Misfiring Engine

[Vanden Perre]

I have noticed that after driving 30 to 40 km only the engine of my S3 start misfiring above 3500 to 4000 RPM. Each time I take the spark plugs out I notice they are black. I remove the black deposit with a steel brush and the engine is running perfectely for another 30 to 40 km. Then again I have to scrub the spark plugs. Can anyone tell me what to do?

[type26owner]

Spark plug brand and part number?
-Keith

[pereirac]

Sounds like the mixture could be too rich or the timing's off so you are getting incomplete combustion which is then carbonising your plugs so that the car is misfiring??

[gjz30075]

Coil could be going bad. If its not working, plugs can't fire and they'll load up.

[Vanden Perre]

<!--QuoteBegin-type26owner+Oct 18 2004, 08:42 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (type26owner @ Oct 18 2004, 08:42 PM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> Spark plug brand and part number?
-Keith [/quote]
Bosch Super RO 185

[Vanden Perre]

<!--QuoteBegin-pereirac+Oct 19 2004, 07:42 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (pereirac @ Oct 19 2004, 07:42 AM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> Sounds like the mixture could be too rich or the timing's off so you are getting incomplete combustion which is then carbonising your plugs so that the car is misfiring?? [/quote]
Mixture (set up of carburetors) was the path I intend to follow. Timing (I did not think of it) but I will check it as well. Thanks for your answer.

[Vanden Perre]

<!--QuoteBegin-gjz30075+Oct 19 2004, 05:01 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (gjz30075 @ Oct 19 2004, 05:01 PM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> Coil could be going bad. If its not working, plugs can't fire and they'll load up. [/quote]
What do you mean by "oil could be going bad"? I change the oil very often (every 1500 approx). Please explain what you mean. Thanks for your answer.

[pereirac]

Are your plugs resistive ones? I have always used non resistive NGKBP7ES plugs.

[type26owner]

Sorry. I'm unable to cross reference those plugs with the known types which are the correct heat range for the twincam. If they're too cold though they would behave just as you've described. I would start there and not assume they are the correct ones. Common for the counterman to sell you the wrong type if you leave it up to them to choose.
-Keith

[types26/36]

I would agree with PERIERAC, sounds rich at higher rpm, could be the fuel pressure is to high causing flooding at higher revs..........needle & seats leaking? float level too high ? think I would fit a set of recomended plugs champion N7Y or NGKBP7ES check fuel pressure, change needle & seats and check float levels.
p.s. Dont forget to check the air filter eliment.
Brian.

[jopalm]

FWIW, I believe that was the "coil" (i.e ignition coil) not "oil" that was referenced above...

[cliveyboy]

What carbs are you using.
Clive

[Hamish Coutts]

A long shot but are you sure the thackray washers are not too compressed? Think the gap should be 40 thou.
The vibes from the engine may cause fuel foaming in the float chamber at high(ish) revs. Symptom of this is a missfire & loss of power.

Hamish.

[1964 S1]

We're all over the boards on this one....

So far:
1. type of spark plug
2. fuel mixture
3. timing
4. coil
5. countermen
6. fuel pressure
7. air filter
8. thackery washers
and I say, 9. battery.

Please, please, let us know the answer !

[types26/36]

1964 S1,
I'm not following you there, are you saying the battery has a fault (dead cell etc?) there is a bad connection or some other issue with the battery?
Brian