[dayzfordays]

I have recently purchased a K2 R600.
It was a very cheap find, and going into it I know there would be some problems to fix, but a few hours of work to get a half price bike is worth it for me.

The problems were found very quickly. I am unable to give the throttle more than 10 percent power. If I twist the throttle past 10% the bike will get louder and lose power (almost like it was bogging). I checked the fuel pump, air filter, spark plugs, and fuel injectors and all were in perfect condition. (Previous owners took very good care of this bike)
However, after removing the throttle body, I was able to get a look at the top of the valves and notices a thick coating of carbon buildup. Looking into the combustion chamber underneath the valves showed a similar story.

I have dropped out the engine and taken it inside to work on over the winter.
So far I have removed the cylinder head and I'm going to begin cleaning the tops of the pistons and valves.

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As you can see, there are filthy. This is my first engine rebuild, but I've heard from other forums that this is an unhealthy amount of carbon buildup.

As shown in the first image of the valves, there appears to be a gradient of build up. The left valves looks almost pristine, where the right valves is caked so thick that I couldn't scratch it off with a knife. My theory is that the person before me did not put the cylinder head gasket on correctly and negated to follow a star pattern when attaching the bolts causing the gasket to not be seated evenly.
My other theory is that I need to replace the piston rings. They are possible leaking oil from bellow the pistons.

My question to you (the fine human taking the time to read this online plea) is the following.
Is it more likely that the cylinder head gasket was leaking oil into the combustion chambers? Or is it more likely the pistons themselves were leaking oil from failed piston rings?
or do you believe that this is caused by something else entirely?

Any insight is appreciated, and thank you for your time.

 

[bentoverhard69]

How many kms are on the engine? Im no expert on engines but I couldn't imagine it building up that much carbon, could very well be oil. Especially when you apply throttle is when the most pressure would be exerted on the rings. Have you performed a compression test and or fuel flow test?

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[Mb1500]

Since you’re in there already I would go for a full rebuild. A leak down or compression test would have been nice to know but since you’ve already got it apart it doesn’t really matter.

 

[what?]

I've rebuilt a few engines.

Did you perform a compression test on each cylinder prior to break down?

Unless it's a like new engine, I'm not seeing all the carbon buildup in your pics.

Assuming the head is flipped over, and the left is #4, and the right #1, I do see some color differences though.

Engines with 10's of thousands of miles are going to have some carbon built up in them.

 

[BillV]

"I checked the fuel pump"
How? To expand on what bentoverhard said, do the fuel flow test as described in the service manual. Bogging is normally a clogged main fuel filter. People look at the strainer and think that there's no problem without realizing that the main/finer filter is elsewhere.

I don't understand how a poorly seated gasket would lead to heavy carbon buildup. I'd be expecting low compression and/or a coolant leak. Too bad you didn't measure the compression and checked to see if it changed when you put some oil in the chambers. Your buildup does seem to be concentrated in one cylinder. That sounds more like rings or an oil seal. Down2Ride750 has some pics of his head here and following. I think he cleaned it with wire brushes and glass beads.

 

[dayzfordays]

How many kms are on the engine? Im no expert on engines but I couldn't imagine it building up that much carbon, could very well be oil. Especially when you apply throttle is when the most pressure would be exerted on the rings. Have you performed a compression test and or fuel flow test?

The engine has 57K miles, so quite a few. It's just odd to me that the build up is mostly on the right cylinder and not evenly distributed throughout the engine.

"I checked the fuel pump"
How? To expand on what bentoverhard said, do the fuel flow test as described in the service manual. Bogging is normally a clogged main fuel filter. People look at the strainer and think that there's no problem without realizing that the main/finer filter is elsewhere.

You're correct, I only checked the main filter, but it was pristine and the tank itself had zero rust or debris in the fuel. It is possible the main filter is clogged, but I am doubtful.
Would a clogged main filter explain only bogging at high power output? The engine runs perfect until I lay on the throttle past 20% ish.

Did you perform a compression test on each cylinder prior to break down?

Sadly I did not, Looking back I should have done more tests before tearing apart the engine.
After taking off the throttle body and seeing all the build up on the valves and on the piston heads I just assumed the issue was further in the engine.

There is a lot more build up on the right cylinder (#4). In anyone's experience, can thick carbon build up on valves lead to bad compression? Can it prevent the valve from sealing?

 

[dayzfordays]

Since you’re in there already I would go for a full rebuild. A leak down or compression test would have been nice to know but since you’ve already got it apart it doesn’t really matter.

I'm going to rebuild the engine as far as I'm able. The piston walls themselves have no build up, just on the piston tops and valves. Should I open up the crank case and replace piston rings or would cleaning the piston tops and valves be enough?

I will send some more pictures as well to help anyone willing to get a better idea of what I have.

 

[dayzfordays]

This is the valve bottom of cylinder 4:

And the top of valve 4:

Lots of build up, even on the outside of the valve. My theory is that the valve is not making a proper seal and fuel is leaking back to the intake.

