70HP Yamaha low rpm problem

[Woogie]

Hi there, i've got a small problem with my Yamaha 70 which only happens at low rpm, it seems as if it is struggling to hold the rpm up to around 1500 and sometimes on opening up the throttle it struggles for a couple of seconds and then is ok

[Ken]

Woogie,
It could be a number of things, but if the motor has set up for any length of time without being run,say four months or longer, then probably the carbs are gummed up, and particularly the low speed jets.
If the outboard has not been de-carbonized in the last two years, I would do a shock treatment with Seafoam. This would not only de-carbonize the motor, but also could quite possibly clean up the carbs. If not, then I would remove the jets and clean with Berryman's Chemtool. If that doesn't work, then tear carbs all way down and clean and replace gaskets (install a carb kit).
Like I said, it could be a number of things - if the plugs are fouled, then replace.
If you don't already have one, get yourself a manual at yamahapubs.com - it will pay for itself.
Good luck,
Ken K

[Woogie]

Thanks Ken, I haven't de-carbonized and i've had the motor for 1 1/2 yrs so i'll try that first

similiar problem

similiar problem...bottom carb overfills with fuel and pushes it out the top of the carb. pulled all carbs and removed bowls inspected and cleaned all jets etc with carb cleaner and put back. still same problem. runs on choke but will not idle with weak rpms. could it be from the fogger used to winterize. maybe bottom plug is fouled? what else needs to be checked here?

First thing I'd check and possibly replace are the plugs since their the cheapest.
Then go from there, sounds like you've done alot of trouble shooting already.

would a fouled plug cause the gas to flow out of the top of the carb like its doing now?? i guess it has to go somewhere if its not firing...

Not sure if a fouled plug could cause the gas to flow out of the top of the carbs but plugs are cheap.

I just tore my 70 Yamaha engine block apart last week to home out cylinders 1and 3 -- also having to re-bore #2
so I'm learning as I go. I took alot of pic's as I broke down my engine, to post.

Good luck on your project, folks here should be able to help you along.
I'll post my pics' on here later tonight.

anyone else have this problem? 1987 70 hp

[boats.net]

The float valve in carb is not seating or a hole in float, if have to run on choke then carbs still have plugged passages or plugged jets.

been there

rebuilt mine last spring lost number 2 cylinder sleeve mine is a 1990 this year 1st time out had same problem cleand carbs the bottom float was gummed up and stuck cleaned the carbs new plugs changed fuel runs great didnt take long was done in an afternoon (when i say rebuild new everything crank,rods,berrings,1 piston,rings,gaskets,oilpump,all new bolts everythingwas still cheeper than a powerhead)