2 stroke outboard. Any ideas?

stu9000

stu9000

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Old Yamaha p45 2 stroke. Was working great but now stops about 2 minutes at high revs.

I've checked the fuel filter, the lines and the tank has been cleaned. The carb has been cleaned several times including the needle bit. Water flow seems OK. It isn't hot or steaming. I changed the plug which did seem a bit oily but the new plug isn't getting build up. The spark is good. Starts absolutely fine. Then stops unless throttle right back. Feels like fuel starvation but I cannot work out where. Maybe running rich but I can't find a way to adjust this. Any ideas?
 
Are you saying it runs at high revs for about two minutes, then stops? Does sound like fuel starvation. Check vent is working in fuel tank, then suspect fuel pump. That's where i would start anyway.
 
stu9000 said:
Old Yamaha p45 2 stroke. Was working great but now stops about 2 minutes at high revs.

I've checked the fuel filter, the lines and the tank has been cleaned. The carb has been cleaned several times including the needle bit. Water flow seems OK. It isn't hot or steaming. I changed the plug which did seem a bit oily but the new plug isn't getting build up. The spark is good. Starts absolutely fine. Then stops unless throttle right back. Feels like fuel starvation but I cannot work out where. Maybe running rich but I can't find a way to adjust this. Any ideas?
Click to expand...
Impeller. Check the tell tale.
 
OK Im getting very confused now.
She starts well.
Runs flawlessly for about 2 mins and then stops dead.
If I react quickly and drop the revs it runs ok, but it dies if I increase the revs.

I checked the fuel lines and petrol is getting to the float bowl.
The water out never gets hot so I don't think its seizing.

I have taken the carb to bits three times today. Parts all soaked in white spirit.
No debris. The needle looks fine. The outer casing bolt thingy that the needle goes into looks clear.

Could it be electrical?
The old plug end cap disintegrated. I bought a new one and some 7mm ht lead and that has been working well.

I changed the spark plug. The old one was oily which made me wonder if the fuel was a bit old, or maybe had a bit too much 2 stroke oil in it. I put fresh fuel in and have not dosed it with 2 stroke oil yet. I have not noticed any build up on the new one yet.

Ill try another plug when it arrives.
Ill take the carb apart again and fiddle with the settings. But its pretty basic so not much to change.
Ill get some fresh from the forecourt fuel.

What else could i check?
 
I had exactly the same problem with my mercury 3.5. I stripped the carb down numerous times and cleaned out the jets. Eventually I decided to sell it as parts and then a second hand carb came up on ebay. It was a risk but it worked perfectly from day 1.
 
A couple of ideas----
If it runs well until it warms up and then wont run well until cold then it could be running too rich, a bit like an old car with the choke stuck on.
The other thing is the ignition coil. These can fail when hot thus showing a good spark when tested but then failing intermittantly as they overheat.
 
stu9000 said:
Old Yamaha p45 2 stroke. Was working great but now stops about 2 minutes at high revs.

I've checked the fuel filter, the lines and the tank has been cleaned. The carb has been cleaned several times including the needle bit. Water flow seems OK. It isn't hot or steaming. I changed the plug which did seem a bit oily but the new plug isn't getting build up. The spark is good. Starts absolutely fine. Then stops unless throttle right back. Feels like fuel starvation but I cannot work out where. Maybe running rich but I can't find a way to adjust this. Any ideas?
Click to expand...
The symptoms certainly suggest a fuel flow problem but you seem to have covered the obvious possibilities.

I believe the carb is similar to that in this diagram : https://cdn.boats.net/MTA/d/1/MTY2NTgy-16849671.png
If so
Check that the float falls freely
check that the needle is not sticking in the seat (#12)

Double check the main jet (#5)

Screw # 16 may be the idle mixture screw ( some parts diagrams identify it as such, some don't )

The high speed mixture is adjusted by moving the position of the clip #20 on the metering needle #19 ( note its current position before you alter it)
 
VicS said:
The symptoms certainly suggest a fuel flow problem but you seem to have covered the obvious possibilities.

I believe the carb is similar to that in this diagram : https://cdn.boats.net/MTA/d/1/MTY2NTgy-16849671.png
If so
Check that the float falls freely
check that the needle is not sticking in the seat (#12)

Double check the main jet (#5)

Screw # 16 may be the idle mixture screw ( some parts diagrams identify it as such, some don't )

The high speed mixture is adjusted by moving the position of the clip #20 on the metering needle #19 ( note its current position before you alter it)
Click to expand...

Fantastic advice as ever.
The diagram exactly matches my carb.

The float does fall freely but the needle did seem to stick a little on rising.
The main jet is definitely clear.
Screw 16 is the idle.
The high speed mixture adjustment is my best hope. Ill be looking at that tomorrow.

Thanks again

S
 
Biggles Wader said:
A couple of ideas----
If it runs well until it warms up and then wont run well until cold then it could be running too rich, a bit like an old car with the choke stuck on.
The other thing is the ignition coil. These can fail when hot thus showing a good spark when tested but then failing intermittantly as they overheat.
Click to expand...

Hmm lets hope its not the coil. Is there a way to test for this?
 
stu9000 said:
Fantastic advice as ever.
The diagram exactly matches my carb.

The float does fall freely but the needle did seem to stick a little on rising.
The main jet is definitely clear.
Screw 16 is the idle.
The high speed mixture adjustment is my best hope. Ill be looking at that tomorrow.

Thanks again

S
Click to expand...
Make sure you note the original setting for the mixture

If the float needle is sticking it could well be the cause of your trouble. Some ( soft tipped ) needles clip to the float arm so that they are pulled off the seat. Check if this should be so

You imply in #1 that it will keep running if you throttle right back. If that is so the coil is not likely to be at fault Spark should be able to jump 1/4" in free air
 
I think it's fixed. I tried changing the needle setting but the problem persisted so I returned it to the original setting. I also took the float bowl assembly to bits. I ran the engine with the plastic float removed and it still died on me which made me think there was a blockage somewhere in the lines. The solution was taking the fuel in spigot on the carb to bits. I found a small amount of fibre in the metal pipework which I think was enough to cause fuel starvation at high revs.
 
stu9000 said:
.... I put fresh fuel in and have not dosed it with 2 stroke oil yet. ...
Click to expand...
It's probably going to seize if you run it with no oil in the fuel!

Another thing to check is the fuel tap assmbly into the tank, there is probably a little gauze inside the tank, which is probably full of crud.
I'd strip and clean the tap etc, or at least back flush to clean the gauze and empty the tank via the filler cap.
 
TernVI said:
It's probably going to seize if you run it with no oil in the fuel!

Another thing to check is the fuel tap assmbly into the tank, there is probably a little gauze inside the tank, which is probably full of crud.
I'd strip and clean the tap etc, or at least back flush to clean the gauze and empty the tank via the filler cap.
Click to expand...
Two good points , especially regarding the fuel

I think, however, you will find that the fuel tap is remote from the tank and that there is an inline filter between it and the tank which the OP says he has checked

Strange that there is enough debris getting into the carb inlet connection to severely restrict the fuel flow unless the filter is defective
 
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