Yanmar SB12 Fuel Pump Problems - SailNet Community

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  #1  
Old 05-09-2010
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Unhappy Yanmar SB12 Fuel Pump Problems

My 1978 went to bed last fall operating perfectly. This spring it won't start. Assuming fuel issues, I cleaned the fuel filters and bled the system. No go. Further diagnosis show the low pressure fuel side OK, but I have no pressure at all on the high pressure side.

I have fully diassembled the fuel pump all all looks fine. No dirt, no broken springs, etc. Still, when the engine is turned over with the high pressure line taken right off, there is no fuel coming from the output of the fuel pump.

Does anyone have any ideas on this?

Homer Shannon
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Old 05-09-2010
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are you talking about the primary fuel transfer pump if so just go to autozone or any auto parts store and buy low presure electric fuel pump 5-15 psi,maybe about $30 bucks,much better and more reliable than the origional diafram pump.if its the injector pump and you not getting fuel at the injector try squirting a little ether into the intake,mine sometimes gives me truble after not being run for a while
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Old 05-09-2010
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Yanmar SB12 Fuel Pump

No. This is not the low pressure side. That is working fine. I'm on the high pressure side. All is well bled to the high pressure pump but no fuel comes out of the output side (to injector) of the pump.

I have spoke with two people who had some input:

Comment 1: Replace high pre$$ure pump. Had same problem and it fixed it on a Yanmar GM-3.

Comment 2: It looks like the plunger and plunger barrel in the pump are replaceable. Replace both as a kit. Probably less expensive than the whole pump, if available. Also, replace needle valve while in there.

My next step is to find out of Torrington or other Yanmar diesel distributor can provide the pump parts.

Any other input? I'm out of ideas.

Homer Shannon
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Old 05-11-2010
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More Info - Not the Pump

OK, my injector pump is not bad. The problem was a misunderstanding of how the regulator works. Unlike most machines, the regulator is wide open when fully shut. I had it backed off. Closing the regulator develops pressure in the pump and to the injector.

However, after bleeding at the injector the motor still won't start. I put a touch of ether in it and it does ignite and run for a couple of rotations. (I only used a very little amount!) My next step it replace both filters and re-bleed. If it still won't start, I'll take a look at the injector.

BTW, had I needed a new injector pump, Gulf Coast Composit, www.gulfcoastcompostit.com, has the pump for $249 or you can get the "plunger and barrel", the main wear component of the pump, for $63.

Homer Shannon
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Old 05-11-2010
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it sounds like your on the right track,if your not getting even a tiny amount going to the injector its probably not the injector,i'm still betting on lack of prime
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Old 05-12-2010
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Define "not even getting a tiny amount"

Sawingknots:

What do you mean by "not even getting a tiny amount" of fuel at the injector? I am getting fuel at the injector if I losen the feed line at the injector and turn the engine over. The fuel only comes out a few drops at a time but I believe this is normal and I am not passing any air.

As stated before, I am going to replace both fuel filters, but I think I have an injector problem.

Homer Shannon
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Old 05-12-2010
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yes,that amount is normal,it does sound like an injector problem,you should be able to get it checked at a local diesel engine shop.its possible you have a compression problem but i would investigate that injector.with good luck and patience you'll get there
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Old 07-27-2010
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Yanmar SB12 Starting Problem Resolved

I'll close out this thread and add some comments that may be useful to others. My problem turned out to be dirty filters, both the lift pump filter and the primary filter. I replaced these, set everything back according to the workshop manual and the engine started right up.

I learned quite a bit about the injector pump and it's regulation in the process and I think I am in a position to be pretty helpful if anyone on the list is in need of assistance with this engine.

Despite comments I see about "Yamar-hammer" vibrations and noise, this has been a reliable engine that performs reasonably well pushing an 8600lb boat. Next year I hope to try out one of CDI's Perfect Pitch propellers because I don't think the engine is over worked and a little more thust would be useful.

Homer Shannon
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Old 07-27-2010
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great,i'm happy for you,bleeding these engines can sometimes be a little tricky,oh oh that reminds me i need to change my filters too.i doubt you will be able to get much more performance out of a ysb12 in a 8600 lb boat,just keep the bottom clean and don't use too big an alternator
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