I have an Onan genset in our 94′ Winnebago Class A Vectra. I am unable to start it! It worked perfectly prior to my changing the rubber fuel line link, due to age cracking, between the metal vehicle line and the input side of the fuel pump. I have checked and rechecked all fuses, wiring, etc. I even tried blowing in the rubber input line! Putting fuel in a can and disconnecting the fuel line at the carburetor reveals no fuel intake by the pump. I tried filling the rubber line to the pump and from the carburetor to no avail. Is there some sort of airlock or priming method I need to do to reactivate the pump? I am stumped! Thank you. —Doug W.
Most of the Onan generators have a start/stop/prime switch such as this one.
Press the switch to the Stop/Prime position (down) and the light should blink and then stay on steady and the unit is primed. Also, check to see if there is a Winter/Summer lever. If so, this will adjust the mix ratio. Try this a few times and if it still doesn’t start try troubleshooting the following.
Generator won’t start, try these steps
With any combustible engine, we look for two things: spark and fuel. My first question is does the starter engage and the generator physically turn over trying to start? If the battery is low, it might not be turning fast enough to start so you might need to add a battery booster.
Let’s assume it is turning over. The next thing I would suggest is to remove the spark plug. Keep it connected to the spark plug wire, ground it to the case, then crank it over to verify there is a spark. If not, then it’s probably the coil. If there is a spark, we need to look at the fuel supply.
The first thing I would do is change the fuel filter at the generator as it could have gotten clogged or even collapsed. It’s frustrating when something works perfectly, as you indicated, and then doesn’t for what seems no apparent reason. I call these “gremlins,” as they appear out of nowhere and cause issues and sometimes disappear again!
It could be the fuel pump, which I believe is mechanical on your unit rather than electronic. See if you can disconnect the line after the pump and crank it over to see if you get fuel coming out. Make sure you have the hose in a container. If nothing comes out, it would seem to be the pump. If it does, then I would assume the carburetor is varnished and needs to be cleaned or rebuilt.
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.
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PS: Update…. it was a “gremlin” which crawled in thru the new fuel line and knocked out the fuel pump! (Well, nothing in the fuel line – just the gremlin which sometimes shows up from someplace unknown and inflicts it’s effects someplace else!) With the new fuel pump the engine starts two to three times faster than previous.
I’ve seen an engine that wouldn’t start, start suddenly when the air filter fell of accidentally. Make sure it isn’t the air filter.
As I mentioned, I disconnected the fuel line at the top of the output line to the filter and the input line, which is the one I replaced. Also, I didn’t mention the fuel pump is electric and there is also a fuel solenoid in the line – which has power to the terminals. The carb. is clean and the bowl is empty. I didn’t check a spark plug as I didn’t do anything electrical – just changed the aged input fuel line. The pump and solenoid are located at the back of the genset – meaning to change either – I will probably have to pull the genset out! I agree with Dave – it is one of those gremlin things! Thanks for the ideas!
Also, I do NOT have the newer version with reset switch system. It’s either on or off – and it turns over like normal – full speed – just no fuel flow.
When the fuel line was installed, did the poster check for a kink in the hose?
Yes Tom – The line is only about 14″ long and runs directly to the bottom of the electric fuel pump. It has power to the terminals by the way.
Not even a mention of LOW fuel in gas tank thats below the pick up for the Generator! Seems Dave misses the obvious reason for most items!
Was that last sentence really necessary ?
I agree with you. It seems there are so many experts out there that seem to know more. Many of Dave’s answers are met with people who seem to think they know more and need to be ugly about it. Don’t have anything nice or positive to say don’t say it.
Perhaps that comment wasn’t necessary, I do apologize for it. however I’m not the only one that has noticed discrepancies in Daves answers, just look back at some of the replies from his answers! I’m by no means an expert on much of anything, but I’m observant! We the readers count on Dave’s answers to be accurate & to the point!
Sorry if this offends anyone!
Dave: The fuel tank is full to the top. The genset is supposed to work down to about 1/4 tank.
My “nice” Onan has a non-rebuildable carb. Replacement is over $400.
I understand that you can buy on Amazon for around $100. I haven’t yet but it’s the first place I’d look
Needed an out of stock carb for snowblower dealer wanted $150 but not available Amazon had it for $40
Same here. Replaced it once. Next time I’ll just get a new NOT AN ONAN generator. I’ll figure out a way to put a quiet inverter generator in the hole that holds that big green boat anchor. Our 2300 watt Honda does everything that our 4000 watt Onan does, just better, quieter, and easier to maintain.
Coachman in one of their class A’s uses a NPS 5500 generator which has a Yamaha engine.