Help! Onan 4K generator refuses to start and stay on

[Kennyg]

Here I go again. Am at home now and I tried the generator again. It started, but only for about 15 seconds and then shut down. During this short time it ran rough and the exhaust blew constant blue smoke which I assume is excessive gas. As I stated before I did take the carb apart an soaked in cleaner and blwe air thru all the holes. So, where go I go from here?
Should I be replacing the carb or pull the carb entirely from generator and soak it in carb cleaner. Nothing seems to work.

[Kennyg]

Grit dog wrote:
What he said ^.
Gasoline or LP? Presume gasoline.
Does it start and run 15 sec repeatedly or was it one and done?

Blue smoke is oil.
Not necessarily an issue. Could be from sitting, could be burning a little oil but still ok.
A lot of people don’t even notice, but most engines, new or old, in my experience, will blow a little blue smoke on startup. Once in a while. Could be a chunk of carbon holding a valve slightly open, sticky ring that frees itself up or any other number of things.

If it does it every time cold and then clears up, likely worn top end valves etc. if it smokes after warmed up and constantly then likely rings.

Is the crankcase over full ( gas draining into case, stuck float on a gravity fed, primer stuck on and you didn’t notice etc)? If so it could be sucking in diluted oil. Could also make it not run right, maybe.
From there, could be carb plugged up
Need more history and symptoms.
Old gas, sat for a long time?
Original question is it repeatable runs and dies?
If no restart, does it fire on ether?
Is the fuel pump working consistently? Did you check it?

This is a replacement carb only two years old. The oil in crank was replaced at same time as carb. I over filled this jan. removed the excess and noted it was already dark brown. Replaced original sparkplug this january. When starting, it is repeatable start and stops. Pump does work. removed gas line and attempted start; gas flowed out of line when start button is engaged.

[ndrorder]

whemme wrote:

jyh818 wrote:
Are you below 1/4 tank of gas in your RV. I think it prevents you from using the generator if your RV fuel tank is below 1/4 tank.

If that was true the generator would not even start and run for 15 seconds. Problem sounds to me that you may have a defective Onan fuel pump.

Not exactly. There is about 15 seconds of runtime worth of fuel in the carb bowl when it is full. Without 1/4 tank or more or with a failed fuel pump, then the bowl wouldn't be replenished.

[jdc1]

You can replace that Onan pump with a low psi off the shelf pump (under $30).

But, my money is on the float level.

[whemme]

jyh818 wrote:
Are you below 1/4 tank of gas in your RV. I think it prevents you from using the generator if your RV fuel tank is below 1/4 tank.

If that was true the generator would not even start and run for 15 seconds. Problem sounds to me that you may have a defective Onan fuel pump.

[jyh818]

Are you below 1/4 tank of gas in your RV. I think it prevents you from using the generator if your RV fuel tank is below 1/4 tank.

[bobndot]

If u are talking about a 2007 model Onan, it could be a lot of things at that age As said check oil level first. If you are in the habit of using the genny while off level that could possibly be an oil related internal problem over time. When was it last serviced by someone that knows the Onan ?

[fourthclassC]

While that 15 seconds run time seems short for this issue, all my Onan 4k watt gens. Required new fuel pumps. The known issue shows up as the engine runs for a while then quits. Just FYI. But that 15 secs. may be related to some other issue like you said on related to the carb. Depending on the year, the choke linkage has also caused me problems in the past.

[Grit_dog]

What he said ^.
Gasoline or LP? Presume gasoline.
Does it start and run 15 sec repeatedly or was it one and done?

Blue smoke is oil.
Not necessarily an issue. Could be from sitting, could be burning a little oil but still ok.
A lot of people don’t even notice, but most engines, new or old, in my experience, will blow a little blue smoke on startup. Once in a while. Could be a chunk of carbon holding a valve slightly open, sticky ring that frees itself up or any other number of things.

If it does it every time cold and then clears up, likely worn top end valves etc. if it smokes after warmed up and constantly then likely rings.

Is the crankcase over full ( gas draining into case, stuck float on a gravity fed, primer stuck on and you didn’t notice etc)? If so it could be sucking in diluted oil. Could also make it not run right, maybe.
From there, could be carb plugged up
Need more history and symptoms.
Old gas, sat for a long time?
Original question is it repeatable runs and dies?
If no restart, does it fire on ether?
Is the fuel pump working consistently? Did you check it?

[enblethen]

Blue smoke is not normally gas but oil.
Check your oil level, It may have too much
When was last time genset was run? Could be sticky valve.
When was oil changed last time?

[pianotuna]

next time you get it fixed use only premium fuel and treat it with seafoam.

It would not hurt to try some seafoam right now.