Onan Generator Issues

[imported_scott_m]

Not sure if this is the right forum. I spend a lot of time over in the Mercury section. Anyway, I've got a 1988 vintage gas powered Onan 6.5KW generator. This gen is fresh water cooled. The unit has pretty much been rock solid reliable over the past 7-8 years I've owned it. It's always used a good bit of oil (leaks and burns some), but my understanding is this is pretty normal. This unit also does not have an oil filter, so it basically changes it's own oil every 50 hours or so. Other than occasional oil changes and a new set of plugs (yikes) two year back, it has been great. Recently, the generator has started backfiring under load. At first it seemed like it would only pop and then stumble a little bit as the load was coming on line (for example when the AC compressor would start up), but this past weekend it was just popping and stumbling all over the place....it never does die, but it just sounds terrible. I'm pretty sharp mechanically, but don't know much about these generators. I'm thinking maybe a carb rebuild?<br /><br />Sorry for the long post and if this is in the wrong place, please feel free to move it. Thanks in advance!

 

[ALAG3]

Re: Onan Generator Issues

Can't specifically help, but below I have posted two sites that have been great in helping me with my Onan in my motorhome...<br /><br /> http://www.funroads.com/onanstore/osHome.jhtml <br /><br /> http://www.rv-coach.com/index.html

 

[Reel Poor]

Re: Onan Generator Issues

If it has points and condensor........they are probably fried after 7/8 years.

 

[imported_scott_m]

Re: Onan Generator Issues

I don't think it has points and condensor...seems like I remember it being more like an outboard - stator and trigger kind of thing and of course I do not have the manuals here they are on the boat. Thanks for the links.<br /><br />Other ideas?

 

[pine island fred]

Re: Onan Generator Issues

Could the fuel be old? fred

 

[imported_scott_m]

Re: Onan Generator Issues

The fuel is a little old, however was treated with SeaFoam when the tank was filled a couple of months ago. I think the gen does pull off of my port tank - I think thru a water sep, so I need to change that, just have not been there early enough in the day to work on it in this heat.

 

[imported_scott_m]

Re: Onan Generator Issues

Bump

 

[DJ]

Re: Onan Generator Issues

"Backfiring/Pop" means lean condition.<br /><br />Genset carbs take a brutal punshment from the vibration.<br /><br />It's time for a carb. "freshening".

 

[imported_scott_m]

Re: Onan Generator Issues

I guess I'd describe it as a pop, then a stumble in RPM's. Almost always it will recover and come back up to normal RPM /120 volts. I'm 'leaning' towards the carb as well, however it is my understanding that setting these things up is a pain as far as dialing in the hertz.

 

[Reel Poor]

Re: Onan Generator Issues

Be sure to note exactly which holes the throttle control springs are hooked in. When I did my carb I thought I could remember where they went. Had to order some gaskets and they took about a week to get. Maaaannn......those springs and a short memory drove me crazy. <br /><br />Other than that...A piece of cake.

 

[imported_scott_m]

Re: Onan Generator Issues

Thanks for the advice Reel Poor.

 

[jlinder]

Re: Onan Generator Issues

I had a lot of experience with the ONAN 5KW generator of that vintage. One of the problems we had was that if you run it very lightly loaded it will carbon up and give the same symptoms you are talking about.<br /><br />Our "cure" was to run the generator and load it up to (or near to) rated capacity for about 20-30 minutes. We plugged in lights and heaters to do this.<br /><br />It made a world of difference.<br /><br />Oh, and the advice about replacing points, rotor, etc. is right on.

 

[jlinder]

Re: Onan Generator Issues

Reel Poor,<br /><br />I have found that a digital camera is a great tool. Take a picture of everything as you go. Then when re-assembling have printouts of the pictures with you.

 

[Reel Poor]

Re: Onan Generator Issues

Thanks for the advice Jack. You know how the sinerio works out. Its only two springs.

 

[jlinder]

Re: Onan Generator Issues

And you have to be careful how you set up the generator. You will find the voltage varies a lot from fully loaded to lightly loaded.<br /><br />We used to set them to be high unloaded, but not so high that it damages equipment. Around 125 volts. Then take a look at how the voltage drops when you turn on all your equipment.<br /><br />The problem is that you don't want it so high it damages your stuff, but not so low that the air conditioner is struggling to run with voltage is too low.

 

[BillP]

Re: Onan Generator Issues

I've had way more backfires from electrical problems than fuel related. Does it have points or not? If so, try a new condensor and check points before doing anything else. If that doesn't do it check the coil...use a spark checker to see how far it sparks.