I have replaced my worn out onan in my '83 318 with a fresh rebuilt long block and it runs great, starts easily. Recently though when I flip on the PTO my engine chokes out and dies. This happens whether it is idling or running at half throttle. My idle rpm is set at about 1300. I have tried adjusting the low speed idle screw and think it might be better but next time I start the tractor it will do the same thing. Maybe when it is well warmed up it will help the condition. I believe the rebuilt governor is working as it should. Anybody have any suggestions or help? Thanks
PTO kills the engine on my 318
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Gerald,
If the engine dies as though the key was turned off when you engage the PTO, it most likely is a safety interlock issue and not a carburetor tuning or engine loading related one.
Here is the wiring excerpt:
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Does the same thing happen if you move the ground speed lever out of the Neutral slot? If so then it likely is a fault in the seat switch, the wiring bock to that switch or the fuse at F2 (2 or 3 amps depending on year model...)
What you do not see above is how the 'bypass' is designed to allow the engine to run when the ground speed is in Neutral even if the operator is not in the seat. That network comes into the TDCM pin 7 and is shown below, spread across two drawings:
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...Sorry for the multiple wiring excerpts, but the full schematic is too large to post here and still read it clearly.
If I have guessed wrong and your issue truly is limited to the PTO engagement, then look for a seized bearing in that assembly...
Good luck and let us know what you find.
Chuck
If the engine dies as though the key was turned off when you engage the PTO, it most likely is a safety interlock issue and not a carburetor tuning or engine loading related one.
Here is the wiring excerpt:
Does the same thing happen if you move the ground speed lever out of the Neutral slot? If so then it likely is a fault in the seat switch, the wiring bock to that switch or the fuse at F2 (2 or 3 amps depending on year model...)
What you do not see above is how the 'bypass' is designed to allow the engine to run when the ground speed is in Neutral even if the operator is not in the seat. That network comes into the TDCM pin 7 and is shown below, spread across two drawings:
...Sorry for the multiple wiring excerpts, but the full schematic is too large to post here and still read it clearly.
If I have guessed wrong and your issue truly is limited to the PTO engagement, then look for a seized bearing in that assembly...
Good luck and let us know what you find.
Chuck
Thanks for your response. Don't think it is electrical and it does also do it when the tractor is in forward motion, but it does get better when it seems to completely warm up. The PTO was replaced within the last 5 years but that doesn't mean it can't be causing me a problem. I wired around the seat switch with a little jumper wire. The PTO switch has recently been replaced. Maybe I can start checking voltages?!? Gerry
Chuck, it just don't sound or act like it is electrical. It's not like you turn off the key and just die, if you can understand what I mean. It will try to overcome the load of the blades on the engine and 1 out of 10 times might win and resume normal RPM. ???
Gerry, there's a quick way to determine whether your problems are mechanical binding in the PTO or electrical.
Unplug the PTO coil lead. It's at the front of the tractor, at the end of the pigtail coming out of the coil. Get on the tractor, start it up, turn on the PTO switch, and move the hydro control out of the neutral slot. If the tractor continues to run normally, then your problems are at the PTO. If it dies, your problem is in the safety switch wiring.
Check the resistance of the PTO coil at the connector. Should be 3-4 ohms.
To check for mechanical blocking in the PTO, take the drive belt to the mower off. If the PTO (plugged into the harness) engages and runs properly, your mechanical problems are in the belt-driven accessory (mower).
I wouldn't spend much time with a PTO that is jamming up. Have you checked the air gap through the three windows in the housing? Spec is .018, and if the adjustment is too tight on one or more windows, the brake won't release with the PTO engaged. Other than that, pull the PTO off the tractor and inspect for problems inside.
Hank
Unplug the PTO coil lead. It's at the front of the tractor, at the end of the pigtail coming out of the coil. Get on the tractor, start it up, turn on the PTO switch, and move the hydro control out of the neutral slot. If the tractor continues to run normally, then your problems are at the PTO. If it dies, your problem is in the safety switch wiring.
Check the resistance of the PTO coil at the connector. Should be 3-4 ohms.
To check for mechanical blocking in the PTO, take the drive belt to the mower off. If the PTO (plugged into the harness) engages and runs properly, your mechanical problems are in the belt-driven accessory (mower).
I wouldn't spend much time with a PTO that is jamming up. Have you checked the air gap through the three windows in the housing? Spec is .018, and if the adjustment is too tight on one or more windows, the brake won't release with the PTO engaged. Other than that, pull the PTO off the tractor and inspect for problems inside.
Hank
Thanks Hank. To bring you up to date, I went out today, started the engine and turned on the PTO at about 1/2 throttle. The engine coughed, choked and died. I than removed the belt to the deck and then checked the PTO adjustment and did re-adjust one side that was too closed. The deck pulley turned free and easy. It was difficult to turn the PTO clutch like it is dragging. I then re-started the engine and engaged the PTO, everything worked correctly, engaging and disengaging. I re-installed the belt to the deck, started the engine and flipped the PTO on to engage the PTO clutch. I discovered that if the engine is at slow idle the engine keeps running but if I engage the PTO at half throttle the engine will cough, choke and try to die. Do you know if the PTO pulley should spin freely when not engaged and the engine not running? Maybe that's a problem.
