91 yamaha 150hp...cutting out, losing RPMs.

[sandusk]

Hi, i am new here. i chanced upon this site while trying to figure out what is wrong with my outboard. <br /><br />the outboard i have is a 1991 yamaha precision blend 150hp. it has about 400 hours on it, and was running great up until a few weeks ago. i was coming back from fishing at about 4000 RPMs and it just cut out and went down to 2500, and would not go any higher then that. i stopped and fiddled with a few things on it and got back under way and everything was fine. since then it has gotten so bad that it does not even have enough power to get the boat (18 ft whaler) on plane. <br /><br />so far i have put new fuel pumps on it, fuel treatment through the gas, new plugs, took the bottom carb off today and cleaned it up, etc. initially i suspected one of the coils was bad because it seemed like the bottom plug on the left bank would always look sorta fouled. my dad has a fluke meter and determined that the coil was fine, so i didnt bother replacing it. today i took the bottom carb off and had a look inside. there was a decent sized goober floating around in there that i removed, but after i put the carb back on it still ran like crap. <br /><br />any ideas? thanks in advance, <br />Zack Worrell

 

[rodbolt]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

first lets start with a logical test sequence, otherwise we chase farts in the wind. test the compression, test the spark on all 6 with a gap tester capeable of a 7/16ths gap. if spark and compression are good look at the linkage that goes to the magneto timer,the oil pump and carbs, repair any deficiencies. next remove all the carbs for cleaning. its just a motor,nothing magic, its goes suck,squeeze bang and blow, I am thinking it lost anything to suck. did you get any visual or audible alarms when it laid down? have you actually tested the audible alarm to see if in fact it is capeable of working?<br /> good luck and keep posting

 

[thefishingfreak]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

you're like me.<br />very handy,<br /> but have no idea how yamaha's "work"<br />get a yamaha mechanic to give it the once over, and you'll save yourself a ton of headeaches.<br /><br />and, don't run it like that, or you'll smoke a piston <br />mike

 

[sandusk]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

well, i did check compression, it was something like 95psi on all of the cylinders. my dad got me all scared about testing the spark, saying it would blow me off my seat if i somehow didnt have it ground properly. should i just pull plugs out one by one and turn it over to get the visual?<br /><br />the alarm system for this boat hasnt worked for years, same with pretty much every other gauge except the tach. i am skeptical about puting much money into fixing gauges and things of the such because my dad is always threatening to sell the boat. thats why i dont just take it to the dealer to have them figure it out.<br /><br />Could you give me an idea of how to check the "magneto timer"? last time i deal with a magneto it was on a briggs and stratton.<br /><br />Also, when yo urefer to the oil pump you are just talking about the oil injection system right? i can see the oil moving through the clear tubes into the intake while the engine is running, they all seem free of obstructions. come to think of it, it seems to be going through oil sloer then it usually does. if the oil injection system was not working wouldent that make the engine run lean and actually hit more RPMs? <br /><br />Anyway, sorry for my rambling. thank you very much for your replies. i think head outside and try to figure out if i am getting adequete spark.

 

[rodbolt]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

dude <br /> i cant help ya<br /> if you dont wish to maintain it your on your own. maybe seahorse or someone will step in<br /> good luck and keep posting

 

[seahorse5]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

Without an alarm system you could be killing your motor by running too hot or from a lack of oil. Losing rpm to 2500 could be the engine warning kicking in or the loss of a few cylinders. You have maintenance to do before you try a haphazard troubleshooting sequence.<br /><br />Get the proper service manual and understand what you are attempting to do before pulling things apart.

