25hp wont stay running

guys
i have a 1988 yamaha 25hp, 25SG model, two stroke tiller.
had the carbs rebuilt by the local mechanic 8 weeks ago, and he also suggested i buy a new plastic portable 6 gallon fuel tank and fuel line and primer ball. i bought the best ones from bass pro shops.
right after the rebuilt carbs, i took it out and it ran perfect for probably an hour, off an on, stop and restart, etc.
within these 8 weeks, i have started it here at the house at least once every two weeks. no problems.
yesterday i was out fishing, it started right up, and ran at top speed for probably 10-15 minutes, then it bogged down, and although it was still running, it acted as if it were running on one cylinder, or a fuel problem. i shut it off, pulled the plugs, which looked fine, and within 10-15 minutes of setting, started it up, and it ran perfect for about 5 minutes this time, then did the same thing, bog way down and sputtering.
at that time we started fishing, and within about 45 minutes wanted to move on to another fishing spot.
started right up and ran for 8 minutes, and bogged down again.... this problem never went away.
right after it would bog down, i pulled the cowl and touched the engine and both coils and cdi unit, and all were not hot at all, everything seemed ok.
also, i did have the vent screw fully open on the plastic fuel tank. but right after one mishap i unscrewed the fuel cap and it vented quit a bit. but the primer ball was NOT collapsed.
so, on the next run i kept the fuel cap only half on, making sure it was getting vented enough, and it still bogged down.
i am at wits end..... do any of you have any suggestions ?
could the coils or cdi unit be failing ?
although the female end of the quick disconnect is new, its the original male end thats in the engine, and it does seem to be worn, since when i connect the female to it it will rock back and forth. im thinking maybe that connection could be faulty and sucking air ?
im going to order a new male connector and give that a try, and was just wondering if any of you had any other suggestions ?
thanks guys...

Re: 25hp wont stay running

any suggestions guys... ?
thanks much

Re: 25hp wont stay running

Hi Fishfink. The symptoms you're describing make me think that some of your electronics are overheating, failing and causing you to drop a cylinder, then once the motor has time to cool, it will again run normally. Thanks to the recent cleaning and rebuild, the carbs should be good and the new tank and lines are a great addition as well, so fuel shouldn't be an issue, and the motor will start and run which means your compression is ok, which means there must be an issue with the spark. I don't know much about electronic ignitions myself, but if you do a search here in the Yami forum for testing an ignition system, I'm sure you can find something that will get you started. Good luck.

Aside form this particular issue, how do you like your motor? I've heard good things about yami 2-strokes. Is is an "Enduro" model? I think they have red decals, rather than blue.

Re: 25hp wont stay running

I have a 1987 25esh and it seems to be doing the same thing except at WOT is has an intermitted slight miss. I pulled the plugs to watch the spark and one looked like it was only firing about half the time. Other one looked real good.

Re: 25hp wont stay running

kfa4303 said:

Hi Fishfink. The symptoms you're describing make me think that some of your electronics are overheating, failing and causing you to drop a cylinder, then once the motor has time to cool, it will again run normally. Thanks to the recent cleaning and rebuild, the carbs should be good and the new tank and lines are a great addition as well, so fuel shouldn't be an issue, and the motor will start and run which means your compression is ok, which means there must be an issue with the spark. I don't know much about electronic ignitions myself, but if you do a search here in the Yami forum for testing an ignition system, I'm sure you can find something that will get you started. Good luck.

Aside form this particular issue, how do you like your motor? I've heard good things about yami 2-strokes. Is is an "Enduro" model? I think they have red decals, rather than blue.

Click to expand...

thanks much for the input kfa4303...... for now i have ordered a new male fuel disconnect that bolts to the front of the motor, and a fuel pump diaphragm. if these dont fix it i will either take it to my mechanic and let him diagnos it, since i dont know much about electric, or i will order two new coil packs and go from there.

i have only had the engine since september and this was my first fish trip with it, but i do like it a lot. its a big improvement over the 4 stroke 15hp honda i did have on it. with just me in the boat it wil get to 31mph.. im really happy about that.
it has the blue decals... 25SG model
thanks again for the help..

