520H No Start - Timing issue or something else?

[TC10284 109]

Have a 73502 model 520H. Swapped engines since the other p220g was bad (rear piston broken off from shaft). Put in a P220G from another 520H - model P220G-I/10955G P/N 941811 and S/N B963491005

 

Got everything back on it. New gas, new plugs, new coil (as a test). Turn it over and won't start. It has gas on the plugs. I can smell it. Plugs are new - NGK TR5. Compression I believe is good. ~120psi on the front cyl and ~125psi on the rear cyl. Valves have also been adjusted as I was installing the replacement engine. 

 

Took plugs out. Rear plug seems to get fire pretty well. Front plug seems a little more difficult getting fire. Not sure if it's just that I'm not touching it to a good enough ground or not. Doesn't seem to always spark when I touch it to various unpainted contacts. Tried swapping plugs and wires from front to rear, rear to front, etc. Same spark. Haven't replaced the condenser coil yet, but I can if suggested. I have a new one on hand. 

 

Putting gas in the carb and/or the cylinder doesn't help anything. Doesn't even try to start running.  

 

Have already tried replacing the coil with a new one. Same deal. 

 

When I turn it over and it exhibits this symptom, it stops the starter completely, and takes a second for the starter to start turning over again. And when this happens, I can normally see unspent fuel vapor come out of the exhaust and it is also shot out of the top of the carb in a rather strong burst when it does this. 

 

Not sure what's going on here. Timing issue? Possibly water in the cylinder(s) causing a steam backfire?

Any ideas? 

Edited November 21, 2018 by TC10284

[lynnmor 6,762]

Download the Onan manual on this site.  You can then check the ignition timing by rotating the engine by hand with the plugs out or with a timing light while cranking.  What I am suspecting it the trigger or trigger key located behind the flywheel.  The trigger is simply a plastic ring with two magnets in it, the earlier black ones had problems.  Also, using the manual, test the ignition module located next to the trigger ring, of course do this first before removing the flywheel.  There may be other problems, but I would start with getting the spark correct.

[TC10284 109]

23 minutes ago, lynnmor said:

Download the Onan manual on this site.  You can then check the ignition timing by rotating the engine by hand with the plugs out or with a timing light while cranking.  What I am suspecting it the trigger or trigger key located behind the flywheel.  The trigger is simply a plastic ring with two magnets in it, the earlier black ones had problems.  Also, using the manual, test the ignition module located next to the trigger ring, of course do this first before removing the flywheel.  There may be other problems, but I would start with getting the spark correct.

 

I'll check on the trigger as soon as possible. I have a new one from replacing an ignition module, but the original trigger was fine. 

[TC10284 109]

43 minutes ago, lynnmor said:

Download the Onan manual on this site.  You can then check the ignition timing by rotating the engine by hand with the plugs out or with a timing light while cranking.  What I am suspecting it the trigger or trigger key located behind the flywheel.  The trigger is simply a plastic ring with two magnets in it, the earlier black ones had problems.  Also, using the manual, test the ignition module located next to the trigger ring, of course do this first before removing the flywheel.  There may be other problems, but I would start with getting the spark correct.

 

Just to confirm, when you say "trigger", you mean the ignition rotor like this, correct?

https://www.ebay.com/p/Cummins-Onan-166-0767-Ignition-Rotor-P216g-P218g-P220g-Engine-Models/1041962748?iid=292774622857&chn=ps

 

[WVHillbilly520H 10,369]

2 minutes ago, TC10284 said:

 

Just to confirm, when you say "trigger", you mean the ignition rotor like this, correct?

https://www.ebay.com/p/Cummins-Onan-166-0767-Ignition-Rotor-P216g-P218g-P220g-Engine-Models/1041962748?iid=292774622857&chn=ps

 

Yep trigger=rotor

[TC10284 109]

OK, got the trigger/rotor replace today. Did not see anything physically wrong with the key or the old rotor. Replace the rotor with my new one, put everything back together and immediately got better spark. 

Engine turned over and ran! Sweet! 

 

Only issue I'm having at this point is that it doesn't want to idle as low as it should. I'd estimate it's running around 20 to 25% throttle. 

In addition, when the choke is all the way open (all the way down), it hunts a lot until I open the throttle at least half way or more. Runs smooth if I leave choke maybe 25% closed. 

Carb has been cleaned and soaked prior to putting it back on the engine. 

 

Any ideas on this? 

[WVHillbilly520H 10,369]

4 minutes ago, TC10284 said:

OK, got the trigger/rotor replace today. Did not see anything physically wrong with the key or the old rotor. Replace the rotor with my new one, put everything back together and immediately got better spark. 

Engine turned over and ran! Sweet! 

 

Only issue I'm having at this point is that it doesn't want to idle as low as it should. I'd estimate it's running around 20 to 25% throttle. 

In addition, when the choke is all the way open (all the way down), it hunts a lot until I open the throttle at least half way or more. Runs smooth if I leave choke maybe 25% closed. 

