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Won’t achieve full throttle

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Cherokeekid079

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Hi, I’m looking for an answer to my problem that we’ve been working on for a couple of months. We have a speed boat with a Johnson 140 2 stroke on it. The problem is it won’t run in the water. We put the muffs on and it runs perfect but as soon as we take it to the ocean it won’t achieve full throttle. We’ve replaced all electrical components except the rectifier. Motor has good compression on all cylinders. Brand new coils plugs and wires. Rebuilt the throttle bodies And put a brand new fuel pump. Always use fresh gas and mix 50:1. We put a new water pump and thermostat’s. If anyone knows what I’m missing I could use some help!
 
When and how did the problem begin? Storage? It "seems" to run perfect on the muffs, but it isn't "loaded". Do you have a model #?
 
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Picked up the motor from someone who had it sitting in there garage.
We had one good run and it never ran good again. Started working on it from there. Part by part still the same. Runs and idles in the water but won’t rev up. When we throttle up it will go to 1500 rpm then bog down till it stalls?
we thought maybe the stator was bad so we replaced the timer base and stator!
Still the same!
 
There are 2 different versions of a 140 HP.-----Post model # or pictures.------Start with a compression test.----Guessing and replacing parts can be expensive.
 
Under load, you will require much less fuel, that is what I would focus on. I would look at your tank and supply line up to the fuel pump, or try a remote tank (6 gallon). Could be something as simple as a defective vent, or primer bulb, collapsed hose. Check out this picture, just last year, ethanol? Happened up in the middle of nowhere Ontario. October, nobody for 30 miles. Lucky I caught it right away.
 

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timguy said:
Under load, you will require much less fuel, that is what I would focus on. I would look at your tank and supply line up to the fuel pump, or try a remote tank (6 gallon). Could be something as simple as a defective vent, or primer bulb, collapsed hose. Check out this picture, just last year, ethanol? Happened up in the middle of nowhere Ontario. October, nobody for 30 miles. Lucky I caught it right away.
Click to expand...

Supply line is auto 3/8 fuel line coming from a 6 gallon tank
with a inline fuel filter glass see thru to fuel pump.
Everything is good I’m guessing cause fuel filter stays full
and primer bulb stays rock solid.
 
Have you pushed in the coupling ball with a toothpick or something, then pumped into a container to make sure you have adequate flow?
 
Yes we have check the tank fitting by pushing the ball valve and connected it to the tank to see the flow into another tank and the flow seems ok.
 
Cherokeekid079 said:
Hi, I’m looking for an answer to my problem that we’ve been working on for a couple of months. We have a speed boat with a Johnson 140 2 stroke on it. The problem is it won’t run in the water. We put the muffs on and it runs perfect but as soon as we take it to the ocean it won’t achieve full throttle. We’ve replaced all electrical components except the rectifier. Motor has good compression on all cylinders. Brand new coils plugs and wires. Rebuilt the throttle bodies And put a brand new fuel pump. Always use fresh gas and mix 50:1. We put a new water pump and thermostat’s. If anyone knows what I’m missing I could use some help!
Click to expand...
Two possible causes I have heard of is plugged exhaust port or and exhaust leak.Have you tried running it without hood on the water?
 
We have replaced all lines going from the fuel pump to the fuel tree and to the throttle bodies. We didn’t want to take any chances cause the motor had been sitting before we got it. Also all vacuum lines have been replaced with new ones.
 
I think it’s in the throttle bodies I might just order a new rebuild kit for them and rebuild them again cause the first time we thought the floats wasn’t opening enough so we bent the mount to let the float open more and maybe that was a mistake!
 
That compression is low. That's the small bore 1.8L motor and should have around 130-140 psi. These motors have a bridge port exhaust and if overheated the bridge expands and scuffs exhaust side of piston.
 
faztbullet said:
That compression is low. That's the small bore 1.8L motor and should have around 130-140 psi. These motors have a bridge port exhaust and if overheated the bridge expands and scuffs exhaust side of piston.
Click to expand...



I thought 100 psi was ok but if your saying that that’s low then I guess I have to look for a new motor thanks
 
Did you do the compression test warm motor and with all plugs out with a known accurate gauge and a full battery with fast cranking speed? Don't jump to conclusions just yet. You have quite a bit $$$ invested already. Do another compression test, if possible and report to us. Your symptoms of "bogging", then stalling are not sitting in my mind well as a low compression situation. The "lack of power", very well could be low compression, however. Once it stalls, what is your restarting procedure?
 
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timguy said:
Did you do the compression test warm motor and with all plugs out with a known accurate gauge and a full battery with fast cranking speed? Don't jump to conclusions just yet. You have quite a bit $$$ invested already. Do another compression test, if possible and report to us. Your symptoms of "bogging", then stalling are not sitting in my mind well as a low compression situation. The "lack of power", very well could be low compression, however. Once it stalls, what is your restarting procedure?
Click to expand...



I did the compression test cold motor with a no charge on the battery. I guess I can try tomorrow when I get home from work after I run the motor for a bit and update you guys with the results. On the other note we took it out last weekend and we couldn’t go past 1500 rpm. If we throttle more the motor just Boggs out if we cut the throttle back it will remain running.
If the motor stalls it starts right up no issues. The motor will run just off idle all day but sounds like there’s a miss to it sometimes which is weird. Out of the water it runs with no misses like it only misses in the water under pressure. I wish I had taken a video that day to show the symptoms!
 
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Cherokeekid079 said:
I think it’s in the throttle bodies I might just order a new rebuild kit for them and rebuild them again cause the first time we thought the floats wasn’t opening enough so we bent the mount to let the float open more and maybe that was a mistake!
Click to expand...
Now you reminded me of an issue a long time ago about a Honda 2 stroke scooter that drove me crazy trying to figure out.Started and idles great and once rpms increased and tried take off it BOGGED OUT and died.Ended up being the reeds even though I could not see anything wrong with them as far as air gaps etc..New reeds and it ran like new.
 
newyota said:
Now you reminded me of an issue a long time ago about a Honda 2 stroke scooter that drove me crazy trying to figure out.Started and idles great and once rpms increased and tried take off it BOGGED OUT and died.Ended up being the reeds even though I could not see anything wrong with them as far as air gaps etc..New reeds and it ran like new.
Click to expand...


We’ve replaced the reeds but I can take a look at it and see if there’s anything going on there thanks!
 
Did this " failure to perform " develop instantly ?-----Tested crankcase compression??-----Made sure all wires from CD going to the correct coils ?
 
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