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Fuel System Questions...

H

haydenfox

Member
Background: 2004 90 hp Mercury ELPTO. Recently rebuilt carbs and had a tank cleaning. Also put new plugs in.

After rebuilding the carbs the motor had a pretty bad sneeze. I got that worked out with some PITA needle adjustments. On the hose it idles around 950 RPM and any adjustment to the idle screw causes the motor to die. FWIW, the motor has always idled high for my liking. In the water it idles closer to 800 RPM but doesn't idle as well as on the hose, almost as if it will die. I'n not sure if it's relevant but I also have to give it a little more throttle to start in the water. The RPMs shoot about 3000 when I do this. Why is there an idle/starting difference between the hose and the water?

Motor ran well on the water sans a slight hesitation at around 3500 RPM on the way to WOT. It has always done this and I have always had to slowly feed throttle or it dies. What causes the hesitation?

After sitting for a few minutes it wouldn't start and the bulb was losing pressure during the process. This was the first time during the process that this has happened. I got her started, got home, put her on the hose and since it has been fine. What might cause the inconsistency with starting and the bulb pressure? Are they related?

TIA
 
On a hose the exhaust is wide open to atmosphere.------In the water the exhaust is restricted.--------This is an important fact.--------So much so that on the latest greatest E-tec motors there is a valve in the exhaust housing to put back pressure on the engine.
 
Yes they run / start different on a hose.----There is a wee bit of pressure on the exhaust ports when motor is in the water.---facts on primer bulb----The primer bulb is a manual pump.-----Simply put it does NOT stay hard once the motor is running.
 
Thank you. I've been out a couple times since the post and it is now idles at 1000 rpm. This is high, although only a little higher than pre-carb clean, etc but I have had less hard starting, stalling and over all just better idle speed. It's not even as loud as it used to be. Is this too high? Will it eventually cause damage?
 
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