89 yamaha 40 stall at idle after 10 seconds

[STeeLGuT]

Runs fine at high speed. I think it is an ignition problem. I have almost ruled out a fuel problem, I have manually choked each carb as it is stalling and no change. After it stalls, it will start right back up without choking it or raising the warm-up lever, but then it will stall again after the same amount of time. If I raise the warm-up lever or drive the boat before it stalls, it will stay running but when I eventually go back to idle it will stall rather quickly.

 

[jim dozier]

Re: 89 yamaha 40 stall at idle after 10 seconds

If it runs fine at high speed it probably isn't your ignition. Verify by checking for a strong blue spark on each cylinder. Also check for bad cylinder by pulling plugs one at a time (recommend grounding the loose wire). Run a compression check to make sure all cylinders are up to snuff. <br /><br />You may be running rich at idle for any of several reasons. This is consistent with the easy restarts. Try disconnecting the fuel line at the engine and see if the idle changes after a bit. You seemed to have ruled out running lean with the choke exercise.<br />Causes of running rich<br />1. Improper setting on idle mixture screw<br />2. Stuck open carb float valve<br />3. Leaking inner fuel pump diaphragm

 

[STeeLGuT]

Re: 89 yamaha 40 stall at idle after 10 seconds

I used a timing light. When it starts it is roughly 5 degrees BTDC, and when it is about to stall, it jumps to 10 degrees ATDC. I found in a manual that at idle it should be 5 degrees ATDC. So I will adjust the rod going to the CDI unit. I guess it uses a setting when it starts and then changes. Then I put it to full throttle and adjust it to 25 degrees BTDC. I see how the marks work now.