115 Yamaha 2 stroke - Heat Soak starting issue or Vapor Lock ??

[03YAM115]

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 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.

[99yam40]

heat soak is my guess. heat from motor cooking the fuel out of the carb bowls flooding the motor with rich gas fumes
are you idling a few minuets before shutting down after a hard run across the bay?

looks like your motor has a choke , make sure those plates are opening all the way and not stuck

[03YAM115]

Thanks, for the reply.
I agree, probably heat soak. But why now after all these years ?
The choke isn't stuck open.
I have not been letting idle after a hard run...and I know that is recommended by Yamaha. However, it never did this until about 3 years ago. I will try letting idle next time and see what happens. I did readjust the carb idle screw and that seemed to help. (A "qualified" mechanic set it wrong)

[99yam40]

I was thinking the choke plates are not opening all the way not stuck open.

could be the motor is getting hotter than it use to do to some restrictions in the cooling passages from years of saltwater use.
which Texas flats you running?

I hang around the east end of East Matagorda Bay

[rejesterd]

Have you ever replaced the fuel pump? If not, that might be worth trying (considering how old it is). But I would think it's more likely to be related to the exhaust manifold leaking. That's something that would all-of-a-sudden-after-many-years cause it to heat soak.

[pstephens46]

Have you ever replaced the fuel pump? If not, that might be worth trying (considering how old it is). But I would think it's more likely to be related to the exhaust manifold leaking. That's something that would all-of-a-sudden-after-many-years cause it to heat soak.

What other symptoms might be related to the exhaust manifold leaking?

[03YAM115]

Thanks for the input.

I replaced the fuel pump about 3 years ago as preventative maintenance.
I don't see any symptoms of exhaust manifold leaking. But maybe it is leaking. How would I determine if it is leaking ? Maybe I should check cylinder temps after a good run.
It runs great other than this heat soak/starting issue.

[03YAM115]

I run the flats around Rockport and down to South Padre. Been stuck a few times because I got over confident but never needed a tow. That Shallow Sport will run scary shallow.

[03YAM115]

"could be the motor is getting hotter than it use to do to some restrictions in the cooling passages from years of saltwater use."

99YAM40: You may be correct about the cooling passages. I had this same thought. When it warms up a bit I will try to clean them out with something. Any suggestions other than "Salt Away" ??

[99yam40]

I run the flats around Rockport and down to South Padre. Been stuck a few times because I got over confident but never needed a tow. That Shallow Sport will run scary shallow.

I do not like a boat to run in water so shallow that the boat cannot float out when it stops, but from what I have heard all you can do is never let off until you find deeper water.

I have a cousin with places down in Rockport, lots of wide open water down there.
we killed the flounder over here this year. had not caught flounder on plastic like that in many years

[99yam40]

"could be the motor is getting hotter than it use to do to some restrictions in the cooling passages from years of saltwater use."

99YAM40: You may be correct about the cooling passages. I had this same thought. When it warms up a bit I will try to clean them out with something. Any suggestions other than "Salt Away" ??

I have heard good thinks about Rydlime Marine descaler.
drop the lower unit, pull the stats( put covers back on), hook up a circulation pump piped to the tube heading to power head,, catch all of the solution in a bucket to circulate

I used citric acid on my brothers C60.
pumped a heated solution thru a warm motor for a few hours
I would think the Rydlime is a lot better, but have not used it myself yet
Citric acid power is cheaper

[rejesterd]

How would I determine if it is leaking ? Maybe I should check cylinder temps after a good run.
It runs great other than this heat soak/starting issue.

You got it.. take a temp gun to different spots on the engine. The problem is determining what the the expected operating temperature should be, as I don't think the service manual specifies that.. so I would ask around about that. The only other way to know is to take the thing apart (as far as I know).

If it's not a partially-blocked cooling passage and everything else is in order (carbs, compression, cooling system parts), then I would have to suspect overheating due to exhaust corrosion/leaking.

[pstephens46]

[QUOTE=rejesterd;n221113]

You got it.. take a temp gun to different spots on the engine. The problem is determining what the the expected operating temperature should be, as I don't think the service manual specifies that.. so I would ask around about that.

Got what? Take a temp and shoot spots on engine to determine an exhaust leak? Ask around who? People that have done the same on a well functioning engine? You gotta stop with the ghost hunts. Read Yams posts to learn how to direct people in logical steps.

[pstephens46]

I do not like a boat to run in water so shallow that the boat cannot float out when it stops, but from what I have heard all you can do is never let off until you find deeper water.

I have a cousin with places down in Rockport, lots of wide open water down there.
we killed the flounder over here this year. had not caught flounder on plastic like that in many years

Flounder are a bonus fish here. How do you fish the plastics? Bump on bottom with a float?

[99yam40]

Flounder are a bonus fish here. How do you fish the plastics? Bump on bottom with a float?

soft plastic like Norton Bull minnow (paddle tails) is what I usually throw, but have been catching a lot of flounder on gulp curly tail grubs.
I fish in shallow water flats along the edges of grass or shell. 6 to 12".
sight casting to reds. the flounder hang out there too but only see them when they spook and head away).
I do normally use a small (2 -3" long)cigar shaped cork 12 to 18" above the lead head just to help keep the line on top of the water so I can keep the lure off of the bottom.
with reds you cannot real it fast enough to keep them from trying to eat even the cork some times, but with flounder we slow the retrieve down so the lure rides just off the bottom