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03 yam 2 stroke Vapor Lock/Heat Soak ??

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03 yam 2 stroke Vapor Lock/Heat Soak ??

Old 12-10-2019, 06:12 PM
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Default 03 yam 2 stroke Vapor Lock/Heat Soak ??

2003 Yam 115 2 stroke
Runs Great EXCEPT: It will not start after running 30 min. AND then sitting for 30 minutes. Starts cold fine. Starts hot fine IF I try to restart it right away. BUT if I run it for say 30 minutes across the bay and then let it sit for 30 minutes, it is difficult to start. Acts like it's flooded. Will finally start if I open up the throttle to 3/4 or full throttle like on any flooded carbed engine.
Could this be Vapor Lock ?? OR some other kind of Heat Soak issue ??
Using Ethanol free gas for last 2 yrs.;. Carbs are clean. Well maintained by yours truly. Original Owner. Otherwise runs great.
Recent maintenance over past 2 years includes overhauling carbs twice, draining fuel tank, poppit valve, TStats, impeller, water/fuel separator filter, plugs, compression check, micro filter cleaned, flushed with salt away.
Any ideas ??
Boat is 18 ft Shallow Sport run on the Texas Flats. Otherwise runs great.
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Old 12-10-2019, 09:25 PM
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Those old v4 used to to tough to start cold so we would richen them up an1/8 to a 1/4. Might try that.

sounds like you have another issue also, maybe fuel pump leaking down.
Old 12-11-2019, 09:17 AM
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Vapor lock generally denotes a lack of gasoline getting to the motor. Given what you describe about being able to start the motor if the throttle is opened up, that tends to indicate to me too much gasoline.

Are the choke plates being returned to their fully open position?

Have the carburetor float height positions been verified to be at the correct setting? You might try adjusting the float height to reduce the fuel level in the bowl on the chance that might help correct the issue.

As noted make sure the fuel pump diaphragms are in good condition.
Old 12-11-2019, 12:28 PM
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Originally Posted by alloyboy View Post
Vapor lock generally denotes a lack of gasoline getting to the motor. Given what you describe about being able to start the motor if the throttle is opened up, that tends to indicate to me too much gasoline.

Are the choke plates being returned to their fully open position?

Have the carburetor float height positions been verified to be at the correct setting? You might try adjusting the float height to reduce the fuel level in the bowl on the chance that might help correct the issue.

As noted make sure the fuel pump diaphragms are in good condition.
Alloyboy - You may be on to something. I had this thought also. It starts easily when cold or hot. But if I let it sit for 30 minutes after running across the bay, then it acts like a flooded engine; and won't start or just barely starts and dies when i try to put it in gear. If I do get it to start then its barely running and I need to slam it in gear real quick to clear out the carbs or it dies. Or just start it in with 3/4 to full throttle to clear it out.
The fuel pump was replaced 3 years ago.
So, What would cause it to flood out after shutting down for 20-30 minutes hot ? Maybe the float bowls ? Maybe the idle mixture screws ?
If I stop and try to immediately restart, it fires right up with just a tap on the starter. So it has something to do with letting it sit for 30 minutes.
Old 12-11-2019, 12:47 PM
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Originally Posted by PeteH View Post
Those old v4 used to to tough to start cold so we would richen them up an1/8 to a 1/4. Might try that.

sounds like you have another issue also, maybe fuel pump leaking down.
PeteH - I did richen up the idle mixture screw last year by 1/8 and you are right it helped quite a bit on Cold starts.
Old 12-11-2019, 10:56 PM
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Three years is a long time. A couple of good lean sneezes and a tired fuel pump diaphragm may tear.

Check them for the heck of it, doesn’t cost anything.

Kinda gotta return to the basics to diagnose something like this.
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Old 12-21-2019, 09:33 AM
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Originally Posted by PeteH View Post
Three years is a long time. A couple of good lean sneezes and a tired fuel pump diaphragm may tear.

Check them for the heck of it, doesn’t cost anything.

Kinda gotta return to the basics to diagnose something like this
.
PeteH - I talked to an old mechanic here who also suggested a torn fuel pump diaphragm, so I am probably going to try fixing this first. But, would this cause it to flood out after sitting 30 minutes but otherwise run fine ?
Old 12-21-2019, 12:04 PM
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Who knows, really?

In theory, at speed, it burns off any excess fuel that makes it into the crankcase.

At idle or after sitting it floods that cylinder.

Cheap fix or at least cheap to eliminate one issue.
Old 12-21-2019, 07:22 PM
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Originally Posted by PeteH View Post
Who knows, really?

In theory, at speed, it burns off any excess fuel that makes it into the crankcase.

At idle or after sitting it floods that cylinder.

Cheap fix or at least cheap to eliminate one issue.
Yeah, I agree. But I will have to wait for it to warm up a bit here in Texas before I take the boat out.


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