Yamaha 9.9 4-stroke stalls

[hcccs 0]

I rebuilt the carburetor of my Yamaha F9.9BM (6G9 S 008982 Z 1994). It starts really easy but sounds like it's running on one cylinder and when I throttle up the slighest it stalls. I ran it again, wihout hood and when I put my thumb close to the carb intake it reved up. It seems like my thumb acted like a choke and lowered the intake pressure (increased the suction).  Any ideas?

[Mercury_44XS 378]

It seems lika you still having fuel starvation problems.

 

This engine has a "twin ignition coil" and fires (spark) on both cylinders at the same time, but they are in different cycle. Eg. cyl #1 is in compression cycle and ready to fire, but cyl. #2 is in the end of exhaust cycle. Therefore we can exclude ignition problems, except spark plugs, which one of then can be defective.

 

Did you check the "choke plunger" on top of carburetor with two wires?

It is electrically and automatic operated.

This "choke plunger" or enrichment valve decreases AFR at cold start to appr. below 10:1 and the gradually increases to normal levels at 14.7:1.

 

Have you checked compression?

 

If there is low compression on one of the two cylinder, it might increase temporarily when you put your thumb in the carb air intake and choked the engine (decreasing AFR, more fuel, less air).

 

If you don´t have a compression tester, you can dismantle one spark plug at a time and crank enginge by hand on the flywheel and check and compare the resistance caused by compression. Crank flywheel clockwise (RHR).

 

//Pär

 

 

Redigerad 14 Juli av Mercury_44XS

[hcccs 0]

Thanks for your response.

So, it is a waste spark ignition system. Interesting.
I've taken the carb apart again and looked it over. The choke plunger is spring loaded and it moves but I can't test it electrically, or can I, put 12V on the leads? I tried to make a compression test but my probe wouldn't fit because the spark plug recesses are to narrow. It's even difficult to put a finger to the plug holes. I don't think though that there's a problem with the compression. The motor was totally submerged in sea water for 24 hours last autumn so I had to take it home, empty engine and gearbox oil, put it in my sauna for a couple of hours. I then test ran it and it started and I put it in my cold garage over the winter. In the spring it didn't start and I found out that there had been deposits in the carburetor so I bought a kit and overhauled it. I wonder if there is some stop somewhere else in the motor that I don't know about.

[Mercury_44XS 378]

7 minuter sedan skrev hcccs:

The motor was totally submerged in sea water for 24 hours last autumn so I had to take it home, empty engine and gearbox oil, put it in my sauna for a couple of hours.

If a outboard is totally submerged, you have immediately rinse everything with ethanol and blow it dry with compressed air. Change engine oil, clean carburetor, fuel pump and fuel lines. Test run in water and let the engine run for at least 1–2 h.

 

Sorry but I think your outboard is beyond salvation if you don't buy a lot of new parts.

 

//Pär