Diesel Over Revving

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The Grand Pooh-Bah
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Location: Idaho

Thu Jul 04, 2019 1:30 pm

I'm working on a 8KW Generac with the 70939 1.0 L diesel Shibaura S753 engine. It has sat for 10+ years. I have changed all the filters and fluids.

When it starts up it goes into high rev and the fault light kills power to the solenoid and fuel pump. The engine continues to run very rough at a slower speed. I have to pinch off the fuel line to stop the engine. ( I didn't know the lever next to the injector was a manual method of sliding the rack)

I pulled the solenoid and the rack is not moving when I try pushing on it thru the hole where the solenoid was. (I tested the solenoid - Good) I pulled the injector pump and the rack slides like butter. The linkage that is attached to the rack moves freely. The spring tension on the linkage isn't very strong though. It doesn't seem to have enough tension to move the rack. The stop lever moves the linkage, the governor lever does not.

I have reinstalled the injector pump several times and can not see how the lever could possibly get hung up. The rack appears to be pushed forward and does not spring back.

Help!!!!

I can't seem to find a service and repair manual for this engine, only the owners manual.
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Generac 8KW Engine # 70939 1.0 L Shibaura S753 Alternator Data: Model 00449-0 SN 3113852 120/240v 1800 RPM
The Grand Pooh-Bah
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Thu Jul 04, 2019 2:24 pm

After further fiddling. It appears the stop lever does not move the linkage enough to actually move the rack back and forth enough to make a difference. It is moving the rack maybe an 1/8" or less. Something seems to have gone astray with the governor or stop lever or ?
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Generac 8KW Engine # 70939 1.0 L Shibaura S753 Alternator Data: Model 00449-0 SN 3113852 120/240v 1800 RPM
78buckshot
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Thu Jul 04, 2019 4:28 pm

I have zero experience on that engine, I guess the next thing would be to disassemble the governor to investigate the hang-up, maybe sat with water or just rusted in high speed, I assume it is a mechanical governor and at rest it would be in the high speed position.
The Grand Pooh-Bah
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Fri Jul 05, 2019 10:05 am

Wish I could fine a Service & Repair Manual on this engine.
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Generac 8KW Engine # 70939 1.0 L Shibaura S753 Alternator Data: Model 00449-0 SN 3113852 120/240v 1800 RPM
Birken Vogt
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Fri Jul 05, 2019 9:20 pm

This engine was used in Northern Lights generators and tiny Ford tractors also but I have not been able to come up with a service manual to download. You might have to break down and buy one.

Take off the governor covers and see if you even need a service manual though.
The Grand Pooh-Bah
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Sat Jul 06, 2019 12:02 pm

I removed the timing gear cover today and everything looks good, as in no broken parts.

Now that I have the timing cover off and the ability to see how things work I'm concerned that the throttle adjustment bolt might be the issue. The lock nut that locks the throttle bolt is at the head of the bolt, not down the bolt where it would lock the adjuster in place. I can see there was some yellow paint marking the factory setting, but nothing on the bolt to show me where it should be set. These are the type of things I would hope to find in a service & repair manual, if I could find one.

Image

Can someone tell me the proper setting of this adjustment. Circled in red.
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Generac 8KW Engine # 70939 1.0 L Shibaura S753 Alternator Data: Model 00449-0 SN 3113852 120/240v 1800 RPM
The Grand Pooh-Bah
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Sat Jul 06, 2019 8:20 pm

After pulling the timing gear cover off and not finding any broken parts I put my attention back to the injection pump. After close examination I found that one of the pins that slide back and forth when you slide the rack was not engaged. I removed the two screws and the rack. I rotated the pin so that it would engage in the slot on the rack like the other two. I put it back together and reinstalled.

It is running much smoother but still over revving and now it shuts off when the fault light goes on. It will not shut down with the stop lever. The stop lever linkage is moving the rack with full motion.

What now?
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Generac 8KW Engine # 70939 1.0 L Shibaura S753 Alternator Data: Model 00449-0 SN 3113852 120/240v 1800 RPM
Chris
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Tue Jul 09, 2019 10:40 am

After some searching I believe this is the engine service manual for that unit: https://shop.gentekpower.com/products/g ... ual-070939

I have recently been adding them to the site as a digital download and stumbled across it.

Hope this helps!
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
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The Grand Pooh-Bah
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Location: Idaho

Thu Jul 18, 2019 1:18 am

Got my injector pump back. It was fine. Re-installed and it is still over revving. Adjusting the throttle lever does not change anything. It seems to be something with the Governor.

When the engine is not running should the rack be towards the radiator or towards the back of the engine.

I have read that the throttle lever is set at the factory. Does anybody know where the factory setting is? How many threads or measurement should the adjustment bolt be into the bracket.

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Generac 8KW Engine # 70939 1.0 L Shibaura S753 Alternator Data: Model 00449-0 SN 3113852 120/240v 1800 RPM
Chris
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Thu Jul 18, 2019 8:32 am

In the service manual it talks about properly timing the injection pump using special shims and also shows a 2nd governor adjustment screw in the opposing position as the one you show here. Mind you it's for the marine version of this same engine, but I wouldn't see why they are different..?
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
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