Onan Troubles--It lives!

inspectorwoody · July 10, 2011, 09:23:06 PM

The ol' Onan on the LT30 has me nervous. :D

New fuel tank, lines, primer bulb, fuel filter. Oil filter, oil, air and pre-filter changed.

Replaced one spark plug...I left the other one at home on my desk. :

So we used a 12 volt plug cleaner on the other one. Cleaned up nice. Gapped them both to the specs.

First time....Choked, squeezed primer bulb until stiff and it took right off. Ran nice other than a spit/sputter type of thing. Nothing seemed odd.

Second time....Forgot to choke. Squeezed primer bulb. No start. I had it flooded big time. >:(

Sat from November when I got it until a few weeks ago when I started if for the first time. I'd say 2-3 weeks between the first time and this time.

Ended up pulling both plugs. New plug was nice and clean, just wet. Old plug was black with carbon and didn't seem wet at all.

Turned it over and gas shot out of the cylinder closest to the mast rails like a geyser.

Nothing out of the other cylinder.

Replaced plugs and got it running.

Things seemed fine until I started to operate the hydraulics.

I ran the clamp all the way in and had it almost back to where it would engage the Y activator and BOOM.

Big back fire.

Same thing happened when I tried operating the turner. Would get to a certain point and BOOM.

It did sit out side for quite some time before I got it but the guy had it running while I was there. I don't believe he had it covered.

Compression check is next.

What should the numbers be?

Carb kit wouldn't hurt it I'm sure.

I won't be getting back at for a few days so I'm hoping to compile some thoughts and suggestions and go from there.

Thanks.

Magicman · July 10, 2011, 10:01:01 PM

Check your oil level. Chances are that your carburetor float stuck and the needle didn't seal in the seat. That will allow the fuel to flow through an open valve and fill the cylinder. It usually then bleeds past the rings and overfills the crankcase.

The filled cylinder will usually just lock the engine up on the compression stroke. Yes, sometimes the engine will backfire and create a huge cloud of smoke. You might also experience a wet and dripping exhaust.

Jeff · July 10, 2011, 10:16:35 PM

What magicman said. Had the same problems, took off the top of the carb and cleaned it out and that solved them. I have to clean the carb a couple times a year.

https://forestryforum.com/board/index.php/topic,12878.msg179819.html#msg179819

MartyParsons · July 10, 2011, 10:27:29 PM

Hello,
If it related to the hydraulics, then check the ground under the battery box. If the lower rail is rusty being outside you may not be getting a good ground and it may make the ignition do wierd things. If you think it is a fuel related issue then as stated above clean the carb.
Marty

Don_Papenburg · July 10, 2011, 10:30:36 PM

When you get to 1000 hrs. consider a rebuild , consisting of new rods ,pistons rings and bearings. The crank should be good at a thousand hrs. The rebuild at that time will save a lot of expense later on as parts wear . I never had any of the trou bles you guys had with the carb . But mine was on a 420 deere . The electric clutch would kill the motor as it got older .

inspectorwoody · July 11, 2011, 08:01:19 PM

MagicMan touched on something I should have mentioned....

When I was priming the bulb, it sounded like gas was spilling. It must have been pushing it all in to the cylinder it blew out of when I pulled the plugs. It blew it out the muffler too.

So at idle it was fine, but when the motor is loaded by the hydraulics, than it would cause more fuel to dump which would result in the back fire. ???

Jeff-- Thanks for the link. I ran across it in a search but didn't read too much but I will now. ;)

With everything thing that happened at once, I didn't know what it could be. Was trying to search for a combination of things.

Marty -- I think it is a fuel problem but I know the contact strip, lower rail etc. need some TLC so I'll keep that in mind as I chase this issue.

Does anyone have compression numbers right off hand? I'd like to check while I'm messing with it. More for a sense of relief hopefully. :D

Seems like a black or sooted plug could mean a lot of things.

Given the information I provided, what would you guys think the culprit would be?

Thanks again.

I should have an update towards the end of the week. Bad part about not being able to keep it home. :

inspectorwoody · July 11, 2011, 09:02:45 PM

I was able to find and download a service manual so I got the compression numbers.

If anyone else is wondering, it says 75-115.

Magicman · July 11, 2011, 11:07:11 PM

You should not be able to pressure fuel past the needle/seat and into the cylinders.

