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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14908
Experience:  Certified on Onan and Generac generators
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I have an Onan Marquis Gold 5500 that won't start... I

Customer Question

I have an Onan Marquis Gold 5500 that won't start... I started it up a few days ago and it ran for 20 minutes and shut off... then I started it again and it ran for a few hours perfectly. The next morning I couldn't get it started again, and was about to give up when it started working. Ran perfectly for about 4 hours, and I shut it off. And I haven't been able to get it started again, since.
JA: Do you have fuel in the tank? If so, is the shut-off valve open and the fuel clean?
Customer: Tank is full of brand new fuel. I don't see a shut off valve; but I haven't changed anything since when it ran for hours; so I assume it's open.
JA: Do you plan on doing the work yourself?
Customer: I believe that I can
JA: Anything else we should know to help you best?
Customer: It's giving me error code 36. I tested the fuel pump, and it seems to be working properly. I do have a new fuel pump and a new fuel filter, just in case. I just discovered that the oil seems to have a bit of a gas smell to it. So I'm thinking the carburetor needs to be cleaned and the oil and oil filter changed -- but I want to make sure I don't do that, and then just immediately have it flood again if a spark plug also needs to be replaced... or if there's something else I haven't thought of. The carburetor was replaced a little over a year ago -- and I have been running it under load every 4-8 weeks for at least 2 hours... so I'm not sure how it would be the carburetor again, already.
Submitted: 3 months ago.
Category: Small Engine
Expert:  Hank F. replied 3 months ago.

Hello, my name is ***** ***** I am going to assist you with this.

Gas in the crankcase is a sign that gas is flowing through the carburetor, and seeping down through the cylinders.

This is caused by a bad carburetor, usually a stuck or damaged float needle.

This carb is a CARB-compliant unit, and is not supposed to be opened up at all. There are no parts available for it.

A bad carb is just supposed to be replaced.

Yes, you will need to change the oil and oil filter.

Check the spark plugs. Normally, this alone would not be cause to need to replace the plugs, but only a visual check can determine if the plugs need to be cleaned or replaced.

Customer: replied 3 months ago.
Hey Hank -- thanks for the quick reply. I do know this unit isn't supposed to be opened at all; but I was basing the possibility off of one of your posts to the exact same issue that someone else posted in 2011, here ( where you recommended that it may work.Also, I was basing it on the fact that the unit was replaced with a brand new carb right around December of 2015, and I have been running it usually every 3-4 weeks for a couple of hours with both air conditioners on for about 2 hours, and I think I let it go 8 weeks once because it was in the shop for some repairs and I couldn't access it while it was there.Could it be that bad already with having kept that close of an eye on it and running it regularly??And would you suggest even bothering trying to clean it or should I just replace?
Expert:  Hank F. replied 3 months ago.

Trying to clean it or not is entirely your call.

I do not even try in the shop, as the failure rate is over 50%. By the time I figure labor, it is just more cost effective to the customer if I just replace it.

Another reason I don't recommend trying to clean is that you can not get any parts for it at all. The bowl gaskets dry up and shrink pretty quickly, and you can't get one. Also, the needle on these things is extremely fragile. As often as not, you will break the needle trying to get the altitude adjust knob off.

Customer: replied 3 months ago.
Good to know -- and this is normal for it to have already failed after being so new, and me having run it regularly under a full load? It just seems insane that it would already be bad with me having been running it regularly, and it being so new. I mean -- I'm sure this is the problem... but... in the future, how can I make sure I'm not replacing the carb every year? Everything I can find online says to run it for 15-20 minutes once a month, and I was running it for a couple hours every 4 weeks with the exception of the one maybe up to 8 week stretch where I couldn't run it while it was in the shop.
Expert:  Hank F. replied 3 months ago.

No, it's definitely not normal. But it does happen.

I have had a couple of carbs be bad right out of the box, straight from the factory.

Today's gas formulation starts to go bad in as little as 30 days.

The best thing you can do is to run it a bit more often, and to make sure you always have fresh gas available.