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Discussion Starter · #1 ·
Hi guys, new to forum, I own a 1978 446 Case with the 16 horse Onan engine.
I love this tractor, I use it to cut and pull my trailmower side by side to cut 7.5 acres of grass. Works fine.
I'm having issues now with the motor running smooth.
I went out today and adjusted valves to onan specs, reset points to spec. I did notice the breather reed was missing the spring and washer that hold it down, and I replaced that. After reassembling everything and adjusting carburetor to start up specs, the motor fired right up, and within a minute was running rough still.

I tested compression, it's at 90 PSI on each side, I guess thats right between the 75 or 115 psi margin, so I figure that must be good enough to run smooth.
Pulled plug wires while running, the engine slugged a bit, but stay running which leads me to belive the firing and spark are good.

What am I missing here? I just can't seem to get this thing to run smooth as it did before. Are there any wiring issues I should look into? Thanks for looking
 

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Just to clarify: Was it running rough before setting the valves?

If not, I'd take another look at the valves.

Otherwise:

Did you adjust the carb after the engine warmed up? The initial setting is never 'right on' just approximate.

Be sure the intake manifold is sealing well, as I assume you removed it to set the valves.
 

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Discussion Starter · #4 ·
Kenc: It was running rough before the valve job, thats why I decided to do the valve job and look into what might be causing this problem. I can't seem to get the rough to smooth out with the carb adjustment. I'm only making small increment changes to the idle screw and it just doesn't seem to help. I'm going to mess with it some more today, and see if I can't get her to warm up longer and try adjusting from there. I'm just not sure if I may be overlooking something. What do you suggest by looking at the valves further?

Boomer: I had removed the heads a while ago to clean them, everything looked good. not too dirty. Gaskets looked good too.
 

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Discussion Starter · #5 ·
Kenc said:
Just to clarify: Was it running rough before setting the valves?

If not, I'd take another look at the valves.
Are the valves able to be removes for inspection/grind by the pulling the intake valve covers and heads and tearing down the springs?
What would be indicators on the seat or valves that I need to rework them?

Also I should of mentioned earlier, when this engine runs, it spits gas out of the carb, not a lot, but enough that worries me. I just ordered a new upper end gasket kit to refresh gaskets.
 

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Discussion Starter · #8 ·
I just came in from tinkering, and I couldn't get the idle to smooth out, the choke had to be darn near close to stay running, and it was running rough. Blue smoke, backfiring, and a few flames out of carburetor...
I'm not sure why all of a sudden this is giving me problems... It seems that my electrical is fine. I'm going to wait for replies from replies from you veterans of Onans, before I decide to tear the valves out. If by chance the seats are bad, is this a costly repair that a shop has to perform?
 

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Scott,
Thanks for coming and joining. Please post the model, spec and serial number of your engine so that our knowledgeable members are positive which engine you have. The advice can be a lot more accurate if you do that.

It certainly sounds like a carb issue.

Do you run an in-line fuel filter? Have you ever removed the fuel tank, cleaned it out, removed the screen that may be present in the outlet, replaced the fuel line 100 percent from the tank to the carb?

How about the vent hole in the cap on the gas tank? Is it blocked or open? All of these things can cause problems with fuel delivery.

Cheers,

Tom A.
 

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Discussion Starter · #10 ·
Hydriv said:
Scott,
Do you run an in-line fuel filter? Have you ever removed the fuel tank, cleaned it out, removed the screen that may be present in the outlet, replaced the fuel line 100 percent from the tank to the carb?

How about the vent hole in the cap on the gas tank? Is it blocked or open? All of these things can cause problems with fuel delivery.

Cheers,

Tom A.
I do run an inline fuel filter, the fuel tank appears to be free and clean of dirt and debris. I have not replaced fuel line, it appears in good order, no cracks or kinks. Vent hole is free and clear as well.
As far as the screen you speak of, I'm not sure about that, I seem to get plenty of fuel though. It's not acting like it's starving for fuel, it's just running rough as heck.
I have a Case model #446-78 with a Onan B43M-GA016/3622A Serial #K833720102
 

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Scott,
According to a previous post, you said that the choke had to be on nearly 100 percent just to keep the engine running. To me, that indicates a lack of fuel reaching the engine cylinders OR...... air being sucked in AFTER the carb, thus leaning out the mixture dramatically. This can happen if the gaskets between the engine and the manifold are compromised or if the seal between the two halves of the intake manifold is likewise compromised.