 

[sandusk]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

listen, its my dads boat, he does not give a **** about it. he just buoght a new 33 foot grady. me pissing away my college money on a boat he intends to sell is a dumb investment. if it was my boat , i would take the time to figure out the warning system and cobbled up wiring, etc. all i want ot do is use it to fsh until he finds someone to buy it from him for like 3k.<br /><br />does anyone want ot help me? or am i just going to get ridiculed for not maintaining my dads boat properly?<br /><br />thanks for the replies..<br /><br />Zack Worrell

 

[rodbolt]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

here your telling us you wish for someone to send you to collage and you want someone to tell you how to fix something. why dont you take some inititive and buy 2 or 3 service manuals then I could possibly try to help. i suspect you have a fuel problem but by removing only one carb and not all you have demonstrated an unwillingness to help yourself. I will help any and all that try to help themselves but there is only so much I can do. do you have a service manual and if so which one? good luck and keep posting. and remember daddy has no responsibility to send you to college. like I told mine self mtivation is the key but they did not believe me until they were working cause I am not springing for college cause they showed no ambition in high school.

 

[bonitoman]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

Sandusk, I would not go to college if I were you. It sounds like you need to spend the money on a good marine school so that you can learn how to repair your own engine. The sad thing about most kids with college degrees is that there are no jobs out there for them. At least you could always find work on outboards , auto, lawn mower equipment. snow mobiles and if you are really smart Helicopters.

 

[sandusk]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

hey Rod, when i say "pissing away my college money" i am talking about the money i have saved up this summer for college in the fall. chances are my dad will sell this boat soon after i get it running properly, so in a way i am helping him. all i want is to use it to fish for a few days before he sells it. spending money on service manuals for a boat that is going to be gone in a week or 2 is not real economical, especially if you are not getting any of the proceeds from the boat when it is sold.<br /><br />As for the carb i took off..... i took the bottom carb off not because i felt like """Demonstrating an unwillingness to help myself"""", but because the cylinders fed by the bottom carb were the ones that were fouling the spark plugs.<br /><br />"Bonitoman" i appreciate your wisdom, but it does not take a college degree to realize that you dont know **** from shinola. LOL... let me ditch out on my plans for the university next year so i can hit the local tech school and learn how to repair my outboard properly....<br /><br />Again, thank you for the replies. i do appreciate the help. tomarrow i will take the other 2 carbs off and see what i can find.

 

[bonitoman]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

Sandusk, As I said before do not waste your money on schooling. You need a new personality. With an attitude like yours you are lucky that you made it this far in life. Good Luck By the way I have a B.S. degree in Comp. Science that I received 20 years ago.

 

[Ray Neudecker]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

Hard enough to repair engines when the owner is willing to invest time and money in it. One which has been neglected is the worst to get back right. There is no magical free way to do what you want.

 

[edgutgesell]

Re: 91 yamaha 150hp...cutting out, losing RPMs.

Hi Sandusk,<br /><br />You said that the oil warning system lights are not working. Correct? The lights are green, amber, and red. If they were working, most likely the red would be on. When the green is on, both tanks, the large subtank in the boat is filled with an ample amount of oil. If the large tank in the boat gets below a certain amount of oil, the amber lamp comes on warning you to fill the large tank. The main oil tank on the engine has three oil level switches in it. One switch turns on the pump in the large subtank to keep the engine tank full. A lower switch turns on the red light to warn you that the oil in the main tank on the engine is getting dangerously low. At the same time it is warning you with the red light, the oil control unit on the engine (the rectangular box with the toggle switch) sends a signal to the engine which does not let the engine to run over 2000 rpm. When you are running at about 5000 rpm, the oil pump feeding the engine adds oil at about 50 to 1. When running below 2000 rpm the oil to fuel ratio is about 200 to 1. This is done to conserve oil until you can correct the problem.<br /><br />First thing I would do is to get the model # off of the plate on the mounting bracket and order a repair manual from Yamaha. (About $50)<br /><br />When you get the manual, I would fix the oil warning light system. There are procedures and schematics that if you know anything about electricity and have a simple multimeter you can troubleshoot the oil system yourself. That system could become functional just by replacing bulbs. The lights could also be inoperative because of a defective control unit. (about $200)<br /><br />The oil system on Yammie engines is very good, with an excellent warning light system. I wouldn't consider running my engine without the warning lights being functional!!!<br /><br />Ed G.