VST Filter Replacement on 2001 OX66 250hp

[hyd-n-seek]

Hi,<br /><br />I've found some great threads on problems that people have experienced w/ the rpms dropping out abruptly on these engines, and it seems that the likely culprit is either the VST filter or the O2 sensor. My buddy is going to give me a hand cleaning the O2 sensor this weekend, but I'd like to check out the VST filter as well. Based on what I've read (and seen in the SELOC Yamaha manual), it looks like the whole VST unit needs to be removed from the block, and to get at the filter, one needs to remove the tank (via nine screws). The SELOC manual refers to the filter as an "electric fuel pump filter" (picture shows it as round, divided into six wedges) -- is this the same thing as the VST filter referred to in other threads? The SELOC manual doesn't explicitly outline a procedure for this filter's replacement -- its just mentioned in the "VST Overhaul" section. So, a few questions:<br /><br />1. Is my understanding of the procedure for the VST filter access correct?<br />2. Do I need to replace the VST gasket regardless of its condition if I have to drop the tank?<br />3. If it is, I've seen a few threads on repriming the VST, but no one conclusive recommendation on if and how to do it. Can someone provide one?<br />4. Is there a better manual for someone who wants to do/learn their own maintenance on this engine?<br /><br />Thanks in advance for your replies.

 

[rodbolt]

Re: VST Filter Replacement on 2001 OX66 250hp

I never remove the tank completely. takes to long. it does need to be unbolted from the block. I loosen as many of the screws as I can before unbolting to access two on the back.<br />weak lift pumps can create the same issue.<br /> if you have the O2 sensor test harness you can test it before and after cleaning, no good way do do it otherwise.<br />a bad O2 sensor wont cause a high speed shut down but it can cause a high speed lean condition that burns pistons.

 

[John from Madison CT]

Re: VST Filter Replacement on 2001 OX66 250hp

I tried to replace the vst filter without removing the tank, but I have problems removing the small screws on the top of the VST tank, and had to do so on a bench.<br /><br />Make sure you have the proper size Philips screwdriver for those small screws.

 

[hyd-n-seek]

Re: VST Filter Replacement on 2001 OX66 250hp

Thanks for the responses, guys. So what I'm gathering is that the "VST filter" is, in fact, the same thing that the SELOC manual refers to as the "electric fuel pump filter" (circular, with six pie-shaped wedges), and its connected to the bottom of the electric fuel pump that sits inside the tank. I appreciate your patience - I truly wants to learn the ins and outs of this engine, but I want to make sure I'm going down the right path the first time I go at thest maintenance and troubleshooting projects. Thanks again.

 

[bernieb]

Re: VST Filter Replacement on 2001 OX66 250hp

I take it that your engine is "dropping out abruptly" and if so does it restart instantly? if so i had that problem with the same year and hp, efi, and it was the main system relay (200 bucks)and cured the problem. But just maybe it was water that was my problem ,but anyway it hasn't done it since.

 

[jwbergeron]

Re: VST Filter Replacement on 2001 OX66 250hp

I just cleaned my VST filter, if you haven't done it get a new seal for the tank, its nearly impossible to reuse as it swells up with fuel.