If you have one of those propane torches used for soldering copper plumbing around, then run your engine, open the torch to let the raw propane escape and move it close to the key areas of the intake. If the engine picks up.....you have an air leak.
 

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Discussion Starter · #12 ·
Hydriv, yes, this makes sense to me. I just tore the upper half down, and inspected everything again, the intake gaskets may be suspect. I will have to wait for the new gaskets to arrive.
I also removed the gas tank and emptied the gas, and no particulate were found, and the screen mentioned above in this post was loacated and it was found to be clean and free of dirt and debris. The inline filter is clean, as well as the hose front to back. I am going to clean carb thoroughly while waiting for gaskets to arrive.
I would like to inspect valves outside of engine if it's possible to do this without tear everything apart.
Does camshaft need to be removed to remove valves?
 

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One of the problems with neoprene gas lines is that they harden with age and then they don't seal properly. This poor sealing problem can allow air to get sucked in past the poor seal.

I cannot help you with the valve question but Boomer will be along at some point and he will advise you on that issue. That's why I have Boomer, Bart, Ken and two Bobs on this site. They are smarter than I am. :sidelaugh: So, hang in there. We will get to the bottom of your problem.
 

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scott
your engine S.N. says it was built in Nov. 83.
i do not think the manuals are at this site yet.
SO, at this time please join the yahoo onan engine site.
there you can download the parts and service manuals.

your camshaft doesn't have to be removed to remove the valves.
did you use any new gaskets the first time around?
normally if the valves are leaking,a regular valve job is all that is needed.
(grinding the valves and seats)
good luck. boomer
 

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Scott
Your problem is a perfect excample why a CYLINDER LEAKDOWN test should have been done before you tore it down again......would tell you if a valve was leaking, which by fact was spitting gas I think it is.
Heads need to come off...intake/exhaust manifolds off....remove valve covers and using valve spring compressor take out the two valve keepers per valve.....inspect each valve and seat VERY carefully as you take each one apart to see if you can tell. Fact that choke had to be full on sounds like manifold leak or dirty carb. You said you adjusted idle screw but never said about main jet screw....did you ever back it out? Intilal setting from book are just ball park settings. Bob M
 

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Discussion Starter · #17 ·
boomers_influence said:
scott
your engine S.N. says it was built in Nov. 83.
i do not think the manuals are at this site yet.
SO, at this time please join the yahoo onan engine site.
there you can download the parts and service manuals.

your camshaft doesn't have to be removed to remove the valves.
did you use any new gaskets the first time around?
normally if the valves are leaking,a regular valve job is all that is needed.
(grinding the valves and seats)
good luck. boomer
Yes, this is the second engine in this tractor. The original sits on my garage floor with a broken rod and hole in the top of the block. I bought this with the second engine installed about 3 years ago.
I have not used new gaskets yet, but I have them ordered now.
I will pull the valves and inspect them as well.
Maybe this is a stupid question, but if the seats need to be ground, then I have to take the engine to the machine shop, correct?
 

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Discussion Starter · #18 ·
xfolkboat said:
Requiring choke to keep running,, and progressive deterioration in running, is often a sign of a bad ignition component.
I'ver tested and traced everything electrical, and can't find any reason to suspect points or condensor, or wiring to the coil, or up from to the stator?... I'm beginning to suspect the valves and maybe the intake manifold gaskets are suspect.
 

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Discussion Starter · #19 ·
robynrj said:
Scott
Your problem is a perfect excample why a CYLINDER LEAKDOWN test should have been done before you tore it down again......would tell you if a valve was leaking, which by fact was spitting gas I think it is.
Heads need to come off...intake/exhaust manifolds off....remove valve covers and using valve spring compressor take out the two valve keepers per valve.....inspect each valve and seat VERY carefully as you take each one apart to see if you can tell. Fact that choke had to be full on sounds like manifold leak or dirty carb. You said you adjusted idle screw but never said about main jet screw....did you ever back it out? Intilal setting from book are just ball park settings. Bob M
I haven't torn the cylinder heads down yet, and the valves are still in.
I can still do a leakdown, correct?
 

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Scott430446 said:
xfolkboat said:
Requiring choke to keep running,, and progressive deterioration in running, is often a sign of a bad ignition component.
I'ver tested and traced everything electrical, and can't find any reason to suspect points or condensor, or wiring to the coil, or up from to the stator?... I'm beginning to suspect the valves and maybe the intake manifold gaskets are suspect.
Just thought I'd mention it, as the condensor breaks down it causes running issues very like running very lean Including a 'lean burn" smell.
 
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