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1992 Onan Microquiet 4kw - Spec "A" - Lacks Power


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  #1  
Old 08-08-2017, 08:11:14 PM
jscmanson jscmanson is offline
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Default 1992 Onan Microquiet 4kw - Spec "A" - Lacks Power

I have a 4KY 2100 Spec "A" (The first version of the microquiet series) RV gas generator that I picked up for cheap, and I am trying to get it running. So far, I have replaced the Fuel Pump and filter, both electronics boards (Regular and control board), and I just put in a new carburetor. The unit will start and run, but runs at a slower speed, it never accelerates to the point where the governor would kick in and reduce the throttle setting (the throttle setting never varies from full open). I have verified that the choke is off (fully open) when running in summer temps, particularly when the unit heats up, so that is working OK. I am drawing from a fresh tank of gas, no evidence of vacuum leaks from what I can see (I haven't yet done a smoke test to verify this though), the unit does backfire through the carb quite often when I am trying to start it - meaning a lean fuel mixture....

The generator is putting out about 100 volts AC, certainly below spec, but it's not running at full RPM, so I don't think that's a problem, at least not yet. I have checked all resistance readings etc on the regulator and generator windings, everything checks out OK (I have a flight systems breakout box (G-man)that lets me monitor voltages and resistances during running conditions).

I have done a leakdown test and it was about 25%, pretty good for a 25 year old generator, so it's got compression in theory.

So my next steps ....

1. Smoke test - look for vacuum leaks between the carb throttle body and the cylinder intake - everything looks tight visually;
2. Check to see if the crankcase ventilation reed valve is working (I am getting a bit of minor oil leak happening at the bottom of the generator pan after it runs for a few mins, it looks like the oil is seeping out the oil switch wire, maybe the crankcase is building up pressure....
3. Check to see if the compression release system is not releasing when the unit fires up, resulting in poor compression when running.. This one requires a complete strip down of the unit.


Any other things I should be looking out for?

Thanks in advance!!

John
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Old 08-08-2017, 08:25:45 PM
len k len k is offline
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Default Re: 1992 Onan Microquiet 4kw - Spec "A" - Lacks Power

I squirt a thin stream of gas down the metal carb intake while it's running.
If it comes off of WOT then it's either starving for fuel or there's an air leak into intake.

Could take spark plug out and rotate flywheel to see if it's dragging a lot.

Manual numbers and link to them
ky--SERVICE--(2-97)--(A-G)--981-0503.pdf <---------------------read this one
ky---PARTS--(6-99)--(A-J)--9810246B--from cd.pdf
http://www.twinslan.net/~n0nas/manuals/onan/

Schematic is figure 12-2 ( back of manual)

Do you smell smoke from the genhead?
Check if engine is starving for gas first. But to check genhead is not shorted and loading down engine could unplug ac voltage reg, that should prevent genhead from making power and loading engine. But would have to hot wire gas pump and disconnect kill switch wire J1-6 to spark coil. Without making AC after you release start switch control board should ground J1-6 to kill magneto spark, (just like on lawn mowers)

Last edited by len k; 08-08-2017 at 08:47:32 PM.
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Old 08-08-2017, 11:53:00 PM
jscmanson jscmanson is offline
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Default Re: 1992 Onan Microquiet 4kw - Spec "A" - Lacks Power

Thanks -I will try the additional fuel idea, I have gone through all of the resistance measurements with the 'G-Man' connector, all resistance readings were in range - unless it's a flying short or something like that - I am wondering if that compression release thing is malfunctioning, would prevent proper compression, I hope it's not as it's a major repair, at least time wise - but maybe I should be stripping this thing down anyways due to it's age..... J
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Old 08-09-2017, 12:27:57 AM
len k len k is offline
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Default Re: 1992 Onan Microquiet 4kw - Spec "A" - Lacks Power

I believe flying short would be in rotor , that would reduce magnetic feild and voltage out the stator would be reduced. But that would result in a reduced load on engine, not an increased load.

Don't know if this one has compression release, that sounds like something thats in gasoline pull start engines, and diesels, you would have to read the manual.

Last edited by len k; 08-09-2017 at 12:27:47 PM.
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Old 08-09-2017, 09:58:21 AM
Combustor Combustor is offline
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Default Re: 1992 Onan Microquiet 4kw - Spec "A" - Lacks Power

Had a motor recently with the same symptoms. Seems it had been in storage a while, rust and carbon in the muffler had come loose and was blocking a spark arrestor screen inside. Try it without the muffler to check the fault. Regards,
Combustor.
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Old 08-09-2017, 11:36:00 AM
jscmanson jscmanson is offline
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Default Re: 1992 Onan Microquiet 4kw - Spec "A" - Lacks Power

Thanks guys, I will try the muffler removal as well. And the flying short - yes you're right it would be the other way around.

There is an internal compression release pin, it's in with the crankshaft unfortunately, so it's a job to get at it. I'll try the other options first this weekend.

And I will also try the 'no ac power' option that Len has suggested, after verifying the starved fuel test.

My plan:

1. Squirt fuel while running.
a) if engine speeds up check for either starved fuel, or vacuum leak, else..

2. remove Muffler. If engine doesn't speed up...

3. Hot wire (bypass) fuel pump, carb solenoid, bypass ign kill wire. If engine doesn't speed up...

4. Strip down and check the compression release mechanism in crankshaft housing. If that doesn't work...

5. Sell parts on ebay :-)
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Old 08-09-2017, 12:29:02 PM
len k len k is offline
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Default Re: 1992 Onan Microquiet 4kw - Spec "A" - Lacks Power

sounds reasonable. Let us know what you find.

Last edited by len k; 08-09-2017 at 12:44:20 PM.
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