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A 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 offline
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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 offline
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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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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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  #51  
Old 08-07-2017, 01:34:34 PM
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Default Re: A JB Performance Question

Quote:
Originally Posted by JohnnyC View Post
..... is your JB firing on both cylinders? And if so, is it firing properly? Are you absolutely positive?
From cold start feel both heads , see if one is lot cooler than other.
Pretty easy to do.
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  #52  
Old 08-07-2017, 03:11:50 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

Gentlemen after hearing how your JBs operate I am beginning to get worried that I may have a problem, but hear me out I am not so sure. First to respond to the comments/questions:
1) Jim, wrt the frequency drop, Yes I agree with your statement

2) Scoops: What do you mean by "roll of the line near Leon's"? Are you referring to the factory build spec revision? I suspect you are. My JB was built to Spec P in 1966, consequently it has a slightly different designed governor spring/adjustment procedure. That may be a clue as to the performance difference, maybe not, I do not know.

3) Vanman, Yes it goes immediately full throttle upon application of a 4 Kw load. But it pains me to see it struggle to recover.

4) Handyhiker, I adjusted the sensitivity a long time ago to just meet the 5% frequency requirement with no hunting, but I used a 4 KW load consisting of six 120 volt, 660 watt ceramic cones. The JB when connected to the house does handle the 5500 watt electric dryer, but the freq dips to about what 55? hertz and the voltage also drops out of spec but it recovers and ends up OK. I do not like this kind of performance. Yes it will start the 3 ton AC with some help from a couple of back emf motors I first start and the AC has a hard start kit installed.

5) Johnny that is a very good question! Yes both cylinders are firing. The only maintenance I have done since 1970 was back a few years ago when the solenoid shift starter failed and then a few years later, I changed the plugs and opened the gap to 0.030 inch or was it 035 and replaced t he points/condenser and reset the timing to I believe points first to 0.020 inch gap and then set the stop timing to 5 ATC.

6) Motorhead, I have not done any major engine overhaul to my JB since 1970. I am now 80 but I am concerned enough about this that I intend to try and fix it short of opening it up. Was looking the other day for my compression tester, but cannot find it.

What really bugs me is that 50-55 Hz dip. Did I read scoops sees a similar dip? Would like to know what factory spec his JB was built to. Maybe there is nothing that can be done about this matter. After all, the machine does easily carry the name plate load and then some. Thank you all for the advice.
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Old 08-07-2017, 03:38:12 PM
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Default Re: A JB Performance Question

If it's struggling to pick up a 4 kw load, there is definitely a lack of hp, at least temporarily. JohnnyC may still be on to something. It may have a cylinder that goes dead only when cold and only under load.

I would try listening closely at the exhaust when trying that experiment. You'll definitely notice if one cylinder stops firing for a few seconds.
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  #54  
Old 08-07-2017, 03:51:07 PM
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Default Re: A JB Performance Question

Leon in regards to the popping back thru the carburetor. My YD end J.B. did the same thing. It would "pop" back at no load or when a large load was suddenly dropped from the generator. What fixed my problem was richening up the LOW speed jet for the gaseous fuel circuit. I feel it was too lean and when the carburetor/governor went to idle or near idle position on the throttle shaft the idle circuit wouldn't supply enough fuel, causing a lean condition producing the back fire. When time permits, I will try to video what my generator response time is.
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  #55  
Old 08-07-2017, 04:09:17 PM
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Default Re: A JB Performance Question

Leon,

Yes, rolled of the factory line..
see here for my spec p:

https://www.smokstak.com/forum/showthread.php?t=168851

And I saw mine drop to 56hz, but it responded to teh 4k load in 1 sec or less, not 4.
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Old 08-07-2017, 04:19:57 PM
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Default Re: A JB Performance Question

Leon, Adjusting the valves on your engine, while opens it up, is nothing major to do. Being that the JB has both pistons going up and down in unison, all you have to do is bring the engine up to TDC and adjust the cylinder that does NOT have a valve open. Turn the engine another 360 degrees and then set the other cylinder. Even if NO valves are tight, you will at least know what it ISN'T.
Plus Leon, If no valves are tight, YOU will have more positive bragging rights about the STOUTNESS of the "J" series engine.
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  #57  
Old 08-07-2017, 07:17:21 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

My JB runs smooth as a top. Very little vibration and both cylinders are working. I frequently listen to the exhaust. I even put my hand against the tail pipe and the exhaust pressure is very even between both cylinders. Back a few years ago, I was concerned du to the slight hiccups in the exhaust, not popping but it did not sound right at NL So based on you guys recommendation, I changed the plugs and opened the gap from .025 to .030 or .035 and that cured the irregular NL exhaust sound. From what I know and can tell the exhaust sounds OK. I will need an assistant to check the exhaust sound as it struggles to recover. Even though it is slow to respond, it does so very smoothly best I can tell.

Today I tried blowing air into the Garretson vent as it struggled to recover. That did not help. If anything it made matters worse, that is it caused a not very smooth recovery.

I like BRAE's idea of tweaking the idle jet at NL. I can stop the popping by enriching the hi speed jet but then the recovery is even worse.

All that is left is to check the timing. I will have to do it statically. Might as well first check the point gap and make sure the timing advance mechanism is working.

If that doesn't solve the problem, then I may do a compression test. Test results from 1970 were 88 & 90 #'s. Wish we could hear from some more folks who have one of those earlier JBs, that is spec P or earlier.
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Old 08-07-2017, 07:39:21 PM
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Default Re: A JB Performance Question

Leon

here you go.

4500watt load

https://youtu.be/efwi7pk2hXM
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Old 08-07-2017, 08:24:39 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

Scoops thank you for the video. My impression of your presentation tells me by the audio your JB starts like mine. The other thing that jumps out to me is your frequency seems to jump around quite a bit. My JB does not do that.

I am beginning to think my JB ignition timing spark advance is not working or not working correctly. I have only twice set the ignition timing using the engine-stopped method. Once in 1970 and then a few years ago when I replaced the points.

I need to obtain an automotive timing light so that I can check it with the JB running.
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Old 08-07-2017, 08:43:21 PM
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Default Re: A JB Performance Question

Why keep fiddle farting around with this? Jeesh, you've got a 30 year old KN regulator. It's due to be replaced regardless.

Go here:

https://carbturbo.com/product-category/regulators/


and get a replacement. Get a KN-039-122. It's genuine Garretson, and has a primer button.


https://carbturbo.com/product/garret...co-kn-039-122/

Meanwhile - YES check the ignition timing - simple enough...
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