Engine idle issue

Joined
May 15, 2020
Messages
9
I bought this engine that had been sitting for a few years. A 1979 johnson 235. I estimate it was sitting for 3 to maybe 5 years. I went through the carbs, replaced the water pump and lower unit oil. Engine wasn't stuck or hard to turn. I got it running but it has a really hard time idling. Only way to get it to idle right is to basically turn the idle screw (timing advance i guess) almost all the way in. I knew this didn't seem right so I double checked all the idle jets and idle air passways. Everything is clear. The guy who owned it before me had put brand new carbs on the engine. Took the boat out and it runs great at high rpm. It bogs at probably 25% throttle for a little bit. I have a feeling its because the throttle plates are opening the throttle valves early. But I can't get the engine to idle with out turning that screw in a bunch. Do you guys thing I have a stuck ring? Engine runs great otherwise the idle problem. Likes to shut off in reverse and forward, unless the screw is all the way in. Been doing the decarb procedure and haven't noticed a big difference.
 
Joined
May 15, 2020
Messages
9
went to go and do compression test today, wasn't able to get it started to warm up. Even with starting fluid. Tried to start but couldn't. My cold reading are 100,90,80 and the other side was 40,90,50. Gonna take the head off that one side at least.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,885
No surprise to me at all.----I do not have enuff fingers and toes to count how many times I have seen this kind of damage.----Every one of these crossflow engines will suffer this fate.-----You bought it like that.-----That is why he put new carburetors on it in desperation !!----Simple trouble shooting seems to be a lost art !
 
Joined
May 15, 2020
Messages
9

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,885
In 1980 the 235 HP went to a 3.625 cylinder bore and different heads.-------So the 78 models were 149 cubic inch and at 235 Crankshaft HP were fairly stressed.-------Few bought them as fishing motors.-------Most have gone ---" boom " ----already.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,933
Your is a 149 ci hump motor, seen a to of flatback 200's under 235 cowls. Now if you where my customer, I would try to steer you away from repairs as to costly to repair and motor is only 175 at prop. better off saving parts money and part it out on Strictly OMC on facebook...Then find you a 60° 150 or 175........................JMO
 
Joined
May 15, 2020
Messages
9
I got a killer deal on ebay and bought a used low hours power head from a 1985 235. Engine is identical besides the exhaust cover, same bubble back style just a spot for something to mount on it. I only got the block so I installed the flywheel, ignition system and carburetors to the newer engine. The motor runs great just the idle is way to high, even at the lowest setting. I suspect the difference in idle rpm is a carburetor issue. I know the carbs are different between the years but I thought it would work. I know the old block was a 3.5 diameter piston while the newer one is a bigger piston with less compression or something. Did I make a big mistake? Seems like I need smaller idle jets. Thanks for any input
 
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