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An Onan JB Performance Question


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  #61  
Old 08-07-2017, 08:50:07 PM
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Default Re: A JB Performance Question

Scoops, your JB sounds good. As for your frequency meter, it seems to refresh very, very rapidly giving the impression your Hz is all over the place.

Leon, to start with do a compression test on both cylinders. Recheck your point gap. Check the gap on your plugs and ensure that the plugs are not fouled and ensure they burning correctly (both spark plugs). Spark plugs can tell many stories of how the motor is running if you can read them correctly. These are simple things to do without too much effort and zero cost. If you lived with 40-50 miles I'd run over there on the weekend to assist.


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  #62  
Old 08-07-2017, 09:07:32 PM
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Default Re: A JB Performance Question

Leon, I second Jim's opinion on either replacing or rebuilding your regulator. The diaphragm can harden and maybe not be as responsive. When you blow pressure to the vent of the Garrettson, it opens the port in the regulator due to pressure on the one side of the diaphragm. That's why the engine ran rough, it got real rich fuel mixture. I have rebuilt one of the regulators but for a couple of my builds, I have just bought a new Genuine, Garrettson. The one on my JB now has the 12 volt solenoid bleeder/enrichener which mechanically pushes the diaphragm and the gas flows into the engine. The solenoid is also adjustable on its stroke to regulate the amount of flow while it is energized.
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  #63  
Old 08-07-2017, 09:30:35 PM
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Default Re: A JB Performance Question

Motörhead I was thinking maybe the JB was not getting enough fuel as slowly returned to normal speed. Apparently that was not the case. My original plugs were Champion H8, I believe. They were no longer available so they sold me if I recall a Japanese equivalent.

I am going to purchase a comp gage and a auto timing light. I first need to clean off the timing marks and see if the advance is working correctly. I need to get my ambition back, remove that from tin and briefly fire up the JB and check the spark advance.

Back in 1970 during my refurb, I do not recall taking the JB spark advance mechanism apart. I do recall changing the points and setting the timing statically. I hope I do not have to disassemble the spark advance mechanism, small parts, hard to see etc. What's with the small hole on the back of the breaker plate, Onan says to make sure it is clear? I do not recall ever thinking about that as an issue.
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Old 08-07-2017, 09:45:42 PM
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Default Re: A JB Performance Question

Leon, Here is a cross reference chart for the H-8. I have always liked NGK or Denso spark plugs in air cooled VW's. Major reason was that they didn't stick in the plug threads when you pulled them out 5 years later.

http://www.sparkplug-crossreference....rt/CHAMP_PN/H8

From what I saw online, the H8 is still available. NAPA auto part stores are usually good for ordering stuff that they don't usually stock.
If you weren't on the opposite side of the country, I'd come over and loan you my timing light and compression gauge. Both are US made units.
I'll ship them to you to borrow if you can't find any quality ones.
With new computer cars and no distributors, most mechanics don't have timing lights. I'm still one of the OLD Dinosaurs!
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Old 08-07-2017, 10:03:29 PM
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Default Re: A JB Performance Question

I use NGK and nothing else. NGK threads are 1000 times better than Champion. BMW use NGK brand plugs too as well as other high end plugs.

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Old 08-08-2017, 01:32:48 AM
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Default Re: A JB Performance Question

Leon, if you still want to use Champion spark plugs, the updated part number for the "H8" is now "H8C" stock number "587", still tha same plug, also which my 4.0 cck uses.
also a lot of auto parts stores loan tools like, auto zone, advanced auto parts, and o'reilly.


I know that this is a apples-to-oranges comparison, but i
did a load test on my "UN-type" square head gasoline 4.0 cck (converted from sisson type choke to onan type choke), at NL ~65hz and 129vac (on my gens without volt regs i like to keep my volts a bit on the high side.) anyways at "FULL-OVERLOAD" of ~5,600W (actual measured, by v*a) YES you read that right, 5,600W!!! full-overload hz was ~59hz
the load consisted of 4, 1500w space heaters ( 2 "ceramic-type" and 2 nichrome wire coil-type, both fan-forced type)

windings are protected by a 2 pole 15a square-D QO type breaker, this gen has a 120v only or 120-240v selector switch installed on it. (if you want details on it, just ask me.)
if i perform my "load-test" :-) for very long (~10min?) the qo breaker WILL trip.

