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Fuel starvation problem?


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  #1  
Old 10-20-2014, 08:20:11 PM
JohnnyC JohnnyC is offline
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Default Fuel starvation problem?

I may have a fuel supply problem while running my 15.0JC 18R under load, but just wanted to run this by everyone.

Scenario #1) My set is running off of a small BBQ propane tank with a standard BBQ tank regulator fed directly to the carburetor. I regulate the flow by tweaking the tank valve until the motor runs smooth. I never tried to heavily load my JC but today I hooked up a high powered heat gun which drew 13 amps. The JC handled it with no problem. The Onan motor ran smooth as if nothing was hooked up drawing a load. I added an additional 10 amps (electric circular saw) and the JC bucked, the governor appeared to go to wide open throttle (or very near WOT) and the JC bogged down while running very rough and eventually stall. If I manually close the throttle plate so it is against the idle set screw, the motor will run smoother, but RPMs are well below 1800 RPMs and the governor arm is fighting me to open the throttle which I assume is normal. Is it possible the small BBQ regulator cannot supply enough propane to meet the demand? I varied the tank's valve from almost closed to wide open with no positive effect.

Scenario #2) I finally hooked up my OEM demand regulator and electric solenoid shutoff switch in line with the same BBQ tank and regulator as mentioned in scenario #1. When I try to start the JC, it will not start UNLESS the throttle plate is manually held completely closed (against the idle set screw). When the throttle plate is held in this position, the set will start easily, run smooth but RPMs will be below 1800 RPM which would be expected since I am holding the throttle plate against the idle set screw. At the same time the governor arm will be fighting me to open the throttle which is normal, but the set will quickly stall if I let the governor take over.

As an added test, I wanted to see how much propane flows through those little BBQ regulators and it appears not much as well as there is not a lot of pressure either. It seems like a soft breeze at best and my tank is full. There were no specs on the BBQ tank regulator.

Why does the OEM demand regulator in line with the BBQ tank regulator make matters worse?

So, does this sound like fuel starvation in both scenarios?

JohnnyC
New Jersey
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  #2  
Old 10-20-2014, 08:28:06 PM
MBB MBB is offline
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Default Re: Fuel starvation problem?

Did you play with the adjustment screw on the carb? It is probably set to rich. Thats why it will idle but not take more fuel. I guess it could be to lean also but wouldn't expect it to start then. Obviously you cant get it to run properly until you get the correct regulator.
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Old 10-20-2014, 08:39:51 PM
soundbos soundbos is offline
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Default Re: Fuel starvation problem?

Yes the small bbq rgulator drops the preasure to about 9-11 inch the demand reg wants tank preasure about 75 to 150 lbs
Most bbq regulators also have a small opening so a burst hose wont leak to much

Butch
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Old 10-20-2014, 08:51:02 PM
len k len k is offline
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Default Re: Fuel starvation problem?

Also can't run a JC long on a 20 # tank, ices up. Think a JC wants~ 280 k BTU/hr , 20# tank is only good for ~ 45 k BTU/hr, ~ steady state, ~ room temp.

I think demand reg usually wants a lot lower presure than 100psi , unless it has a primary regulator built in also. Propane tank pressure can be ~ 300 psi at ~ 125 deg F.
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Old 10-20-2014, 09:17:01 PM
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EricWood EricWood is offline
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Default Re: Fuel starvation problem?

Your demand regulator needs 11" Water Column, in sufficient volume. Your BBQ regulator is not going to give you that volume. Some folks have said they can run JB/JCs on a small bottle and BBQ regulator, I was never able to run mine very well on such a set up, and also had to "massage" the throttle as you stated, from idle, and slowly release it to rated speed.

You need to get a properly sized Primary Regulator, before you can fine tune the rest of the engine. Did you rebuid the KN regulator?-- I don't recall if you did, but it may need fine adjustment.

Need to find an appropriate regulator such this: http://www.smokstak.com/forum/attach...2&d=1304127897

Its a Fisher combination unit--small portion reduces tank pressure to 10 psi, large part reduces it to an adjustable (11"WC in this case) output.

Then, the power screw on the carburetor will need to be adjusted. Need to adjust it until engine will fire and come up to speed unaided. Then, apply full load (if possible) and fine tune as needed.
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Old 10-20-2014, 09:48:09 PM
Thaumaturge Thaumaturge is offline
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Default Re: Fuel starvation problem?

Could it perhaps be a problem from the excessive flow regulator now mandated for smaller LP tanks? I've tripped those on 5 gallon tanks just trying to run two burners on an LP stove. It's a ball valve with spring and magnet. Too much flow will cause ball to get near enough to magnet to stick. Spring won't push ball back till almost zero flow. To reset it I close tank valve with just one burner lit and wait for barely audible "tink" as the ball retracts before slowly opening the valve again. Will then run two burners again. PITA.
Doc
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Old 10-20-2014, 09:50:07 PM
JohnnyC JohnnyC is offline
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Default Re: Fuel starvation problem?

