1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

[cmitchell]

my 1999 yamaha saltwater series 2 outboard has just had the water separater replaced,and three carbs rebuilt,as well as new water pump impeller replaced just for good maintenance.the engine runs great except when you get to 4000 rpm it kicks in more rpms and then drops back to 4000.this also happens at full throttle which for now is 4900 and jumps to 5100 just for a second and then back to 4900.It does this constantly kicking in and dropping back with a couple of seconds in between.I would take it back to the shop that did the maintenance on it but i bought the boat in St. Augustine and that is 7 hours away.the first owner says that full throttle has always been 5500 rpm but i have never seen more than 5100 rpm.I know this has to be an easy fix and i pray that someone knows the answer.thanks

 

[rodbolt]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

Hello<br /> try pumping the fuel primer bulb while under power. the fuel pumps should have been done with the carbs. almost sounds like a fuel issue. also check all the resistor caps on the plugs. the caps are about the only weak link yamaha had with the carbed motor by 99. good luck and keep posting

 

[cmitchell]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

Thanks rodbolt,i will do a little checking but someone else said that i might have an air bubble in my fuel line restricting flow?have you ever hjeard of this?

 

[rodbolt]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

Hello<br /> yes I hear stuff like that all the time. it is possible for the fuel to have a restriction and the vacum in the lines becomes excessive causing the fuel to boil at about 50 degrees f.if you suspect a fuel restriction place a vacum gauge in the line between the fuel pump and engine check valve. at wot it should read less than 6" hg. if it is more fix the restriction and rebuild the pumps. its time to start eliminating potential problem sources. good luck and keep posting

 

[wtrojan]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

Clifton, I’m no expert, but air in fuel could be caused for example by malfunctioning fuel line connector, particularly by faulty gasket on the female part. Look for air in your fuel filter assembly, the plastic, semitransparent one. As far as I understand, the filter bowl should be full of fuel, naturally with the motor running.

 

[rodbolt]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

Hello<br /> actually the filter bowl will remain at about half full. why I dont know but I test 25-30 motors a year at WOT with a vacum gauge installed going across shallowbag bay. all seem to stay about 1/2 full. its something to do with the vacum drop across the filter. I am not a fluid engineer so maybe someone else is. all I can tell you is the bulb wont stay hard( its on the suction side of the pump) and the filter wont stay full.<br /> loose connections will allow air but not any trapped air bubbles. good luck and keep posting

 

[cmitchell]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

Hey rodbolt,I just had the chance to run my engine and pump the fuel bulb.Sorry but this didn't help.I knew it couldn't be that easy.For me it always has to be difficult and expensive.Please explain what wot means.I am a novice but i am not scared to tincker.I have taken my yamaha waverunner carbs apart and rebuilt.If you have any small jobs i can start with to try to eliminate my fuel problem I will try all easy fixes before I have the "man" come out and repair it.Thanks for all help!!

 

[rodbolt]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

Hello<br /> I assume you have a manual. remove and reclean the carbs. make sure the Main jets are in the correct position if there is more than one size jet. makes sure all the floats are at the right height. the ignition system on that motor is fairly reliable, sounds like a fuel issue. if you can do wave runner carbs these will look even easier. good luck and keep posting

 

[BRIAN03]

Re: 1999 175 yamaha saltwater series rpm hickups at 3/4 to full throttle

The saltwater series engine is an efi engine. Fuel injectors are in the intake manifold. The most common failure on that engine is the low pressure fuel pumps monted on the port side of the engine. There is three of them on a v6 efi. If one of the diaphrams is bad it will surge and lose power above 4500 rpm. They should be changed every 200 to 250 hrs of service. If the fuel pumps check out. I would put a fresh set of of sparks plugs in. If that checks out. You need to change the o2 sensor. If will make the engine surge up and down on the top end. You should use only Yamaha lube for oil and run ring free every tank full of gas.