9.9/15hp WOT issue (update)

[Mr. Bwok]

I have a lack of power at the top end of my 1976 9.9Johnson with a 15hp carb. Had the same issue with my 9.9 carb on it. I can coax the power by squeezing the bulb, but iust feels like it is off a bit from what it should be. When it is cold it seems screaming fast then after running for a while it appears to loose something. Idles perfect, hole shot is great, just will not max RPM randomly. Carb has been cleaned completely and rebuilt. Spark plugs are new and gapped to 0.30, compression 103/105, new coils and point set to 0.20 armature plate has no wobble. Could it be a carb float. I leveled it with the gasket? I pulled the welch plugs on the carb and cleaned the passages. Any ideas how to get my top end power back?

 

[bktheking]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Maybe losing spark after things heat up under the cowl? Maybe some dirt in the carb still, lines new?

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Maybe losing spark after things heat up under the cowl? Maybe some dirt in the carb still, lines new?

Hey there. Thanks for help on my previous issues. Everything is great except for this slight power loss at WOT. I do not see how it can be a spark issue I built a whole new wire harness to deal with a spark issue previously and the points and condensers are new. I guess I can check it on the weekend. The other reason i am thinking it is not spark is that the engine runs brilliantly all the way through the rpm range then just seems to run out of steam. No misfires, no stumbles etc. I just pulled the carb off earlier today and the main jet was clean there was not dirt at all, I did not pop out the welch plug as I had just done it two days agao to clean the three openings.

The lines are not new and I just realized i may have forgot to put a clamp on at the fuel feed to the carb. Would that affect it? I did not have a long time to test it today, but it seemed that a pump or two of the primer bulb helped it reach the rpms it is supposed to.

 

[bktheking]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Fuel system has to be pretty tight to eliminate air or fuel leakage. I've noticed on the 15 that sometimes the choke rod like to pop out which will drop the rpm, is the rod on the choke installed properly and the tang to hold it holding it well?

 

[Daviet]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Usually if squeezing the primer makes the engine pick up and run properly, you have a defective fuel pump. Remove the pump and see if there is any fuel in the hole that mates to the block, if so you have a broken diaphram.
The pump could be weak even if it is not leaking.

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Fuel system has to be pretty tight to eliminate air or fuel leakage. I've noticed on the 15 that sometimes the choke rod like to pop out which will drop the rpm, is the rod on the choke installed properly and the tang to hold it holding it well?

Usually if squeezing the primer makes the engine pick up and run properly, you have a defective fuel pump. Remove the pump and see if there is any fuel in the hole that mates to the block, if so you have a broken diaphram.
The pump could be weak even if it is not leaking.

Well I will defiantly make sure that all the lines are buttoned up and free of cracks and missing clamps. The choke is functional, but i will make sure it is not tipping closed a bit when under high vacuum.
I will also pull apart the fuel pump. I have done it on my 35hp, it is bit fiddly, but easy to do. I will for sure do a few more runs with it to see if the primer bulb trick keeps the rpm's high before diving in.
This motor sat in my boat shed for nearly 12 years before I pulled it out early this summer for my kids to use, I am surprised that I am only having a few issues. The kids do not notice the lack of top RPM, but it bugs me. Plus I love projects and this has been a great one.

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

I did edit up top, But I forgot to mention that this same power drop off happens with my 9.9 carb on it as well. So it has top end power issues with 9.9 and 15hp carb. It is like it is starving for fuel or air. it wants to go, but just can't. I am thinking fuel pump?

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Bump.

 

[bktheking]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

You said it ran fine cold only after it heated up it does it, usually fuel pumps don't come and go, if you have a spare pump try it.

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

You said it ran fine cold only after it heated up it does it, usually fuel pumps don't come and go, if you have a spare pump try it.

That is what it appeared to me it is hard to tell because i have about 2kms of no wake zone to travel on before i can open it up. I cheated for a few seconds and the feeling was that it had the top end. Either way the top that should be there is not.. The fact that it did it with both carbs kinda rules Carburetor issues out, but I am going to pull it again and have a look when I replace all the fuel lines. DO you know the size of lines I need?. Also how would i know if the spark at the top end is week. Coils new, points new condenser new and it runs perfectly all the way to top speed, just seems off a few rpms from what it used to be.