Other valves, namely valve 1 does not have this. This is the same valve that is clean on the bottom.

Cylinder walls.

So so far. From what I've gathered from this thread and your generous support:

I should have done more tests before I took apart the engine - Noted
No build up on the cylinder walls so piston rings should be good not taking apart the crank case.
Fuel filter could still be the problem

Do these photos give any further insight?
Please and thanks!

 

[BillV]

"Would a clogged main filter explain only bogging at high power output? The engine runs perfect until I lay on the throttle past 20% ish."
That's exactly what happens with a clogged filter. High fuel demand associated with elevated RPM and throttle leads to bogging. The flow test will tell all. Dirty gas will do it. You won't like the price of a new filter.

When I first started reading your thread I was thinking in terms of it running very rich. But the concentration in certain cylinders suggests otherwise. A clogged injector would make things go lean.

 

[dayzfordays]

The flow test will tell all. Dirty gas will do it. You won't like the price of a new filter.

How do I go about testing the fuel flow? is there a device I hook it up too or do I just run the pump into a measuring glass and time the flow rate.

I cant just buy an after market pump right? I have to buy the fuel pump assembly...
I also own a 03 SV650. The pump looks identical. Could I pump that pump into my bike a test it? are they compatible pumps?

 

[what?]

Is that spark plug screwed in all the way? If it is, I think it's the wrong plug length?

Since you're already in there, I think you said over 50K miles on it? Yes, I'd at least get a fresh set of rings.
I'm still not convinced you needed to tear in to this motor in the first place.
But such is life.
While you're in there, make what you can spec'd like new for sure.

 

[Mb1500]

This is the valve bottom of cylinder 4:

View attachment 574267

And the top of valve 4:

View attachment 574268 View attachment 574269

Lots of build up, even on the outside of the valve. My theory is that the valve is not making a proper seal and fuel is leaking back to the intake.

Other valves, namely valve 1 does not have this. This is the same valve that is clean on the bottom.
View attachment 574270 View attachment 574271


Cylinder walls.
View attachment 574272
View attachment 574273


So so far. From what I've gathered from this thread and your generous support:

I should have done more tests before I took apart the engine - Noted
No build up on the cylinder walls so piston rings should be good not taking apart the crank case.
Fuel filter could still be the problem

Do these photos give any further insight?
Please and thanks!

if it was me, without having prior test data compression or leak down yes I would be tearing it all the way down. At the minimum checking everything crank bearings ring end gap etc.

I don’t pull engines for nothing and the worst thing I could think of would be having to pull the same engine twice in a short time frame.

 

[BillV]

"How do I go about testing the fuel flow? is there a device I hook it up too or do I just run the pump into a measuring glass and time the flow rate."
You just run it into a measuring cup, graduated cylinder, etc. for 30 seconds or so. It's spelled out in the service manual.

People buy those $60 pump motors on ebay thinking that they will solve things. It's rare that they make any difference as the OEM motors are fairly robust. I'm not a fan of it but people sometimes back flush the filter. Search here as all this has come up many times before.

+1 on the plug length. I couldn't tell that anything was in there.

 

[dayzfordays]

Is that spark plug screwed in all the way? If it is, I think it's the wrong plug length?

No, I have them just a couple turn in for storage during the disassembly. They are the correct sizes.

You just run it into a measuring cup, graduated cylinder, etc. for 30 seconds or so. It's spelled out in the service manual.

People buy those $60 pump motors on ebay thinking that they will solve things. It's rare that they make any difference as the OEM motors are fairly robust. I'm not a fan of it but people sometimes back flush the filter. Search here as all this has come up many times before.

Sounds good. I will test the pump and check for its flow.
If the flow is incorrect, then I will need to buy the Fuel Filter Assembly correct? Suzuki 15410-42F00 - FILTER ASSY, FUEL | Partzilla.com
That's an expensive piece of plastic... any after market solution?

 

[sradmad600]

No, I have them just a couple turn in for storage during the disassembly. They are the correct sizes.



Sounds good. I will test the pump and check for its flow.
If the flow is incorrect, then I will need to buy the Fuel Filter Assembly correct? Suzuki 15410-42F00 - FILTER ASSY, FUEL | Partzilla.com
That's an expensive piece of plastic... any after market solution?

BillV did warn you 😂

 

[BillV]

"after market solution?"
People sometimes drill a hole through the element and add an external filter. There are some cheap auto store filters or Holley makes a higher quality part with a replaceable element. I've always thought that someone could make a part that would replace the OEM filter and accept the Holley element. It would be cheap at $100. But it hasn't happened.

 

[bentoverhard69]

At this point you gotta wonder if it's worth the rebuild or just to get a new engine. If you had done compression tests you could have some difinitive information on its current health.

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[peter079]

Any oil in the airbox? Where the crankcase vent hose comes in to the airbox, there is usually a piece of foam there. Was there a lot of oil on this foam?