1977 Johnson 55hp stalls at idle and won't rev over 1200rpm

Chevyls6

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Hello everyone, I'm new to boating this year. I purchased an old trihull and an unknown condition Johnson 55hp 2 cylinder. So far I've replaced the coils, stator, plugs (ngk 2129), fuel pump, rebuilt carbs and changed jets to the size listed in the parts manual. I tried to take this boat out last week and couldn't get it to idle without misfiring and stalling. Also top speed was around 7mph at 1200rpm. The week before I had it running around 24mph. Not sure where to go from here. I have tried synching the carbs and the throttle linkage to the cam. Cylinders are at 110psi and 115psi compression. Base timing was set to 4* btdc. Not sure what full advance is as the manual says don't rev the engine with no load. Any help is appreciated.
 

racerone

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Compression should be 140 + on those.-----Time to remove cylinder head in my opinion.
 

Chevyls6

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So you think it's a head gasket failure ? Is that a common thing with these? If it is a worn out powerhead I may just junk it.
 

racerone

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I say the compression is low.------Perhaps a bad gauge ?------Up to you to do the trouble shooting and inspection as I can not see or touch your motor.
 

flyingscott

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Why did you re-jet the motor? 140 psi is on a brand new rebuild so yours may not be bad. Did all this happen after you worked on it?
 

Chevyls6

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The gauge is ok I think. It doesn't get used much and is well built.

I rejetted because when I did the carbs the Jets were no. 58 but the manual calls for 54D jets.

Also the carbs are the adjustable idle mixture type not what originally came on the engine. I simply swapped the Jets from the original carbs that came with it but we're not installed on the engine.

Before I did the work it didn't want to idle either but it had a lot more power. Maybe the Jets are too small. The first time I had it out I had to raise the idle speed and advance the base timing all the way to get it running strong enough to not stall when put in gear.
 

flyingscott

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Now, what you fail to realize is the jets go with the carb. Put the old ones back in do a link and sync and adjust the carbs.
 

Chevyls6

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Ok I can do that no problem. However even before it wasn't idling correctly. What about the Reed valves ? Do they ever go bad ? Even with the other jets installed it wasn't running right.
 

jimmbo

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Misadjusted Timing and Wrong Carbs, Gee I wonder why it isn't running well.

Any idea what the carbs you are using are off of?
Does it have a Spark that can jump a 3/8" gap?
Are both carbs getting Fuel, floats properly adjusted?

Broken/bent Reeds are not a common problem. A bad reed reveals itself by spraying fuel out of the carb throat

Do you have the correct(factory) service manual?
 

Chevyls6

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Misadjusted Timing and Wrong Carbs, Gee I wonder why it isn't running well.

Any idea what the carbs you are using are off of?
Does it have a Spark that can jump a 3/8" gap?
Are both carbs getting Fuel, floats properly adjusted?

Broken/bent Reeds are not a common problem. A bad reed reveals itself by spraying fuel out of the carb throat

Do you have the correct(factory) service manual?

Rudeness is not appreciated. I did my best to adjust the timing with the info I had. I used the 3* +/- 1* from Mr Joe Reeves. It wouldn't idle at all with the timing any more retarded than that.

I don't know what the carbs are from but they have fixed main jets, adjustable idle jets, and the same bore as the originals. Spark has not been tested over a 3/8 gap but I will. Both carbs have fuel and the floats were set according to the seloc manual. I've been using a multi-year / horsepower manual I bought online not the exact factory manual.
 

racerone

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Just for your info and for you to do more research.-----Timing at idle does NOT matter and looks after itself.-------Throttle opening relative to timing does matter.-----And MAXIMUM timing advance is the only timing you set.----Maximum timing is set at the factory and rarely if ever needs adjusting.
 

Chevyls6

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Just for your info and for you to do more research.-----Timing at idle does NOT matter and looks after itself.-------Throttle opening relative to timing does matter.-----And MAXIMUM timing advance is the only timing you set.----Maximum timing is set at the factory and rarely if ever needs adjusting.

Ok that's very different than the car engines I'm used to. What's the screw on the idle side of the timer base for then? Adjusting idle speed ?
 

flyingscott

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Put up a pic of what you have specifically the power head. Do you even know what the carbs you are using are from? I am pretty sure around 1980 that block changed displacement so they aren't the same. Joe reeves method does not set idle timing it only sets wide open throttle timing. The screw under the stator should be for wide open throttle timing not idle timing. Maybe it's time to find a mechanic willing to work on your motor.
 

jimmbo

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Rudeness is not appreciated. I did my best to adjust the timing with the info I had. I used the 3* +/- 1* from Mr Joe Reeves. It wouldn't idle at all with the timing any more retarded than that.

I don't know what the carbs are from but they have fixed main jets, adjustable idle jets, and the same bore as the originals. Spark has not been tested over a 3/8 gap but I will. Both carbs have fuel and the floats were set according to the seloc manual. I've been using a multi-year / horsepower manual I bought online not the exact factory manual.


The last couple of Months there has been a Tsunami of owners trying to adjust 'Idle TIming' and fiddling with the sync between spark and throttle in an Attempt to set the Idle speed. And it gets a little tiring/frustrating

Most 3rd Party Service Manuals are not even good reading material for the Outhouse, and the paper is too slippery to use as Wipes.
Since there are often changes from year to year on engines, a model specific service manual is really the only way to go as it will explain what every adjust screw/threaded rod is for.

If the carbs are the same size(venturi bore, as well as throttle bore, it doesn't mean the fuel flow calibration will be correct before or after a Jet swap. If the carbs came from a 50 HP or a 60 Hp, the calibration may have been different because of differences in Exhaust Tuning(again, what applies to 2 stroke engines is different than to car/truck engines), Off Idle fuel delivery could be different, etc etc etc.

It was mentioned above about a Displacement change, that happened in 76 when the 41 cubic in. 50 hp became a 44 cubis in. 55 hp. In 1980 the 55 hp was upgraded to 60 hp, same displacement(internal changes though)
 

Chevyls6

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Put up a pic of what you have specifically the power head. Do you even know what the carbs you are using are from? I am pretty sure around 1980 that block changed displacement so they aren't the same. Joe reeves method does not set idle timing it only sets wide open throttle timing. The screw under the stator should be for wide open throttle timing not idle timing. Maybe it's time to find a mechanic willing to work on your motor.

Let me see about getting some photos. I don't know what they came from, would the casting number help? It's got 2 screws under the stator. 1 for the minimum travel of that timer base linkage and one for maximum travel. I asked around about mechanics in the area and there is one who does omc outboards about 40 miles north.
 
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