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1990 yamaha 40hp fuel issue

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keeth

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Hey guys. Iv run into a bit of a conundrum. I finally finished putting the console in my boat and took it out for a spin. Ran into an issue, it was running out of fuel at WOT so id stop prime it and back at it. When I got home i put the new tank and bulb in it alomg with a nee fuel pump for giggles. Now im having the exact opposite problem. I took it out last night and could run at WOT no problem but it would big for a couple minutes until on the plane. I took the silencer off and the lower chamber in was full of fuel. I ordered the correct pump but naturally its different so I'm wondering if the difference could be over pumping the lowest carb and the closest to the main feed lime for all the carbs. The inlet snd outlet of the pump are the nect size up so I'm really thinking thats the problem. What do you guys think?? Thanks!
 
keeth said:
Hey guys. Iv run into a bit of a conundrum. I finally finished putting the console in my boat and took it out for a spin. Ran into an issue, it was running out of fuel at WOT so id stop prime it and back at it. When I got home i put the new tank and bulb in it alomg with a nee fuel pump for giggles. Now im having the exact opposite problem. I took it out last night and could run at WOT no problem but it would big for a couple minutes until on the plane. I took the silencer off and the lower chamber in was full of fuel. I ordered the correct pump but naturally its different so I'm wondering if the difference could be over pumping the lowest carb and the closest to the main feed lime for all the carbs. The inlet snd outlet of the pump are the nect size up so I'm really thinking thats the problem. What do you guys think?? Thanks!
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Referring to above in bold...can you explain what your talking about. Big? Lower chamber? And how is the new fuel pump "naturally different"...and I'm not asking about how similar the new pump looks to the old pump. The inlet/outlet should be should be the same size as old pump.
 
Sorry, big was suppost to be bog. The "naturally its different" was sarcasm because I tend to get the wrong parts at the worst possible times. The inlet outlet are bigger than the old pump, they are also in different spots on the pump. Also the main block in the center of the two metal plates, it holds the check valves in it is a good bit thicker. As to the chambers, the silencer has 3 chambers, one for each carb. The lowest chamber, carb number 3, was full of fuel.
 
Well those who have been looking at this, it wasnt the fuel pump. Got the right one in today and ran it. Still bogs and still fuel in the silencer box. Still have the miss fire at idle. I did find something weird maybe someone has ran into. It doesn't miss with the #3 spark plug wire off. It actually ran smoother. Obviously #3 cylinder has some sort of problem. As a side note I was wide open today cruising about 22 mph and hit a sand bar(just the motor) props of have a florida flats boat. Floats in 6" of water. But what puzzled me is it ran great after that. Great power and no fuel smell. So I'm wondering if I have a stuck needle valve causing over fueling and and the jolt nocked it loose for a bit. I rebuilt the carbs at the beggining of the summer with mew seats and valves and it didnt do it before. Food for thought ill keep ya posted. Thanks.
 
At this point im probably talking to a wall, however iv made progress. Pulled the carbs, cleaned again. This time with much more aggression. Like 150 psi air nozzle. Blew some sort of gunk from deep in the idle circuit. Wouldnt you know the miss at idle went away. I began to look down the throats of the carbs and noticed that #3 carb at idle was drawing fuel through the main jet while the others were not. Also the idle mixture screw doesnt seem to do anything on that carb. I have no idea what would cause that. Iv googled to the ends of the earth and used google translate to look at something written in Hindi. Nothing. If any of you guys have an idea id greatly thankful. I also reset the float heights to exactly 15mm as the book calls. Thanks guys
 
keeth said:
At this point im probably talking to a wall, however iv made progress. Pulled the carbs, cleaned again. This time with much more aggression. Like 150 psi air nozzle. Blew some sort of gunk from deep in the idle circuit. Wouldnt you know the miss at idle went away. I began to look down the throats of the carbs and noticed that #3 carb at idle was drawing fuel through the main jet while the others were not. Also the idle mixture screw doesnt seem to do anything on that carb. I have no idea what would cause that. Iv googled to the ends of the earth and used google translate to look at something written in Hindi. Nothing. If any of you guys have an idea id greatly thankful. I also reset the float heights to exactly 15mm as the book calls. Thanks guys
Click to expand...

Thank you for posting results! This is very helpful for others. :cool:
 
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