Yamaha F80AET only running on 2 cylinders for about 30 seconds before stopping

[Dipper78]

Hello all

Any help or assistance in diagnosing the fault I have with my engine will be appreciated.

I have a 2003 F80AET that will start and run for about 30 seconds before dying.
Having removed the air intake I have discovered that there is no induction through the Carbs supplying cylinders 2 and 4. Cylinders 1 and 3 draw and therefor it is only these 2 that the engine runs on before cutting out.

Before I get too involved in stripping the engine down can anyone offer insight or specific areas of investigation - next best move?

Kind Regards
Jim

[fairdeal]

have discovered that there is no induction through the Carbs supplying cylinders 2 and 4.

hmmm. no "suck" for suck, squeeze, bang, blow ?

perhaps a compression test on those cylinders to confirm no "squeeze"
a peek in through the spark plug hole (w/ borescope if available)
remove the valve cover and see what's going on with the cam & valves

[Dipper78]

Fairdeal

I have just this minute acquired a compression test kit, next available opportunity will aim to confirm no "squeeze" I do fear that it will be quite an involved strip down. However, rarely are things beyond repair, I have limited experience working on outboards. Can you recommend the best place to find a comprehensive workshop manual for this engine?

Borescope is a great idea I must know someone with one.

Thanks

Jim

[walleye1]

Yamaha Service Manuals.pdf

[Dipper78]

Walleye1

Thank you I will search through to determine part number and search from there.

Cheers
Jim

[zenoahphobic]

I think we need a bit more information. There will always be some suction even with a hole in the piston (2?). The only way would be that those two pistons aren't moving, and if that is the case you would have massive damage that you would hear when it does run. At least you would have had a Big Bang moment.

Having said that I had a Briggs and Stratton slasher that just went quiet and freewheeled to a stop, just like it was switched off. The clue came when the starter effortless spun the engine with no start. The con rod had completely broke into bits but did not interfere with the crankshaft! Mind you the engine was horizontal, the bits just laid there in the bore, the crankshaft happily spinning from it's inertia for quite some time.

[pstephens46]

I think we need a bit more information. There will always be some suction even with a hole in the piston (2?). The only way would be that those two pistons aren't moving, and if that is the case you would have massive damage that you would hear when it does run. At least you would have had a Big Bang moment.

Having said that I had a Briggs and Stratton slasher that just went quiet and freewheeled to a stop, just like it was switched off. The clue came when the starter effortless spun the engine with no start. The con rod had completely broke into bits but did not interfere with the crankshaft! Mind you the engine was horizontal, the bits just laid there in the bore, the crankshaft happily spinning from it's inertia for quite some time.

Zeno....

What is a slasher?

On another note, the Warmblood continues to
progress. We didn’t realize how young a 6 year old horse truly is. He got a little big for his britches awhile back. Got a solid tune-up from a pro and has been steady since. Unfortunately this pro lives in FL. 4 hours away. Need a cowboy/cowgirl on call nearby. Just in case he decides to go off the rails again. Which he will...

[Dipper78]

Zenoahphobic

I have only just started investigation into the problems with this engine, over the weekend I will check compression and have a look at Cams etc. The engine was not running at all when I took ownership of it but felt I paid a fair price for the boat and trailer given a non running engine.

Since then I have had it running but only on 2 cylinders, being a naturally sceptical I feel that it not running was possibly contrived, not being seized gives some hope of repair. Deciding whether or not the cost of repair will be economical or not is the difficult part. The whole cause and effect equation. Once I have an idea about the damage that has been done I will be looking for and asking for insight into what may have caused the problems we find

Unfortunately I do not know what caused the engine to fail which would obviously be useful information. I personally did not experience a "big bang moment"

I will post any further information as I get it.

Regards
Jim

[zenoahphobic]

Zeno....

What is a slasher?

On another note, the Warmblood continues to
progress. We didn’t realize how young a 6 year old horse truly is. He got a little big for his britches awhile back. Got a solid tune-up from a pro and has been steady since. Unfortunately this pro lives in FL. 4 hours away. Need a cowboy/cowgirl on call nearby. Just in case he decides to go off the rails again. Which he will...

It's funny the language differences. A slasher is a grass and small scrub cutter usually self propelled and walk behind (hence slashing).
Yes persist with the warmblood. Good to have someone else regularly available to ride them. He'll come good after 15 years of age!,

[rodbolt17]

test the spark,do a leakdown test, in this case a compression test is quick and easy.
most likely the carbs are gummed up and as soon as the enrichment shuts off it dies.
you have to have a manometer,4 channel, to correctly sync the carbs at reassembly.