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K340 - one cylinder runs rich and other lean

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keith103

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Nov 12, 2013
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122
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Aurora, Denver,CO
Hello all,

My Kawasaki 340 ( on a MiniMax ) runs off a Mikuni carb.
I noticed the rear cylinder is running consistently richer than the front.
This is shown by the front spark plug running very clean, and the rear plug fouled up and oily.

I also verified this by moving the CHT probe between the two cylinders and the front cyl reads about 70 degrees more than the rear at full throttle.
But the front cyl is still running CHT within limits ( 340 to 350 at full open throttle. ) Just that the rear cyl reads low - 260 to 270 at full throttle.

I also verified the CHT reading with an infra red thermometer. So the CHT gauge appears to read accurate.

Since CHT is within limits, my only issue is I cannot get correct tuning for the engine.
Presently, the front plug is running too clean / white, which means front is slightly too lean. The rear plug is just right - coffee / tan color.

All thoughts and suggestions appreciated.

Thanks
 

proppastie

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NJ
Air leak? How is rear tan and oily and fouled at same time?
 

keith103

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Nov 12, 2013
Messages
122
Location
Aurora, Denver,CO
The engine is new from J Bird. It has only about 15 hours, mostly break in, taxiing practice and a couple hops on the runway, Not flown on the pattern. The carb boot is not damaged or torn.
 

keith103

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Nov 12, 2013
Messages
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Location
Aurora, Denver,CO
I have given a couple Youtube links - one showing the full plane, and the other the engine before installation. I dont have a close up picture right now of the engine on the plane.



Engine installation.jpg
 

keith103

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Nov 12, 2013
Messages
122
Location
Aurora, Denver,CO
I had the same exact engine on a mini max. You have to ensure the carb is seated in the boot correctly and then cock it to the front or the back to even out the mixture.

Good to know that. I had checked and made sure that the carb is perfectly vertical. I will now try tilting it either way and see how that works out.
Thanks
 

Billrsv4

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Sep 29, 2016
Messages
139
Location
NW Oregon
Hello all,

My Kawasaki 340 ( on a MiniMax ) runs off a Mikuni carb.
I noticed the rear cylinder is running consistently richer than the front.
This is shown by the front spark plug running very clean, and the rear plug fouled up and oily.

I also verified this by moving the CHT probe between the two cylinders and the front cyl reads about 70 degrees more than the rear at full throttle.
But the front cyl is still running CHT within limits ( 340 to 350 at full open throttle. ) Just that the rear cyl reads low - 260 to 270 at full throttle.

I also verified the CHT reading with an infra red thermometer. So the CHT gauge appears to read accurate.

Since CHT is within limits, my only issue is I cannot get correct tuning for the engine.
Presently, the front plug is running too clean / white, which means front is slightly too lean. The rear plug is just right - coffee / tan color.

All thoughts and suggestions appreciated.

Thanks
Keith,
You need to do a compression or leak down test on both cylinders. For the cylinders to be that far apart indicates possible damage internally. Assuming you are using the fan cooled version it is typical for one cylinder to run a small amount hotter. IIRC that is a piston port engine, and super simple. 90 degrees difference shows something is not healthy in the rear cylinder.
Bill
 

sigrana

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Joined
Oct 19, 2010
Messages
63
Location
Australia
Hello all,

My Kawasaki 340 ( on a MiniMax ) runs off a Mikuni carb.
I noticed the rear cylinder is running consistently richer than the front.
This is shown by the front spark plug running very clean, and the rear plug fouled up and oily.

I also verified this by moving the CHT probe between the two cylinders and the front cyl reads about 70 degrees more than the rear at full throttle.
But the front cyl is still running CHT within limits ( 340 to 350 at full open throttle. ) Just that the rear cyl reads low - 260 to 270 at full throttle.

I also verified the CHT reading with an infra red thermometer. So the CHT gauge appears to read accurate.

