Yanmar SB8 injector pump issue

[Sochal]

I private messaged Wotname since he appears to be the resident expert, but wanted to see if anyone else has any suggestions.

We recently had an issue where I think we ran the tank out of fuel so we’ve been bleeding the lines and we can’t seem to get any fuel into the high pressure lines past the the delivery valve on the top of the injector pump. We appear to have good fuel pressure right up the line to the pump and when I loosen off the delivery valve I can see that the plunger is pushing fuel up, but when I thread it down, even half way, the fuel will not push through.

We aren’t getting any squeak from the pump so we’ve been trying to tweak the adjustment on the regulator, but that doesn’t appear to be doing anything to help, so I’m wondering if the regulator is having a issue, but when we took it apart everything looked fine including the needle so we are kind of stumped.

Any thoughts would be much appreciated

[Compass790]

Welcome to the forum Sochal,
I would guess you have air in there somewhere if you havent mucked up the adjustment. Wotname will reply when he has time. I think the linkage adjustment is pretty vital & you have the same pump as the yse8 & ysb8 AFAIK. Try searching Wotnames posts or yse8 or ysb8 as he has coached others thru the adjustment. Halifax sailor was a recent one I think.

this link may help:https://www.cruisersforum.com/forums...or-221204.html

[Halifax Sailor]

Originally Posted by Sochal

I private messaged Wotname since he appears to be the resident expert, but wanted to see if anyone else has any suggestions.

We recently had an issue where I think we ran the tank out of fuel so we’ve been bleeding the lines and we can’t seem to get any fuel into the high pressure lines past the the delivery valve on the top of the injector pump. We appear to have good fuel pressure right up the line to the pump and when I loosen off the delivery valve I can see that the plunger is pushing fuel up, but when I thread it down, even half way, the fuel will not push through.

We aren’t getting any squeak from the pump so we’ve been trying to tweak the adjustment on the regulator, but that doesn’t appear to be doing anything to help, so I’m wondering if the regulator is having a issue, but when we took it apart everything looked fine including the needle so we are kind of stumped.

Any thoughts would be much appreciated

welcome to the forum sochal,

I did indeed go thru a major issue with my ysb8. Compass and wotname were instrumental in getting my "fine little one lunger" working like new. Mine started two years ago with slow starting and I went thru many fact finding days. Thoughts were fuel delivery at first so I looked for bad pumps, leaks, replaced all fuel lines, filters, even dumped about 5 gal of diesel that may have been bad (was about 3-4 years old). I had reset the valves, checked the fuel pickup and cleaned the tank as well. I did listen for the squeek of the fuel hp pump and I did have that. So I did not touch mine. The issue was a blown head gasket, many holes/leaks. Replaced that with new valves and a cleaned head, all new approprite gaskets, and to the delite of all, it starts like new.

Don't get discouraged, these guys know what they are talking about, I certainly didn't when I started this journey. But now I know all about this "little engine that could." I was lucky when I pulled mine apart, when I inspected the piston and after the head was cleaned, it looked brand new (in my opinion). Oh, and I had the injector rebuilt with a new noozle as well.

Might be frustrating right now, but I can assure you when you figure it out, it is so amazing when you turn that key, it starts and you did it!!

The whole story is on thie forum....
https://www.cruisersforum.com/forums...ives-me-crazy-
264918.html


If I can help, plse ask,

Ric

[Wotname]

Originally Posted by Sochal

I private messaged Wotname since he appears to be the resident expert, but wanted to see if anyone else has any suggestions.

We recently had an issue where I think we ran the tank out of fuel so we’ve been bleeding the lines and we can’t seem to get any fuel into the high pressure lines past the the delivery valve on the top of the injector pump. We appear to have good fuel pressure right up the line to the pump and when I loosen off the delivery valve I can see that the plunger is pushing fuel up, but when I thread it down, even half way, the fuel will not push through.

We aren’t getting any squeak from the pump so we’ve been trying to tweak the adjustment on the regulator, but that doesn’t appear to be doing anything to help, so I’m wondering if the regulator is having a issue, but when we took it apart everything looked fine including the needle so we are kind of stumped.

Any thoughts would be much appreciated

My apologies for the delay in getting to this thread - been kinda busy lately.

The very first thing to know is the injector pump (IP) used on the SB8/12 (and YSE8/12) operates on a very different principle than just about any other IP found on other small marine diesels. This fools a lot of people until they grasp the difference.

Most IPs have a fuel rack that varies the volume of fuel on the low pressure side of the IP. The IP then pressurises that volume of fuel and delivers to the injector. If more fuel is required, the fuel rack delivers more fuel on the low side. If less fuel is required, the fuel rack delivers less fuel on the low side. The pump plunger just pressurises the volume of fuel that the rack gives it. Pretty straightforward.


The SB8 IP does not work this way! The pump plunger pressurises the same volume of fuel each cycle. If less fuel is required, the regulator assembly (regulator spindle and needle etc) bleeds some of the fuel from the high pressure side back to the low pressure side. To get full fuel, the regulator needle valve must be fully closed. To get less fuel, the regulator needle valve opens ever so slightly and allows high pressure fuel back into the low pressure side of the IP.

As the regulator needle only requires a tiny amount of movement to go from full fuel to no fuel, it has to setup exactly as described in the manual. Unfortunately for the directions for setting it can be confusing when doing it for the first time - don't ask me how I know this. Once you get the hang of it, it quite easy.

I strongly suggest you follow the setup procedure as described in this thread - https://www.cruisersforum.com/forums...or-221204.html (as mentioned upthread by Compass790).

I have attached a couple of pictures here but you should really read the entire thread to fully understand the procedure.

If you are still having problems after setting up the regulator assembly correctly, please come back here.