Leon, tomorrow i plan on taking a video just for you, of me abusing my 4.0cck with the 5,600w load from a cold start with a very short warm-up period of 30 seconds max, (shhhhh, just don't tell the onan protection services police )
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Old 08-08-2017, 07:01:43 AM
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Default Re: A JB Performance Question

Quote:
Originally Posted by turtmaster View Post
Leon, if you still want to use Champion spark plugs, the updated part number for the "H8" is now "H8C" stock number "587", still tha same plug, also which my 4.0 cck uses.
also a lot of auto parts stores loan tools like, auto zone, advanced auto parts, and o'reilly.


I know that this is a apples-to-oranges comparison, but i
did a load test on my "UN-type" square head gasoline 4.0 cck (converted from sisson type choke to onan type choke), at NL ~65hz and 129vac (on my gens without volt regs i like to keep my volts a bit on the high side.) anyways at "FULL-OVERLOAD" of ~5,600W (actual measured, by v*a) YES you read that right, 5,600W!!! full-overload hz was ~59hz
the load consisted of 4, 1500w space heaters ( 2 "ceramic-type" and 2 nichrome wire coil-type, both fan-forced type)

windings are protected by a 2 pole 15a square-D QO type breaker, this gen has a 120v only or 120-240v selector switch installed on it. (if you want details on it, just ask me.)
if i perform my "load-test" :-) for very long (~10min?) the qo breaker WILL trip.

Leon, tomorrow i plan on taking a video just for you, of me abusing my 4.0cck with the 5,600w load from a cold start with a very short warm-up period of 30 seconds max, (shhhhh, just don't tell the onan protection services police )
Good idea for Leon to go to oriellys or somewhere and borrow the tools he needs I've done it before. They can probably trust him with the tools. We're all pulling for him to get that JB tuned up.
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  #68  
Old 08-08-2017, 11:24:50 AM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

The only reason I mentioned H8's is because that is what came with my JB. I Alsor found out that our local AutoZone store will loan me a compression tester for free. Not so on the timing light which I can buy from Wallmart for ~ $13. Have relatives visiting for the next couple of weeks so I will not be able to work on the JB until then. However, I am tempted to run that comp test since it is so easy to do. I got a feeling my JB timing is suspect, but that takes more doing cuz, I have to remove the front shroud and clean the timing marks. If I go that far, I intend to R&R the starter at the same time. I intend to take lots of pictures, too. Thanks for the encouragement, it really helps.
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  #69  
Old 08-08-2017, 03:52:27 PM
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Default Re: A JB Performance Question

Leon.
That hole on the timing assembly is to let oil in to lubricate the shaft for the points advance mechanism.
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  #70  
Old 08-20-2017, 05:19:12 PM
Leon N. Leon N. is offline
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Default Re: A JB Performance Question

It was a nice afternoon here today so I decided to run a dry compression test on my JB. To do this I purchased a new compression gage for just under $10. I could not find my old one I used back in 1970 when I refurbished my JB.

Well the results surprised me to say the least because I was expecting numbers like I recorded back in 1970 that is 90 & 88 PSI.

Well I measured 145 and 140 in the two cylinders. If this new gage is accurate and truth full, that explains why I can get rated output and then some on natural gas.

Can someone refresh my mind and tell me how from the factory build sheet, for example, one can tell if his JB is a Hi or lo comp design?

I always thought my JB was of the lo comp design. Were all those JB's with a comb carb were lo comp engines?

Next step when I get a chance is to check the "running" timing. That will take some doing because I have to make visible the flywheel timing marks.
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