2004 F200 Rich burning Cylinder #1

[Canskan1]

Have a 2004 Yamaha F200 that is burning rich only in #1 cylinder. All other 5 cylinders are burning very, very clean. Swapped (after cleaning) injector 1 with injector #2 and swapped a clean spark plug into #1 cylinder. Again, cylinder #1 is burning rich and rest of cylinders are again very, very clean, compression in cyl #1 is 143lbs. ..... any Ideas for me to look for? Saw similar Yamaha F200 posts on this phenomena occuring in cylinder #1 on other forums without any definite conclusion found. Thanks in advance.

[greasyshaft]

The crankcase blowby gases enter the intake silencer just above #1 runner. I see the symptoms you describe all the time, I don't believe it is a problem.

When testing compression on a four stroke you should have throttle wide open.

[99yam40]

leakdown test tells a better story than a compression test.
And do it on all cylinders

[greasyshaft]

leakdown test tells a better story than a compression test.
And do it on all cylinders

And it also hurts more when a 20" breaker bar comes around and nails you in the face

[rodbolt17]

do the test correctly and you wont find out why its called a breaker bar.

[greasyshaft]

believe it or not I learned

[boscoe99]

Try it with an airplane motor with a five inch bore piston and a four foot long propeller blade. One wack and next time you will make sure that someone is holding onto the propeller blade when the test is being done.

[zenoahphobic]

But it is also a good way to loosen flywheels and harmonic balancers!

[Canskan1]

The crankcase blowby gases enter the intake silencer just above #1 runner. I see the symptoms you describe all the time, I don't believe it is a problem.

When testing compression on a four stroke you should have throttle wide open.

Thanks greasy...... so far that seems to be the most plausible reason since others are seeing the same thing with that same cyl #1. CS

[rodbolt17]

if you have excessive blow by then you also get excessive fuel contamination of the oil which makes it run even richer.

that's why a leakdown test can find if the rings can seal or not, a compression test cannot find it.

its also why you never leave the breaker bar on the nut nor stand with your head inside a prop arc radius.

its simply painful sometimes.

[greasyshaft]

if you have excessive blow by then you also get excessive fuel contamination of the oil which makes it run even richer.

that's why a leakdown test can find if the rings can seal or not, a compression test cannot find it.

its also why you never leave the breaker bar on the nut nor stand with your head inside a prop arc radius.

its simply painful sometimes.

... See even rodbolt nails himself in the head on a regular basis

[rodbolt17]

the usual red dot is from beating my head against the wall.
typically when trying to explain precision blend to another tech.

typically 4 strokes are not quite as sensitive to TDC when you apply air as a two stroke.
but yes many moons ago I was having problems with the flywheel moving on a 200 Yamaha.

I got another tech to hold the bar, he could not and it whacked me.

I made a flywheel holding tool.

[Canskan1]

Leak down tester arrived today.... thanks for the caution on getting thumped!!

[rodbolt17]

remove all plugs.
find TDC 1 compression stroke.
from there follow the timing marks and test in the fireing order.
next question. what is the firing order.
its 1 2 3 4 5 6.

[Canskan1]

Well did my first ever leakdown tests with the new tester and got some pretty good results..... at TDC cyl #1 only leaked 1 %. (90 lbs on left gauge and 89 lbs on right gauge). Tested the other 5 and 3 were at 2% and 2 also at 1%. So pretty happy about that for sure!! Love this test as it is pretty easy and can tell you a lot!! Also had a spark tester and getting good spark to cyl #1 too. So, must be the crankcase blow by hose dumping into #1 air intake causing the sooty lookin spark plug. Oil on dip stick is still the color of new yellow honey... thanks for your help guys.....and oh, didn't even get my bell rung!!