Idle Problem/Bleed Inserts? Reed Valves?

[astroglass_81]

1980 Mercury 90 HP Outboard
Model: 1090620 90ELPTO
Serial: 7179095

Alrightythen, I've cleaned carbs, fuel tank, performed timing & sync. Engine idles pretty good (@1200-1600rpms, which I think is a lil high) till you put it in gear (about 800 rpms), like loading on and off trailer. Seems to load up, flood and die , then you have to wind and wind to get started again, and rev up to clear it out. I have adjusted carbs till I think I have worn the threads down, to yet still a rough idle in gear. I am thinking that the carbs ain't the problem. I heard the other day that I need to check to see if carbs are spitting gas out of the front of throat, at idle with a timing light, to determine if reed valves are not working properly. Then another guy said I needed to check to see if bleed inserts were in place. He said sometimes that they push out and go out in the water. I was wondering if one or both of these could be my problem? Also, if the powerhead has to be removed to get to the bleed inserts? I think the one guy said powerhead would have to be disassembled to install reed valves if they were bad. This engine seems to run very good at just above an idle to high speed. Just fustrating to get on and off the trailer (as you know, a good idle is needed especially with a wake from a passing boat or a crosswind is present) For a visual, boat crossed up at trailer, and engine floods and dies. You guys have helped me alot since I got started with this boat, and I surely am grateful for this forum. Hats off to the pros-and thank y'all very much

 

[Chris1956]

Re: Idle Problem/Bleed Inserts? Reed Valves?

Astro, The bleed restrictors are under the transfer covers. They have a small effect on the idle quality, and I think they should be a last resort for you. The reed valves are under the crankcase cover and to replace them you need to remove the crankshaft. The good news is that reed valves are very durable, and unlikely causing your problem.

On that motor, it is difficult to set the idle mixture on the three carbs. You need to set it rich nough to accelerate, but lean enough to idle reasonably well at 850-900RPM in gear. I have a simple method involving trial and error to set the carb mixture. Make sure the carb floats are set properly and the inlet needles are sealing properly.

Start and warm the motor, in the lake. Now try to adjust the idle jet screws until you have the smoothest and fastest idle you can get. The carbs are now synched, although the mixture is likely too lean to accelerate. Lower the idle to about 1000RPM, and put it into gear and try to accelerate. If it takes off smooth, you are done. If it stumbles, open the top carb screw 1/8 turn and try to accelerate again. if it stumbles richen the mid carb 1/8 turn and try again. If it still stumbles, richen the bottom carb 1/8 turn and try again. Repeat the top-mid-bottom carb sequence again if necessary, until it accelerates well and idles acceptably.