Yamaha 99 four stroke runs rough until warmed up

I have had an ongoing problem

I have had an ongoing problem with the motor on our sailboat. When started cold it runs on what sounds like one cyl.and wont throttle up until this missing clears. I replaced the carb. as we saw indication of a previous owners attempts to do some magic. This had o effect. I pulled the head and inspected the bores and at this time had a good shop re guide the head as well grind the valves. Valve settings were done to spec and guess what.....same thing still happens. Once warm the thing is flawless but get up in the morning and try to get it started you may as well go back to the bunk cause it can take up to 30 minutes of low idle to make it smooth out. New plugs new fuel as well connectors hoses and tank all to no avail. Could I have a bad brain box or coil. What is the procedure and electrical values to test these. Yes I have a really good meter

"Bill, these motors prefer low

"Bill, these motors prefer low idle when cold and will take a minute or so to warm up to allow smooth off idle runing. If they take more than a minute of warm up, look at a partialy stuck open thermostat. I found with the many 9.9s I've owned that in winter time it was best to kick the motor into gear with the boat still tied up to the dock. I could increase the throttle quicker by doing this and shorten the warm up period. Not a hundred percent positive but I think you get proper timing advance with the motor in gear as opposed to just lifting the fast idele lever in neutral. I got into this routine every morning so that after my run to the fishing grounds the motor would run well as soon as I refired it."

"Thanks for your reply,
Have

"Thanks for your reply,
Have tried the in gear trick with out success. Do you know if there is current to the oil pressure sending unit or is ir a ground activated circuit. I disconnected it and ran the engine and could feel the presence of power.I have not put a meter on it to read the output. I guess what I need is the test proceedure and values for the coil and the ignition modual as well the stator if anyone has this data. Also what should the compression read on a gage? I am going to pull the motor of in the early spring and get it on my bench for further trouble shooting.I would hate to write it off as these are the best motors for this application."

"Bill, I have the best Yamaha

"Bill, I have the best Yamaha mechanic coming over tonight for a Christmas party. I'll get him to read through your posts and give you his opinion, before he drinks to much! If anyone can can point you in the right direction its him. Rollie"

"Bill, to much snow here last

"Bill, to much snow here last night and he never made it over. I see your in Kelowna so it is quite cold right now. Was it doing the same thing in summer? If not I know that the carbs will tend to ice up if you throttle up in cold weather. There has to be enough heat coming from a warmed block to keep the ice from forming in the carb jets. Rollie"

Rollie

Sounds like you got

Rollie

Sounds like you got nailed with winter as well!

These engine problems are related to warm wheather operation as the boat is winterized anually.

"Bill, Yes over a foot of snow

"Bill, Yes over a foot of snow here right now! To test the electrical component theory...and to confirm or discount it...start the engine and get it to where it is missing...pull a plug wire (with insulated plyers) and see it the engine changes or quits, do this to each plug wire one at a time. If there is no change when you pull a wire, that clyinder isn't working, if it quits running..that is a good cylinder. If each plug wire results in a change for the worse, look for a fuel problem or even a stuck open thermostat that prevents the engine from coming up to temp. Rollie"

carb needs a good cleaning and

carb needs a good cleaning and check the prime start

Dear Just in Time

The carb

Dear Just in Time

The carb is brand new as well the complete fuel system as per previous post
Prime start is a heat activated coil that enriches the mixture for about one minute then pulls off for normal operation.This comes with the new carb and is operating normally.Really need the specs for testing the electrical side of this motor. Will contact a few dealers to see if their techs are willing to provide this information.

"valves adjusted?
oil over fi

"valves adjusted?
oil over filled?
old gas?

check for spark on both cylinders, could be bad spark plugs or wire"

Rollie

Did you get a chance

Rollie

Did you get a chance to show your mechanic the problem I have with the Yamaha 9.9? Would really like his opinion regarding this.

Happy New Year

Bill

"Bill, sorry no, he is now dow

"Bill, sorry no, he is now down in Arizona for a month with the new girlfriend playing golf. Hopefully you will have it figured out before he's back"