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An Onan JB Performance Question


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  #41  
Old 08-06-2017, 10:20:27 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: A JB Performance Question

Quote:
Originally Posted by Leon N. View Post
...Do you mean to tell me your YD equipped JB does not show any appreciable frequency dip and recovery time lag?
No. The YD sets have no appreciable voltage drop. Frequency droop has nothing to do with the regulator, it's purely a function of the governor accuracy and speed.
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  #42  
Old 08-06-2017, 11:12:06 PM
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Default Re: A JB Performance Question

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Originally Posted by JohnnyC View Post
Leon, I think we need someone with a mag end to run the tests. Regardless, it is hard to believe a droop down to 50 or 55 Hz no matter how brief under normal loads would be considered normal. Who here has a mag JB?

JohnnyC
New Jersey

mine rolled off the line near Leon's.
i don't have my natural gas line run yet, all i have is
1 20 lb tank, not sure if it will keep up with a 4k load.
if you all think it will, i'll try it tomorrow.

---------- Post added at 11:12:06 PM ---------- Previous post was at 11:10:09 PM ----------

i think onan dan has a mag 7.5 too and he's on natural gas.
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  #43  
Old 08-07-2017, 01:51:30 AM
Vanman Vanman is offline
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Default Re: A JB Performance Question

A couple thoughts occurred to me.

Leon, when your JB is cold, and you apply the 4 kw load, does the throttle immediately go to wide open as soon as the speed drops? If the speed is going as low as you stated, it certainly should be. It could be that your governor is sluggish when cold, perhaps gummed up. I have a Briggs with a lazy governor. Slow to respond.

Popping back through the carburetor makes me think of leaking intake valves. Something has to ignite the mixture in the intake manifold.

Keith
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  #44  
Old 08-07-2017, 03:36:54 AM
Leon N. Leon N. is online now
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Default Re: A JB Performance Question

It's 3:30 and I must get up to take my better half to a distant hospital for eye surgery. However, I will recheck my JB hopefully later today. I always thought this was normal operation because if I apply loads incrementally, the JB voltage and frequency stay within the specified limits and I never had any other JB to compare it too and most importantly, Onan says nothing about dips only recovery time.

Yes it sounds like the governor is slow to respond. As I think back, it seems to me the position of that governor spring on the governor actuating arm is somewhat arbitrary when looking at the pictures in the manual. I will check, but I believe the throttle goes full open when applying the 4 kW load. Thank you for the info. More later.
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  #45  
Old 08-07-2017, 04:43:47 AM
Handyhiker1 Handyhiker1 is offline
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Default Re: A JB Performance Question

I do not have a JB but on my JC and other Onans they have the sensitivity setting for the govenor. Is is possible that it is just not set sensitive enough and that makes the govenor slow to respond?
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  #46  
Old 08-07-2017, 10:56:52 AM
Leon N. Leon N. is online now
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Default Re: A JB Performance Question

OK I am back. Wife's eye surgery went well. She has to wear an eye patch for a day.

I went out and removed my JB front and top cover so that I could see the throttle position and movement. Yes, the throttle goes full open when I dump a 4 KW load on it from a NL position. It takes about 4 seconds to recover to 1800 RPM. I also took a picture, see attached of the governor arm and governor spring attachment point to the arm. As you will note, my JB was built to spec P and contains an early version of the governor spring/adjustment mechanism as shown in 967-500, pages 24 & 25.

When I set up my JB I followed the instructions in 967-500 and my JB does meet the frequency spread as shown in Table 2, page 25.

All the Onan procedures say is adjust the sensitivity for a "maximum" without hunting. That is exactly what I did back in 1970. The procedures say NOTHING about the specified 2 second recovery time. Subsequently I had to increase the NL frequency to 61.5 to prevent hunting and still stay with in the 5% frequency tolerance. I was advised this was probably due to excessive wear on the fly ball governor when set at a 60Hz NL frequency.

As for the occasional popping at only NL, if I open the hi-speed carb jet to stop it, I then cannot meet the 5% frequency requirement.

This problem blows me away. Sure would like to hear from any JB users, especially those who have the early designed governor arrangement as show in my attachment.

I appreciate any and all suggestions.
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  #47  
Old 08-07-2017, 12:58:06 PM
JohnnyC JohnnyC is offline
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Default Re: A JB Performance Question

Leon, I have a very stupid question. So stupid that I am embarrassed to ask, but I will ask anyway... here is my question: is your JB firing on both cylinders? And if so, is it firing properly? Are you absolutely positive?

JohnnyC
New Jersey
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  #48  
Old 08-07-2017, 01:10:26 PM
Ray Lynch Ray Lynch is offline
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Default Re: A JB Performance Question

My JB has a YD end. With a resistance load of 3 KW already applied, I start my well pump (approx. 48 LRA). Governor responds instantly with a barely discernable "blip" from the set. My NL freq. is set at 62.5 Hz. With my typical house running load, set freq is 60 Hz.
My set is dialed in to run my house. I'm not concerned that it may not be able to adjust quickly to a 4 KW load cold. If I tried and it didn't, could probably re-adjust it to handle this cold load.
And maybe solve 1 "problem" but create 3 more in the process.
Ray
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  #49  
Old 08-07-2017, 01:10:29 PM
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Default Re: A JB Performance Question

Leon, My late, YD end JB pops every so often at no load too.
I am going to the basics for the prime mover: 1) Do a compression check. 2) check the valve clearances. I think I have suggested this before and can't remember if you have ever done this step since your overhaul many years ago. A slightly tight valve can cause low power, sloe response issues
3) If you have a timing light, check to see if the mechanical advance is working freely. The advance mechanisms can get sticky and not actuate properly. A RETARDED spark timing will cause slow engine response.
These steps are what we did on air cooled VW's. This is "Apples to Apples" comparisons being they are air cooled, have adjustable, solid lifter valves and had mechanical advance units in the distributors. Some VWs had vacuum advance too and if the little hose leaked or broke, they had slow acceleration.
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  #50  
Old 08-07-2017, 01:31:43 PM
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Default Re: A JB Performance Question

Leon,

I just ran a check for you. mag end, but running on propane.
Started it up, hit 4k load, and it went to 56 hz, but seemed to recover
in a second or less.

I will do a video later today when I have a helper, as I couldn't film and
turn on the heaters at the same time, but i was watching the hz and I saw it drop to 56 for a second.
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