twodownzero
NM
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Joined: 06/07/2014
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MEXICOWANDERER wrote:It points to a fuel starvation issue. Classic symptoms.
It's classic for a lean condition, generally caused by fuel starvation, but he could be sucking air around the throttle somehow as well. All air must pass through the carburetor or the fuel mixture will be wrong.
Verify proper compression, if ignition timing is adjustable check that, and if that is good, go back to focusing on fuel system issues or vacuum leaks.
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Chum lee
Albuquerque, NM
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lakecityemt wrote:Chum lee wrote:"I assume from the backfiring?"
I can't see it or hear it run online. That said:
Backfiring implies that unburned mixture IN THE INTAKE tract is being ignited and burned. (not the exhaust) Can you confirm that? Backfiring is a classic condition of a lean mixture which would point to a vacuum leak somewhere in the intake. Are all the breather hoses connected properly? Is the (new) carburetor properly seated on the manifold with all the gaskets? When hot, a lean mixture can lead to pre-ignition/detonation which may sound like a backfire.
What happens if you manually force the choke on with the engine warmed up, loaded, and backfiring? (richen the mixture) Any improvement?
Do you have a compression tester? If so, does the engine meet the compression specs?
Chum lee
Chum you might be a bit over my head, LOL... I will ask him to try and manually adjust the choke when its backfiring. No compression tester.
OK let's try something simple. Your carburetor should have an altitude compensating adjustment screw. It has some control of your fuel mixture adjustment which should be set for your current altitude. It that set correctly? Having it set too high for your current altitude can create the symptoms you have. For example: If you are currently at 1500 feet altitude, adjust (turn) the screw so that the pointer is between 1,000 and 2,000 feet. Look at the screw adjustment on the carburetor, it will be obvious.
Chum lee
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Chris Bryant
Arden, North Carolina
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Joined: 03/26/2003
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If it started suddenly, I would bet on a broken valve component- spring or rocker arm.
-- Chris Bryant
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Chum lee
Albuquerque, NM
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Chris Bryant wrote:If it started suddenly, I would bet on a broken valve component- spring or rocker arm.
Yes, I've seen that (and/or a tight valve clearance) on 5.5, but IMO, it would happen all the time, even when cold. How does that explain this: "It began backfiring and then dying when a load was placed on it. . . . . . until it dies then gives an overheated exhaust code."
I'm assuming that later after cooling off, it runs (semi) normally when warming up and NOT under load. A compression check and a look at the valve train/clearance is in order. Interesting issue. This is a NEW generator!
Chum lee
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185EZ
Infinity and Beyond
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Joined: 09/28/2018
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lakecityemt wrote:For the past year I have been searching for answers and replacing parts with no improvement.
What year is this toyhauler?
Did it run right the previous year?
Have you checked that it has proper gas flow from the tank?
Have you tried loosening gas cap while running?
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lakecityemt
Alaska, United States
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Joined: 08/15/2019
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Chum lee wrote:lakecityemt wrote:Chum lee wrote:"I assume from the backfiring?"
I can't see it or hear it run online. That said:
Backfiring implies that unburned mixture IN THE INTAKE tract is being ignited and burned. (not the exhaust) Can you confirm that? Backfiring is a classic condition of a lean mixture which would point to a vacuum leak somewhere in the intake. Are all the breather hoses connected properly? Is the (new) carburetor properly seated on the manifold with all the gaskets? When hot, a lean mixture can lead to pre-ignition/detonation which may sound like a backfire.
What happens if you manually force the choke on with the engine warmed up, loaded, and backfiring? (richen the mixture) Any improvement?
Do you have a compression tester? If so, does the engine meet the compression specs?
Chum lee
Chum you might be a bit over my head, LOL... I will ask him to try and manually adjust the choke when its backfiring. No compression tester.
OK let's try something simple. Your carburetor should have an altitude compensating adjustment screw. It has some control of your fuel mixture adjustment which should be set for your current altitude. It that set correctly? Having it set too high for your current altitude can create the symptoms you have. For example: If you are currently at 1500 feet altitude, adjust (turn) the screw so that the pointer is between 1,000 and 2,000 feet. Look at the screw adjustment on the carburetor, it will be obvious.
Chum lee
Hey Chum,
The altitude adjustment is correct.
We removed the plug and now it runs properly under a load!!
Now what? LOL Can I leave it out? Probably not if its a spark arrestor
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lakecityemt
Alaska, United States
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Joined: 08/15/2019
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185EZ wrote:lakecityemt wrote:For the past year I have been searching for answers and replacing parts with no improvement.
What year is this toyhauler?
Did it run right the previous year?
Have you checked that it has proper gas flow from the tank?
Have you tried loosening gas cap while running?
2013
Been trying to fix since it acted up 3 years ago... Dad visits once a year and tries to fix it while here...
New fuel pump and we are not running from the tank, directly from a fresh gas can below the generator.
Spark arrester removed and now it runs under a load.
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185EZ
Infinity and Beyond
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Yay!
Also, electric fuel pumps aren't good for drawing or sucking fuel.
Having the tank below the pump isn't good
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lakecityemt
Alaska, United States
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Great thought, but instead of it pulling 35 feet from the tank its now pulling it less than 2 feet. Problem also happened with fresh gas from the tank.
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time2roll
Southern California
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Joined: 03/21/2005
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lakecityemt wrote:Good Morning.. Im hoping to find the Onan guru's that are here... For the past year I have been searching for answers and replacing parts with no improvement.
I have an Onan 5500 with less than 100 hours in my toyhauler. It began backfiring and then dying when a load was placed on it. I have so far replaced the carb, fuel pump and filter, fresh gas directly from beneath the gen. Once it starts backfiring, if the load is stopped, it continues to "put put backfire" until it dies then gives an overheated exhaust code (I assume from the backfiring?). Plugs were replaced, now currently testing to see if there is spark to both plugs. Please someone help me solve this issue!!! I'm in BFE Alaska in a perm set up, there's no ONAN tech here so I'm on my own... Thanks for ideas and suggestions!! Backfire through the exhaust is often too rich. Backfire through the carb is too lean.
If no ONAN service I would look for a lawn mower or small engine repair shop.
I would be tempted to remove the carb and apply fuel pressure and see if it leaks. Rich will tend to foul the plugs black and lean will have them normal to extra white.
If an ONAN tech sees your message they will want the exact model number and serial number to avoid playing 20 questions.
2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675w Solar pictures back up
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