1987 yamaha 150

[gutshot grouper]

I am working on the neighbors 150 hp Yam. The main jets will spit fuel, but don't want to flow a steady stream, even when pumping the primer bulb. I pulled the carbs and dropped the float bowls and a little sediment was in the bowl, but nothing remarkable for an old motor. I pulled out all the screws which access various air passages, float bowl drains, main jets etc, but cannot find any reason that they will not flow fuel normally. I don,t have any problem replacing the diaphragms in the two fuel pumps, but seems to me that the bulb would have the same effect as the fuel pump and that it should run right. It will turn about 2500 rpm and about 3500 with choke modulated on and off. ny possibility that the crank seals are worn to the extent that it will not suck fuel? Thanks

 

[Ray Neudecker]

Re: 1987 yamaha 150

You need to replace the fuel pumps (not rebuild) disassemble the carbs and properly soak and clean, Replace the bowl gaskets and also the filter assembly mounted on the motor. Unlikely the sealing rings are a problem, much more likely you have a fuel restriction.

 

[rodbolt]

Re: 1987 yamaha 150

I agree with ray. the carb design is such that all fuel circuits are used at high speed. you really need to study carb design and terms. you will never ever see fuel flowing through the main jets. even if you see some fuel at the emulsion tube you cannot tell by eye if its the correct amount.replace the pumps and throughly claen the carbs but first use the basics of trouble shooting.<br /> good luck and keep posting

 

[gutshot grouper]

Re: 1987 yamaha 150

Thanks guys, I should have suspected as much with all the little passages, I guess the low speed and high speed circuits are both having an effect ,, will take both your suggestions to heart, The Old Shadetree Mech. ,P>S> I'd rather work on Detroit Diesels, they're easier.

 

[rodbolt]

Re: 1987 yamaha 150

if it wasnt for that nasty diesel smell I might almost agree with you. the carbs have a high,intermediate and idle passages. does the carbs your working with have two floats per carb?

 

[Ray Neudecker]

Re: 1987 yamaha 150

87 model should be the double bowl carbs.

 

[gutshot grouper]

Re: 1987 yamaha 150

Yup, two floats per carb, I worked them over tonight, poured carb clean thru all small passages and blew them out with compressed air, I still wonder if the diaphragms cannot be simply renewed rather than buying newfuel pumps,, I will bet that the pumps cost a lot more than they are worth, any good reasons why I can"t replace the rubber parts?? I am just doing the guy next door a favor, just as i did when I fixed the tilt motor and the start solenoid,, Gutshot in Raleigh

 

[Ray Neudecker]

Re: 1987 yamaha 150

My experience on those pumps that age is that many times the plastic housing has warped and the repair is only temporary. The pumps are available for about $30.00 each. Much easier and cheaper than building a power head. Since the labor rate at shops has risen to a level where the labor to rebuild is greater than the cost of the pumps, very few even consider rebuilding any more. Lack of dependibility of the repair has caused me to take that approach.

 

[rodbolt]

Re: 1987 yamaha 150

I am with Ray again

 

[gutshot grouper]

Re: 1987 yamaha 150

Thanks guys, I priced out the complete pumps at 70 bucks per pair, but I am going to cheap it out and just put in the two diaphragms, I am a bone head , but if I am wrong, you will be the first to know,, I have worked on a lot of two strokes, mostly motorcycles and i just wish for a gravity feed from the tank. My experience on the diaphragm type pumps has all been bad, especially on the small B&S four stroke lawn type engines. I would think the outboards would go the car route and use an electric pump, Gutshot in Raleigh