Yamaha 15hp Enduro wont run - Please help!

[Tspringer]

My family and I are currently anchored in Lake Sylvia in Ft. Lauderdale and trapped on the boat. LOL.... cascading failure galore! Westerbeke generator wont start, main engine alternator is dead and the dinghy engine won't run. Lets just say the peeps are nearing mutiny.

I have a new to us recently purchased 1995 or so Yamaha 15hp Enduro 2-stroke. First time we put it on the dinghy, she fired right up and ran great for about 2 minutes before the prop hub spun. Then she would rev but not go, like a slipping clutch sort of thing - classic spun prop hub.

So I got a new prop and installed it. Tried to fire up the engine - it will fire up with the choke out and revs up quick and then dies.

I removed the carburetor from the engine, replaced the fuel pump diaphrams and sprayed carb cleaner all over everything cleaning it all out as best I could with emphasis on the jets and such. Also replaced the fuel filter. I could not get a complete carb rebuild kit, nobody in Ft. Lauderdale has one in stock.

My efforts on the carb gave no result. I pump the bulb until its hard - pull out the choke, give it 30% throttle and pull the starter cord. The engine will fire, rev up and then die. Same thing over and over. Pushing in the choke after it fires seems to make no difference. Leaving the choke out makes no difference. Fires - revs - dies. Giving it full throttle after it fires does nothing. Cutting the throttle back after it fires does nothing.

Any suggestions on what to try are greatly appreciated. Also any recommendations on a good 2-stroke Yamaha guy in Ft. Lauderdale are appreciated.

Note - I do not know what model engine this is. There is no data plate on the engine mounting bracket as there should be. The guy I bought it from thought it was a 1995 model. It is very clean and was supposedly lightly used in fresh water only - purchased in Northern Alabama the seller used it on a fishing jon-boat. The local Yamaha dealer here in Lauderdale thinks it is a 15MLHT based on photos of the engine and the carb design - the last letter T which is year model could be incorrect.


Terry

[Spot]

Sorry to hear of your (continued) troubles.

Sounds like a fuel delivery issue.

Did your new dinghy arrive? Close to amenities? Paddle ashore and treat them to dinner?
What will it take to get the main alternator fixed/replaced/wired to work correctly?
I hope you can make repairs and all can enjoy boating a bit more.

[tkeithlu]

Terry, I'm sorry to hear it, and particularly because it may be really hurting the future of your dreams. That kind of day is just frustrating.

From here, I can't see whether the spark plug is wet (fuel in, not spark?), the plug is sparking (take out, ground it, pull rope, look for spark on each rotation), the fuel is old, or other possible causes, and on little two-strokes there are a bunch of causes.

Right now, what's the best you can do? Can you get a tow to a marina? Once the peepers are full of grilled cheese, you might have time to start through this mess, and with specific questions maybe some people on the forum more knowledgeable than me could help.

[Vasco]

Take the carb apart again. Clean with carb cleaner. Make sure the jets are clean. Might have to do it a couple of times. Just fixed a buddy's yesterday. If you're using fresh fuel and there was no cruddy fuel left in the hose you'll be fine.

[Sardean]

There are two jets in the carby, the easy jet to find one is the run jet that is in play at higher revs, this does not sound blocked. The hard to find jet is the idle or low revs jet ,this sounds like your problem. Remove both jets and clean with thin wire. Also clean the little holes in the side of some jets. I find a strand of wire from untwisting some fishing trace works best. Let me know how yo go.

[Sardean]

[Sardean]

Part 4 is the main jet , the tiny holes in its side may be blocked and make it run badly. part 5 is the idle jet which will be blocked as well and make it so it won’t start without choke and won’t run at low revs. Note when taking out the brass locking screw ,part 3, use an exact size screwdriver even if it means filing the sides so it fits perfectly or you can damage the brass screw

[sparrowhawk1]

+1 fuel delivery problem. After it stalls open the drain plug on the carb bowl, if no fuel comes out you know that's your problem. Most likely it's the needle valve. It opens enough to fill up bowl so the engine will run briefly but can't keep up with demand. Dissemble and clean.

[a64pilot]

You can eliminate the fuel pump by pumping the bulb, if the bulb is tight it doesn’t matter if the pump works or not, there is still fuel in the carb. Remember that cause you can get home with a bad pump by keeping the bulb filled.
I’m betting you need to clean the carb well, you need to watch a you tube or something to know what to clean, carb cleaner isn’t going to do much, but be careful with wire as you can easily ruin a jet, better to use mono filament fishing line.
A stuck needle valve is another’s possibility, you know how to set the float level etc?

[rbk]

I agree with pulling the jets but before that pull the plug boot and check the connection. Those new two part plugs are notorious for the screw top terminal unthreading and causing spark problems. It all appears tight until you remove the boot and the terminal is now stuck inside the boot. It’s getting harder and harder to find a true solid core plug it seems. I’ve almost blown sled engines from them popping off cursing along, filling the cylinder with fuel then making connection again = massive backfire. Surprised the plug didn’t shoot through the hood.

[skipmac]

I had the same problem with an outboard, same symptoms. Pulled the carb apart and completely cleaned it with no change. Got desperate and started trying random things. When I replaced the spark plug problem cured.


My motor was a single cylinder and the Yamaha two so less likely that the plugs are the problem but wouldn't hurt to check the spark if the carb cleaning doesn't work.

[Tspringer]

THANK YOU for all the replies - great info and very helpful.

We are heading over to Pier 66 Marina to get a slip for a few days later this morning. I really hate paying $200 or so a night for a slip but sometimes you just have to bite the bullet. We are on the waiting list for the Ft. Lauderdale downtown docks and Cooley's landing so hopefully we can get in there soon. The weather is fantastic right now and for the first time in a few weeks a great window is open to head to the Bahamas so that plus the holiday being past should mean some cheaper marina slips will open up.

I have a referred local tech coming tomorrow to help me troubleshoot the generator and alternator / batteries. I am going to take the Yamaha apart again and do as suggested in this thread to clean the jets with care and really clean everything. If that does not do it - I will likely just buy a new carb, they are not crazy expensive.

I did pull both spark plugs prepared to replace them but they look new and have no carbon buildup. Given that the engine will initially fire and rev quickly but then dies I do not think spark is the issue - it's fuel. The idle jet having problems or the float not working correctly seem like likely suspects that I will check very close.


Terry

[gonesail]

take it to a dealer and trade for one that works

[skipmac]

Originally Posted by gonesail

take it to a dealer and trade for one that works

Well I'll be happy to take any 2 stroke Yamaha 15s you want to get rid of. One of the best small outboards made. Lighter that comparable 4 strokes, reliable and fast.



OP may be having an issue but unless the engine is totally blown (very unlikely) this motor is well worth the effort to get it running.

[a64pilot]

The Yamaha Enduro 15 weighs 40 kg, or 88 lbs. that is 5.87 lbs per hp.

The Suzuki 20 four stroke weighs 99 lbs, or 5 lbs per HP

The Yamaha two stroke Enduro 25 HP weighes 118 lbs
For 4.8 lbs per HP

For the HP the four stroke Suzuki is lighter than either two stroke Yamaha.