Jeff · July 12, 2011, 08:24:41 AM

Once again like Magicman said, and another thread for you from my past onan troubles.

https://forestryforum.com/board/index.php/topic,13941.0.html

Needle and seat sticking putting gas in the crank case.

inspectorwoody · July 12, 2011, 05:18:48 PM

Both those threads hit the nail on the head. 8)

Thanks Jeff

I'll have to drag the lap top along so I can read while doing it. :D

Thanks again everyone. ;)

Jeff · July 12, 2011, 05:21:13 PM

Another thing that I always do now is run the engine out of gas and disconnect the fuel supply. when the needle and seat were sticking, even when the engine was not running, it would fill the crank with gas if the gas line was connected and the vent shut. Pressure would build in the tank if the sun got on it and push gas through the carb.

Hilltop366 · July 12, 2011, 08:56:13 PM

I put a in line shut off on my B & S because of an occasionally sticking float. Just got to remember to use it.

inspectorwoody · July 16, 2011, 05:59:12 PM

Opened up the carb and was surprised to see there wasn't that much junk in there.

Gave it a good bath in some carb clean and air.

All ports etc. seem to be open and clear.

Made a crude looking gravity fed deal that I hooked up to the carb while it was apart.

Let gas run and begin to fill, when I pushed down on the needle, it stopped the flow of fuel. The needle and float seemed ok right from the start.

An oil change etc. and I'll try it again.

I hope this fixes the problem. :-\

inspectorwoody · July 16, 2011, 10:14:53 PM

After my last post, I went out and ran some more tests.

A bit cooler out so I could stand to be in the shed. :D

I'm going to explain the way I see the results and SOMEONE please correct me if I'm wrong.

I let the gas run free this time with out messing with anything to see how it reacted. These first two photos were the outcome the first few times.

My thoughts....This is where the problem is. The gas is allowed to fill up so far that it overflows over the sides etc. If the carb was together, it would dump down in the cylinder.

The next two photos are the outcome after a few more runs.

This is how it should be IMO. Gas came in, filled up a little and quit.

If I'm wrong, please correct me. ;)

Hilltop366 · July 17, 2011, 03:58:45 PM

If I understand you correct it sounds right.

What did you do to make the difference?

Jeff · July 17, 2011, 05:27:25 PM

Without the top on the carb, the float assembly may pull up farther at its pivot then it would if it were together, not closing the needle and seat allowing gas to continue to flow.

inspectorwoody · July 17, 2011, 08:08:45 PM

I didn't do anything different.

I made sure there was plenty of gas feeding the carb so there wouldn't be a supply issue question.

I'm going to do it a few more times to see if I can pick up on anything.

Here is a video. The photos I've already posted. Video work isn't very good as I was trying to keep the hose kinked unitl I had the camera ready etc.

"http://www.youtube.com/v/6dF7HUArePE?version=3

bandmiller2 · July 18, 2011, 07:12:25 AM

Woody,your float level is too high,as Jeff said you really need the top on the carb.Are the two floats gas logged or has fuel leaked inside them??Is the seat under the needle sometimes their removable and missing .Set the float level lower as per the book usally done by bending the float arms.Small engines I always have a good shutoff and run dry,if you can put a drain cock in the bottom of the carb fuel bowl for complete drain. Frank C.

Hilltop366 · July 18, 2011, 10:22:24 AM

I am not too familiar with this kind of carbs,
but I can't see what the difference would be if the top was on. From what I can tell the needle & seat is on the opposite side of the pivot point from the float so unless the top holds something in place that would make the float or needle move out of position and jam, it should work properly with out the top in place.

Going by the video it looks like one time the needle did not close properly and caused the carb to over fill, causing the "high float look" from the spring on top of the needle being pushed down or the float arms flexing, in the last try on video the needle closed and the float level looks normal. If this interpretation is correct my thinking would be that the needle/seat would be at fault by not always seating properly. Look for worn needle, needle rubber tip bad if equipped, something stopping the needle from moving freely, float leaver or pivot pin binding.

If I am way off base then please refer to the first line of this post. ;)

Jim_Rogers · July 18, 2011, 01:28:56 PM

I'm sure you've already check, and my story maybe way off, but I did have a similar problem once.

I called the service company near me and they sent over a tech/mechanic because I told them I had a "carburetor" problem.
So this guy showed up, took the top off my carburetor because I told him that was the problem and it wasn't running right. He cleaned it all out and we did just about everything he could think of to make it run right and it wouldn't. Over and over we tried. And it still wouldn't run right.

Finally he pulled a spark plug wire off the coil and the end was all corroded and green. It wasn't the carburetor at all, it was the coil. I replaced the coil and wires and then it ran fine.

Another old trick an old time mechanic showed me when my backhoe (580 Case, with 159G gas engine) wasn't running right, and we thought it had sucked some junk into the updraft carburetor was to just put your hand over the mouth of the carburetor while it was running poorly. This "starved" the carburetor of air and created a great suction on your hand. This suction sucked the junk in the carburetor into the engine, and cleared itself out. I have used this trick several times when I have accidently let the backhoe gas tank run dry.
Now, I don't let it run dry as a landscaper who was in here once told me not to do that as it can suck junk from the bottom of your tank into your carburetor.