Re: 25hp wont stay running

Wow 31 mph out of a 25 hp is pretty dang good. My neighbor has a big 115 Yami and loves it. I've never owned a "new school" motor with electronic ignitions aside from my little 3 hp air-cooled Gamefisher. I run an old '66 20 hp Johnson myself. She's a little rough around the edges, but is very reliable and will push me in my 14' tinny at +20mph. Where abouts in South Florida are you? I'm in the frozen North of Tallahassee! It's a bone-chilling 75 F today I think I'm gonna take the boat out before winter really does get here.

Re: 25hp wont stay running

kfa4303 said:

Wow 31 mph out of a 25 hp is pretty dang good. My neighbor has a big 115 Yami and loves it. I've never owned a "new school" motor with electronic ignitions aside from my little 3 hp air-cooled Gamefisher. I run an old '66 20 hp Johnson myself. She's a little rough around the edges, but is very reliable and will push me in my 14' tinny at +20mph. Where abouts in South Florida are you? I'm in the frozen North of Tallahassee! It's a bone-chilling 75 F today I think I'm gonna take the boat out before winter really does get here.

Click to expand...

yes, i was surprised at the 31mph myself. although it is a really light 14ft aluminum flat bottom, and that was just with me and nothing else in the boat. here is a short video of it right after i got the carbs rebuilt 8 weeks ago.

Jon Boat yamaha 25hp two stroke - YouTube

i like older motors, for their simplicity....
im down here in hollywood/pembroke pines... yea, im sure you are probably 15* cooler up there in north florida. im a florida guy, and dont like anything above 60*. lol

hope to get my male and female quick disconnect fuel tank fittings and the fuel pump diaphragm in by weeks end, then try it out after that.... if i still get the bogging at WOT, i will then take it to the mechanic and let him figure out whats going on with the electric... dont want to throw parts at it if that aint it.

thanks

Re: 25hp wont stay running

I have '94 25 Yamaha 2 stroke that's doing almost the same thing. It idles fine for a little while, then it starts bogging down. If I let it die, it takes forever to get it started again. As long as I kill while it's idling OK, it fires up as soon as I touch the starter.

I also just had mine in the shop and it was all checked out. I'm going to talk to the shop and see if they want me to try a new fuel line and bulb.

Fishfink, several people have told me the inside of old fuel lines could collapse. I believe mine, and yours, is running out of fuel.

Please post if you come up with an answer.

John

Re: 25hp wont stay running

jspriddy said:

I have '94 25 Yamaha 2 stroke that's doing almost the same thing. It idles fine for a little while, then it starts bogging down. If I let it die, it takes forever to get it started again. As long as I kill while it's idling OK, it fires up as soon as I touch the starter.

I also just had mine in the shop and it was all checked out. I'm going to talk to the shop and see if they want me to try a new fuel line and bulb.

Fishfink, several people have told me the inside of old fuel lines could collapse. I believe mine, and yours, is running out of fuel.

Please post if you come up with an answer.

John

Click to expand...

yea, next time i go for a test ride, i will have the cowl off and see if the indie fuel lines are collapsing. i do know the new line and primer ball from the tank to the motor is not collapsing.. thanks

Re: 25hp wont stay running

I'd recognize those FL canals anywhere. Although, we don't really have them here in the "highlands". The boat moves right along without and porpoising and she seemed to hop right up on plane. Can't ask for much more than that. The fact that the motor runs that well means spark, fuel and compression are all there. The compression and fuel delivery aren't likely to change from one moment to the next, so I'd focus on the spark. Great vid too. I just made one myself. Although, it's a little tricky with the tiller in one hand and the camera in the other. I'd love to get a Go Pro, or something similar. Good luck.

1966 Johnson FD-20C, 20hp outboard on a 1959 Arkansas Traveler DUT-14 aluminum runabout - YouTube

Re: 25hp wont stay running

kfa4303 said:

The fact that the motor runs that well means spark, fuel and compression are all there. The compression and fuel delivery aren't likely to change from one moment to the next, so I'd focus on the spark.

