One potential reason for the CO trigger is the exhaust is inside the weathershed. Every video I've seen regarding this unit says to shut off the gas completely prior to starting on propane. Many say that when it's cold out, it doesn't want to start on propane.

In my experience as a mechanic normally backfires are caused by exhaust leaks. Its really easy to check, allow the engine to cool down but really cool down. Using a shop vac, tape the vacuum hose to the exhaust muffler outlet so it doesn't leak than turn on the vacuum cleaner and you will be able to hear vacuum leaks. Do this with engine off and it's ok to hear your throttle plate have a whistle sound. This can also be done on automobiles for backfiring iss and O2 sensor code issues.

I read somewhere when using propane to open the tank valve slowly. Open too quickly, the regulator safety will restrict the gas flow.

Well brother you just showed us how to convert from gas to propane while this thing runs. I too have had issues with propane. At least we know now you proved you can swap to propane while it's running. Good to know and thank you. I just bought this and had the same issues with starting on propane. Serious backfires and RPM up and down until it quits on LP. Gas seems to work fine but this dual fuel system has issues at start up using propane. Hope it powers my hut. Guess I'll see here soon when I test this thing I just bought.

It may be from switching back and forth between fuels. If there is fuel in the carburetor when you switch to propane mode, I can see the engine vacuum sucking both fuels into the cylinder. Try shutting off the gasoline and run the generator until it stalls. Then try switching to propane. That’s my guess anyway.

I just bought the same generator and after 3 hours and a dead battery decided to communicate with the supplier. No result but after a deep dive into the web, someone stated that the spark plug that comes with the generator sucks. so it was recommended to use a new plug. i bought the E3.22 plug from Home Depot. Right away it started in both the propane and gas modes. Good luck

A weird thing about propane regulators. If there is no pressure on the line when it's turned on it will just trickle gas. Try turning on the tank and letting it sit for a minute or two so the trickle pressurizes the line. Once the line has pressure it will flow normaly. To see what I'm taking about try turning on your grill with the all the burners on you will notice you get almost no flame. Then turn off the burners wait a minute then try to light them again and they will function normally. I believe it's a safety thing incase the hose breaks. I believe you're not getting enough fuel flow so its misfiring then blowing in the muffler.

The CO2 sensor might be going off if there's a intake leak (carburetor to engine) the vacuum cleaner test will indicate that kind of leak. Gasoline engines are vacuum pumps so checking for vacuum leaks is always a good idea.

Tell us you didn't read the owner's manual without telling us you didn't read the owner's manual.

Had same issue....take out air filter and see if it runs ok. If it does...replace filter with new

When using propane, you need to shut off the fuel valve, if it’s open, it’s a possibility that you’re feeding your propane back through your gas tank

My somewhat educated guess (I have the same model) is a problem with the fuel selector switch. I have only run mine on propane since new, never had gas in it. Starts up and runs perfect every time. The only difference in my setup is using 40lb propane tanks with the regulator that came with the unit. @bentaylor2519 has a point about the length of your gas hose, it might not be allowing enough pressure to the generator. Any way, good luck getting it sorted out!

I am having the same problem with propane. A buddy of mine recommended removing the regulator from the propane tank entirely because he seems to think it has an internal regulator? I am hesitant to try that though.

Bought a Durostar, same as a Duromax, and will bypass the CO sensor before even starting it. Green and blue wire on my gen and another Duromax gen on utube. Also, open the LP tank valve very slowly as a fast surge of LP can trigger a safety ball inside the valve. And will replace spark plug with NGK.

don,t feel so bad. I bought a dual feed westinghouse 9500. Started every mont and no problems. Was gone and waited 3 months and gas just poured out carb and no start. Generator is only 5 montghs old and under 45 minutes run time. Spent $300 to overhaul carb and ran good. Then 6 weeks later same problem. Even had stabil in gas from the start. This Westinghouse is a piece of crap. Have a old generator with the same gas for 5 years and during Texas Febuary freeze started great. It will run of propane but during a hurricane I will need 250 gallon tank.

I have the same model. It ran good for a first 4 days, then the multimeter stopped working and then carbon monoxide detector light came on, machine got shut off and never be able to start back up. It’s sad to buy this generator as a back up in case of emergency, but unable to use it when you need it the most

Have you tried to warm it up in gas mode then switch to propane?

Turn off your gas value when using propane, and only on when using gas.

To fix the problem just wiggle the choke lever into the correct position, its located above the air filter,,,,,the choke lever seems to work differently for gas vs Propane.

