Onan 2.8: new carb installed, now runs too fast and overvoltage

[Andy Waddell]

If the throttle plate is closed on both and the governor link hole is in the same place, there is nothing wrong with the carb. The only thing that could be different is the index of the throttle plate shaft and lever that is pressed on
NOT AN ISSUE, THEY'RE IDENTICAL
Can you close the throttle until the adjusting screw in your picture hits the stop tab ?
YES
You should be able to move the link, with your finger, to the idle position where the adjustment screw hits the tab.
YES
You don't show the other end of the throttle link. Are there different holes to place it in ?
NO

Are there any bends in the rod that can be bent slightly to shorten the rod?
NO

[twinboat]

Did you change the carb spacer ? That would move the carb.

[clifford j]

TwinBoat,,,wow great thought. Spacer thickness !!

CLIFF

[Andy Waddell]

Originally Posted by twinboat

Did you change the carb spacer ? That would move the carb.

No. Everything is identical to original installation.

[twinboat]

If everything is in place, nothing is binding and it runs fine, I would put a slight "S" bend in the throttle rod and then fine tune with the adjustment screws.

The other option is to move the governor arm, on the shaft. There is usually a simple procudure to follow, when doing it.

If it won't hold a set RPM, then it may be an internal govenor problem. Rare but not unheard of.

Good luck.

[TQ60]

The generator should be " closed loop" meaning the controller sees output and adjusts throttle to get correct.

First test is to manually control engine to see if it will idle smooth and slow then have good speed at all ranges of rpm.

That will confirm carb is just fine.

Old carb was hunting indicating the controller was open loop or lost or bad carb so bad that full throttle was close enough.

The controller is regulating the governor so look for maybe a loose wire or reset maybe.

Do review the manual as there must be something to test this.

Over raving tends to remove connecting rods...

[twinboat]

Originally Posted by TQ60

The generator should be " closed loop" meaning the controller sees output and adjusts throttle to get correct.

First test is to manually control engine to see if it will idle smooth and slow then have good speed at all ranges of rpm.

That will confirm carb is just fine.

Old carb was hunting indicating the controller was open loop or lost or bad carb so bad that full throttle was close enough.

The controller is regulating the governor so look for maybe a loose wire or reset maybe.

Do review the manual as there must be something to test this.

Over raving tends to remove connecting rods...

All inducations are that this is a mechanical governor. No electronics.

[TQ60]

Still applies...

Old school then if rpm based the weights are bound or if voltage based loose wire.

The short of it is the unit is not closed loop now.

Switching to lawnmower engine mode the throttle pulls in a spring to put pressure on the governor.

The spring will pull throttle full open and governor pulls it down to balance the spring force.

Switching to generator mode a spring pulls throttle wide open to better start unit then governor pulls it back.

If it was hunting before then bad carb and or governor or both.

Now engine runs well and fast but governor is not controlling it.

Focus on that as engine side is fine...for now.

Running too fast is good thing ( indicating engine good)

Try to find manual on unit to confirm how governor should be tested and adjusted.

Me is guessing maybe one link could be missing or in wrong place maybe too.

[okcnewbie]

I'm pretty sure this was a pic of mine when running. Yours looks different to me.

[mel s]

Originally Posted by Andy Waddell

Hi there. Have an Onan 2.8 KV series Spec K in our 2004 Coachmen Freedom 258DB. When we got it last fall the generator was surging and hunting. I disconnected the main fuel line and plugged it then ran a separate feed of a strong Seafoam and fuel mixture and that seemed to do the trick and cleaned it enough to give smooth running. I drained the carb bowl via the bowl screw on the bottom and stored the vehicle for winter.

This spring I got the vehicle out of storage and brought it home. Gen started and ran fine, but seemed to occasionally want to hunt a bit again. I figured what the heck, I have no idea what this thing has been through before we got it so I'll go ahead and pop for a brand new Onan carb for it for peace of mind. (Onan says their carbs aren't rebuildable, they must be replaced).

Got the carb a couple days ago and installed it. (Should say now that I was a Service Engineer for General Motors Corporate for 29 years, so let's just say I'm REAALLY comfortable working with engines, and have rebuilt hundreds of carbs and engines, etc. I know my way around a wrench and engine).

Installing the carb was a piece of cake, nothing to it. A little fiddly since there was not a lot of room, but figured out how to safely get the old one out and the new one installed no problem. Started her up, and it ran nice and smoothly but seemed to be running a lot faster than the old one did. No way to really tach it to tell for sure, but it most certainly was running quite a bit faster than the old-carb engine. Decided to measure at one of the outlets (had the gen plugged into the coach), and saw 165 volts!! Yeah, she was running a bit fast, huh?!! Shut her down, then connected my surge protector between the gen and coach since it has a voltage display. Read 141 volts. Tried adjusting both the engine speed and governor sensitivity screws (of course counting my turns so I could put them back to original), and got no significant change. Fiddled with the carb and linkage and everything seemed fine, but decided to pull the carb and check the linkages and carb one more time to be really sure there was no binding or differences between the old carb and new. Nope, nothing different. Compared the carbs side by side very closely and there's no difference. Carbs are also stamped with the same part number.

Put it back together, same thing. Starts and runs nicely, but way too fast. Surge protector reads 141 volts. Called and spoke with the tech at the place I bought the OEM Onan carb from; he's been doing gens for 25 years and has never heard of this problem. We talk a little and agree that there's nothing that a carb could do to make this happen short of differences in the position of the butterfly links or something, but no...that's not it. The carbs are identical in that regard.

