Motor looses power at full throttle but picks up rpm’s when I decrease throttle

[Ga Aquadog]

I recently found a 1990 Johnson 9.9 motor still on the original shipping pallet. Never run. Has been in storage for 32 years. Hard to believe but true. I bought a new 3 gallon gas tank, fuel line primer bulb & fuel line fitting. I have used it 5 times. Always starts on first or second pull. Ideas great. Runs smooth at low and medium throttle but as I approach full throttle it loose power and runs slow again until I back off to about 3/4 throttle. Then it picks up speed to what feels like full throttle. When I increase the throttle it slows down again. Then I slowly increase throttle and it speeds up until I get close to full throttle and it does the same thing. It is hard to keep the throttle at the spot where it runs the fastest. If I increase it just a little it runs slow and I start the whole process over. Any help would be appreciated.

 

[Pappy]

Does it run smoothly when the RPMs decrease?
or
Does it sound rough and did the RPMS drop quickly?

 

[Ga Aquadog]

Yes Sir. It runs smooth and picks up speed when I decrease throttle. Doesn’t sound rough just looses power and rpm’s drop quick. When I slowly decrease throttle I reach a spot where it starts to increase speed. If I increase throttle too much it will repeat the same problem. Starts on first or 2nd pull. Ideas smooth, runs smooth, never ruff at any speed. I appreciate any suggestions you can give me.

 

[Pappy]

The first thing I would check is sync and link. There is a pick up point for the carburetor throttle roller where it contacts the mag plate advance cam. check that first. Check for broken plastic parts. I know..."it's new" but it is still 32 years old.
Secondly the carb will need to come off and be checked. High speed jet for sure needs to be checked. Buy an OEM kit while you are at it and renew the carb after a thorough cleaning.
The water pump is also 32 years old and I would not run it until changed out. Again..OEM parts are your friend here.
I am hoping you are running double oil for the first tank of fuel?? A good proper break-in will insure a good long life from that engine.
By the way, that engine looks like a newer model than a 1990, What is the model number on the tag on the port mount bracket?

 

[cyclops2]

LOSS of enough fuel flow at WOT. Find the blockage. I COULD even be a animal nest built into the carburetor inlet. Been there.

 

[Ga Aquadog]

The first thing I would check is sync and link. There is a pick up point for the carburetor throttle roller where it contacts the mag plate advance cam. check that first. Check for broken plastic parts. I know..."it's new" but it is still 32 years old.
Secondly the carb will need to come off and be checked. High speed jet for sure needs to be checked. Buy an OEM kit while you are at it and renew the carb after a thorough cleaning.
The water pump is also 32 years old and I would not run it until changed out. Again..OEM parts are your friend here.
I am hoping you are running double oil for the first tank of fuel?? A good proper break-in will insure a good long life from that engine.
By the way, that engine looks like a newer model than a 1990, What is the model number on the tag on the port mount bracket?

 

[Ga Aquadog]

The plate is missing on the bracket. I just noticed the Emissions Tag in the other side of the motor bracket. It says 1999 year.
I will order a carburetor kit and water pump. If I don’t need it now I’am sure I will later. Your help is greatly appreciated. Wish I could repay the favor.

 

[poorthang]

clasic sign of main jet rstriction.

 

[Ga Aquadog]

clasic sign of main jet rstriction.

Thanks for the input. I will check that too.

 

[Ga Aquadog]

I found a number in the freeze plug - 4547415. Will this number help me find the model number for my motor?

 

[Pappy]

Nope! The model number if a 1999 should be on the port transom bracket and have "EE" in it.
If you are just worried about getting the correct part. Not to worry. Parts for that engine covered a lot of years. Lots of commonality in that platform.

 

[RaisedByWolves]

I will order a carburetor kit and water pump. If I don’t need it now I’am sure I will later.

You need the impeller now.

If you wait to change it it might disintegrate while in use and you will have to fish the pieces out of all the water passages and this is a P I T A!!!

Shouldn’t take more than an hour to change it out on a motor like that.

 

[Ga Aquadog]

Just an fyi. I called BRP with the number on the freeze plug. They said it was my serial number and were able to look up my model number using that number. Great customer service.

 

[Pappy]

Well? Was it a 1999?

 

[Ga Aquadog]

Well? Was it a 1999?

Yes Sir. Model # J10REE. Thanks again for your input. I received the carburetor kit & water pump rebuilt kit yesterday. Hope to get time this weekend to work on it.

 

[Pappy]

Have a 3/8-16 nut ready for the starter! Take a good look at the orientation of the starter lock out lever and spring as well as the orientation of the starter housing. When you remove the starter keep it pressed together and put the nut on to keep it together. No need to remove the rope just hang the assembly over the side. Now is a good time to change out all of the old fuel lines as well.

 

[Ga Aquadog]

Have a 3/8-16 nut ready for the starter! Take a good look at the orientation of the starter lock out lever and spring as well as the orientation of the starter housing. When you remove the starter keep it pressed together and put the nut on to keep it together. No need to remove the rope just hang the assembly over the side. Now is a good time to change out all of the old fuel lines as well.

I think you sent this to me by mistake

 

[Pappy]

You have to pull the starter to get to the carburetor!! I am saving you some time and headache.......

 

[Ga Aquadog]

Not electric start

 

[Pappy]

I know it is not. I can tell by your model number.
You still have a manual STARTER on the port side that blocks removal of the carburetor.