Since CHT is within limits, my only issue is I cannot get correct tuning for the engine.
Presently, the front plug is running too clean / white, which means front is slightly too lean. The rear plug is just right - coffee / tan color.

All thoughts and suggestions appreciated.

Thanks
I owned two of these engines. If the engine you have has only one carburator, it is likely that the carburator is leaking on its attachment to the splitter. One of mine did. An other possibility is a leaking spark plug, which will make one cylinder run very rich. If the engine does not have a cooling fan and duct but is only ram air cooled by the propeller's flow, you will have a constant problem. That is why I never use ram air cooled in-line engines.
 

Dana

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Apr 3, 2007
Messages
9,441
Location
CT, USA
Check for a leak at the intake manifold to cylinder gasket, and do a crankcase pressure test to look for a leak at the rear crankshaft seal.
 

poormansairforce

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Just an Ohioan
Good to know that. I had checked and made sure that the carb is perfectly vertical. I will now try tilting it either way and see how that works out.
Thanks
Not so much vertical but cocked side to side i.e. front to back. Since it's a new air-cooled engine and your front cylinder is running warmer than the rear cylinder then it's pretty obvious you have a mixture problem. If you actually have seals that are bad then that needs to be addressed by Jbird. You need to try to get a little bit more fuel into the front cylinder and since the fuel can't turn as quickly as the air you probably need to cock the carburetor so it's pointing towards the front cylinder slightly more.
 

keith103

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Nov 12, 2013
Messages
122
Location
Aurora, Denver,CO
Not so much vertical but cocked side to side i.e. front to back. Since it's a new air-cooled engine and your front cylinder is running warmer than the rear cylinder then it's pretty obvious you have a mixture problem. If you actually have seals that are bad then that needs to be addressed by Jbird. You need to try to get a little bit more fuel into the front cylinder and since the fuel can't turn as quickly as the air you probably need to cock the carburetor so it's pointing towards the front cylinder slightly more.
Got it. I will try it out and post an update if it gets resolved.
Thanks
 

keith103

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Nov 12, 2013
Messages
122
Location
Aurora, Denver,CO
Thanks for all the suggestions. I love this forum. There is a wealth of knowledge out here, and a genuine willingness to share that knowledge. This is always my first stop when I have questions.

I will try out the various suggestions and see what works, and give a feedback.
 

keith103

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Joined
Nov 12, 2013
Messages
122
Location
Aurora, Denver,CO
Just wanted to give an update.

Turns out the carb was pointing slightly towards the rear cylinder.
Actually it was probably just a couple degrees to the rear ( as seen from the top ). Not too obvious unless one looks carefully.

Adjusted the carb boot so the main body of the carb was facing the inlet manifold square on, and the two cylinders started getting balanced amount of fuel flow, and both plugs are now showing identical mixture readings.

Thanks for all suggestions and ideas.
 

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poormansairforce

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Mar 28, 2017
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Just an Ohioan
Just wanted to give an update.

Turns out the carb was pointing slightly towards the rear cylinder.
Actually it was probably just a couple degrees to the rear ( as seen from the top ). Not too obvious unless one looks carefully.

Adjusted the carb boot so the main body of the carb was facing the inlet manifold square on, and the two cylinders started getting balanced amount of fuel flow, and both plugs are now showing identical mixture readings.

Thanks for all suggestions and ideas.
Glad you figured it out.
 

MadRocketScientist

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May 16, 2009
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Location
Canterbury, New Zealand, Earth, Milky Way Galaxy.
Just wanted to give an update.

Turns out the carb was pointing slightly towards the rear cylinder.
Actually it was probably just a couple degrees to the rear ( as seen from the top ). Not too obvious unless one looks carefully.

Adjusted the carb boot so the main body of the carb was facing the inlet manifold square on, and the two cylinders started getting balanced amount of fuel flow, and both plugs are now showing identical mixture readings.

Thanks for all suggestions and ideas.
Thanks for posting the solution! Small bits of information like this can make diagnosing problems easier for others. Sometimes the thing to look out for isn't always obvious.
 
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