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Message started by JonBiddle on 09/11/14 at 08:09:54

Title: Severe carbon buildup on one valve?
Post by JonBiddle on 09/11/14 at 08:09:54

While cleaning my carb I took a peek into the intake port, and noticed some concerning buildup of what looks like carbon on the top of the right valve, although the left valve looks clean.

Clean (left) intake valve
http://i.imgur.com/ehtj3vR.jpg

Dirty (right) intake valve
http://i.imgur.com/wIAccVP.jpg

Does anyone know what this indicates? My best guess at the moment is the valve isn't closing all the way and has been building up carbon due to a bad seal with cylinder.

Thanks for any help or insight you guys can offer!

Additional context:

It's a 1995 LS650 that I bought this season as my first motorcycle. I don't think it was well maintained by the previous owners, and I've been working on getting it running right and having a lot of fun learning about motorcycle mechanics along the way! The power seems good, but there is a high-pitched noise with each stroke of the engine that as best as I can tell is maybe an air leak or perhaps a timing issue with the valves.

Title: Re: Severe carbon buildup on one valve?
Post by Dave on 09/11/14 at 08:27:08

Well, it could be one of several things. The valve seal might be leaking a bit of oil, the valve clearance might be adjusted a bit too tight, or it could have a valve or seat face that is not sealing well.

I would check the valve adjustment and confirm they are in spec....then just ride the darn thing and not worry about it. If the issue is a failing valve or seat it will give you plenty of notice that it is going...it will become hard to start and performance will decline due to the low compression.

You might use some Techron in the fuel to help clean the back of the valve. Buy a bottle and mix it with the fuel in the recommended dose, and just keep adding it until you use the bottle up.

For your whistle....make sure the intake is well sealed and there is no air leak. Also check for exhaust leaks.

Title: Re: Severe carbon buildup on one valve?
Post by JonBiddle on 09/11/14 at 08:32:15

Thanks Dave! I'm going to try doing a compression test on the engine this weekend as well as the things you suggested. We'll see how it goes :)

Title: Re: Severe carbon buildup on one valve?
Post by Serowbot on 09/11/14 at 08:39:19

Great photos... ;)...

Title: Re: Severe carbon buildup on one valve?
Post by verslagen1 on 09/11/14 at 08:54:47

5D666B7C6D617A7C676F627D0E0 wrote:

A too tight valve would cause the valve to overheat, which is very rare for an intake valve. The hot valve would cause the carbon build up.

Any true backfires?

Title: Re: Severe carbon buildup on one valve?
Post by JonBiddle on 09/11/14 at 09:33:57

The only backfires I've noticed is if I quickly roll off the throttle and occasionally when I kill the engine it backfires. Recently the bike has been harder to start (I've only put about 100 miles on it), which is why I was cleaning out the carb.

Title: Re: Severe carbon buildup on one valve?
Post by verslagen1 on 09/11/14 at 09:37:41

True backfire - out the carb
or afterfire - out the tailpipe?

Title: Re: Severe carbon buildup on one valve?
Post by JonBiddle on 09/11/14 at 09:58:27

Ahh okay. I think they have all come out of the tailpipe, although I can't be 100% sure because I don't have anything to compare it to sound-wise.

edit: I should note that the bike has only about 6,000 miles on it, which to me seems pretty low for a 1995.

Title: Re: Severe carbon buildup on one valve?
Post by Digger on 07/13/15 at 14:20:11

FWIW, I'm seein the same exact thing - starboard intake valve dirty, port one clean...

While I personally would not describe the bulldup on my starboard valve as "severe," the OP's pictures look very similar to my situation, with my buildup perhaps being a bit worse than his.

Bike had 13.9K miles on it when first observed. Burns no oil that I can tell, yet.

See my signature block for other specifics on the bike.

Title: Re: Severe carbon buildup on one valve?
Post by verslagen1 on 07/13/15 at 14:54:53

Digger, as Dave and I concur, it's most likely a valve adjusted too tight and not sealing. The valve has to sit on the seat long enough to cool. The carbon looks just like the carbon that accumulates on top of the piston.
If you could, get an eyeball on a stick and look at the top of the piston to rule out oil from below (worn rings) vs. from above (worn guide).
if it's not oil, then it's gas additives. ARCO used to be famous for the sulfur content and build up on sparky.

Title: Re: Severe carbon buildup on one valve?
Post by justin_o_guy2 on 07/13/15 at 15:23:22

I was rebuilding a Raptor 650, wasn't sure of the valves. Leveled the head upside down and put gas in it. Gas will go thru pretty quick. All four were leaking. I dunno how the head is designed up there, transmission fluid is pretty thin, need something that doesn't evaporate fast or risk blowing stuff up.
A garage might look like a great place to work on stuff, but if there's a gas water heater or clothes dryer or just some random spark, it can get ugly fast.

