Carbon deposits and oil burning

[gropula]

Hi, it's me. The guy with the weirdest issues ever. It's a long story, but has been resolved. Enjoy.

 

I bought the bike for cheap with 57k km, four and a half years ago. I changed the plugs at 72k km. Noticed the plug on no.2 cylinder was white. Assumed it's running lean on that cylinder. Had the injectors ultrasonically cleaned, changed the vacuum hoses and thought it would fix it. It didn't. Continued riding and thinking what else could be wrong. I bought a set of Chinese injectors for testing. No change. Swapped the OEM injectors back. Swapped the injector subharness and the whole electrical harness chasing one other issue. No change to the plugs. Did the valve clearance check and adjustment and starter valve sync. Compression was fine, slightly lower in cylinder 2 but only around 5%, not enough to sound an alarm in my head. 

 

I added the Rapid bike racing and wideband lambda sensor for tuning purposes as I upgraded the bike in many ways. Through testing and logging confirmed that he cylinder no2 is not lean. In fact it's pretty much spot on. Fast forward to this spring, I turned the bike on in the garage, let it warm up a bit while I put on the rest of my gear. Garage is not very well lit and I noticed the cylinder no2 header glowing. The picture is overly dramatic as the phone can pick up more infrared light and show it as red compared to our eyes. Still, it was visibly glowing, just not as much as the pics show. I confirmed my observations with an IR thermometer. The cyl no2 header was 100-150C hotter than the cylinder no.4 at all times, even during warmup it heated up much quicker. 

 

 

Took the sparkplugs out again. Much worse than before. This was around 90k km. Went on the hunt again. Swapping coil position, swapping plug position, swapping injector position, put Chinese injectors in again, confirmed the AFR was good by adjusting fueling and moving the wideband sensor from bung to bung, confirmed that the injector pulses were right and as reported by rapidbike software using an oscilloscope. Tested the OEM injector flow rate by making a DIY flow measuring device. Confirmed the flow is identical across all injectors by weighing the amount of fuel sprayed by activating all injectors simultaneously trough a makeshift harness. Couldn't get to the bottom of it. I gave up again, packed it all up and continued riding trough the spring and summer season. 

 

 

I noticed if I hammer on the bike on the highway the oil level drops. I assumed it's evaporation from extreme heat and high oil temp. Also, it's an old engine, closing in on 100k km so I thought a small amount of oil consumption at extreme loads isn't weird. Continued hammering on it. After one very hard ride thought the twisties I used the highway to get back home quicker. Blasted it to top speed and continued hammering at 180-200km/h for 40km. The Fi light turned on, I stopped it blinked the code for crank position sensor. The bike started cutting out briefly at random moments. I disconnected the rapid bike system, the Fi light went away and the bike didn't cut out anymore. Could at least ride safely. The idle dropped however. Felt like it was running on 3 to 3.5 cylinders. Got home, took the sparkplugs out. The no2 sparkplug has melted away.

 

I lowered a boroscope into the cylinders. Piston no2 had tons of carbon deposits. The valve recesses were rounded off by thick deposits, hardly distinguishable. The circular protrusion that was visible on other pistons wasn't visible on piston no2.

 

 

For reference this is how other cylinders looked.

 

This is where I finally found the source of the issue. It all clicked. The slightly lower compression is a sign of cylinder and/or ring wear. It lets oil into the cylinder, mostly noticable at prolonged high loads. It accumulates deposits. They increase compression a lot, which leads to premature ignition and extreme temps. The headers glow, the sparkplug goes white and eventually melts. I bought PROTEC P4650 CX Carbon X combustion chamber cleaner and went to work. Took 10-15 cycles of cleaning but eventually it cleaned up. I helped break up the deposits by inserting a bottle cleaning brush in the cylinder and spinning it around. It really helped a lot. Here's a pic during cleaning process. In the end it was fully clean, just a shiny piston crown.

 

I checked the valves. The extreme heat wore the valve seat on the exhaust side. I adjusted the normal exhaust valve on cylinder no2. Fortunately the compression stayed the same, the valve itself didn't burn. Other valves were fine after 25k km. With the cleaning done, oil changed and new sparkplugs in it fired right up. No Fi light, no cutting, idle restored, headers didn't glow and IR thermometer confirmed the temps are similar between all cylinders. Took it for a test ride, everything was fine. Connected back the Rapid bike system once I confirmed everything works. Wow, Rapid bike really makes a huge difference. Took it for a second test ride. Made sure to blast it on the highway. Took the sparkplugs out after 70km of mixed riding and a 30km highway blast. Sparkplug was brown-ish like it should be. Lowered the boroscope in the cylinder no2. Deposits already started forming. The circle on the piston crown wasn't visible. The deposits form on the center first.

 

It is what it is. The engine runs great again. I'll use the fuel additive every now and then to help clean the deposits. I think the additive will work well on fresh deposits. Old, dry and crusty deposits need harsh chemical cleaning and mechanical agitation. Fresh, wet deposits might clean up with only the fuel additive. If needed I'll buy another set of Protec K1+K2 combustion chamber cleaner and clean it again in a year or two. Engine rebuild is prohibitively expensive, it's better to buy a used engine. If I find one for a good price I'll buy it. For now this engine will do the job. 

[Morados]

What a journey to find out that the carbon deposits forming inside was the problem, but it makes sense when the engine eats oil, but VFR are well known to not eat up much or any oil at all as far as I know, good job finding the cause!

