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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 17976
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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ONAN CCKA 2 cyl opposed 16 HP circa 1980. Engine purrs when

Resolved Question:

ONAN CCKA 2 cyl opposed 16 HP circa 1980.
Engine purrs when started cold.
After running a few minutes begins to miss fire in exhaust.
Longer it runs the harder it misfires.
Compression 75 llbs in each cyl.
Rebuilt fuel pump.
points and timing spot-on.
Any ideas how to fix appreciated
Submitted: 2 years ago.
Category: Small Engine
Expert:  Curtis B. replied 2 years ago.

curtis b :

Welcome to JUST ANSWER small engines, let me try to help you !!

curtis b :

Sounds like the valves are too tight and need adjusting.

curtis b :

The valve covers are on top of the block and held on with a single bolt in the center. The valve lash is .008 on intake and .013 in. on the exhaust.

curtis b :

As te engine warms, the clearance goes away, and the longer engine runs, the more they leak. After engine cools, it will just repeat.

curtis b :

?/

Customer:

under intake manifold?

curtis b :

??

Customer:

ia access to adjust clearance under intake manifold?

curtis b :

Yes, it is not easly accessable, one will have the vent line in it.

curtis b :

Item image
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curtis b :

The rectangular openings.

Customer:

would compression be a lot higher when engine is cold?

curtis b :

Item image
Full Size Image

curtis b :

It will help compression and power.

curtis b :

Give it a try and let me know how it works. Thank you.

Expert:  Curtis B. replied 2 years ago.
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Customer: replied 2 years ago.
Adjusted Valves... Intakes were OK - Exhausts were way too tight. Engine is not misfiring anymore but still running pretty rough - I suspect I goofed on points setting or carb needs dialed in. Any other thoughts ?
Expert:  Curtis B. replied 2 years ago.
Points set at.020 in., timing should be 20 degrees BTC. I would replace the plugs, reset the points and try adjusting the carburetor. Timing is adjusted by sliding the point box.
Customer: replied 2 years ago.
Curtis - you were spot-on in your diagnosis of engine trouble. That Onan has never sounded since I bought it a year ago. Thank You for your help. John.
Expert:  Curtis B. replied 2 years ago.
Good job!! Thank you!
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 17976
Experience: have worked on and around most engine models for 35 yrs./Polaris ATV expert
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