 

[bktheking]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Do you know if there is any play in the mag plate, possibly the timing is being thrown off? It was a known issue with the 74-76 motors. Line going to the pump is 5/16, from the pump to the carb is 5/32.

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Do you know if there is any play in the mag plate, possibly the timing is being thrown off? It was a known issue with the 74-76 motors. Line going to the pump is 5/16, from the pump to the carb is 5/32.

I actually fixed the Mag Plate. It would not even run before, but you may be on to something. It may be moving a tiny amount at WOT and causing a low spark issue.
I am heading North tomorrow and will be able to play with it and post my result. I am going to replace the line, test the fuel pump for leaks, tighten all fuel lines. water test. If still not performing right, squeeze bulb to see if it clears it up, if not I will pull the flywheel and make sure no play in the armature. I will also pull the carb again and make sure no debris has floated in the bowl after the last rebuild on sunday. I am trying to gather as much info as I can so I do not miss anything while I am diagnosing the issue.

 

[bktheking]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Moving wouldn't cause a low spark issue, it would cause it to lose power cause of the timing being thown off, maybe need some more "fixing" or replacing, I have a spare plate;

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Moving wouldn't cause a low spark issue, it would cause it to lose power cause of the timing being thown off, maybe need some more "fixing" or replacing, I have a spare plate;

It is not missing though. Both cylinders are firing, the best way I can describe it is that I feel like it is running at 7/8th's throttle instead of full. The only reason I know this, is because I have had it running perfect. I am going to have to check compression again. hmmm.

 

[mikesea]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

I agree with this,OR,your tank is not ventng properly,but ,Im not strong on the tank
Usually if squeezing the primer makes the engine pick up and run properly, you have a defective fuel pump. Remove the pump and see if there is any fuel in the hole that mates to the block, if so you have a broken diaphram.
The pump could be weak even if it is not leaking.

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

I agree with this,OR,your tank is not ventng properly,but ,Im not strong on the tank
Usually if squeezing the primer makes the engine pick up and run properly, you have a defective fuel pump. Remove the pump and see if there is any fuel in the hole that mates to the block, if so you have a broken diaphram.
The pump could be weak even if it is not leaking.

Well the fuel pump is 34 years old, the fuel lines inside the motor are 34 years old, so should be looked at anyways. Most of the the other components are new. points, condensors, wire harness, coils and the tank and lines to the motor are brand new and the vent is always open on the tank when running. It still could be crud in the main jet, but highly doubtful as it is happening with both the 9.9 and 15hp carbs.

 

[Rick.]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

Is your throttle plate wide open at full throttle? Best of luck. Rick.

 

[northwoodslivin]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

I would for sure replace your fuel lines, for one they arnt even ethanol approved, also rebuild your fuel pump and while you are at it I would replace the thermostat.

Good luck

 

[Mr. Bwok]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

I have the new fuel lines and it is my friday evening project. I just need to pick up a fuel pump rebuild kit. I notice that none is listed. Is the kit for the mid 80's 9.9/15 non electric start the same?

 

[jmendoza]

Re: 9.9/15hp WOT issue

Re: 9.9/15hp WOT issue

My 1975 was doing exactly what you described, and although the fuel pump was pumping, guess what? I took it apart and found very stiff diaphragms. One corner of the pump diaphragm was pulled inwards due to it shrinking and enlarged one of the four corner holes enough to cause an internal leak, and this was enough to make the engine act up intermittantly. Anyway, I got a pump rebuild kit from Sierra, but new pumps have come down in price from $80.00 to $40.00 dollars so you may just as well get a new one. You must always use the clamps on the carb, and fuel line fittings, or the pump will have problems. I suggest you do as I did and replace all the fuel lines, they get quite stiff ans don't seal well, even with a clamp. Make sure to replace the o rings in the fuel line connectors coming from the squeeze bulb, and connector to the tank, if they leak you get air in the pump and it cavitates.