yamaha 2.5hp 4 stroke warm start issue

R

RichardtheBoffin

Well-Known Member
Joined
12 Oct 2012
Messages
72
Visit site
Are there any tricks or knacks to starting these warm?

Mine refused to start yesterday, mid river.

Stupidly, I did not have a plug spanner with me, but I did try savaging with the throttle open. No luck.

After a long walk lugging it and the boat back to the car, (thank you for the two people who thought that giving me a tow a few hundred yards past their marina was just too much trouble...) I got it back home.

This morning I checked the plug. It's a little sooty, but nothing horrendous.

Engine runs and starts fine now of course.

I suspect that these are very easy to flood and hard to clear once flooded without taking the plug out?

I also noticed that when warm, the motor had a tendency to idle very slow and sometimes stop. Needless to say it's idling perfectly in the water butt now...


Anyone have any similar issues?

It's really annoying as this motor starts first pull, when it wants to and never when it doesn't!
 
From what I understand, many of these little motors are set to run very lean for emission reasons. I wonder if a little adjustment to enrich the mixture slightly might help.
 
Did some more testing.

Motor started and ran no problems. Idle was good and even.

Left it a few hours and came back to it.

Started fine (no choke), put the throttle from start back to idle and it ran ok for a while but gradually slowed down until it just stopped.

Now it refuses to start. (with no choke)

Checked the plug and it's sooty and wet with fuel.

There may be something floating about in the carb, the idle jet is tiny so it wouldn't need much to stop it.

Odd that it ran fine this morning but now the died while idling and won't start.

The wet plug and soot suggests it's running too rich.
 
Wet plug suggests it is flooding.

Try turning off the fuel when it starts to die if it recovers briefly then probably confirms that.

Check float and float valve. Suspect not seating properly.
 
Looking at the service manual, I am assuming that the 'Pilot' jet is the idle jet? (Maybe there is no idle jet and the pilot jet covers idle and slow speed?)

The pilot is adjustable with a special tool which I'll have to make.

Idle rpm is quoted at 1800 to 2000 rpm, which is higher than I would have guessed, I will check it and see what it's running at.

Maybe it's just set to idle too slow and that's why it's getting sooty.

In a tiny dingy, dropping into forward gear at anything over a slow idle can be a bit exciting!
 
RichardtheBoffin said:
Looking at the service manual, I am assuming that the 'Pilot' jet is the idle jet? (Maybe there is no idle jet and the pilot jet covers idle and slow speed?)

The pilot is adjustable with a special tool which I'll have to make.

Idle rpm is quoted at 1800 to 2000 rpm, which is higher than I would have guessed, I will check it and see what it's running at.

Maybe it's just set to idle too slow and that's why it's getting sooty.

In a tiny dingy, dropping into forward gear at anything over a slow idle can be a bit exciting!
Click to expand...

Hi Richard. I wouldnt recommend increasing the tick over to 2000 revs. Keep it as low as possible.If it engages gear when the engine is running fast you can strip the clutch dog. If your plug is wwt this will be your problem. It can either be as stated by Vic a sticking needle valve or a head gasket problem. If its sooty I suggest its the later
 
steve66 said:
Hi Richard. I wouldnt recommend increasing the tick over to 2000 revs. Keep it as low as possible.If it engages gear when the engine is running fast you can strip the clutch dog. If your plug is wwt this will be your problem. It can either be as stated by Vic a sticking needle valve or a head gasket problem. If its sooty I suggest its the later
Click to expand...

I guess it depends on what is meant by "wet". Wet with water would point to a head gasket problem. Wet with fuel to a needle valve problem? I assumed the OP meant the latter.

In #4 I suggested turning off the fuel as it starts to die as a way of confirming , or otherwise, a needle valve problem. I f its flooding then it should recover as the fuel level in the carb drops.
 
VicS said:
I guess it depends on what is meant by "wet". Wet with water would point to a head gasket problem. Wet with fuel to a needle valve problem? I assumed the OP meant the latter.

In #4 I suggested turning off the fuel as it starts to die as a way of confirming , or otherwise, a needle valve problem. I f its flooding then it should recover as the fuel level in the carb drops.
Click to expand...
Good advice Vic, I thought sooty plug,faulty needle/float go hand in hand
 
The plug was wet with fuel.

I'll pop the carb off and take a look at the float and needle valve.

The motor is barely used and everything looks as new.

It has been sat in the garage for 6 months, so there could be some fuel gum floating about in the carb...
 
RichardtheBoffin said:
The plug was wet with fuel.

I'll pop the carb off and take a look at the float and needle valve.

The motor is barely used and everything looks as new.

It has been sat in the garage for 6 months, so there could be some fuel gum floating about in the carb...
Click to expand...

Yes. I’ve had the same problem with the DF2.5 and there have been a couple of forum threads on the issue.

Strip the carb, also clean out the engine’s fuel tank, and ditto the Jerry can you feed it from which is probably where the petrol got degraded.
 
BelleSerene said:
Yes. I’ve had the same problem with the DF2.5 and there have been a couple of forum threads on the issue.

Strip the carb, also clean out the engine’s fuel tank, and ditto the Jerry can you feed it from which is probably where the petrol got degraded.
Click to expand...

Will do.

I have a ride on mower with a twin, air cooled, 4 stroke 14hp, that runs on any old cr@p, you'd think they could make outboards as reliable...
 
RichardtheBoffin said:
Will do.

I have a ride on mower with a twin, air cooled, 4 stroke 14hp, that runs on any old cr@p, you'd think they could make outboards as reliable...
Click to expand...