Years ago, my chainsaw repair man would look at the jet needle valves in my chain saw carburetor with a magnifying glass and when he saw pit marks on the tip he'd change out the needle valves. It maybe something that you may have to do to get yours running right.

The tech/mechanic who did my almost complete carburetor rebuild told me to only run mid grade gas in my Onan engine. Because of the carbon build up with lower grade gas. I did for a long time, but now just run regular, due to the price.

They also sell a carbon build-up cleaner you can spray into the air intake of a running engine to clean it out.

Good luck with your repairs.

Jim Rogers

Jeff · July 18, 2011, 04:32:47 PM

Quote from: Hilltop366 on July 18, 2011, 10:22:24 AM
I am not too familiar with this kind of carbs,
but I can't see what the difference would be if the top was on. From what I can tell the needle & seat is on the opposite side of the pivot point from the float so unless the top holds something in place that would make the float or needle move out of position and jam, it should work properly with out the top in place.

Its not. The needle and seat is directly under the pivot. The top of the carb holds that part of the float assembly down. Without it, the needle could easily not seat.

inspectorwoody · July 18, 2011, 05:30:10 PM

I picked up the gravity feed deal while doing a search. Here is what was posted.

QuoteWith the bowl still off reinstall the needle and the float. If you can rig a gravity fed tank to this you will get raw gas quickly dribbling out of the open carb, now raise the float, it should stop 100% immediately. If it conitnues to dribble even a little I'd replace both needle and seat.

The above being the reason why I left the top off. The fuel would stop when I pressed down on the needle/seat/float arm.

With that I thought it was good to go but I wanted to see what it would do with out doing that.

Floats are empty, no holes or full of anything. All parts are there. I have not pulled the seat out to inspect that. Other parts look to be in good shape.

I'll keep that spray in mind. I think I'll have to pick some up. I'll also inspect the plug wires. There was mention of some electrical issues I'll need to check into.

I think I'll run a few more tests like it is. Than I'll put the carb back together and use the gravity feed to see what happens. I'm thinking I'll be able to tell if the float/needle/seat don't work.

Keep the ideas coming.

I appreciate the help.

Hilltop366 · July 18, 2011, 06:32:52 PM

Quote from: Jeff on July 18, 2011, 04:32:47 PM
Quote from: Hilltop366 on July 18, 2011, 10:22:24 AM
I am not too familiar with this kind of carbs,
but I can't see what the difference would be if the top was on. From what I can tell the needle & seat is on the opposite side of the pivot point from the float so unless the top holds something in place that would make the float or needle move out of position and jam, it should work properly with out the top in place.

Its not. The needle and seat is directly under the pivot. The top of the carb holds that part of the float assembly down. Without it, the needle could easily not seat.

OK I think i get it !

So the top of the carb holds down the loop wire that is the float pivot ? If so then you may be able to hold the loop in the correct position to test, or it may be better to put it together and test.

I still stand by the last statement about the first line in my previous post.

inspectorwoody · July 18, 2011, 09:33:46 PM

Put the carb back together and ran the same test.

No fuel coming out of any where....

When I unhooked the line, fuel came out of where it goes in and than out of the two little holes along the rim of the carb.

Tried looking in some instructions I have to see what those were called but couldn't find it so I apologize for my lack of knowing. :-\

Hopefully the results of that test mean well.

inspectorwoody · March 18, 2012, 12:59:01 AM

This update is long over due and I apologize for that.

I got the carb put back on and the engine started and ran. Still did the popping,cackling etc.

Thought maybe since the motor had sat for long, it just needed to be ran and may be full of carbon or a valve adjustment.

I finished working on things during the summer and into fall before putting it away last fall as I don't have a heated building to work in.

Dug it out a few weeks ago and took it to another forum member to have them finish things up and go through it to make sure everything was good to go.

It was determined that the engine wasn't coming up to full power etc. and not to run it much until the reason was found.

Today I did a compression test and had 110lbs in one cylinder and zero in the other.

My heart sank.

So off came the head and this is what I found:

I was told this is caused by a leaking valve and once I replace the parts and adjust the valves, I shouldn't have any problems and I hope that the guy is right. :D

So now I'm parts shopping. Got a lead on some but need to make sure I have the right spec letter of my engine.

The mill is already to go to work but the engine needs some TLC so hopefully sooner than later, the ol' neglected LT30 that I rescued will be sawing some lumber.