Technical Loss of power - feels like a rev limiter

[fuzzyface]

Hello all, I've got a problem that has me baffled:

Over a period of about 3 days, she went from driving just fine with some pep, to a complete loss of power, especially at the top end. Acceleration was generally sluggish and it felt like you hit a 'rev limiter' at progressively lower revs. First it was right around the shift points (30/50/70 kph), but came down about 10 kph on each gear over the 3 day period. No matter how hard you stepped on the gas, the motor would cut out for a moment until you dropped below (20/40/60 kph) and then kick back in.

At a stop, it revs all the way up.

I have checked fuel pump and pressure, fuel lines, rebuilt the carb, replaced the plugs/wires/points/condensor/cap and adjusted the tappets. Compression is 110 and 109, which is what it was when I did the first tune up a few months ago.

All our work has brought the 'rev limiter' feel up about 7kph on each gear, but there still isn't any power. The whole thing is sluggish, and I'm still getting that 'rev limiter feel at about 30/47/68, and can't to more than 80 in 4th gear (I used to have no problem hitting 90).

Thanks a ton everyone...

-Benjamin

 

[jackwhoo]

I had exactly same symptoms with a heavily soiled fuel filter.

 

[thepuddlejumper]

I had a similar problem many years ago in my Gamine, it turned out to be a worn petrol pump push rod. My problem was it ran fine at slow speeds but once you tried to go faster or up a steep hill it was very reluctant and slowed down, it would Rev up fine standing.

Ralph

 

[1500500]

A blocked or partially blocked main jet can also cause those symptoms

 

[the hobbler]

Have you checked that the Bakelite spacer between the carb and the cylinder head is not warped (which they are prone to do) and that the engine is therefore running very lean---it would rev up 'of-load' but not 'pull'?

 

[fuzzyface]

Hello! Thank you all for the suggestions. I know it's not the carb (which I just rebuilt) or the fuel filter (which I just replaced). I ordered a new fuel pump to see if that's it. For a bakelite spacer, is this the part: http://mrfiat.com/italian/fiat/fiat-500/fuel-system/fiat-500-n-d-f-l-carburetor-spacer.html and would it be obviously warped, or just a little?

I'll try both...

-Benjamin

 

[the hobbler]

Yes Ben, that is the part I was referring too. Before you go and fill 'Mr Fiat's' pockets with your hard earned cash, check it. Get a sheet of thick glass (it will be nice and flat), attach a sheet of fairly fine emery-cloth to it and see if the spacer is flat, or warped. If it only slightly warped, flatten it out yourself on the emery cloth---only replace it if it is badly warped.

 

[jjacob]

You don't mention if you are running points or electronic ignition. A change in dwell (point gap) can cause this. So make sure the point gap is correct if you are running points and make sure you see 18 degrees of advance at 3000 rpm.

I would not rule out the carburetor yet. You could have a fuel float that has a pinhole in it, and the float is flooding the carb, or the float may be set too high and you are running out of gas at higher engine speeds.
As others have mentioned a lean condition could be caused by a failing fuel pump.
Since this seems to have come on all of a sudden, my thoughts would be fuel pump, or carburetor float or carburetor blocked jet.
John

 

[fuzzyface]

Thank you all. It'll be a few days before I have a chance to tear things open and have a look, but I'll report back...

-Benjamin

 

[Labman]

Check your tappets again. I had a very similar issue and when I removed the valve cover, one of the tappet adjuster nuts was completely off and lodged in between the valve springs. The tappet was unscrewed almost all the way out and because of that, one of the valves was not opening up all the way. I reinstalled the nut and readjusted and now it's running like a champ again.