Title: Re: Severe carbon buildup on one valve?
Post by Digger on 07/23/15 at 10:46:27

7A697E7F606D6B69623D0C0 wrote:

Hi Ver,

Just an update on the intake valve clearances:

Both intake valves showed 0.003" of cleanrance, which is what I set them at almost 4000 miles ago. (FYI, the book says the range of allowable clearances for the intake valves is 0.003 - 0.005 in).

Took a quick peek at the top of the piston, as seen through the spark plug hole. Looked the same color as the spark plug insulator did - kind of a mid-level gray color. No black carbon-y stuff in sight.

Will take another peek at the top of the piston after the head cover is removed and I can get a better angle...

Title: Re: Severe carbon buildup on one valve?
Post by Digger on 07/23/15 at 10:49:39

6A757374696E5F6F5F67757932000 wrote:

Hi Jus,

I get your idea. One could drizzle some type of fluid on top of the closed intake valves and let it set there for a while (while the head in still on the engine and the engine is in the bike). Then, one could come back later and see if one of the valves looks like it's letting more fluid through than is its twin...

Any other ideas of what type of fluid to use? Tranny fluid doesn't sound like too bad of an idea so far...

Title: Re: Severe carbon buildup on one valve?
Post by justin_o_guy2 on 07/23/15 at 11:15:39

Well, I dunno,, seals inside, what they like,
I like the idea, but what to use?
Hunting a leak, want it thin.
Don't want evaporation to throw you off.
Measured amounts, each valve, difference equals leak,

Title: Re: Severe carbon buildup on one valve?
Post by Art Webb on 07/23/15 at 15:53:16

trans fluid is a bit thicker than gas of course, but not too thick for this i think, and it's a pretty decent solvent / lubricant, I'd say it's not a bad choice for what you have in mind

Title: Re: Severe carbon buildup on one valve?
Post by Dave on 07/23/15 at 19:25:33

There is also the possibility that the valve seal on that side is a bit leaky, and is allowing oil to run down the valve stem and onto the bottom of the valve.

Title: Re: Severe carbon buildup on one valve?
Post by justin_o_guy2 on 07/23/15 at 19:28:22

Correct, and the valve seat test will point the finger.

Title: Re: Severe carbon buildup on one valve?
Post by Dave on 07/24/15 at 04:08:51

233C3A3D20271626162E3C307B490 wrote:

Correct, and the valve seat test will point the finger.

We are not talking about the same "seal".

You are looking to check the seal of the valve seat and valve face with the liquid test. I am suggesting that maybe the valve stem oil seal is leaky on one of the valves.

I am not sure how you are going to do your liquid test....the valve is not level in the head, so I don't know how you are going to get the liquid to cover all of the valve from the carb spigot side. I would think that a "leak down" test using air would be far easier.....remove the spark plug and put air pressure in the cylinder through the spark plug hole, and see if any of the valves are leaking. If you hear air in the muffler the exhaust valves are not sealed, air in the intake and those valves are not sealing, air in the oil breather and the rings are leaking.

Title: Re: Severe carbon buildup on one valve?
Post by Gary_in_NJ on 07/24/15 at 09:08:24

6D565B4C5D514A4C575F524D3E0 wrote:
[quote author=233C3A3D20271626162E3C307B490 link=1410448194/15#16 date=1437704902]Correct, and the valve seat test will point the finger.

We are not talking about the same "seal".

You are looking to check the seal of the valve seat and valve face with the liquid test. I am suggesting that maybe the valve stem oil seal is leaky on one of the valves.

I am not sure how you are going to do your liquid test....the valve is not level in the head, so I don't know how you are going to get the liquid to cover all of the valve from the carb spigot side. I would think that a "leak down" test using air would be far easier.....remove the spark plug and put air pressure in the cylinder through the spark plug hole, and see if any of the valves are leaking. If you hear air in the muffler the exhaust valves are not sealed, air in the intake and those valves are not sealing, air in the oil breather and the rings are leaking. [/quote]

In order to conduct a proper leak down test:

1) ensure that the piston is at TDC. Put the bike in gear and have someone sit on the bike to ensure the engine stays at TDC during the test.

2) Don't just fill the cylinder with air. Use a leak-down tester (HF has 'em) that has two indicators, one for reference pressure and one for cylinder pressure. I usually use 70 pounds as the reference pressure.

3) A 10% differential is considered acceptable between the reference pressure and the cylinder pressure.

4) Conduct the test on a warm engine.

Title: Re: Severe carbon buildup on one valve?
Post by justin_o_guy2 on 07/24/15 at 17:10:01

Good Going Gary! Sounds like a Genuine mechanic talking. I admit, I'm good at just fixing stuff, but others sure can be better. I Like that answer.
Thanks for stepping in.