I can manually pull down the engine speed by regulating the governor with my finger/pulling back the linkage, so it can be done/the linkage isn't bound up. Governor internal mechanism itself is working; when the engine starts and build a little speed you can see the governor arm moving in response to the pressure buildup inside. Have attached a couple photos of the linkage (yep, I pulled the whole damn generator from the vehicle so I could get the lid off and get a good look at everything. A lot of work but no result).

So, there I am. Both me and the tech at the generator shop have no idea where to go next with this. Any ideas? How could installing a new IDENTICAL carb in design and function cause a "runaway" engine speed? Hoping someone out there has seen this before and can help me out! Thanks.

Originally Posted by Andy Waddell

I'm with you on the "new carb = problem there" even though a carb shouldn't do it, but I hate to spend another 180 bucks to have TWO carbs that result in a gen running too fast. I'm gonna talk with the place I bought the carb and ask if they'd be willing to sell me one at cost to see if a different new one cures the situation.

As far as low hours on the gen, the RV was stored indoors for its entire life before us, and we've used the gen for, oh, four hours or so. I would run it under load when the RV was in the driveway to exercise it, and also we used it a few times at rest stops to run the microwave to make lunch, etc. It seems to produce power just fine. I think it's probably OK.

Andy Waddell
Are you sure you don't have an intake leak causing the "fast run/high voltage output"?
Even experts can screw up the "carb to manifold gasket", (and therefore the air-fuel mixture), when replacing a carburetor.

BTW a Kill-A Watt meter is useful when adjusting the run of a generator... to obtain the the correct output voltage and frequency (Hz).

Mel
'96 Safari

[TQ60]

The very first photo looks like it is an arm attached to a shaft protruding from engine.

This looks a lot like the governor from the engine.

If so then that part is purely mechanical and used to govern the frequency part of the engine and voltage may have other means.

Not sure if over rev or over voltage for certian so ASSUMING for this post voltage is high purely due to over rev. (Kill a volt good suggestion for frequency counter..will need to remember that GREAT idea!).

In first photo there is a lever to left with multiple holes and an adjustment screw.

The holes allow different attack ratio for the lack of better term of how the governor reacts to engine loads.

Screw adjusts against spring to allow speed adjustment.

First while stopped check all linkage and me thinks all should move freely and be positioned at full throttle.

Now manually move linkage to make sure it can go to idle position.

If real stiff the spring may be in wrong hole as PO may have messed it up trying to fix it.

After all checked start unit and see how the arm moves.

Give it a little help by gently pushing it to see how it responds.

You could shift spring to different position to see if it helps.

The governor may be broken as well.

Remove the spring and start the unit.

Pull the throttle manually and as the engine speed is higher the force should increase to reduce throttle.

[ChasA]

I agree with Mel, it could be an intake leak. I have repaired a lot of small engines and have seen it a few times. A small air leak will cause the engine to run faster. It's easy to check with an oiler or some grease.

[twinboat]

An intake leak will increase engine speed because the air is leaking in beyond the "closed" throttle plate. It will also create a lean mixture.

This generator has a constant speed governor that holds the throttle plates open until a set speed is reached.
In that situation an intake leak would produce a low power situation due to a lean mixture. With any load the rpm would drop.

The engine speed controls the cycles and the voltage of the generator head.

Many are set at 3600 rpm, the speed that produces the 60 cycles. Some belt drive units, overdrive the generator head, so the engine can run slower and quieter.

Inside the block is a flyweight assembly that spins off the cam or crank shaft. The faster it turns the more centrifugal force it creates.

This force is used to move the lever that pulls back the throttle rod, partially closing the throttle.

The goal is to balance the force of the governor to the rpm of the engine. That is the job of the heavy spring.

Increase tension and the speed goes down, decrease the tension and the speed increase.

If the engine is going too fast, the spring tension needs to be increased. If it can't, the rod can be shortened slighty to close the throttle. If you don't want to bend the rod, adjust the governor lever on the governor shaft.

To set the cycles, build the poor man's hertz gauge.
String 2, 60 watt incandesent, 120 volt bulbs in series, with 2 male plugs. Plug one end in shore power and one in the generator. Carefull with the hot plugs.

With the generator running, the bulbs will light dimly but flash. Find the speed that they stop flashing and both glow steady and you have the same 60 cycles as your house.

Or just plug in a Kill A Watt meter, set it to hertz and adjust it.

[Andy Waddell]

After thinking and rethinking and etc. I finally decided to go ahead and try to make the governor adjustments myself, as I could always take the thing in to a Cummins/Onan dealer and have them do it if I couldn't make it work out. I found the service manual for the gen online so I had the correct procedures and hertz to set at various speeds/loads.

I went to Harbor Freight and bought a $60 DVM that could also measure Hertz (search for 98674 at the HF site), as that's what you're looking for when making speed and load adjustments. Bit the bullet and made the adjustment at the main governor arm that I felt was the main "culprit" and was able to dial everything in after that. Basically I pulled the throttle down by hand and set it to the correct hertz, as that's the first thing you're supposed to do, to set the "idle" hertz. Then I let the governor control it and ran it at no-load (2 amps total draw) and got the required Hertz with screw adjustment, then turned on every light in the coach, turned the AC on high fan and coldest, and also put a big bowl of water in the microwave and ran that on high for 4 minutes. Pulled 24 amps and was able to adjust to the correct hertz. Once the microwave shut off it adjusted nicely to the new "medium" load of the AC and lights. After a minute I turned on the wave again and she took the hit of the new current draw in stride, no bobbles or hunting, just loaded down and worked it!

So, the end of the story is that the new carb actually DID take the governor out of it's "normal adjustment zone". It needed a relatively major adjustment at the governor shaft and then I was able to pull everything in. Hopefully if someone else has this problem in the future they will also have the gumption to go ahead and do what seems to need to be done, even though it seems to be "off the scale" of what should be necessary.

Thanks to all for your ideas and help!!