Tomorrow I will do as you suggested, checking the coil resistance and removing the PTO to see if I can find anything wrong on the inside or why it's dragging. Thanks again Hank, I appreciate you trying to help me with this problem. Gerry
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Gerald
I have a 318 w/Onan and a 46" deck. All the instructions I have read say to slow the engine to idle before engaging the PTO switch. I have never tried to engage the mower deck at speed and I don't think I ever will. The PTO clutch has some sort of internal brake that slows down PTO when you turn the switch off. I think it is some sort of safety, That may cause too much drag at a higher initial engagement speed.
I guess I'm saying, it sounds like it's doing what it's supposed to.
Gene
I have a 318 w/Onan and a 46" deck. All the instructions I have read say to slow the engine to idle before engaging the PTO switch. I have never tried to engage the mower deck at speed and I don't think I ever will. The PTO clutch has some sort of internal brake that slows down PTO when you turn the switch off. I think it is some sort of safety, That may cause too much drag at a higher initial engagement speed.
I guess I'm saying, it sounds like it's doing what it's supposed to.
Gene
Thanks Gene. What you say does make sense. What bothers me is that this just started happening within the last couple of weeks. Before this the engine never slowed or stalled whether the engine was at idle or 1/2 throttle. Just makes me wonder if something else is happening. Usually when we start the tractor, we advance the throttle to get out into the yard and just flip on the PTO and the engine never slowed or hesitated. So what has changed? I will start practicing this procedure and see if my problem continues at idle speed. Gerry
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Gerald,
The PTO should be engaged at part throttle and not at idle...mowing should be done at WOT
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The PTO pulley should NOT spin freely when the engine is not running and the clutch not activated. The brake on the PTO should keep you from turning it with the clutch not energized, so what you described in your post #46 regarding that is normal.
Has this symptom always been evident with this replacement engine, or is it a new problem?
Chuck
The PTO should be engaged at part throttle and not at idle...mowing should be done at WOT
The PTO pulley should NOT spin freely when the engine is not running and the clutch not activated. The brake on the PTO should keep you from turning it with the clutch not energized, so what you described in your post #46 regarding that is normal.
Has this symptom always been evident with this replacement engine, or is it a new problem?
Chuck
Gerry, the PTO has a "safety" brake that stops pulley rotation when the PTO is turned off. If the PTO armature gap is too tight, it will engage without fully moving from the brake. If the gap is too open, the PTO won't engage reliably or not at all, particularly when hot.
When adjusting the gap, I use an .017 "go" and an .019 "no go" feeler. The .017 feeler should slide in freely. If you have to adjust one or more points, do a recheck of all three until you can walk around and feel the proper gap without adjusting anything.
On my 318, once the engine is warmed up (takes several minutes), I can engage the PTO with a 50" mower at any throttle setting between low and high idle. In practice, I generally rev the engine up a few hundred RPM from low idle, then flip the PTO switch. With the engine warmed, I can move the throttle to full throttle in about one second, and the engine will speed up smoothly as I do it. If I get a flat spot in acceleration, or misfiring, either the engine is not warmed or the main mixture is too lean.
I'll note here that my carburetor has an adjustable main jet in place of the standard fixed jet. So that acceleration test verifies that the main mixture adjustment is set correctly.
I'm at 5000 ft. altitude, so have no real idea how the fixed jet setup behaves at sea level.
The most common lean carburetion issues with an Onan engine are a plugged idle jet and air leaks in the intake manifold. Those are regularly discussed in postings here.
Hank
When adjusting the gap, I use an .017 "go" and an .019 "no go" feeler. The .017 feeler should slide in freely. If you have to adjust one or more points, do a recheck of all three until you can walk around and feel the proper gap without adjusting anything.
On my 318, once the engine is warmed up (takes several minutes), I can engage the PTO with a 50" mower at any throttle setting between low and high idle. In practice, I generally rev the engine up a few hundred RPM from low idle, then flip the PTO switch. With the engine warmed, I can move the throttle to full throttle in about one second, and the engine will speed up smoothly as I do it. If I get a flat spot in acceleration, or misfiring, either the engine is not warmed or the main mixture is too lean.
I'll note here that my carburetor has an adjustable main jet in place of the standard fixed jet. So that acceleration test verifies that the main mixture adjustment is set correctly.
I'm at 5000 ft. altitude, so have no real idea how the fixed jet setup behaves at sea level.
The most common lean carburetion issues with an Onan engine are a plugged idle jet and air leaks in the intake manifold. Those are regularly discussed in postings here.
Hank
Gerry, the PTO has a "safety" brake that stops pulley rotation when the PTO is turned off. If the PTO armature gap is too tight, it will engage without fully moving from the brake. If the gap is too open, the PTO won't engage reliably or not at all, particularly when hot.
When adjusting the gap, I use an .017 "go" and an .019 "no go" feeler. The .017 feeler should slide in freely. If you have to adjust one or more points, do a recheck of all three until you can walk around and feel the proper gap without adjusting anything.
