Leak Down and Possible Valve Help

[ecd2004]

cbr 600f2
I got some help from Rick last year trying to sync the carbs on my bike but the number 4 cylinder won't sync. We went through it and cleaned it twice and it was cleaned prior to that at strictly dirt in canton, ct. It passed a compression check so Rick said that the next step was a leak down test, he said that he'd help me but I wouldn't be able to get back down there so I'm not going to even ask. Is there anyone in the area who could do do a leak down test and tell me what's going on? whether a valve or something else? (I'm not familiar with engine internals)

The bike will be in New Hartford, CT until christmas time-ish and then it is probably going up to boston.

Or would it be easier to just get a shop to do it?

[aldend123]

The compression numbers on all cylinders were good? I'm not sure you need to go with a leak-down if the numbers are good. A melted, sticky, or dirty valve would hold open and leave you with low compression numbers on the problemed cylinder.

Do you have the compression numbers written down? (if not, good habit to write them down each time you sample them and keep them for record)

[ecd2004]

no, i dont have them written down, they were done at a shop and I didnt have the foresight to ask for them.

How can I tell if they're sticky and whats the best way to clean them?

[Ryno]

It would be worth checking your valve clearances. Like was stated above, if you have a tight valve etc. then the compression numbers would be low, but it's worth having as much info as you can. You sure you don't have a vacuum leak or anything on that cylinder?

[stoinkythepig]

I am voting with vacuum leak. I don't think a leak down will tell you much about idle issues. That said, does it actually have idle issues? What running symptom are you attempting to fix?

[aldend123]

no, i dont have them written down, they were done at a shop and I didnt have the foresight to ask for them.

How can I tell if they're sticky and whats the best way to clean them?

Well now you know learn something every day.

Not easy to clean valves without engine disassembly beyond running cleaning products such as Seafoam, or Techron etc. Products like this are available at auto parts stores, and their effectiveness in treating your problem is definitely debatable.

As others have requested, more info please.

I'm guessing a crack in the boot that connects the carb to the head?

[ecd2004]

Couple notes, I've run seafoam, lots of it, and the compression check was done while the valve clearances were being done. There are currently no running issues except rick said a slight misfire but I cant hear it. The problem is just that the sync adjustment screw on that carb does not have a wide enough range to bring it into adjustment (if i remember correctly, it may have not made any difference at all). The cylinder is running lean.

How would I check for a vacuum leak? is that something to do with the engine? could that be something like a header gasket or something? The carb boots were inspected and did not have any residues, cracks, nothing

[Degsy]

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It's a carb issue with carb 4. Vacuum leak, torn diaphragm, blocked channel, float height etc etc.

[stoinkythepig]

The throttle plate in carb 4 might be loose or bent.

You can check for a vacuum leak with a propane torch. Turn it on high, but don't light it. Aim at at different areas where a vacuum leak might be present while the bike is running. When the propane replaces the air in the leak, the engine sound will change as the mixture goes from lean to rich.

[ecd2004]

are you guys saying that it cant be a dropped or improperly seated valve because it passed compression? or that it is more than likely that it is a carb/vacuum leak? I've been through the carbs 3 times with people who definitely know what they are doing and I would just think that we would have noticed anything that was broken/bent/cracked...

[aldend123]

are you guys saying that it cant be a dropped or improperly seated valve because it passed compression?

In short, yes. But we are operating under the assumption that your compression numbers are "good". But without seeing the actual values, we are believing whoever said they were good is right. If you had 150-150-150-125, and 125 is your problemed cylinder then that isn't "good", that is a sign. Be less concerned with reaching a number, and be more interested in differences between cylinders in the reading.

You can also spray starter fluid in the same manner described using propane. Just another option.