F80 Backfiring and Shaking at Idle

[mattro51]

I have a Yamaha F80 that is, what appears to be backfiring through the air intake. This happens at random intervals (10-20 seconds apart) with no increase or decrease in frequency with change in RPM. When the motor appears to backfire it sounds almost like a "tick" and the motor hiccups for a split second. The motor also shakes excessively while at idle, smoothing out with increased RPM's. Thus far I have changed the plugs and fuel lines. Other than being slightly annoying these problems do not seem to affect the idle, acceleration or running of the motor in general. Any help would be appreciated.

[almetelo]

Hi!

Is your outboard a carburator model?
You may have a clogged/dirty jet/s. Unfortunetaly this is common on these models.
You need to clean them and re-sync carbs.
If is your 1st time may need 3/4h to do that and a special tool.

If your model is EFI give us some more info.

Good Luck

[mattro51]

It does have carbs.

[almetelo]

If you want to do it your self we can give you a few tips.
Anyway my recomendation is get a pre-fuel filter with water separater (if you dont have it-) this will reduce/prevent the trouble of water from fuel in carbs and this happen again... Also if you motor will be stored a couple of months drain the carbs.

Good luck

[mattro51]

I have taken the carbs off of a honda 4 stroke and cleaned them but never tackled a Yamaha. It looks a little more complicated than the honda but seems manageable. Also I don't have the sync tool. Any tips on removal and installation as well as location of a sync tool would be appreciated. Thanks.

[mattro51]

Also what are the chances that this is a timing issue?

[almetelo]

At 1st sight my guess is that may be a fuel problem.

These engines have this "symptomes" when carbs are dirty/clogged or water in the fuel. (I have a F100 carbed and I already have seen that...) Not always we can clean the carbs properly a 1st attemp.
To clean the carbs use compressed air and if dirty use a product to clean them. I use brake cleaner fluid but you may find others at your own tast and maybe better (or not) Make sure you remove the carburetor rubber parts when using some products. To remove the carbs I take off the intake/air filter, carbs and mainfold all together in 1 piece and is much easyer work on it.
Because is your 1st time doing this I recomend you take some pics in case of doubt later.
After fit all again on motor you'll need to synchronize the carbs with vaccum gauges / carburetor synchronizer/balance. After all 4 carbs synchronized you must tune the air/fuel mixture.

[almetelo]

Have a look on videos and attachment

Yamaha F60 - YouTube

Outboard Yamaha 50 HP carbs synchronization - YouTube

Good luck

[madharchod]

i dont know if you can get hold of the spray called "start ya bastard" it is a Aussie invention but i tell you it works magic with carburater and efi models engines just saturate the carbs and the keep spraying in the intake manifold and rev the engine slowly until the spurting and coughing goes away . you dont have to open or synchronize the carbs all this spray does is cleans the shit out of the carbs and dissolves every bit of grit and grind there is inside leaving your inside carb like new
cheers

[mitch]

start ya bastard

Machard geez some of your ideas

Thats a load of bullshit .... ya a ****y wobbler start ya bastard is the same as c r c aerostart a ether based starting aid it wiil not clean bloked jets all is doing is replacing lean fuel caused from blocked jets

clean your carbs paying attention to idle jets

[rodbolt17]

there simply is no mechanic in a can.
you can spray a 55 gallon drum of snake oil down the carb throat and never touch the internal passages and jets.
backfire through the intake is a classic sign of a lean air fuel ratio.
as ign timing is con*****ed in pairs don't chase that rabbit.

[madharchod]

ha ha ha since when have Yankee started to know about Ozzie products to ya Mitch there are so many products made by start ya bastard and one of this is the carb cleaner ,if only you know the difference between CRC and start ya bastard its just like your head and your hind side buddy

[mitch]

So you mean throttle body carby cleaner made by nulon not start ya bastard also made by nulon ya been in fiji to long ya should put down the kava bowl and step away

also kava will not clean carbs

I think you might have a id ten t fault stop *****ing

[mattro51]

Chill boys and girls. I'm going to pull the carbs, clean and see what happens. Anyone know of any tutorials out there for this. If not I can manage.

[99yam40]

a carb is a carb , cleaning should be no problem.
Now setting after reinstalling maybe different story

See what your service manual calls for
4 strokes seem to require a multichannel manometer