2007 25 hp Yamaha 4-Stroke Start Issues

[novascotia_zodiac]

Model: F25MLHF

Use and Maintenance: Located in Nova Scotia, Canada. The outboard is used about once every week or two from April through October. It is not winterized because it is used about once every month or two during winter. It is professionally serviced each autumn. They change the gear oil, engine oil and filter, and every two years they change the impeller and spark plugs. The carburetor has been cleaned using an ultrasonic cleaner in 2018. It is stored inside all year, and looks almost brand new inside and out. Previous to me, the owners were a volunteer fire department, who rarely used it.

Issue: The outboard typically starts well when cold and soon after turning off. To start the motor, I open the vent on the gas tank, pump the bulb on the line going from the tank to the ouboard, put the throttle at start and pull the cord.

The issue is when it has been running then is turned off for roughly 30 minutes to an hour. It is then much harder to start, requiring multiple pulls of the cord and more throttle, to the point where it revs high once started. When pulling the cord while it hasn't yet started, there is a smell of gas, perhaps like it is flooding.

Thanks!

[99yam40]

fuel pump leaking into crankcase maybe.

or maybe heat soaking after running causing fuel in carb to boil out cause an over rich condition

[panasonic]

Did this problem start after the carb was cleaned in 2018?

Where are you in Nova Scotia?

Yam..this engine has a mechanical driven fuel pump I believe.

[novascotia_zodiac]

99yam40, what is "heat soaking"? Google only spits out things in reference to tempered glass.

panasonic, I'm near Yarmouth, NS, a paradise for those who like to explore nearshore islands.

This problem did not start after having cleaned the carburetor in 2018.

You can check (https://www.yamaha-motor.ca/our_comp..._catalogue.php) and look up my outboard to see which parts it has, which assume is very important to enable proper diagnosis of this problem.

I'm certainly not very experienced in outboards, but I keep wondering if it is a problem with the prime starter (and or the sensor it relies on to read the engine temperature) that mine is equipped with. Anyone with experience in diagnosing prime start issues?

Thanks for the comments thus far.

[rejesterd]

If you open the fuel tank vent and pump the bulb again after it's been off for 30 minutes, does it get any easier to restart? Also try removing the cowling just after you shut it off. If it starts easier when you do that, you know the problem is related to heat buildup.

You have to get the service manual to really check the prime start assembly, because it involves measuring the plunger length and comparing it to the spec in the manual. There's a section that tells you how to check it.

But I would start with the plugs. Take them out and see how they look. If they're wet, replace them. Assuming it starts fine with new plugs, then there's something wrong in the starting system.

If the plugs look fine, then start looking at the fuel system.. carburetor mostly. This is all out of the service manual for a larger carbureted F50. If you get the manual for the F25, you can follow them.

[99yam40]

some F motors have fuel coolers, some did not have primestart,
but I cannot find his F25MLHF to look at what his has.
can someone pick out the correct parts diagram for this motor on our parts section?
https://www.boats.net/catalog/yamaha...and-later/25hp

[TownsendsFJR1300]

some F motors have fuel coolers, some did not have primestart,
but I cannot find his F25MLHF to look at what his has.
can someone pick out the correct parts diagram for this motor on our parts section?
https://www.boats.net/catalog/yamaha...and-later/25hp

Probably not listed as it may be an "out of USA" engine....

Here's a very close one, with a carb (many are FI'ed) F25 MLH:
https://www.boats.net/catalog/yamaha...405/carburetor

Looks like a mechanical fuel pump (as noted above):
https://www.boats.net/catalog/yamaha...lh-0405/fuel-1

[99yam40]

do you know what the 0405 represents?

I was thinking it represented it is for a 2005

I was looking at the 0407 and it showed up as not PS and pulse fuel pump, so was very confused.
( looking again, I must have looked at the non F25 by mistake)

I know some of the mechanical pumps on small F motors had water cooling, but I do not see that on the one you showed

To the OP,
heat soaking is just a term for heat rising after shutting off the motor( no more cooling water flowing to remove heat from the motor)

Yamaha did recommend running the motor at idle for a little while before shutting down after hard runs to help cool down the motor some to help with this type of thing

[TownsendsFJR1300]

do you know what the 0405 represents?

I was thinking it represented it is for a 2005

I had no idea what those numbers represented, just trying to find something close..

[panasonic]

99yam40, what is "heat soaking"? Google only spits out things in reference to tempered glass.

panasonic, I'm near Yarmouth, NS, a paradise for those who like to explore nearshore islands.

This problem did not start after having cleaned the carburetor in 2018.

You can check (https://www.yamaha-motor.ca/our_comp..._catalogue.php) and look up my outboard to see which parts it has, which assume is very important to enable proper diagnosis of this problem.

I'm certainly not very experienced in outboards, but I keep wondering if it is a problem with the prime starter (and or the sensor it relies on to read the engine temperature) that mine is equipped with. Anyone with experience in diagnosing prime start issues?

Thanks for the comments thus far.

Yam and FJR1300 the OP supplied the link for the Canadian Yamaha parts site above.
However he did not post his exact model number/ serial number.

Zodiac please post the Model number off the transom bracket...it starts with the number 6. It may have a separate tag with the year on it as well.

I suspect you have a problem with the prime start thermovalve on the carb. It works like this:

Engine Cold..The needle is retracted allowing fuel to past through the enrichment passage, providing extra fuel for cold start. As soon as engine starts power is applied to the valve heating it up and causing the needle to slowly extend and close off the passage as the engine warms up.

When the engine is shut off, power is loss to the valve allowing it to retact slowly again to open the enrichment passage for the next "cold" start.

However, it should not retract so quickly that it opens up the enrichment passage on an engine that is still warm enough to start on its own, without any enrichment.

It appears your Prime Start valve is working on the cold starts....but perhaps is retracting to quickly when the engine is shut down causing it to flood when trying to start warm. These small F15/25 should start first pull when warm and everything is working properly.

These Prime Start thermovalves are known to fail sometimes, all be it, they seem to fail where the needle won't retract at all making the engine very difficult to start when dead cold...the opposite of your problem.

Or as already posted it is vapor locking from heat soaking..

May have the service manual for your engine..will look after you post the model #.

I am in Nova Scotia as well....near Halifax.

[boscoe99]

He is in Canada boys. Different model designations used up there. Have to go to the YAM CAN website to view his parts catalog.

[boscoe99]

I am in Nova Scotia as well....near Halifax.

Summers end, around the bend, just flyin'

[99yam40]

He is in Canada boys. Different model designations used up there. Have to go to the YAM CAN website to view his parts catalog.

I tried, but could not find the F25MLHF he listed

[novascotia_zodiac]

Thanks again for the comments!

panasonic, hopefully the last photo that I've uploaded has the model number that you're looking for. I've also uploaded photos of both sides of the outboard.

If the issue is heat soaking, then is there a fix? I can try taking the cowling off to see if that helps, but it would be nice to fix the problem.

I'd rather just replace the prime start rather than try to measure the plunger length, and see if that helps, as long as it isn't too overpriced. There is a Yamaha dealership nearby that I can get it from.

panasonic, that would be great if you had a copy of the service manual for my outboard! If I can't figure it out with the help of people on here, do you recommend a good place in the Halifax area that would be able to help me. I haven't been successful with my local dealer.

[panasonic]

Summers end, around the bend, just flyin'

Lots of time left yet....all of Aug, Sept, and Oct!! You wont be out in October with your shorts on though...which is fine with me.

If it never went over 20C I would be fine with that, I don't like the heat.