My 1993 suzuki rf 400 has had new plugs and leads,its starts fine from cold but after i drive it gets a misfire and smells of fuel and wont start as easy while hot. its also important for u to know ive had a head gasket done recently.

As long as it runs fine on warm days,
I wil advice u to replace the cold start switch,,...

check plug for good spark, if bad replace plug check ht lead and cap. if all good when plug out look at piston if can for hot spots. unlikely but while plugs out might as well look. could be inlet valve,your need a compression test to see if you have a bent valve not closing properly. could try the old way of putting finger over spark plug hole and turn engine. should be enough pressure to blow past your finger. obviously do this on cold engine. as you can see its a bit of a tick list. let me know how you get on, if that dont sort it we move on to the carb.

could be a number of possible faults.1/crank sensor not working when hot,trace this and pour cold water on it(dont do this if it is not by crank pulley as water isnt good for modules etc) and retry.2/sparkplugs worn,but usually they would fault more on cold start.3/fuel pump cuts out when run,try wacking tank from underneath and retry.though I would concentrate on nil spark caused by a faulty ignition module or crank sensor.
Next time it fails to start.pull off a sparkplug lead,make a quick test plug with an old(but working)sparkplug.pull the side wire away from the center electrode 5mm and insert into plug lead.earth ground the plug on its thread against metal on the engine.crank and check for spark visually,don't be tempted to hold the plug while cranking.if nil spark we will have to test further which is faulty sensor.if it sparks ok we will need to test for fuel.
testing for fuel is easy.
when it fails,unclip air filter housing,while engine is being cranked,spray an aerosol based carburettor cleaner into air duct to engine,it should start and run while spraying and stop when you stop spraying if fuel delivery is the fault.fuel pump will then need testing/replacing.
be careful not to spray onto ignition or any areas of spark

The cold pipes means the bike is not firing on those cylinders. Replace all the plugs and start it. Or you will need some elecrical diagnosis. Chaz Moto DC

I don't know if I can solve it but it sounds to me like you're not getting enough fuel. has it been sitting awhile or just start doing this randomly? If it's been sitting there's a pretty good chance you'll need to clean you carburetor. when gas sits in the bowl of your carburetor for too long it will get thick and smell almost like varnish. My Suzuki 250 4x4 had a similar misfire and cleaning the carb fixed mine.

If it is hydrogen sulphide it could be coming from an overcharging battery, but in view of the misfire it sounds more like an over-rich fuel mixture could be fouling up your catalytic converter. Best course of action is to get a proper diagnosis at your garage or if you are technically minded you can buy a cheap interface cable and download free VAG diagnostic software and then do it yourself.
Hope this helps! D.

Hi,
The early 300 SL suffered from dodgy HT leads and spark plugs if not regularly maintained, the problem with Mercedes Benz though is that the cars have so many features that it is almost impossible to diagnose without seeing the car. Some things to try (in this order) are : - Spark plugs, Ht leads, remove and clean Distributer Cap, replacement of HFM sensor (common fault), if none of these help then faults have been known in throttle valves and fuel pumps/filters

Happy fault finding