90hp Nissian won't open up

[Dodgeram67]

2000 model 90 hp Nissian just got boat water ready and motor runs fine on muffs. Took it out Sunday and on the 20 foot sea ark the motor won't run wide open. Throttle all the way forward and it runs 12 mph. Brought boat home, took carbs off and apart and cleaned them good and ran boat today and same issue. I did notice if I bumped the choke that it would pick up a few rpm and then noticed if I tilted engine way up with prop about to blow out it got to running faster and faster and topped out at 27 mph. Any ideas of issue. I check several other things and they all seemed ok. Plugs good, all cylinders firing. Plenty of gas, diaphram looked good, fuel filter clean, fuel bowl full.
Any help or ideas would be appreciated.

 

[Sea Rider]

Welcome to Iboats.

That's a 2 stroke motor ? fresh or salt water usage ? Does the motor maintains the original prop factory delivered with. Have you done a Hub Slip prop test to determine if the prop it's doing its homework right ? Let's start with the simple troubleshooting and then go from there..

Happy Boating​

 

[Dodgeram67]

Thanks for the reply Sea Rider. Yes sir 2 stroke, fresh water, it has a stainless steel prop but it doesn't seem to have any slippage, not sure of pitch.

 

[Sea Rider]

Thanks for the reply Sea Rider. Yes sir 2 stroke, fresh water, it has a stainless steel prop but it doesn't seem to have any slippage, not sure of pitch.

You're welcome Dodgeram 67,
To make sure the prop doesn't have any slippage will need to perform a Hub Slip Test at wot, know how to perform the test ? If that's the current prop that came with the motor since new that's already a 21 year oldie...

Happy Boating​

 

[Dodgeram67]

I don't think the prop is slipping cause the rpm's aren't going sky high, rpms are really low at wide open throttle and the boat isn't really loaded down. Seems to me it is a fuel problem, especially if it seems to help when I push the choke in really fast. When I took carbs off and bowls off I pulled both jets out of it and blew carb cleaner through everything. Air bleeds were 2 1/2 rounds out, while running it today it wasn't idling well so I screwed each one in one round. All carbs were opening at the same time. I am at a loss on this one.

 

[dwco5051]

Wild guesses but since the difference was only when the engine was tilted one of the carbs might have a float hanging up. What is the condition of the hose from the tank to the motor? Perhaps it is kinking with the motor down or the inner hose liner is shot and not getting enough flow until the motor is raised and takes some of the tension off.

 

[Dodgeram67]

Thanks dwco I just had carbs off and cleaned them out, but that could be the problem. Fuel line is pretty straight even when tilted up. Now I do not know how old fuel lines are. Probably wouldn't hurt to replace them.

 

[pvanv]

Year of manufacture is irrelevant. You did not say, but you likely have an M90A.
Clean the carbs with a proper overnight soak and try again.

 

[Dodgeram67]

It's a 2000, it's in original post. I think it's an NS90A. 10-4 on over night soak. I though I got them cleaned out good, but maybe not. Thinking about taking it to boat guy. Hate I can't fix it.

 

[Sea Rider]

I don't think the prop is slipping cause the rpm's aren't going sky high, rpms are really low at wide open throttle and the boat isn't really loaded down. I am at a loss on this one.

Prop hubs don't go bad from one day to another takes time to fully go kaputt for the wot rpm to climb high with associated thrust lose. It's a simple water test which will avoid unnecessarily tampering the whole motor if were the culprit. Up to you if going that route as a starter, take the motor to a mechanic ?

Happy Boating ​

 

[Dodgeram67]

I agree I don't think it is the hub. It has me stumped. Time for boat mechanic.

 

[MattFL]

If it worked fine when you put it away and now doesn't work fine, the most likely cause is plugged up carburetors. Especially if bumping the choke makes any sort of improvement. If you have compressed air, I would re-clean the carburetors and follow the carburetor cleaner up with compressed air. Also make sure all of the carburetors have fuel in the bowl when you take it apart, in case one or more aren't filling up with gas. One other thing to check is if you're getting spark on all spark plugs.

 

[Dodgeram67]

We have had this boat a few months and previous owner said it was running fine, we swap trailers, ran all new trolling motor wiring and new turf on all the decks, new trolling motor, new paint on boat, it has been a project.
I'm thinking about pulling carbs back off and checking to see if they all have fuel. When I cleaned them before I didn't blow through carbs with air just carb cleaner. Question after all the jets are out and just the body of the carb how many small holes are in it that can get plugged?

 

[pvanv]

Several spots, especially in the low speed circuits.

 

[Dodgeram67]

I pulled carbs off again this morning, took them all apart, carb cleaner and blew air all the way through, put it back together, had another set of plugs, put them in and ran it a little while ago. No change. Taking it to a mechanic this evening. Will update everyone when I know something. Thanks for all yalls help.

 

[Dodgeram67]

Update, took to mechanic today and before I left town a few hours later he called and said it was in better shape. Whoever deleted the oil injection left some things not plug so big vacuum leak, also it wasn't in time on low in or high end. And main issue is it has an 18 or 19 pitch prop and he said it needed a 15. A buddy has one I am going to try. We did run it on the way home and it did better but still bogs, put the wife on front deck and it helped.

 

[MattFL]

Wow, that sounds like it was all out of sorts. The info on the prop sounds odd to me, do you know any more about the back story on that boat/motor combo? Did the previous owner use that same motor on the same boat with an 18" prop successfully before you bought it? The difference between 18" and 15" pitch is very big, so if it's having trouble with a 15" then it never would have worked with an 18". So my suspicion is that either that boat and motor were just paired together and never set up correctly, OR there's still a very big problem with the motor and it's not making anywhere near rated power.

 

[Dodgeram67]

Just got back from test number 5, tried a different prop, same issue. Motor cranks and idles fine, but will not go wide open throttle. You can bump choke and it will pick up about a mile an hour and I can get it up to about 25 with some work. I have had carbs off twice now, and unless something inside carb body is stopped up, all the jets are clean. Mechanic said compression was 130 130 145, he said carbon may have the one a little high.

 

[Dodgeram67]

Spoke with mechanic and he said my magnito plate wasn't up to the voltage allowable for it to function properly. Would that cause it not to open up, and why does hitting choke help that? Is magnito plate the correct term for it? He said you have to find it use cause they no longer make that part. Just my luck.

 

[Dodgeram67]

Was hoping to get a confirmation from some of the experts on here about magnito plate. I found one on line and ordered it. My question is, will flywheel come off without a puller, and is the magnito a plug and play or does it have to be set in a certain position?