Carb has been cleaned and soaked prior to putting it back on the engine. 

 

Any ideas on this? 

Fresh non ethanol fuel? Did you change ALL the fuel lines from tank to carb with a new filter? Because ethanol breaks down the rubber from the inside out leaving rubber residue to clog filter and/or make into carb (already been down that path after cleaning carb but not replacing lines)...also the fuel petcock in the tank has a brass filter that can become clogged from the ethanol as well, but if it's still hunting/surging most likely it's carb/fuel related...

[TC10284 109]

8 minutes ago, WVHillbilly520H said:

Fresh non ethanol fuel? Did you change ALL the fuel lines from tank to carb with a new filter? Because ethanol breaks down the rubber from the inside out leaving rubber residue to clog filter and/or make into carb (already been down that path after cleaning carb but not replacing lines)...also the fuel petcock in the tank has a brass filter that can become clogged from the ethanol as well, but if it's still hunting/surging most likely it's carb/fuel related...

 

I'll check on that. 

It does have fresh gas that was mixed in with some that is maybe 8 months old. Will try some totally fresh and new lines. 

 

Any idea what's causing the fast idle? 

[WVHillbilly520H 10,369]

28 minutes ago, TC10284 said:

 

I'll check on that. 

It does have fresh gas that was mixed in with some that is maybe 8 months old. Will try some totally fresh and new lines. 

 

Any idea what's causing the fast idle? 

The Onan should idle around 1250rpm on the Tach in the dash if it's operational, could be one of a couple things, either the idle speed screw is adjusted in a bit tight or the governor spring may be in the wrong position, check the manual for correct position.

[TC10284 109]

In the mean time, any way to fix the old rotor/trigger? It appears to be in fine condition. I took apart and the two little magnets in it are both still working. Nothing is broken. Don't get what was wrong with it unless the magnets spun out of position somehow. 

[lynnmor 6,762]

1 hour ago, TC10284 said:

In the mean time, any way to fix the old rotor/trigger? It appears to be in fine condition. I took apart and the two little magnets in it are both still working. Nothing is broken. Don't get what was wrong with it unless the magnets spun out of position somehow. 

If it is black in color, throw it away.  If it is gray and the magnets are strong, perhaps the problem was with something else and you got lucky.  That key is not a very robust part and maybe didn't locate the rotor properly.

[TC10284 109]

1 hour ago, lynnmor said:

If it is black in color, throw it away.  If it is gray and the magnets are strong, perhaps the problem was with something else and you got lucky.  That key is not a very robust part and maybe didn't locate the rotor properly.

 

It's the light gray kind. 

This is what it looked like prior to the swap:
 

 

 

 

 

 

[lynnmor 6,762]

Not seeing anything wrong, did you replace the module at the same time?

 

Use the manual to adjust the idle.  Basically, you back off the speed screw located away from the carb near the throttle cable, then adjust the idle speed with the throttle stop screw to 1000 RPM, next adjust the idle mixture screw to get the best idle.  If speed increased, readjust to 1000, lather, rinse and repeat as necessary.  Last, adjust the speed screw that you backed off till it idles about 1300 RPM.

[TC10284 109]

57 minutes ago, lynnmor said:

Not seeing anything wrong, did you replace the module at the same time?

 

Use the manual to adjust the idle.  Basically, you back off the speed screw located away from the carb near the throttle cable, then adjust the idle speed with the throttle stop screw to 1000 RPM, next adjust the idle mixture screw to get the best idle.  If speed increased, readjust to 1000, lather, rinse and repeat as necessary.  Last, adjust the speed screw that you backed off till it idles about 1300 RPM.

 

No, only the rotor. 

 

Messed with it again this afternoon. I believe I've resolved the surging with the idle fuel screw.

 

As for the high idle, I adjusted it as much as I could, but it didn't really resolve it. The only thing that resolved it was disconnecting the throttle cable from the arm that connects to the spring. It looks like the cable is too short. Disconnected it and it starting idling around 1300. With throttle cable connected, it would idle around 2000. 

 

 

Edited November 26, 2018 by TC10284

[Bucko 10]

On 11/21/2018 at 3:59 PM, TC10284 said:

 

If the cable issue does not solve your problem, the "hunting idle" could be that unfiltered/unmetered air is entering after the fuel jet(s). Check the throttle shaft to see if its loose, or has any play in it, causing the engine during its intake stroke to draw air in through the worn shaft; it only takes a small amount. This can cause your symptoms.

 

I'm experiencing a similar issue with a 61 H55; I can actually see the lever on the throttle shaft vibrating when the engine is at idle (needs to be at higher idle to stay running, with partial choke).

 

As to the ethanol fuel, I purchase an additive that can be added to one gallon of fuel that counters the ethanol. I've noticed a huge improvement in the bowl of a carb; I no longer see a "jelly like" substance in the bowl when the tractor sits for awhile. I've also installed a shutoff valve; I will run the carb dry when it sits over the winter months, then I add sta-bol in the gas tank. 

Edited November 28, 2018 by Bucko