Loss of power when accelerating

[theschafe]

I have a 90 Johnson 40hp outboard. It start immediately, idles smooth, goes into gear smooth and runs at low speed smooth. However, once I throttle up at half speed it drops power and stalls unless I throttle back. I have remove the carbs, taken them apart and clean and soaked with carb cleaner. I replaced the plugs. Cleared all fuel lines from obstruction. Replace the fuel filter. Problem still reoccurs. When I push in the choke it goes to full power and when I let off the choke it drops speed and stalls. I have checked the primer ball and it remains hard throughout operation. I thought it could be the fuel pump but between the ball staying hard and the pushed in choke bringing it to full power, I can see how the fuel pump is bad. Did I miss cleaning a high speed jet in the carb? Could it still be the fuel pump? I'm stumped. Thanks.

 

[OBJ]

Re: Loss of power when accelerating

Welcome aboard theschafe!<br /><br />It's possible you could have missed a jet. Did you follow up with compressed air after the soaking and did you remove the high speed jets for inspection/cleaning? Only one high speed jet in each carb.<br /><br />Did you replace any fuel line that had become hard? When this happens, the fuel line can lose it's grip on the connection and suck air.<br /><br />Ignition system good? Both cylinders have good spark?<br /><br />What kind of fuel pump do you have? VRO or standard pump.....better yet....just post the model number of the engine.<br /><br />About the primer bulb....when you say it stays hard, is that like when you first pumped it up?<br /><br />Have you tried another fuel line and primer bulb?

 

[theschafe]

Re: Loss of power when accelerating

The ignition system checks out. Both sparks check out. The fuel lines are pliable and are clamped down. I blew compressed air after cleaning and the carbs sat in a dry area for 3 days before re-installing. I removed the VRO system in 1992 and mix in the tanks. The fuel pump is standard. Pumps only fuel. I have 2 tanks each with lines and bulbs and problem happens with each. The bulb stays hard like when I first prime it to start. I have the original parts and service manual that I bought with the boat. It does a fair job visually breaking down the carb but it doesn't provide much verbal explanation. I got to believe that it is the high speed jets but I can't seem to figure out which one it is. Since when I push in the choke is runs full speed I'm doubting the fuel pump. If I need to get an updated manual for the carbs I will but I'd like to be pretty certain that it's the carbs. Also, ordering a manual takes time and I'm trying to put the boat to use this weekend. I appreciate the reply so far but if there is any additional to get me fishing I will be indebted. Thanks.

 

[Richard Petersen]

Re: Loss of power when accelerating

I can almost laugh when I read your problem. I stay on a summer park . One of the 4 old motors I got running had the exact same problem! Turned out a marine mechanic had worked on the motor carburator last year. He accidently put the choke intermediate lever back on, upside down. Reversed it , motor runs perfect.------ Check the float and float travel with a guage. Also make sure the float pin has a small wire spring holding it to the lever.

 

[theschafe]

Re: Loss of power when accelerating

Wish that was the case but checked that too. Thanks.

 

[Richard Petersen]

Re: Loss of power when accelerating

I take it there is no HI speed needle adjust ? only other cause , dryed out fuel in the main jet or air bleeds. Let the engine sit for 2 or 3 days with FRESH gas in the carb. It WILL soften and run normal again. Let us know if you are gaining.

 

[rodbolt]

Re: Loss of power when accelerating

hello<br /> clean the carbs. you missed something. by pushing the primer your manualy making the fuel mix rich by adding fuel aft of the carb butterflies. its a hign speed jet problem . do NOT try toj ust soak it and run it. a lean out due to a cloggeed or partially clogged carb will eat a piston.<br /> no worries <br /> did you phhsically remove and inspect the jet ?<br />you may have left the emulsion tube gasket off as well. did you use the BRP kits? did you remove the needle seat. some of the diamond shaped pumps had orange rubber check valves that will break apart. test the pump as well.<br /> if you take the filter cap off the pump you can see if it has the orange valves. the valve pieces can hide under the seat or in the carb fuel inlet.

 

[theschafe]

Re: Loss of power when accelerating

Worked late, had dinner with the family and now it is raining so any attempts at suggestions will have to be tried tomorrow. I'll keep you posted. Thanks.

 

[RandyJ]

Re: Loss of power when accelerating

I hope to learn what your problem is... I've got waverunners and a couple of outboards with same problem... I'm positive mine are in the carbs too.

 

[RandyJ]

Re: Loss of power when accelerating

Hmmm... have to use full reply form to get the email notification to topic...

 

[theschafe]

Re: Loss of power when accelerating

Haven't yet to get a chance to work on the boat. Rain and honey do's have filled another weekend. Maybe something during this week's evenings. Which can't be fixed and costs more, a wife or a boat?

 

[RandyJ]

Re: Loss of power when accelerating

What about fuel filter? Have you possibly added an automotive fuel filter inline? That is supposed to be one of the problems some people are having with PWC's.