mambraNC30 wrote:so now two cylinders are messing around (left rear and one in the front). it spits splatters, backfires and doesnt want to idle.
wtf? how can a cylinder be F***n around now that hasnt had any problems before???
dont think i need a compression test. cause the is no oil on the spark plugs. and if i was loosing compression would i be loosing power too???
Maybe, maybe not.
You can't just rule something without testing it. It would help if you understand the process of how the engine works.
1. Petrol flows from the tank into the carbs, the NC30 has a vaccumn operated tap, controlled by a small hose from the tap to one of the cylinders, that only allows fuel to flow into the carbs when the engine is being cranked / running.
2. Petrol and is sucked into the engine from the carbs by a vaccumn created as the piston moves in the cylinder. This might sound simple but you have several variable that need to be set properly.
*Adequate air-flow
*Good cylinder compression to create adequate vaccumn (suck)
*Valves to open / close correct amount and at appropriate times
*Carbs to have appropriate jets, needles, floatheight and jets / passageways to be clean and clear.
3. The petrol air mix is ignited at the right time by the spark plug.
*This is determined by the CDI and ignition timing is automatic, it requires the cams/crank to be set in the right position. Usually an engine wont run at all if the cams are installed propely, it will often bend valves as the piston will hit them.
4. The burnt gasses are expelled from the cylinder.
*This requires the exhaust valves to open / close the right amount at the right time.
As you can see, you need fuel / air / compression / ignition for an engine to run, if you want it to run well you'll see there are quite a few variables that need to be within a small tolerance.
There are usual fail points on the bike though.
-Vaccumn pipe split / leaking.. will cause fuel starvation issues.
-Spark plugs dead... 8mm plugs die easy, usually due to flooding.
-Blocked carbs.. most common running issue, dirty / varnish builds up and blocks jets off causing bad running.
-Split carb rubbers.. the carbs are attached to the engine via rubbers, these go brittle with heat and age and can start leaking air, this also causes crap running.
-Bad float valves / fuel height... sticking floats can cause flooding, overflowing carbs, fuel starvation and incorrect float height can cause a boggy throttle. Expensive to replace with new parts and seldom wear out, most likely dirty causing obstuction or very high mileage.
-Pilot Screws out of adjustment... will cause bad idle.
-Worn cylinder bores... will create uneven vaccumn, bike wont' run right
-Leaking exhaust.. will often present itself as back-fires on the over-run.. bike may be down on power too.
Maintainance items
Valve Cleranaces, Carb Balancing
Valve clearances should be checked every 8000km., (before balancing the carbs!!) if the valves are too loose or too tight they might not be fully opening / closing and cause bad running.
Carb balancing will affect idle, it will be lumpy and not smooth if the carbs are not balanced, they should be checked every
Petrol Tank [Flows]-> Carbs [Sucked into]-> Engine [Pushed]-> Exhaust