Saw another duromax owner with same problem. He solved his by putting in a new Ngk plug. Seems strange, but certainly doesn’t take much money to try. Good luck.

Propane is good in warmer climates. The propane regulator will freeze up in winter with long use. Ask me how I know. If you’re running it on propane shut the propane tank valve off until the engine stops.

Did you switch to a NGK spark plug? The spark that comes with it is a POS.

Hey buddy I have the same one you got the best thing to do is if you're going to use propane turn the propane on turn the gas on start it with gas and then switch it to propane and then shut your gas off and you have to do that every time so try that that's the same as my generator I have

I have one that propane floods it because the propane keeps bleeding through carb even when not running and if valve in motor is open will cause backfire

if it doesn't start on propane you have to put a hotter spark plug call duromax they will give you the number. mine backfired and would not start changed the plus starts perfect. my muffler looks the same

Mine has the exact same dent in the muffler

I have the 13000EH and when starting on propane, i have to hold the choke half way open to start it every time

Need to test propane gas pressure at the unit..... That length rubber hose and regulator on tank doesn't look current...... Depends on the electrical load and engine RPM...... Lower gas pressure will cause backfire and shutdown.

Do not cover up the CO sensor vent. It can tell it is not getting air. Disconnect the sensor and put a jump wire on the Brown and Black wire to bypass the CO Sensor.

I don't know much about propane engines but you might try carb adjustment depending where you are these generators are set for lower elevations from the factory. Also the last gasoline engine I had do what that one is I had to do a valve job on it but before you rip the head off try adjusting them first. Either way contact dura max if you can to get the proper settings. If you don't mind let me know how you make out as I just bought one and I'm always willing to learn all I can even if mine never does this because like I said I don't know propane.

you should always turn off the fuel and let it run dry

I'm having a very similar issue. I started it up last year with no issue, now I can't get it to start. I think it's the fuel selector switch based on the things I'm seeing on the internet and here on youtube. Apparently, it's a known issue.

It is obvious you shouldn’t play with big equipment. Starting gen in cold weather, start on gasoline first for a little warmth in engine, turn off gasoline valve then it will start on propane, do not choke!

Did you replace the spark plug. These machines come with cheap Chinese plugs that don't work so well when they get hot.

Brand new out of the box, it fired right up on gas. a month later....Nothing on either fuel. After reading the comments here, I simply changed out the sp plug to a name brand and it fired up instantly. That stock plug is garbage.

Which NGK plug did you replace the Chinese plug with?

did you just switch from propane to gasoline while it was running?

I just bought the same item but as a 12,000. All the videos I have seen did convince me away from the large propane tank idea and switch over to gasoline. They are saying that its much more efficient with gas. Also, your gas line is a bit long, might be better if it was shorter, and maybe make sure your regulator is allowing the correct pressure to flow, but the videos and reviews I have seen when using gasoline seem to be positive experiences. Not sure about that noise and back firing. Might be a non related issue to the stalling with propane?

Years ago buy one in home depot is almost the same design...is lots and lots of problems whit the carburator.they all clogged and Need to buy new ones almost each 2 years..the only reazon I buy it was very very cheap price ...but they are not not not very reliable..is better that you buy another brand..

It’s the oil same thing got me back fired on me it need oil

I have the exact same problem, is there a solution?

You have to get the exhaust out away from that unit. You're going to destroy it. There is A reason why generators have to be run in a clear open Area if you can't do that pipe the exhaust up and away from the unit

Call the manufacturer. I agree with the other comments. Long propane line may not be helping you. The selector switch is critical to.

Northstar with Honda engine.

mine is doing the same thing.

DID YOU READ THE DIRECTIONS OR WATCH A KZfaq ( HOW TO ) VIDEO ? I'M SURE BY NOW YOU DID READ THE DIRECTIONS, OR SOMEONE SHOWED YOU ? DON'T TAKE MY WORD BUT,WHEN YOU RUN ON PRO. CHOCK OFF- GAS OFF- SWITCH TO PROPANE-ON

its your valves out of adjustment

wow, I’d contact duromax about it. Change the spark plug to genuine ngk or champion, the Chinese spark plugs they come fail right away or last a few hours.

I think it the user for sure,not the machine😐

And turn the gas off bro

Mine works flawlessly. Return it for another

You have three year warranty

Yep, the backfire is from feeding BOTH fuels at one time. You are lucky it didn't catch fire. Whichever fuel you are using, shut off the other source.