Onan in 2072 pop and surges (video inside)
 

Some of you may have read my thread "Would you buy a 2072 with an Onan." Well now that I got it home I've started to tinker with it. When you first start it it runs fine, though just now it took longer than I thought it would to start. Anyway, runs fine for about 5 minutes, maybe less then it starts to surge slightly and occasionally backfire. Here is a video. As you can tell the bang made me jump. Does this sound like a fuel problem? Carb issue?

Here are 2 videos I did real quick on my phone. Both videos are a minute long. Click for video.

In this video it's hard to tell, but at 40 seconds in and the camera shakes, the engine backfired.

http://i161.photobucket.com/albums/t...ps60538fa0.mp4

In this video you can hear the pop. It was popping worse before I tried to take video. You know how that goes, try to show someone and it doesn't do it.

http://i161.photobucket.com/albums/t...ps987a256b.mp4

The topic of the Onan has been discussed on here before I bought the tractor. The first 2072's came equipped with the Onan. The serial number has been verified.

My M20 did that on startup when I first bought it last year.

I think it was my carb because I was getting gas in the crankcase so I cleaned and rebuilt the carb and since then it hasn't happened.

I also noticed my high speed needle had a 'false bottom', meaning it got hard to turn and I think the PO had it set too rich, it had an extra turn or 2 in it before it actually bottomed.

Maybe valves also? others will chime in I'm sure.

Goodluck.

Sounds like a carb issue to me but I've never played with an Onan. Some Sea-Foam in the gas probably wouldn't hurt.

How it surges makes me think carb, but the backfire. I didn't know the carb could make it do that.

I think its running lean. Like one member said on the other thread check the intake manifold. I think its 3 pieces. Check where they come together with carb cleaner. You could tell by looking at the plug.

Look this thread over if you haven't already.

http://www.onlycubcadets.net/forum/s...ad.php?t=32090

I can't view the vids because Norton is telling me it is a "Malicious Web Site"...what's up with that?

Every Onan I own surges some. They are a pia to work on but when they run good there is nothing like them.

IIRC, you gotta pull the exhaust off to pull the intake off. Replace all gaskets and make sure the 2 piece intake manifold isn't sucking air, pull the carb and clean it.
Attachment 56270

It's almost cheaper to replace the carb with a new then buy a rebuild kit.:bash2:

If you need Onan parts, this is the place to go but I have not ordered from them yet. http://onanparts.com/

Some good info here if you have not already seen it. http://www.mytractorforum.com/showthread.php?t=91204

Good luck and let us know how it goes.:beerchug:

Well yes of coarse it can. Too rich can make it backfire.

Is that the B48G like the 982? I remember you guys saying the early 2072's had Onans but no parts book shows it. Probably because if you had problems they just suggested a re-power. I'm guessing it's the B48G.


Brent, I'd tune it up completely (plugs, wires, points/cond). Pull the carb, clean it, clean the fuel system throw a kit in the carb and pull the lifter covers and adjust the valves. Then see how it does.


FWIW, you know what else will make it backfire like that? ..........

Water in the fuel. :bigeyes:

Oh, and lean running engines don't backfire out the exhaust. They backfire through the intake. It's not running lean. Now, I'm not there, but it sure sounded like an exhaust backfire in the vid. :bigthink:

Cool. Lots of good info to get me started. Thank you.

Oh and make sure you don't have a rodent hotel in the tins.

This is always good advice! :ThumbsUp:

Although, that wouldn't make it backfire. Unless they chewed up the point wire. :bigthink:

You're point about the water made me realize it had been sitting for a while. I wasn't implying it would cause the problem, just making sure that it doesn't get run too hot from lack of cooling. :beerchug:

It is the B48G.

It has a brand new condenser in it, so I will get the plugs, wires, and points ordered.

It is definitely coming from the exhaust. Sounds like a gun. That's why the camera shook, scared the bajesus outa me! :Shocked:

He said it started about 3 months ago. Just randomly started doing it. He also said it has never sat outside. So I'm not sure about the water in the tank, but I'm going to check all possibilities. From the original paint I kind of believe it was always stored inside. Other than the decals, the paint on this thing is great. I think the decals pealed a little and someone just ripped them off.

I need to rewatch the video. My dsl at work was lagging.:BangPC:

I knew what you meant Travis. Sorry, didn't mean to imply what it appeared it did. :beerchug:

Just because it never sat out doesn't mean it can't get water in it. A trip home with a fuel tank in the back of a truck in the rain can get water in fuel. :bigeyes:

So can:
condensation
alcohol in fuel "absorbing" it
outdoor fuel tanks
I've seen gas stations get water in their main tanks (always fun when that happens in my area)

I was surprised in the video you can barely hear the backfire. In person it was....well....LOUD. The second video you can hear it better, but still doesn't do it justice.

http://www.weekendfreedommachines.co...35/265537.html

Info....

With it hunting like it is, it sounds lean to me. Does pulling the choke out slightly straighten it out? Also I've sprayed suspected areas in the past, little at a time to see if it smooths out or changes the way it is running. I can't remember for the life of me right now what I used to detect those leaks.

Why does everyone keep saying lean....... you don't get exhaust backfires on a lean running motor.

OK - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich - Lean - Rich - Lean – Rich

:beatdeadhorse:
exactly a backfire is caused by excessive fuel. Running lean is caused by lack of fuel... therefore no fuel no back fire....

Well I can't order parts from the onan site for a few more days. So until then, the tractor will wait.

What about doing a leak down test. Could unburned fuel be going in the exhaust causing it? Just throwing that out there. Onans are known for valve seat issues also.:Huh:

An exhaust backfire is basically unburned fuel. So, your right about that. A leak down test is not a bad idea. But I think it's a carb issue. Brent said the PO told him it started all at once, so unless a seat came out, I'm not sure it's just wear. Although, PO's do tend to exaggerate, and not always tell the whole truth. I don't think I'd go to the trouble of a leak down test until after going through the fuel system and doing a tune up. Just my :TwoCents:

Not a bad idea by any means Todd! :ThumbsUp:

I agree J, I was just throwing that out there. That's what I would also do first (clean the carb). IIRC the one I did I was able to reuse the carb gaskets.