On my 318, once the engine is warmed up (takes several minutes), I can engage the PTO with a 50" mower at any throttle setting between low and high idle. In practice, I generally rev the engine up a few hundred RPM from low idle, then flip the PTO switch. With the engine warmed, I can move the throttle to full throttle in about one second, and the engine will speed up smoothly as I do it. If I get a flat spot in acceleration, or misfiring, either the engine is not warmed or the main mixture is too lean.
I'll note here that my carburetor has an adjustable main jet in place of the standard fixed jet. So that acceleration test verifies that the main mixture adjustment is set correctly.
I'm at 5000 ft. altitude, so have no real idea how the fixed jet setup behaves at sea level.
The most common lean carburetion issues with an Onan engine are a plugged idle jet and air leaks in the intake manifold. Those are regularly discussed in postings here.
Hank
When adjusting the gap, I use an .017 "go" and an .019 "no go" feeler. The .017 feeler should slide in freely. If you have to adjust one or more points, do a recheck of all three until you can walk around and feel the proper gap without adjusting anything.
On my 318, once the engine is warmed up (takes several minutes), I can engage the PTO with a 50" mower at any throttle setting between low and high idle. In practice, I generally rev the engine up a few hundred RPM from low idle, then flip the PTO switch. With the engine warmed, I can move the throttle to full throttle in about one second, and the engine will speed up smoothly as I do it. If I get a flat spot in acceleration, or misfiring, either the engine is not warmed or the main mixture is too lean.
I'll note here that my carburetor has an adjustable main jet in place of the standard fixed jet. So that acceleration test verifies that the main mixture adjustment is set correctly.
I'm at 5000 ft. altitude, so have no real idea how the fixed jet setup behaves at sea level.
The most common lean carburetion issues with an Onan engine are a plugged idle jet and air leaks in the intake manifold. Those are regularly discussed in postings here.
Hank
I have 2 threads to answer. First One, thanks Chuckv for helping. I have 50 hours on the engine now and this just started happening. Until now it has been great with no problems and plenty of power. I just realized in my comment 3 threads ago, this started about 2 weeks ago. Coincidence, don't know, this is when I changed over to Pennzoil Platinum 5w-30 synthetic oil. Can there be a connection?
To answer Hankvc, thanks for your help. I did as you suggested making sure all 3 clutch gaps were the same @ .018, adjusting one can change another. When I replaced the engine I also broke apart the intake manifold and resealed with the recommended clamping method and sealer I found on this great WFM sight. I rebuilt the carburetor with a kit from Onan and cleaned the jet with a torch cleaning tip (it was plugged). I also replaced all the fuel hoses. Today I plan on re-doing the carburetor settings at the recommended RPM (1250) and using a digital tachometer. I will also check the setting on the governor? Also check the intake manifold bolts to be sure they are the torqued correctly. Should I switch back to straight 30w John Deere oil? That don't make any sense! I'm sure at 1/3 throttle the engine will cough, choke out and die. Gerry
One more note I'd like to add. When I replaced the fuel lines, I lost my reserve tank.
To answer Hankvc, thanks for your help. I did as you suggested making sure all 3 clutch gaps were the same @ .018, adjusting one can change another. When I replaced the engine I also broke apart the intake manifold and resealed with the recommended clamping method and sealer I found on this great WFM sight. I rebuilt the carburetor with a kit from Onan and cleaned the jet with a torch cleaning tip (it was plugged). I also replaced all the fuel hoses. Today I plan on re-doing the carburetor settings at the recommended RPM (1250) and using a digital tachometer. I will also check the setting on the governor? Also check the intake manifold bolts to be sure they are the torqued correctly. Should I switch back to straight 30w John Deere oil? That don't make any sense! I'm sure at 1/3 throttle the engine will cough, choke out and die. Gerry
One more note I'd like to add. When I replaced the fuel lines, I lost my reserve tank.
Thanks Bill, I guess, I don't like what your suggesting. That would be a bad thing. The tractor runs awfully good and very strong when it's running. Does not smoke and is using no oil. I can do that check but it might be the end of the week before I can get to it. Gerry
Thanks Bill for your suggestions. Today I removed the air cleaner and adjusted the Idle mixture screw using a tach as per John Deere TM1590 doing it at the recommended RPM's. After I was finished I cut about 1/2 the yard (1/2 acre) stopping and starting the PTO at idle, 1/3 throttle, 1/2 throttle, and 3/4 throttle and never had a stalling problem. The pre-filter was pretty dirty when I got to it. Tomorrow I will cut the rest of the grass and see what happens?!? TM1590 says to adjust the low speed stop screw and the throttle stop screw. I don't believe my '83 318 has a 'low speed stop screw' unless I just can't see it. Gerry
Have no idea Bill. Piece of dirt?? After the new engine and the rebuilt carburetor the idle screw adjustment seems very sensitive. A little bit of adjustment either way does a lot to the RPM's. But I appreciate all the help from everyone. I ran it again this afternoon and it seemed fine, I'll keep my fingers crossed. Thanks again, Gerry
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