4 stroke motorcycle engine smoking details

Every single cylinder motorcycle 4 stroke engine can easily be diagnose if it is healthy or not by identifying the color of the smoke emitted at the end of its muffler. Some say replace this and replace this part, but in the end, the smoke is still there. It must be identified first before getting into conclusion for the repair.

1. Colourless or slightly blue smoke from exhaust

This means that your bike is very good condition. What you can assume is your fuel/air mixture is at the right composition and everything is well burnt in your combustion chamber.

2. Yellow or brownish smoke from exhaust

Your fuel/air mixture is too lean. Too lean means that there is low fuel but high air mixture in your combustion chamber.

Solution: Adjust the fuel/air mixture at your carburetor (or ECU) accordingly.

3. Black smoke from exhaust

Your fuel/air mixture is too rich. High fuel but low air intake. This will reduce your fuel efficiency since the black smoke is your unburnt fuel.

The problem might be at this part:

i. Your air filter is dirty or blocked from receiving air from surrounding.

ii.Your choke is closed

iii. Your carburetor is damaged

Solution:

i.Clean/replace air filter

ii.Open choke

iii.Repair/replace your carburetor.

4. White smoke from exhaust

This happen when your engine oil gets into the combustion chamber.

The problem might be at this part:

i. Piston ring is loose

ii. Piston is worn out

iii. Engine block is worn out/scratched

iv. Valve is worn out/damaged

v. Valve line is worn out/scratched

Solution:

i. Replace piston ring

ii. Rebore block and replace piston

iii. same with no. ii

iv. Replace valve

v. Rebore valve line and replace valve.

Sometimes white smoke can also occur in the morning or you start your bike after it is being left on the rain. The white smoke is the water vapour released from the condensation that happens inside your exhaust. Normally, this happens only for few minutes and then it will be back to colourless again. The difference from white water vapour smoke and white exhaust smoke is the smell. What I can say is, the smell from engine oil being burnt is your combustion chamber is bad. Water vapour doesn't have any smell.