ok, it's official, my car hates me or it is possessed.

a week ago the problem started with an engine hard to start (3-5 seconds cranking) in the morning while before it used to start almost instantly.

day by day the problem got worse with longer starting times and this morning when the engine finally started, it raced to about 4000 rpm by itself for about 5 seconds then died. I tried again, same scenario.

then I tried to help a little from throttle to keep the engine running, just to get a suffocated acceleration and backfiring in carburetor.

things that I checked so far:

- air and fuel passages and jets are clean

- choke ok, moves freely, opens progressively as it should

- accelerator pump ok, good diaphragm, gaskets, valves

- power valve looks ok, good diaphragm, O-ring, gasket and spring (can't test it live, no method)

- needle valve ok, sealing good

- floater ok, airtight and moving freely

- fuel pump ok

- no sticky throttle valve, pedal or cable

- changed electronic ignition with a new one

- changed distributor with a new one

- new spark plug wires

- good spark plugs with correct gap

- checked coil in 2 ways: static with an ohmmeter (values ok) and I got out the distributor, put key contact on, rotated distributor axle by hand and observed a good spark from high tension lead to car ground

WHAT AM I MISSING ? my hair (what's left of it) is grayer by the hour.

have pity.

small update

it's obvious that engine racing has to do with more fuel added by the carburetor (or richer mixture).

I only see 3 possible culprits:

- the choke

- the fuel level

- the power valve

for now, my money is on power valve.

Edited 29 April, 201214 yr by masster

Fuel alone won't make an engine race (on a petrol engine), it will need air to do that...

Sounds like an air leak/stuck throttle butterfly.

My guess would be an air leak from the rubber mounting for the carburettor....it's quite common for them to split and cause your symptoms.

@djaychela

very good point! more fuel AND more air will race the engine.

I am in the process of testing the power valve, often overlooked, but capable of adding unwanted extra fuel and air in case of any faulty component.

the rubber flange base is brand new. I also checked the carburetor body and manifold for any deformation before mounting it.

now I know what I want for my birthday: a SMOKE MACHINE. hopefully there's a model out there that won't cost me an arm and a leg.

meanwhile I'll use a small propane torch.

Just because something is new, doesn't mean it isn't faulty. I've had a few issues with new parts before (including a new wheel bearing that was faulty!), so make doubly sure. Try spraying WD40 onto areas that may be leaking, if so then the engine should slow down a bit as it doesn't burn as well (IIRC).

When checking for air leaks don't forget the brake servo.

I will, thanks.

for now I have a vacuum gauge mounted instead at that port.

short update:

I found some defects as follows:

- power valve: the valve itself got stuck into open position, thus enriching the mixture at idle

- air leak around my new aftermarket VIKA warped carburetor base gasket ( djaychela)

- vacuum timing mobile plate from my new aftermarket VIKA distributor got stuck

all defects were sorted, yet there is not much improvement. the engine is not racing so high, starts easier but still stalls at idle.

important symptom: if I try revving from throttle, the engine is struggling to accelerate, but sounds like it's missing 2 cylinders, agonizes and tends to stop.

so my next possible culprit is the ignition coil. I tested the resistance of primary and secondary coils, they are ok, but that's not proof of normal functioning in full load.

what do you think about my suspicion ?

my ignition coil is the cylindrical shape type. is it equivalent with other ignition coils from older skoda or vw ? I don't have neighbors with skoda felicia to borrow one for a test...

when my coolant sensor gave up it caused mine to stall almost immediately after starting it. Also when my theromstat broke this caused the revs at idle to go up and down between 1100-1300.

Take a look at the spark plugs. I've seen many a fault of poor running that people have put down to being fuel related that has been ignition trouble.

@nu99et18

my car has no sensors, no ECU and on carburetor. Felicia 1.3 LX it says in my car description.

@djaychela

I will change them with some known to be good.

so may I assume that at this stage, and after all I have done so far, my car is fuel&air related issues free?

update:

my spark plugs have no sign of cracks, erosion etc (they are 3 months old, some 600 miles), but they are definitely showing a rich mixture condition, or maybe bad ignition.

so I made a photo of spark plugs and a video to show you how the sparks look like.

Edited 4 May, 201214 yr by masster

the las puzzle piece came in place.

I found the problem in a place where nobody would think of []

I checked very methodically the idle circuit: air corrector, channels in carb cover, channels in main body, cut-off valve, mixture screw. all clean as a whistle and functioning properly.

while I was looking in disbelief (wtf?) my eyes came on the cover gasket and bingo! there was the problem!

when the gasket was cut, one hole was not cleared all the way [:-B] yes, the one that should allow passing fuel from cover to main body (see photo).

I pushed that small piece of cardboard with a match, put carburetor back on and now I have an engine that can idle, ready for final mixture and speed adjustments.

bottom line: for an engine to high revv you need 3 things: more fuel, more air, and more ignition advance. I had it all three wrong as follows:

FUEL - bad part-load enrichment valve stuck open and seeping fuel below stage I throttle plate. that went hand in hand with very poor MPG.

AIR - bad rubber flange for carburetor base allowing more air in and loosing vacuum

IGNITION - stuck vacuum advance rotating plate inside distributor on high advance position

I am glad all is sorted now. thanks for all your help