After my Sprint has been running for 30 mins or so, it develops a bad misfire under hard accelaration noticably after I’ve been in traffic for a while.
When I take the Carb cover off there is always about a dessert spoonful of gunge thats come up through the breather. Is this normal or is something serious afoot?
The engine has been pressure tested by Chris Foulds and another experienced Lotus Technician and nothing seems amiss. I notice several people advocate blocking the hole and diverting the breather to a ‘colostomy bag’ which presumably gets emptied regulary.
If the “gunge” is a grey colour and you are running synthetic oil then it is formed by a reaction between the synthetic oil and water. The presence of water may be due to a very small water leak in the engine somewhere that a pressure test cannot detect or condensation of water in the oil from blowby gases. If the engine does not regularly get up to high temperatures for long enough periods the water can build up in the oil and produce this gunge, especially if the engine has a lot of blowby due to wear or poorly seated rings.
Unless you are sucking this gunge into the carbs then the misfire is more likely due to plug fouling while sitting in traffic. The orginal Lotus plug specifications are too cold for stop start city driving and you may need to use hotter plugs if you do a lot of that style driving. I have found NGK BP6ES are a good compromise for both city traffic use and hard high speed driving in my plus 2
I blocked the hole in the airbox and put a longer breather pipe to a catch bottle. It dramatically improved smooth running and eliminated a hesitancy under acceleration.
Jim