1999 Yamaha 200hp OX66 surging erraticly

[john mc]

Hello, need some help troubleshooting this problem:
1999 OX66 200hp twin, both engines feeding from same tank. After running both at any rpm over 3000, for about 30 min starboard engine starts surging almost like it is starving for fuel. If I throttle back to below 3000 it runs fine but then after 20 minutes it starts acting up again and at one point it will do it also at 2000 rpm . I have taken the following actions but I still have the same problem: replaced water separators, swapped fuel lines starboard to port at the water separators,checked and cleaned anti syphon valve on defective engine, replaced paper filter, replaced 2 low pressure pumps, cleaned VST needle + vst tank, replaced VST filter, replaced fuel regulator + screen + all related o rings and gaskets, cleaned and checked O2 sensor as per manufacturer instructions. I have been running on the aux 50 gal tank with fresh fuel and ring free. If I switch to main same problem. Do you guys have any other ideas?
Thanks in advance for you reply.
jp

 

[rodbolt]

Re: 1999 Yamaha 200hp OX66 surging erraticly

your going to have to check fuel rail pressue and check fuel system vacume at the lift pump intake.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Rodbolt, Thanks for your quick reply. I will check into that upon my return to the US. Thanks again.
John P.

 

[rodbolt]

Re: 1999 Yamaha 200hp OX66 surging erraticly

ok
thursday night I am heading for Lake Guri Venezuela. I wont likly be back online until about the 5th or 6th.
put the vacum guage inline with the lower pump intake. anything over 4"Hg indicates a restriction. less than about 1"Hg may indicate a leak on the suction side.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Thanks Rodbolt, Will follow instructions and I will let you know the results.
Buen viaje
jp

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Update.
Hello Rodbolt, hope you had a nice trip in Venezuela.
I did not do the vacuum test and rail pressure test yet but I did the following:
Cleaned VST filter again (5th time) and found a lot of particles. Had both tanks drained and cleaned (too much work for me and farmed it out). Installed 2 new 10 micron water separators, found a loose connection at the yamaha fuel pressure sensor. Tightened it and ran boat, so far it is OK, will run a few more times and update. I will install the vacuum gage so if the problem arises again I will be able to have a vacuum reading.
Best Regards,
John P.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Update:
Problem is back. After cleaning the VST filter the motor ran fine for 3 days, long idling, full power riding for abour 30 minutes at the time, no problem. Then 4th day, same problem happened after idling for about 30 minutes. Have not performed the vac and pressure tests yet but will do this week.found particles in the VST even though the tanks are now clean. Could those particles come from the oil tank?
John P.

 

[rodbolt]

Re: 1999 Yamaha 200hp OX66 surging erraticly

possibly but I doubt it. there is a filter at the remote tank and another inside the engine tank.
most likly from debris caught in the engine fuel lines and the lift pumps.
there is also a screen behind the fuel pressure regulator that needs attention now and again.
each injector also has a screen.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Update: cleaned VST filter again, found a lot of particles. The fuel tanks have been flushed clean, I also cleaned the remote oil tanks as well as the motor oil tanks, replaced the filters on the remote tanks. The oil was really dirty, it almost looked like a swamp in there! I have tested the boat again 4400 rpm for over an hour and with additional 30 minutes trolling and more full blast speed. Everything seems to be working fine at the moment but I will monitor the VST for those particles. My theory is that when I run the boat for an extended period of time all the particles are sticking to my VST filter, partially obstructing the screen, and therefore creating the starving for fuel condition. If I stop the engines for a while those particles are falling to the bottom of the VST tank allowing the engine to run for a while until they they get stuck again to the filter. I will drain the VST again for a few times and I will keep you posted on the result. I still need to find the source of those particles, it might be the fuel hose or the primer pump maybe still contaminated with old particles, for the moment I will bypass the above with a primer bulb and new hose to the water separator.
Rodbolt please let me know if this makes any sense to you.
Thanks for your help and Best Regards,
John P.

 

[rodbolt]

Re: 1999 Yamaha 200hp OX66 surging erraticly

could be.
try occasionally draining the VST ,then use a can of carb cleaner with the red tube clean the filter.
bend the tube 90*,insert it in the drain hole and flush the filter area.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Thanks Rodbolt,
I will keep you posted on the issue. I am planning to drain and clean the vst filter as you mentioned for the next few weeks. I will let you know the result.
Thanks again,
John P.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Hello Rodbolt,
I have another question for you if you do not mind. I have to fix a leak on the main tilt piston. I do have all the seals and o rings + yamaha tool but the cap seems to be stuck. I am planning to use a propane torch to heat up the casing hoping that it will expand enough so the threads of the cap will be able to unscrew.Do you have any recommendation on that procedure?
Thanks again for your help,
John P.

 

[rodbolt]

Re: 1999 Yamaha 200hp OX66 surging erraticly

none, other than try to draw the tilt ram onto the top of the tool to help hold it in place.
they can be mean to remove.
propane certainly wont hurt.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

thanks rodbolt! Tested the boat today after cleaning remote oil tanks and fuel tank. The engine seems to be working OK. Will keep you posted since I plan to run the boat a few times before declaring victory! I will try to remove the tilt cylinder next week end, will keep you posted on that as well.
Thanks a lot for your help, it is greatly appreciated!
Best Regards,
John P.

 

[john mc]

Re: 1999 Yamaha 200hp OX66 surging erraticly

Hello Rodbold,
Tested the engines a few more timed after cleaning the oil tanks, everything seems to be working fine for the moment, will keep posting if the problem arises again.'
Thnks for you help,
Happy Holidays,
John P.