C40TLRX stumbling or cutting out

[99yam40]

I have had this 1999 C40TLRX start giving me some problems the last 2 times I took it out on the water. It started and idled fine but when I got up on plane it sounded like it was dropping a cylinder and losing some RPMs and them coming back up to normal. The bulb stayed hard and it did not help to pump it while running. I pulled and cleaned the filter and checked the fuel pump. I even pulled the carburetors and cleaned them but did not see anything that could be causing a problem. Took it out again and it started and ran fine for the first few minuets, but fell off of plane and almost died as I was heading back to dock. It would not even idle very well, coughing and such. After running on high idle while I tried choking the individual carburetors with my hand to see if it would make a difference it started to run fine again, but when at high RPMs and under load I could still feel some RPM drop every once and a while. It was suggested that the timing may be changing due to a faulty CDI unit.
Does anyone have any suggestions for me to try and troubleshoot this problem?

 

[robert graham]

Re: C40TLRX stumbling or cutting out

if it runs better when you hand choke the carbs might indicate a lean mixture as caused by air leak in fuel lines/connections or plugged jet in carb. how do your plugs look? if they're very white could indicate lean mixture issue on that cylinder. Good luck!

 

[Casco Bay Outrage]

Re: C40TLRX stumbling or cutting out

I think you got most of the crud from the carbs (engine retest was good at first) but not all.

I suggest you take them off again and really go at it on all the tiny orifices and re-test.

It often takes more than one cleaning to get it all done.

 

[99yam40]

Re: C40TLRX stumbling or cutting out

I went through the carbs again and it still has a WOT cut out, almost like it is dropping a cylinder, but runs fine around 1/4 to 3/4 trottle.
Runs a little rough at idle and coming off of idle but then smooths out until it starts to cut out after WOT for a minuite. But does not stumble comeing out of hole.

I noticed something strange when I started pulling the plug wires while it was idling, when I pulled #1 wire the RPM actually came up and the motor idled a little better, the other 2 cylinders had a RPM drop when I pulled them.

Has anyone seen this before?
If so what could cause this to happen?