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140 Johnson won't rev

S

ship wreck

Contributing Member
Can not get full engine speed under load.

This is a new problem this season. Motor will not rung up to full speed. Three trips out so far and the top speed varied, one trip I could get 4200 for part of the day, another trip could only get 3000 all day. Boat was loaded the same, people, coolers, etc..

I have 120PSI of compression, Spark test good. All four cylinders are getting fuel when tested by pulling a spark plug wire idling on the muffs.

i have replaced all the fuel line checked the pick up in the tank. Gone through the carbs, adjusted the floats, and synchronized the carbs. Checked base timing and verified the mechanical advance, not the actual timing, at full throttle. Motor idles great, stumbles when coming up on the throttle and does not come up to full speed.

Last year it started and idled horribly but ran at full speed with no issues. A compression check found a bad cylinder and the subsequent investigation found a broken ring a full overhaul was done. Could this a powerhead issue? Could I have gotten the pistons in the wrong side? I have not look at that but I'm really out of ideas. It is not leaving a trail of fuel in the water, at idle at least. No way to see that at speed of course. I"m really at a loss.
 
pulled the plugs and scoped the pistons. All have the ramp facing the outside which is correct. Outside is the intakes side and inside, towards the V, is the exhaust or am I mistaken?
 
So that I sure I understand it sounds like I put the Pistons in backwards? That really sucks but at least it answers why it's running the way it's running
 
Pull a cylinder head off and post a picture.----Actually I think the piston would hit the head if it was in backwards.
 
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20170528_153934.jpg

This is how it is installed
 
They is backwards..... :( strange as the late 70's heads are tighter than the 90's models and usually the engine wont rotate with pistons reversed as they hit dome in head.
Make sure the oil hole on rod is correct too when replacing...
 
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so it appears that not only are the pistons backwards but the heads are probably flipped as well. I labeled them before I took them off but I guess I could have labeled them backwards.

So I feel like a real dope but lesson learned.

I'll be pulling it and taking it apart this week. Once I get it out I'll post some pics so the smart folks here can help me make sure the heads are oriented right. I've never had to pull pistons with new rings before but any reason why I should not reuse the rings. I'd rather not spend the $150 on new rings if I don't have to and at that they are not in stock here.
 
Looking at it again I can't have the heads flipped as that is not possible. So I guess they do not interfere? New Pistons were identical to the old except .020 bigger. I did not look at pin height but I'm pretty sure it was the same. Can't compare now as the old Pistons were recycled.
 
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