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I've seen something similar from heavily carboned valves on an engine (on a totally different bike) that was drinking oil from bad rings.

Given that they've put on another 1000 miles since the last report and things are now OK, it's not out of the question that the assembly error caused the valves to get heavily coated, and that it took a while for the buildup to wear off.

Some carbon deposits are relatively soft and crumbly, but some are smooth and very hard, to the point that it's hard to distinguish the deposits from the valve until you clean the valves thoroughly.
 

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Pouring water in the carb was something a friend and I did on my first car to de-carbon it. Looking at the crap coming out of the exhaust pipe indicated it was doing something. .
That valve recession thing happened to my '78 80/7 BMW. The old design liked the lead in the gas. It cushioned the valve seats. Around 1996 lead was removed from gas and different valve, valve seat materials was used.Unusual for that kind of problem now. It was cheaper to buy a salvage lower mileage bike and replace the engine than have the dealer rework the heads...go figure.
The problem of crud build up under the valve shims can be caused by not enough oil pressure to properly flush the shims. A BMW dealer told me about that. Seems with more powerful engines riders were not achieving high enough rpm's to get the oil pressure up. His few minute tuneup was to get the bike up to temp and then hold the throttle open to near redline and pump the crud out of the shim area.
Sounds weird but he was not a bull sh-tter.
Think about it, when was the last time you ran the bike near red line for a period of time? Might need to down shift to 2nd or 3rd or you'd be breaking the speed limit, even in Texas on the 85 mph highway they have there.
 

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Discussion Starter #23
I’m curious, did you just dunk the end of the vacuum hoses into a jar/bottle filled with water? I’ve though about trying something like that on a car motor, but was nervous about hydro-locking it.
Yes took a couple of minutes to empty the bottles. There are some restrictions (Jets LOL) in the Vacuum hoses to damp the vacuum signal so when you use them with a Carb Balance tool they don't jump around.
 

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Discussion Starter #24
Cam ware would result in looser valves.

Tight valves are from the valve recession into the head.
I hope not but can't think of any other cause.
I've seen Exhaust Valves recede into the heads, but never on a motor with hardened valve seats.
I've never seen Intake Valves recede.
And, when the valves are adjusted to spec the leak down test is fine and compression is 160# +/- 10# in both cylinders with a cool engine.
 

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Discussion Starter #25
Pouring water in the carb was something a friend and I did on my first car to de-carbon it. Looking at the crap coming out of the exhaust pipe indicated it was doing something. .
That valve recession thing happened to my '78 80/7 BMW. The old design liked the lead in the gas. It cushioned the valve seats. Around 1996 lead was removed from gas and different valve, valve seat materials was used.Unusual for that kind of problem now. It was cheaper to buy a salvage lower mileage bike and replace the engine than have the dealer rework the heads...go figure.
The problem of crud build up under the valve shims can be caused by not enough oil pressure to properly flush the shims. A BMW dealer told me about that. Seems with more powerful engines riders were not achieving high enough rpm's to get the oil pressure up. His few minute tuneup was to get the bike up to temp and then hold the throttle open to near redline and pump the crud out of the shim area.
Sounds weird but he was not a bull sh-tter.
Think about it, when was the last time you ran the bike near red line for a period of time? Might need to down shift to 2nd or 3rd or you'd be breaking the speed limit, even in Texas on the 85 mph highway they have there.
I have wrung the piss out of it in hopes of getting enough heat in the motor to break loose any remaining carbon.
Valve shims and the Buckets are clean as a whistle. The whole inside of the motor is quite clean.
 

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Discussion Starter #26
I appreciate the thoughts and suggestions. It is a 20-year-old bike, it is what it is.
When we go on a trip we will carry feeler gauges and valve shim kit.
We've got this down to an art now.
 

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I had the exact same experience last summer. I got stuck in Casey Wyonming (very long story) the short story is that your intake valves are likely cupped. This happened on my bike from a poorly seated air filter. Ever decreasing clearance on the intakes. Gets harder and harder to start and to keep running at idle but at speed it's fine. Check the valves and no clearance although 2,000 miles ago I set the intake clearances at max. You will need to rebuild your heads. The mechanic in Wyoming told me I would need to at least replace the valves, and should replace the pistons and just do everything while I am in there.
I found some used heads and am presently in the middle of swapping them out. That was a lot cheaper than rebuilding them. I am not bothering with the pistons, against the mechanics recommendation. If it ends up being a bad call, I'll deal with that when the time comes.
 

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I had the exact same experience last summer. I got stuck in Casey Wyonming (very long story) the short story is that your intake valves are likely cupped. This happened on my bike from a poorly seated air filter. Ever decreasing clearance on the intakes. Gets harder and harder to start and to keep running at idle but at speed it's fine. Check the valves and no clearance although 2,000 miles ago I set the intake clearances at max. You will need to rebuild your heads. The mechanic in Wyoming told me I would need to at least replace the valves, and should replace the pistons and just do everything while I am in there.
I found some used heads and am presently in the middle of swapping them out. That was a lot cheaper than rebuilding them. I am not bothering with the pistons, against the mechanics recommendation. If it ends up being a bad call, I'll deal with that when the time comes.
Now, this answer seems like a big fat BINGO!
 
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Now, this answer seems like a big fat BINGO!
It would explain it, but intake valve cupping aka "tuliping" is not common on an engine after breakin, its common on improperly rebuilt engines or badly over worked engines.
I have seen it in automotive engines used in marine environments for instance, way common in that instance.
What it is:
A tuliped valve has an increased total valve length and the top of the valve has the appearance of a "cup"

This is caused by excessive heat build up in the valve head, if the contact area of the valve is not dumping the heat into the valve seat properly it builds up to the point the metal deforms.
For this to happen in an engine that worked proplerly for years, it seems very strange.
 

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A poor fitting or just a poor air filter will screw with the inlet valves.

I'm trying to catch up with a guy I know for conformation, the story so far is his newish S10 has just had that problem,

Wrong filter from new, now waiting on Yamaha's compensation offer.
 

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If it passes on a leak down test after the valves are set to correct clearance but compression is down from stock numbers the valves are probably cupped or tulip-ed. Cupped valves will lower compression as there is more area in the combustion chamber than when they are not cupped.
 

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Would you be able to detect cupped valves without pulling the head? Maybe with a boroscope with a small mirror on it through the spark plug hole?
 

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I had it happen to one of the original xr500s. The one with the 23 inch front wheel. I got stuck in a one way out canyon and had the bike running while I was pushing it up a very steep section. Starved the upper end from oil and afterwards you could tell that the power was lacking. It was under warranty they pulled it apart several times without finding a problem. The 3rd time they tore it down Honda had them do a CC test where a measured amount of liquid was pored into the head. (Head off the motor upside down with the valves seated.) Because of the tuliped valves it took more than the specified amount to fill it up to some specified mark. What I am getting at is that unless you had 2 heads side by side one cupped and one not you probably could not see that the valves were tuliped. The mechanics had my head apart three times and did not find it until they used the measured CC test.
 
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