[fabio222]

On 12/24/2025 at 1:10 PM, gropula said:

Hi, it's me. The guy with the weirdest issues ever. It's a long story, but has been resolved. Enjoy.

 

I bought the bike for cheap with 57k km, four and a half years ago. I changed the plugs at 72k km. Noticed the plug on no.2 cylinder was white. Assumed it's running lean on that cylinder. Had the injectors ultrasonically cleaned, changed the vacuum hoses and thought it would fix it. It didn't. Continued riding and thinking what else could be wrong. I bought a set of Chinese injectors for testing. No change. Swapped the OEM injectors back. Swapped the injector subharness and the whole electrical harness chasing one other issue. No change to the plugs. Did the valve clearance check and adjustment and starter valve sync. Compression was fine, slightly lower in cylinder 2 but only around 5%, not enough to sound an alarm in my head. 

 

I added the Rapid bike racing and wideband lambda sensor for tuning purposes as I upgraded the bike in many ways. Through testing and logging confirmed that he cylinder no2 is not lean. In fact it's pretty much spot on. Fast forward to this spring, I turned the bike on in the garage, let it warm up a bit while I put on the rest of my gear. Garage is not very well lit and I noticed the cylinder no2 header glowing. The picture is overly dramatic as the phone can pick up more infrared light and show it as red compared to our eyes. Still, it was visibly glowing, just not as much as the pics show. I confirmed my observations with an IR thermometer. The cyl no2 header was 100-150C hotter than the cylinder no.4 at all times, even during warmup it heated up much quicker. 

 

 

Took the sparkplugs out again. Much worse than before. This was around 90k km. Went on the hunt again. Swapping coil position, swapping plug position, swapping injector position, put Chinese injectors in again, confirmed the AFR was good by adjusting fueling and moving the wideband sensor from bung to bung, confirmed that the injector pulses were right and as reported by rapidbike software using an oscilloscope. Tested the OEM injector flow rate by making a DIY flow measuring device. Confirmed the flow is identical across all injectors by weighing the amount of fuel sprayed by activating all injectors simultaneously trough a makeshift harness. Couldn't get to the bottom of it. I gave up again, packed it all up and continued riding trough the spring and summer season. 

 

 

I noticed if I hammer on the bike on the highway the oil level drops. I assumed it's evaporation from extreme heat and high oil temp. Also, it's an old engine, closing in on 100k km so I thought a small amount of oil consumption at extreme loads isn't weird. Continued hammering on it. After one very hard ride thought the twisties I used the highway to get back home quicker. Blasted it to top speed and continued hammering at 180-200km/h for 40km. The Fi light turned on, I stopped it blinked the code for crank position sensor. The bike started cutting out briefly at random moments. I disconnected the rapid bike system, the Fi light went away and the bike didn't cut out anymore. Could at least ride safely. The idle dropped however. Felt like it was running on 3 to 3.5 cylinders. Got home, took the sparkplugs out. The no2 sparkplug has melted away.

 

I lowered a boroscope into the cylinders. Piston no2 had tons of carbon deposits. The valve recesses were rounded off by thick deposits, hardly distinguishable. The circular protrusion that was visible on other pistons wasn't visible on piston no2.

 

 

For reference this is how other cylinders looked.

 

This is where I finally found the source of the issue. It all clicked. The slightly lower compression is a sign of cylinder and/or ring wear. It lets oil into the cylinder, mostly noticable at prolonged high loads. It accumulates deposits. They increase compression a lot, which leads to premature ignition and extreme temps. The headers glow, the sparkplug goes white and eventually melts. I bought PROTEC P4650 CX Carbon X combustion chamber cleaner and went to work. Took 10-15 cycles of cleaning but eventually it cleaned up. I helped break up the deposits by inserting a bottle cleaning brush in the cylinder and spinning it around. It really helped a lot. Here's a pic during cleaning process. In the end it was fully clean, just a shiny piston crown.

 

I checked the valves. The extreme heat wore the valve seat on the exhaust side. I adjusted the normal exhaust valve on cylinder no2. Fortunately the compression stayed the same, the valve itself didn't burn. Other valves were fine after 25k km. With the cleaning done, oil changed and new sparkplugs in it fired right up. No Fi light, no cutting, idle restored, headers didn't glow and IR thermometer confirmed the temps are similar between all cylinders. Took it for a test ride, everything was fine. Connected back the Rapid bike system once I confirmed everything works. Wow, Rapid bike really makes a huge difference. Took it for a second test ride. Made sure to blast it on the highway. Took the sparkplugs out after 70km of mixed riding and a 30km highway blast. Sparkplug was brown-ish like it should be. Lowered the boroscope in the cylinder no2. Deposits already started forming. The circle on the piston crown wasn't visible. The deposits form on the center first.

 

It is what it is. The engine runs great again. I'll use the fuel additive every now and then to help clean the deposits. I think the additive will work well on fresh deposits. Old, dry and crusty deposits need harsh chemical cleaning and mechanical agitation. Fresh, wet deposits might clean up with only the fuel additive. If needed I'll buy another set of Protec K1+K2 combustion chamber cleaner and clean it again in a year or two. Engine rebuild is prohibitively expensive, it's better to buy a used engine. If I find one for a good price I'll buy it. For now this engine will do the job. 

That's excellent work on diagnosing it, well done! 

[Lucca]

Nice bottles Goran...did the job😉. I did not know that EGT was in such difference in your bike. That is bad for valves...but, it's Honda. Very good troubleshooting.