I understand the main problem is the tiny size. The tiny jets of the 2.5 get blocked up very easily. That’s combined with a greater moisture problem in the marine environment, where it’s easier for the fuel to absorb some water content. There have been other threads about it, but the chemistry is beyond me. Larger engines, even just 3.5hp, are much more reliable. There’s an additional problem that small outboards get stored horizontally in cockpit lockers, flooding the cylinder.
 
Today I took the carb off and check the float bowl. There were a few tiny bits of black foreign matter in there...

So cleaned it, checked the jets and emulsion tube, blew it all through with an air line.

I made a tool to set the pilot mixture and set it to 2.5 turns out.

Emptied the fuel tank and cleaned the filter.


Re-assembled and it started first go, with no choke.

I let it idle for a good 20 mins, no problems. Stopped it and re-started a few times, no problems.

Idle speed is 1600 rpm and in gear this drops to 1200 rpm. As someone mentioned I don't want a fast idle as the little dingy will be too fast to maneuver easily.

Checked the plug and it had sooted up a little bit but nothing like before - which was a thick black coating after a minute of idling.

I shall be armed with plug spanner, wire brush etc etc tomorrow and take it out for a run up and down the river.

I might fit a small in line filter as near to the carb as possible as the one in the tank doesn't look that fine.

One thing that did occur to me, as I transport the outboard in the car, I usually run the fuel dry after turning off the fuel tap. I see that there is a drain cock for the float bowl, is that the preferred method as it will flush out any crud?

I haven't used the drain in the past as I don't really like leaving petrol all over the place, but i guess I could drain into a jam jar or something.

It just seems easier to run the motor until it uses up the fuel in the carb.
 
RichardtheBoffin said:
...
Re-assembled and it started first go, with no choke.

I let it idle for a good 20 mins, no problems. Stopped it and re-started a few times, no problems.

Idle speed is 1600 rpm and in gear this drops to 1200 rpm. As someone mentioned I don't want a fast idle as the little dingy will be too fast to maneuver easily.

...
I shall be armed with plug spanner, wire brush etc etc tomorrow and take it out for a run up and down the river.

I might fit a small in line filter as near to the carb as possible as the one in the tank doesn't look that fine.

One thing that did occur to me, as I transport the outboard in the car, I usually run the fuel dry after turning off the fuel tap. I see that there is a drain cock for the float bowl, is that the preferred method as it will flush out any crud?

I haven't used the drain in the past as I don't really like leaving petrol all over the place, but i guess I could drain into a jam jar or something.

It just seems easier to run the motor until it uses up the fuel in the carb.
Click to expand...

Congratulations!

Rather than relying on an inline fuel filter (which I bought but have not installed in the DF2.5) I was authoritatively recommended to stop crud getting into the tank in the first place. I got one of these: https://www.ebay.co.uk/i/142409715335 which I use to filter what goes in to the tank. This was partly because a small inline filter wouldn't survive for long in a marine environment, and partly because this device separates water content from the fuel, and (as I understand) that's what later causes corrosion in the tiny jets of the carb - I'm sure someone can explain how.

Re running the engine dry, everyone recommends to do so, and it has certainly helped me. It only needs the external fuel tap to do this. Then run the engine until it stops, and start it again for good measure. The internal drain tap is just so you can remove the fuel tank for maintenance without spilling its contents.

It's worked for me. Have to say, I wouldn't go for the same engine again if I had the choice. The tiny jets are asking for trouble in an environment where there's water around and it's easy to end up with dirty fuel; and when left on its side with fuel in the carb, the fuel float jams in the shut position when the fuel dries out.
 
Successful run, 40mins there, 40mins back. Never missed a beat.

(probably because I had plug spanner with me...)

Plug was light brown when I checked it after trip.
 
RichardtheBoffin said:
Today I took the carb off and check the float bowl. There were a few tiny bits of black foreign matter in there...

So cleaned it, checked the jets and emulsion tube, blew it all through with an air line.

I made a tool to set the pilot mixture and set it to 2.5 turns out.

Emptied the fuel tank and cleaned the filter.


Re-assembled and it started first go, with no choke.

I let it idle for a good 20 mins, no problems. Stopped it and re-started a few times, no problems.

Idle speed is 1600 rpm and in gear this drops to 1200 rpm. As someone mentioned I don't want a fast idle as the little dingy will be too fast to maneuver easily.

Checked the plug and it had sooted up a little bit but nothing like before - which was a thick black coating after a minute of idling.

I shall be armed with plug spanner, wire brush etc etc tomorrow and take it out for a run up and down the river.

I might fit a small in line filter as near to the carb as possible as the one in the tank doesn't look that fine.

One thing that did occur to me, as I transport the outboard in the car, I usually run the fuel dry after turning off the fuel tap. I see that there is a drain cock for the float bowl, is that the preferred method as it will flush out any crud?

I haven't used the drain in the past as I don't really like leaving petrol all over the place, but i guess I could drain into a jam jar or something.

It just seems easier to run the motor until it uses up the fuel in the carb.
Click to expand...

The best approach is, indeed, to drain the float bowl using the drain fitted, when you leave the engine for more than an week or two. This does clear out the crud before it becomes a problem and ensures 100% drain out which running the engine cannot achieve. I have permanently attached a short length of fuel hose to my 2.5 which pokes out of the casing just below the power head to make it easy to run the petrol out into a small bottle.

I'm not sure why the inline filter would not be suitable for the marine environment? I have installed a small plastic fine filter into the fuel line just before the carb. It should last forever unless it fills with crud which you can see on the outside if you install it the right way around.

Richard
 
You must log in or register to reply here.

Share this page

Top