excess air into the inlet manifold.

The moral then is learn how to carry out your own servicing & if you want a job done DO IT YOURSELF. Went for a drive today its running like a dream. I know I should have take the car back to the garage but that would have involved a trailer etc. I really envy some of you guys who have the stamina & knowledge to be able to whip out an engine and replace it the way you do.

 

[the hobbler]

For some reason the tickover on my 650cc has gone very erratic, when I take my foot off the accelerator the revs are not dropping as they used to the engine speed takes a while to drop down, I am also getting quite a lot of popping through the trumpets (Webber 40 dco which I know is too big for the car but it has run nice & smooth and even in the past ). The engine stalls at under 1000rpm Any suggestions welcome I have checked the accelerator return spring , would an air leak on the inlet manifold cause the problem? and is it worth cleaning the float chamber in the carb? When the car is running at around 65 MPH its great but under 2000 rpm” The car has recently in terms of miles %0 miles ago had a full service including a carb rebuild. The car starts with no problem.

An airleak WILL cause this problem, as will a bit of muck blocking the slow-running jet. Check the float chamber for muck, as well as all the jets.

 

[ClassicFiat500]

Hi The Hobbler I will take your valid advise & take off the the top of the carb & give it a clean tomorrow, do you think its worth taking out the jets or just spraying into them in situ. Couldn’t believe such a basic mistake they made. Only hoping nothing else was missed or left off. Many Thanks again. Barry

 

[the hobbler]

Hi The Hobbler I will take your valid advise & take off the the top of the carb & give it a clean tomorrow, do you think its worth taking out the jets or just spraying into them in situ. Couldn’t believe such a basic mistake they made. Only hoping nothing else was missed or left off. Many Thanks again. Barry

If you have access to an air-line, better to take the jets out (one by one) and give a blast of air through them