Click to expand...

yea, when i took the video it was running perfect.... until this past saturday. it still gets up on plane just like in the video and runs good for 5-10 minutes, then bogs right down like i pulled the kill switch, but will stay running, as if on only one cylinder. im gonna try the fuel fittings and maybe the pump, then go for a test drive. if it happens again i will pull each plug wire and see if its a dead cylinder and maybe a coil....

you got a rally cool boat there. loved the video. i love antique things, especially motorized.
take care

Re: 25hp wont stay running

a timing light or spark tester should show if spark is being lost on one of the plugs.

Fuel testing is simple too http://forums.iboats.com/engine-fre...ow-testing-your-boats-fuel-system-283363.html

Re: 25hp wont stay running

99yam40 said:

a timing light or spark tester should show if spark is being lost on one of the plugs.

Fuel testing is simple too http://forums.iboats.com/engine-fre...ow-testing-your-boats-fuel-system-283363.html

Click to expand...

thanks so much for the info and the fuel testing article... that will come in handy.
today i installed the new male and female quick disconnect fittings, and rebuilt the pump diaphragm. will have to wait til sunday, or next weekend, to give it a test.

i do have a quick question.. i have a VERY SLIGHT fuel leak coming from the diaphragm. when taking the unit apart, the original gaskets were stuck pretty good to the other parts.... im assuming from age. i installed the new diaphragm and gaskets dry. should i have used some sort of sealer ? i totally cleaned all the old gasket material off before installing the new gaskets....
will it "self seal" after a few run ins ? hopefully it will seal up on it's own.

thanks again.

Re: 25hp wont stay running

Is best to replace gaskets . I do not see it healing itself

Re: 25hp wont stay running

99yam40 said:

Is best to replace gaskets . I do not see it healing itself

Click to expand...

thanks much... but i did put brand new gaskets and diaphragm in.
i didnt see any sealer on the original gaskets, so i installed the new ones dry. is that how to install the gaskets and diaphragm, or should i have used sealer ?
thanks

Re: 25hp wont stay running

ok guys, took it for a test run this morning.
after the new fuel pump diaphragm, male and female quick disconnects for the tank, and fuel filter, it does the same thing.
runs awesome for 5 minutes, comes up on plane quick and runs at 30mph, then bogs right down, instantly, after the 5 minutes, and seems to be running on only 1 cylinder.
im now thinking it might be an electrical problem ?

how can i check my two coils ? i have a multimeter, can someone tell me how to check them ?

if i can check them myself, and one or both check out bad, i will replace them myself. if i cant figure out how to check them, i will bring it back to the mechanic for him to diagnose.

thanks guys

Re: 25hp wont stay running

UPDATE UPDATE UPDATE......
PROBLEM SOLVED...

guys, although my oil injection tank mounted to my engine was half full, it was low enough to throw the engine in "safe mode", which retarded the timing and made it run bad, as not to burn the engine up.
i went out for a test run this morning without adding the oil, and sure enough after 4 minutes of full throttle it would die down and was running like on only one cylinder.
shut it off, added oil, had it started within a few minutes, and ran it full throttle, back and forth the canal for an hour, getting it up to 33mph, and it ran flawlessly...

many thanks to everyone who helped me out with this problem...
i am now ready to fish.... thanks

Re: 25hp wont stay running

Schweeeeeet!!!! Gotta love it when it's something simple. Pretty clever little machine (maybe too clever). Keep that oil handy

Re: 25hp wont stay running

kfa4303 said:

Schweeeeeet!!!! Gotta love it when it's something simple. Pretty clever little machine (maybe too clever). Keep that oil handy

Click to expand...

yea, nice and simple... wish i would have thought of it sooner. lol. but it could have been worse... and yes, its a clever little machine for sure... nice to know the oil injection system is working correctly.. and yes, i will now top the oil off every time i go out, and have a spare bottle on board...
thanks again everyone...