Engine dies when rapidly closing throttle

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   My engine tends to die when I close the throttle suddenly - like when maneuvering at low speed to dock and having to quickly shift from forward into reverse. Searching the web suggests that:Idle speed is too low. But in gear idle is around 650, and neutral around 800, which I think is about right. I recently cleaned the carb and set idle at max vacuum etc.
Carb is running too rich. Apparently rapidly closing the throttle cuts off air supply to the engine, creating a temporary rich condition in the intake. Carb is stock standard, so only adjustment to lean it out would be float level I guess.
Any thoughts on the above? Anything else that could be causing this?

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Wilhelm Hertzog Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Senior Member Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349	Post Options Post Reply Quote Wilhelm Hertzog Report Post Thanks(0) Quote Reply Topic: Engine dies when rapidly closing throttle Posted: December-21-2024 at 9:32am
	My engine tends to die when I close the throttle suddenly - like when maneuvering at low speed to dock and having to quickly shift from forward into reverse. Searching the web suggests that: Idle speed is too low. But in gear idle is around 650, and neutral around 800, which I think is about right. I recently cleaned the carb and set idle at max vacuum etc. Carb is running too rich. Apparently rapidly closing the throttle cuts off air supply to the engine, creating a temporary rich condition in the intake. Carb is stock standard, so only adjustment to lean it out would be float level I guess. Any thoughts on the above? Anything else that could be causing this?
	1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer Do not go gentle into that good night. Rage, rage against the dying of the light.

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11212	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: December-22-2024 at 8:04am
	I think I'd richen the idle mixture using the 2 idle mixture adjustment screws on the metering block. If you're adjusted right now for max vacuum and you have a 150 rpm drop when putting it in gear like you say, richen things up going out about 1/8 turn at a time on both mixture screws and see how it acts. You should end up with less RPM drop( 50 to 75 or so) and better response going from neutral to forward or reverse

Wilhelm Hertzog Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Senior Member Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349	Post Options Post Reply Quote Wilhelm Hertzog Report Post Thanks(0) Quote Reply Posted: December-22-2024 at 3:04pm
	Thanks, I'll give that a try and report back.
	1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer Do not go gentle into that good night. Rage, rage against the dying of the light.

MrMcD Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3778	Post Options Post Reply Quote MrMcD Report Post Thanks(0) Quote Reply Posted: December-23-2024 at 1:58pm
	I think Ken is leading you correctly. My 78 Nautique had the same issue. West Coast Correct craft was only 10 minutes away back in the 80's when I had the issue. They gave me the same advice and it worked. Check your advance mechanism in the distributor to make sure it is rotating smoothly each and every time you advance and release the throttle.

Wilhelm Hertzog Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Senior Member Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349	Post Options Post Reply Quote Wilhelm Hertzog Report Post Thanks(0) Quote Reply Posted: January-11-2025 at 8:43am
	Richening things up a bit does seem to have helped, thanks Ken. I have subsequently developed a bit of an off-idle stumble when pulling away, but I'm sure a bit of fine tuning and adjustment will sort that out without too many hassles.
	1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer Do not go gentle into that good night. Rage, rage against the dying of the light.

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11212	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: January-11-2025 at 6:50pm
	I'd probably start with checking that the accelerator pump linkage is adjusted correctly.......no slop at all with the carburetor at it's idle position.....none, not even a little Click on the link and you have a video and also a written procedure. You should have no need to change the cam or the nozzles. Make sure both nozzles are squirting a good stream when you give it some throttle. You can do this with the engine off and if you have the throttle cable disconnected, you can do it all by yourself looking down the primary side of the carburetor. If the stream isn't good, it could be the accelerator pump diaphragm being bad or dirty nozzles link A little slop can make for a pretty bad bog.

Engine dies when rapidly closing throttle

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