Questions? Looking for parts? Parts for sale? or just for a chat,

The WD Motorcycle forum

WD Motorcycle forum
Start a New Topic 
Author
Comment
Too Rich a Mixture?

Am I running too rich if there is a carbon build up round the inlet of the cylinder head?

I run the bike with a bakelite type gasket between the head and the carb flange to prevent boiling the fuel. Is this causing it?

Kind regards

Pat

email (option): sacombsashtrees@hotmail.com

Re: Too Rich a Mixture?

Hi Pat, The Tufnol spacer won't have any effect on the mixture. If the mixture is too rich you first need to establish that the carb is the correct one for the bike and has the correct slide cutaway, jets, needle etc. fitted. If that is the case then check that the float and choke slide, if fitted, are functioning correctly and not causing the richness of the mixture. Then work your way through the carb settings. Bear in mind that the carb works in stages (with a slight overlap between those stages) and each adjustment and/or specification of the various parts affects operation in that stage. For example..The pilot air screw controls mixture strength from zero to 1/8 throttle approx.
If the carb is incorrectly set up, to cure richness you will either have to adjust the pilot air screw, alter the needle position, fit a larger throttle cut away or reduce the main jet size.
If you have just built the bike and are basing your observations on running up the bike in the workshop what you are seeing isn't really a carbon build up, rather a soot deposit. Could you describe in more detail the effect and the circumstances?....Ian

email (option): Ian@wright52.plus.com

Re: Too Rich a Mixture?

Hi Ian

A possibility is that I do not use the bike for long enough runs and don't get it hot enough. However, it does look like carbon as opposed to soot. There is a small soot deposit on the exhaust outlet, but the inlet appears to me to be carbon.

Valve stems and guides all look good.

The spark plug always looks ok, i.e. biscuit brown.

Kind regards

Pat

ps It is the correct carb (I think).

email (option): sacombsashtrees@hotmail.com

Re: Too Rich a Mixture?

Hi Patrick..If the bike is running rich at lower to mid throttle openings it is not unusual to get 'blowback' of fuel vapour from the carb..An M20 without an air filter will often show this from the deposits on the front face of the oiltank...This excess of fuel can lead to carbon build up but I wouldn't expect that to occur very quickly. How many miles have you covered since the engine was last rebuilt?..Ian

email (option): Ian@wright52.plus.com

Re: Too Rich a Mixture?

A 1,000 miles maximum from last rebuild.

It does wet sump. Would burning some oil cause this?

email (option): sacombsashtrees@hotmail.com

Re: Too Rich a Mixture?

Pat is your valve timing correct? Sounds like inlet valve is late shutting. Just a thought.

Nieuwe pagina 1