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The valves could have experienced enough carbon build-up on their exposed stems in their respective port that they stuck slightly open, causing them to get burned (Sticking Valves) I have seen this happen in other engines, primarily small displacement engines.
 

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A single cylinder engine with valves that don't close completely, won't start and idle. Lack of compressing the Air/Fuel Mixture. A valve that is opened .001 inch, from being fully seated, will keep a single cylinder engine from starting.

All Stock Production Engines, has a built in design that rotates the valves, each time that they are actuated. This ensures that the valve face and the valve seat are kept clean from soft carbon build up.

Look on youtube for a BMW overhead cam engine, that is rotating up to 10,000+ rpms. You can see the valves rotating.
 

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I have torn down a number of singles, namely Honda horizontal 50-110 cc engines with sticking valves, as well as MANY power equipment singles (Lawnmower, Generator, etc...) they will start and run, however their is difficulty starting them and they have somewhat of power loss, essentially the same symptoms as tight needing adjusted valves.
 

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If the problem was caused by carbon on the valve seats or stems.....holding the valve open. How could the clearances be in spec? They should have been loose.
 

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Discussion Starter #86
update.....Burnt again at 19000 miles! Just 3000 miles later. This time it was the intake valves. Tech says he inspected fuel pressure, spark plug and spark, all good. Compression Low with large leak down (he says a result of the burnt valves) and valve adjustment was correct. He is stumped. I am furious. Thankfully I bought an extended service plan that covers this but I want a reliable bike!

The bike ran and then just wouldn't start one day. This time the only issue I had with it was what seemed like a sticky choke (yes I know it is fuel injected and there is no choke) When I started it it would increase in RPM as high as 5000 rpm then jump higher every second and bounce back down. It would only stop if I gave it a little rev then it would go back to normal. Tech didn't seem to know what would cause that.
 

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Discussion Starter #89
I sent that to my TECH. Bingo! Not only does he not have the proper tools.....the HONDA DEALER on this island (Maui) doesn't even have it! The tech is having to order them from the mainland....I'll be lucky to have my bike back in three weeks....but at least this time the valves will be New (again) and properly adjusted.
 

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I'm not sure if that really explains your issue though. Failing to measure down into the shim can only make the valve clearance turn out slightly loose. Which shouldn't cause them to burn being loose.
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I just made my own custom feeler gauges by trimming some normal off the shelf feelers with tin snips to make them narrow on the end. And bending them to reach in.
 

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Discussion Starter #91
Hmmm. Bubble burst Will loose valves result in a loss of power? I did notice the last time I rode it (my husband rides it mostly now) that the power was significantly reduced. I thought it may have been my imagination since I don't ride it much anymore. But after it being my only vehicle for the first two years it really seemed gutless on that last ride. At this point I am really hating living on Maui because there is no competition and the complacency is very high....people just don't give a ******************** and charge $$$. This mechanic is the most honest one I have found and tries really hard but one person can't know everything about every bike that may be imported onto this island.
 

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That idle problem sounds quite like the IACV (sometimes called the "throttle body valve) issue mine had. May want to suggest checking it's operation to your mechanic? It's an inexpensive part, when I replaced mine it set me back about $30, oem part from eBay

Sent from my SCH-I545 using Tapatalk
 

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Discussion Starter #96
After fixing the burnt valve issues I had tech do a service. Upon taking out the air filter tech thinks he knows what may have caused the burnt valves. Air filter was covered in oil. He said the only way this could happen was if the bike spent a lot of time on its side....like it did after an accident that happened not long before this happened. He said the oil would fool the O2 sensor into thinking the bike was running rich (when it wasn't) and cause it to adjust it to run leaner when not needed. I'm hoping this was the cause and I can get back to enjoying my bike again without future issues. Thank you all who have replied to this thread.
 

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After fixing the burnt valve issues I had tech do a service. Upon taking out the air filter tech thinks he knows what may have caused the burnt valves. Air filter was covered in oil. He said the only way this could happen was if the bike spent a lot of time on its side....like it did after an accident that happened not long before this happened. He said the oil would fool the O2 sensor into thinking the bike was running rich (when it wasn't) and cause it to adjust it to run leaner when not needed. I'm hoping this was the cause and I can get back to enjoying my bike again without future issues. Thank you all who have replied to this thread.
Sounds iffy. It seems our bikes have a tendency to coat the filter with oil (lightly) through time, due to the PCV and airbox design. If anything, this would restrict airflow and the bike should adjust.
 

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Discussion Starter #98
"Sounds iffy. It seems our bikes have a tendency to coat the filter with oil (lightly) through time, due to the PCV and airbox design. If anything, this would restrict airflow and cause a lean condition."

Interesting that the forum shows you said something different than I received in email. Running too lean will cause burnt valves though. So far it has been the only explanation. There literally is no other possible reason this has happened.
 

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That may very well be the case, as running lean indeed burns valves. But it's not going to come from an oiled up filter. All that will do is reduce airflow, ENRICHING the mixture, not leaning it out. Just saying.

Burned valves can also come from too tight of valve clearances. 600 miles for the first valve adjustment on these bikes; if this service was not conducted, regardless to whether your clearances were correct at the time of measurement after valve failure, could be a more likely culprit.

If I had burned valves in my properly maintained motorcycle after 15k and the only explanation the tech could give me was it was caused by an oiled up filter, I'd laugh in his face. My gut, you may have just gotten unlucky and landed a CeeBee with defective valves.
 

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Discussion Starter #100
That may very well be the case, as running lean indeed burns valves. But it's not going to come from an oiled up filter. All that will do is reduce airflow, ENRICHING the mixture, not leaning it out. Just saying.

Burned valves can also come from too tight of valve clearances. 600 miles for the first valve adjustment on these bikes; if this service was not conducted, regardless to whether your clearances were correct at the time of measurement after valve failure, could be a more likely culprit.

If I had burned valves in my properly maintained motorcycle after 15k and the only explanation the tech could give me was it was caused by an oiled up filter, I'd laugh in his face. My gut, you may have just gotten unlucky and landed a CeeBee with defective valves.
Thats what I'm trying to determine. I had them replaced brand new after the exhaust side burnt from hubby lugging the engine...Toasted spark plug diagnosed that one. Then, 3000 miles later the intake side burnt. Tech says everything was in spec and was stumped as to the cause. He thought that The oil in the filter may cause the O2 sensor to think it is running rich causing the O2 sensor to adjust it to run leaner. He was grasping for whatever might have caused it but really had no solid answer that he could say this is definitely it. I really want to know if I should sell it now with the rebuild before it happens again..... He says Honda's are what he would buy over any other bike hands down based on a mechanics perspective (although he really hated working on my cbr because of all of the clips to get fairings off). He says they are virtually indestructible (accept mine apparently) so he is really thrown off by this.
 
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