Technical Revving(hesitation)

[Drinu]

HI guys,
I have an uno 999cc FIRE. Now when I put it on neutral and I try to rev hard (by depressing the accelerator quickly) it hesitates to rev. This happens both when hot and cold. Is this normal? It sounds like the engine is going to cut. If its not normal what could it be??...timing...leads??

Thanks
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[jjhepburn]

We call that the FIAT stutter, pain in the ass but I think its normal.

 

[(CZ)enda]

Search for "advance", "diaphragm" and similar, it had already been covered many times here.
Also check your filters (fuel/air).

If you have a carburettor Fire, then it may be that the accelerator nozzle inside the carburettor is clogged. This can be checked while looking through the upper part of the carb down - the nozzle is protruding into the inner diameter of the barrel and if you turn the accelerator lever fast, it should squirt in a spray of petrol. Cleaning of the nozzle requires carb removal and complete disassembly, i.e. it is reasonable to rule out the other possibilities first.

 

[alexGS]

As someone once said to me, "it's a motor vehicle, not a chainsaw". Revving the engine when stationary is usually unnecessary I think it's normal for there to be some hesitation... I think yours is fuel-injected?

-Alex

 

[Drinu]

yes its an injection engine. I will check all that you have told me. Otherwise I'll just live with it. Strange thing is that it didnt do it this morning when cold.
Thanks for all your help guys

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[alexGS]

When cold, the coolant temperature sensor tells the ECU to inject more petrol. This may be offsetting the effect of an air leak into the system. Check the vacuum advance pipe/capsule as (CZ)enda said...

A technique that I've read about, but never used, is to spray some WD-40 or CRC (penetrating oil spray) around various parts of the intake system e.g. around the base of the injector unit, around the inlet manifold, with the engine idling. If the engine note changes, you have an air leak at that point.

However, an air leak would affect driveability to some degree (not just idle) so I wouldn't jump to any conclusions Just thought I'd suggest it as something to investigate.

Thanks,
-Alex

 

[M@nticore]

mine did it long ago, and it turned out that the dizzy cap was cracked between two contacts.