Thanks for all the quick and informative responses. I will that the carb was not adjusted by me and without doubt it may have been monkeyed with in the past. When me genset was in service, it was exclusively ran using natural gas. I am running propane for basic test purposes since I do not have natural gas in my garage and workshop. I have natural gas at the house which is about 100 feet away. I think I may need to roll my genset up to the house and plug into the natural gas line to really test it.

I want to comment on the following:
Quote:
Originally Posted by EricWood View Post
Your demand regulator needs 11" Water Column, in sufficient volume. Your BBQ regulator is not going to give you that volume. Some folks have said they can run JB/JCs on a small bottle and BBQ regulator, I was never able to run mine very well on such a set up, and also had to "massage" the throttle as you stated, from idle, and slowly release it to rated speed.

You need to get a properly sized Primary Regulator, before you can fine tune the rest of the engine. Did you rebuid the KN regulator?-- I don't recall if you did, but it may need fine adjustment.

Need to find an appropriate regulator such this: http://www.smokstak.com/forum/attach...2&d=1304127897

Its a Fisher combination unit--small portion reduces tank pressure to 10 psi, large part reduces it to an adjustable (11"WC in this case) output.

Then, the power screw on the carburetor will need to be adjusted. Need to adjust it until engine will fire and come up to speed unaided. Then, apply full load (if possible) and fine tune as needed.
What you said makes perfect sense. I did not rebuild the OEM demand regulator, just cleaned it up and ran a few tests on the bench. Your explanation answers why my genset behaves differently when running the OEM demand regulator in series with my bbq tank regulator than without the demand regulator. It also explains why my bbq tank seemed to only put out little flow and low pressure when I ran an open hose to the bbq tank regulator.

If everyone agrees it is a fuel supply problem I will either need to connect it to the house natural gas line (and I assume I can run the house line directly into the demand regulator) or get a huge propane tank and the correct primary regulator..... Right?

Thanks,
JohnnyC
New Jersey
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Old 10-20-2014, 09:59:28 PM
Ed Sparks Ed Sparks is offline
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Default Re: Fuel starvation problem?

correct. the grill regulator will not flow enough volume to let your JC run anything more than minimum fuel draw. The excess flow safety will trip as the genset calls for more fuel causing it to stall. It will also not run for very long as the surface area in the 20 lb tank can't vaporize fast enough to recover vapor consumed.

I have run my JB on a 40 lb tank with a proper primary/secondary regulator test set up feeding the supply to my fuel line. It doesn't have the excess flow safety.
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Old 10-20-2014, 11:22:02 PM
Doug Reed Doug Reed is offline
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Default Re: Fuel starvation problem?

Johnny, the only reason to even try using the BBQ tank on your 15JC is just to prove that it will start and idle. You can NOT get sufficient flow out of that tank to run the JC at full power, probably not even at half power. If you had an older tank without the new safety devices, then MAYBE it would work, but it isn't worth trying to use it for any adjustments, you'll just screw it up.

I don't remember what you said you had for a regulator on the BBQ tank. But keep in mind that the JC wants about 250K BTU per hour to run at full load, and at no load it is just a little below half that to keep running..... At least according to the Onan manuals.

The most common BBQ grill regulators I've found run about 60K BTU. If you look you can find a few at 120K to 140K BTU per hour. I found one that claimed 200K BTU. If the regulator you are using is less than 140K BTU per hour, you are lucky the JC even starts.

If you want to do any serious tests on your 15JC, you need to get serious about the regulators and the tank. Look at the T-015 manual and choose regulators that match the specs it recommends. You can get by with a 100# propane tank for short full-load runs in the summer if you have the right primary and secondary regulators. Don't expect that 100# tank to run the JC at full power below about 40 or 50 degrees F.

You want the primary regulator at the tank so it feeds propane at 15-25# pressure down the line to the generator. Check the T-015 manual to see if the shut-off solenoid goes before or after the secondary regulator. The secondary regulator drops the 25# pressure down to 11"WC which is what your demand regulator wants. You want the hose to the carb to be whatever the default pipe is on the generator, probably 3/4". All regulators should be spec'ed to flow at least 250K BTU per hour, or even a bit more. Or quite a bit more if you are feeding any other propane appliances from the same primary regulator.

I will admit that I have a 15JC generator that came with two 100# tanks to run the generator at a job site when electricity wasn't available. Probably the only reason it worked in the winter was because the tanks were located inside the trailer topper and picked up heat from the engine when running. Leave the doors closed and the tanks were in summer heat....
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Old 10-21-2014, 08:45:23 AM
JohnnyC JohnnyC is offline
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Default Re: Fuel starvation problem?

Thanks Doug... I have the proper demand regulator with the solenoid on my 15JC skid ready to be hooked up to a fuel supply system that can adequately feed it. Problem is that is 100 feet away and I would need to plumb a line from within the house to outside. Not a big deal, just requires time to do.. In the meantime I wanted to work out any bugs while the genset is in my garage and the only fuel supply is a bbq propane tank. I just wanted to confirm the results of running on the bbq tank was to be expected which it seems to be.

My next step after finishing up a few loose ends on my 15.0JC project is to move the genset to an area where I can plumb in a supply line adequately feed this little green monster.

Thanks,
JohnnyC
New Jersey
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