F100- bad acceleration and rough

[timlloyd]

I have a Yamaha F100 outboard, it doesn't get used much.
The problem started about 10 hrs run time ago, it would be a little rough for 10 mins around mid power then clear and work finn.
Now it starts ok and ticks over ok, as soon as you throttle up even without a load it caughs and runs rough, doesn't reach full revs.
Ive replaced the spark plugs, 2 were quiet black, still have the problem.
I checked the spark and on all HT leads it was a weak spark, tried another lead of a car - still weak.
I pulled the Ht leads off when it was ticking over, each one made it run rougher so i presume they are all working to some degree.
All the wiring looks ok, any ideas please would be greatly appreciated.

[greasyshaft]

What is the model code?

There is an EFI and a carburetor version.

Have you checked the primary fuel filter on the engine for water or debris?

[timlloyd]

Its a carburetor type, i have checked the filter, nothing in it- alslo checked all the float chambers, they all have fuel in them.

[TownsendsFJR1300]

Its a carburetor type, i have checked the filter, nothing in it- alslo checked all the float chambers, they all have fuel in them.

Do you use any fuel stabilizer??

You carb jets are likely clogged from fuel evaporating and leaving varnish (clogging them).

The correct way would be to remove the carbs, access the idle and main jets, PULL THEM OUT (don't just look or blow carb cleaner). Inspect / clean until YOU can see visable light thru them. Some jets have horizontal holes, which all must be cleaned.

Depending on how clogged they are, you MAY get by with running a VERY strong dose of Yamaha's "RingFree" thru the fuel system. If fuel can get thru (no fully clogged jets), this may be enough.

I have had success with very clogged carbs, W/O pulling them apart. By simply draining the fuel (from the float bowl drain screws), then adding STRAIGHT Seafoam into the carb thru the fuel line and letting it sit overnight.

Before trying to crank the engine, DRAIN IT ALL OUT of the bowls (so you DON'T cause an hydralic lock). If your lucky this may work for you..


In any case, once this is repaired, use Ringfree regularly to keep your system clean and a good stabilizer. You may run the engine dry everytime but fuel STILL remains in THE FLOAT BOWLS and WILL cause issues.

Pulling the drain bolts, (draining the carbs), a spritz of air will also help if the engine will be sitting for any long, lenth of time..

[timlloyd]

Ok, thankyou for the advise, ill give it a try and see what happens.

[timlloyd]

I pulled all the carbs off. found one with blocked jet. looked clear but film was over the hole, another partially blocked - Runs great now, will add additive I think to stop it happening again. - Thanks for you help.

[TownsendsFJR1300]

I pulled all the carbs off. found one with blocked jet. looked clear but film was over the hole, another partially blocked - Runs great now, will add additive I think to stop it happening again. - Thanks for you help.

Excellent! Thanks for the update too.

Pay extra for the Yamaha RingFree (it dilutes 1oz / 10 gallons) and use it regularly. If you do, it will be the last time you pull the carbs off.

I like K100 or Gas Shok as a fuel stabilizer, both work EXTREMLY WELL. Any Yamaha stabilizer should be fine too. IME, I would keep away from Stabil, I've had carbs varnish up within a month using that product..

Seafoam is a decent cleaner /Stabilizer as well and is pretty cheap. RingFree definitly the BEST and highly recommended.

[timlloyd]

Acceleration problem

HI AGAIN.

Ive now tested the boat on water, it accelerates to 2000rpm nice and smooth then when you push throttle fully forward it looses all its power then slowly climbs to 3200rpm with not much power.
I've pulled the spark plugs, no1(top cylinder) is blacker than the rest.
I've pulled the no1 carboy off and soaked in it carbcleaner for a few hours- not tested the outcome yet.
tried to get sea foam but I'm in NZ and they will not ship it for me!
Hope you can help.