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Discussion Starter #1
Hi to all,

I am currently facing an issue with my FMX. While it does not smoke not at all (at least not visibly) when it warms up (very hot) it starts to smokes (mainly from the right exhaust). This however does not happen every time that the motor warms up, so the occurrence is irregular. I noticed that a ride with very high rpm provokes the smoking while it occurs for several days and after stops again for a while. It smokes when idling, while when open the throttle it does not increase the amount of smoke.

The only modifications of the FMX is the removal of the anti-smog system and bigger headpipes (Off-Road, Germany). The motor has 43.000 km on the clock.

Any ideas what the problem could be?

Thanks in advance for your time.
 

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Before looking any further, is your oil at the correct level. As too much oil in an engine will find a way out.

I know my NX650 is a nightmare to get a true reading on the dipstick and I always measure the amount i’m putting in after a service.
 

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Discussion Starter #3
Hi ian6760,

yes indeed I am facing the same issue regarding the oil level. I am never sure if it is enough oil inside or if it is overfilled. The truth is that I am trying to have oil in the upper level of the dipstick so I am frequently adding some oil (but not more than 100 ml each time). Yesterday I opened the air-filter box and the oil-cyclone and I noticed some traces-drops of oil (but not a significant amount that justifies the smoke that comes from the exhausts out). Maybe I should not add so frequently oil because due to false readings of oil level I could add more oil that is needed. In compination with high rpm (hence higher pressures) the oil comes out (where?) towards the combustion chamber.

For example today I had a trip of more than 45 km (in traffic) but rode very conservative (low rpm) and no smoke came out.

I'll keep you inform.

Best regards from Athens
 

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If you are serial oil topper, I would drop the oil and filter. Then fill it up again with the right amount of oil measured before you put it in and see what happens. Then I’d look at the results after a few hundred miles before I’d worry about it.
 

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If you are serial oil topper, I would drop the oil and filter. Then fill it up again with the right amount of oil measured before you put it in and see what happens. Then I’d look at the results after a few hundred miles before I’d worry about it.
...but don't turn the engine over to squeeze out the last few remaining drops...i did this and I believe it was that that ruined the oil pump...unltimately led to a new cam, follwers and oil pump :(
 

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...but don't turn the engine over to squeeze out the last few remaining drops...i did this and I believe it was that that ruined the oil pump...unltimately led to a new cam, follwers and oil pump :(


I did almost the same with my previous Honda AX-1 ! But fortunately I killed the machine very quick after realizing what I was doing and finally avoided any damage...
 

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Discussion Starter #7
Hi there again,

the bike still smokes when hot but only after when run with high rpm (not sure how much...). Oil level seems to be OK (in the middle of the stick). When run with low rpm doesn't smoke even if it is hot. I have been advised from Honda mechanic to change piston, piston-rings, seal valves and re-bore the cam, but since the cost is very high I am trying to figure out what could be the cause and fix probably something that is cheaper.
My hypothesis is that since the bike doesn't smoke permanent, there could not be worn piston rings or cam. So, by increasing rpm there is an increase of oil pressure and oil leaks somewhere (found second time some oil in the air-filter box). Is there any point around the head that I could take a look first before going to re-build the cam? Any idea?

Thanks in advance for your time,

Giorgos
 

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The next simple step is to check out the oil breather system, I’m not sure what it’s like on the fmx but on the nx it has an oil trap on the breather. It then has a breather into the airbox, if you’ve had excess oil in the engine this would be an easy escape for it and may account for the oil in the airbox. well worth a check. I’d also be inclined to disconnect the breather from the airbox to see I find it makes any difference to the smoking . In all honesty though, this I see clutching at straws but well worth checking.
 

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If your happy your crankcase breather isn't blocked do a compression test on the cylinder if the compression is low add a little oil into the cylinder repeat the compression test if the compression goes up you need new rings as a minimum. When you strip the engine you will find out how much more you will need
 

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Discussion Starter #10
Hi there,

the crankcase breather puffs nicely. I feel that when the trap is open (disconnected with the air-filter box) the machine runs slightly better (breaths better). Smoking stopped (again). This bike will drive me crazy.

Can I let the crankcase breather (from the trap an on) disconnected with the air-filter box, or will have any impact (long-term) on the motor?
 
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