Johnson J90TLCIM

[Jademountain]

Engine will not idle below 2800 rpms, Found gasket leak between intake and block, after checking all other options, compression on motor is 125, 120, 125, 120.
carbs rebuilt, most of electronics replaced and checked, new hoses and fuel pump, etc.

 

[interalian]

Does the advance arm move back or is it stuck?

 

[jakedaawg]

Check spark with plugs removed using open air gap spark tester.

 

[Jademountain]

Checked all linkage and all was fine, same with the spark tester. Did find a leak in manifold gasket

 

[interalian]

Maybe clarify what you mean by "will not idle below 2800 rpms"? Do you mean it idles at 2800 even with the throttle lever all the way back? If so, check the throttle plates are closing and nothing is hanging up. Maybe post a pic of the throttle area of the motor?

 

[Jademountain]

engine when started runs at 2800 - 3000 rpms, The linkage is working properly, carbs are working properly, going to replace gasket between intake and crankcase as we found an air leak there. also discovered clogged check valves and silicone residue from filler block put in by previous owner.

 

[interalian]

I can't see how an air leak between the intake and crank case could cause a high idle - if anything, that would relieve crank case pressure and make the motor run slower.

Idle is set with base timing and closed throttles. Have a good look at the timer base and make sure it's moving. Check out the link and sync into in the sticky.

**EDIT** - if the flywheel key is sheared, your timing will be affected. Have to pull the flywheel to inspect the key and keyways.

 

[sutor623]

When did this issue start? Did you buy it like this? You need to put a timing gun on it and see where the idle timing is set. Like IA said, the idle is controlled by the timing on these engines.

IA, I have had 2 stroke motors with intake and crankcase leaks idle higher, but be very hard to start.