Onan seems to flood but doesn't

[RED-Z06 2,567]

Ill preface this with, its on something green...it runs like a swiss watch, but...

 

Onan P220G, 877hrs, no smoke or oil use, starts great cold, runs great..if you shut it off, it acts like its flooded for a few minutes, and does blow black smoke when it starts.  Its a Chinese carb, im not happy about that trust me..but that was the previous owners doing.  Ive pressure tested the carb, float needle holds pressure with no leakdown.  Seems like as its shutting down it pulls in enough gas to wet the intake/plugs.

 

My p216g has always done something similar..but nowhere near as pronounced, all oem.

[ranger 1,798]

I don’t know anything about these particular engines but, I would suspect that the fuel in the carb could be expanding / evaporating from the float chamber through the main jet into the inlet manifold due to latent rising heat from the engine when stopped.  This fuel then has a similar effect as trying to start a hot engine on full choke. You could try a wide open throttle setting when hot starting to see if max air flow helps. As for the Chinese carb, I wouldn’t have thought the carb would allow excess fuel to flow when switching off, unless you apply full choke at the same time. One thing to check is if the carb has an insulating, (or if it should have?) gasket between itself and the manifold. These are usually fitted to reduce this type of issue.

[oldlineman 1,537]

Not sure but does this engine have a gas electric solenoid shut off when you turn the key off? If so it may not be working and not shutting down the gas flow. Bob

Edited February 15, 2022 by oldlineman

[kpinnc 14,628]

What he said... 

 

When that big onan spins a few RPMs at shutdown, the fuel pump is still doing it's thing. A solenoid would insure it stays in the bowl.

Edited February 15, 2022 by kpinnc

[pacer 3,177]

You also have to remember that the opposed twins - Kohler and Onan - with the carb sitting on the top of the engine if the needle is 'leaking?' it will drip directly into the manifold and you will not see typical 'flooding' as on the singles.

 

My B43 Onans carb system has a tendency to be very .... sensitive? in the float/needle area.

 

And, bottom line is if excess fuel is getting into the cyl it HAS to get there by by the needle .
 

[RED-Z06 2,567]

2 hours ago, ranger said:

I don’t know anything about these particular engines but, I would suspect that the fuel in the carb could be expanding / evaporating from the float chamber through the main jet into the inlet manifold due to latent rising heat from the engine when stopped.  This fuel then has a similar effect as trying to start a hot engine on full choke. You could try a wide open throttle setting when hot starting to see if max air flow helps. As for the Chinese carb, I wouldn’t have thought the carb would allow excess fuel to flow when switching off, unless you apply full choke at the same time. One thing to check is if the carb has an insulating, (or if it should have?) gasket between itself and the manifold. These are usually fitted to reduce this type of issue.

No insulator unfortunately, probably should have had one given how the carb is situated but one couldn't be added without changing how the air filter and hoses fit up.

[lynnmor 7,813]

Always idle down any engine before turning off the ignition, if the engine is very hot, let it idle a couple of minutes.  A properly operating float, needle and seat will not leave additional gas to flow into the engine.  If the problem persists, lose the Chinese junk.

[RED-Z06 2,567]

21 minutes ago, lynnmor said:

Always idle down any engine before turning off the ignition, if the engine is very hot, let it idle a couple of minutes.  A properly operating float, needle and seat will not leave additional gas to flow into the engine.  If the problem persists, lose the Chinese junk.

This is after idling about 30 seconds.  Float needle holds 9psi indefinitely without popping off.

[kpinnc 14,628]

20 minutes ago, RED-Z06 said:

This is after idling about 30 seconds.  Float needle holds 9psi indefinitely without popping off.

 

Another 'less attractive' option would be to add an inline fuel shutoff, and run the carb dry or at least down a bit before shutdown.

[RED-Z06 2,567]

1 minute ago, kpinnc said:

 

Another 'less attractive' option would be to add an inline fuel shutoff, and run the carb dry or at least down a bit before shutdown.

Definitely would be less attractive, having to crank it to refill the bowl.  Ill probably end up getting a new Nikki carb...just a shame because it absolutely hums when running and the idle is on point smooth.

[lynnmor 7,813]

22 minutes ago, RED-Z06 said:

 Ill probably end up getting a new Nikki carb...

 

Why?  If you don't have one to rebuild, buy one.

[kpinnc 14,628]

2 hours ago, RED-Z06 said:

Definitely would be less attractive, having to crank it to refill the bowl.  Ill probably end up getting a new Nikki carb...just a shame because it absolutely hums when running and the idle is on point smooth.

 

Primer bulb. I absolutely love how it makes all of my "tank under the seat" tractors crank before a full revolution. Saves my batteries, saves my starters, and causes perm-a-grin to all observers- most importantly ME!

[RED-Z06 2,567]

2 hours ago, lynnmor said:

 

Why?  If you don't have one to rebuild, buy one.

Previous owner tossed the original Nikki for the chinese one...he was chasing a problem, problem was no compression on one cylinder.

[oldlineman 1,537]

Can't connect that problem to a bad carb though. Bob

[RED-Z06 2,567]

1 hour ago, oldlineman said:

Can't connect that problem to a bad carb though. Bob

He couldnt get it to idle smooth, he thought a new carb would fix it, didn't...problem was the right side intake valve was hung open .007" on lash.

[oldlineman 1,537]

You would think that if a new China carb didn't fix it he would put the good original one back on. Just sayin. Bob

[RED-Z06 2,567]

5 minutes ago, oldlineman said:

You would think that if a new China carb didn't fix it he would put the good original one back on. Just sayin. Bob

The key switch went out and he replaced it with a push/pull switch for 12v kill, then a push button starter...along with about 12ft of wire, instead of just...replacing the switch.  I literally removed his switches, pulled the jumpers out of the 5pin plug and plugged it into a new key switch and it all worked as intended.

 

Point being, he wasnt exactly a big brain kinda guy 

Edited February 15, 2022 by RED-Z06

[RED-Z06 2,567]

Both head gaskets were blown...both intake valves were too tight...again.  very strange.  The gasket kit was from Isavetractors, i put the old head gaskets back on,  and relashed the valves..runs good again but, still hard to start hot and it had fuel in the cylinders when i pulled the heads off...not alot by any means but, fuel.

 

I think its time to invest in an oem carb...

[oldlineman 1,537]

Check with A to Z and get a used one and rebuild it, should be cheaper, worth checking out. Bob

[RED-Z06 2,567]

Gotta say...50 bucks for a gasket set only to have to put the old head gaskets back in because the new ones blew in 2 hours, not have the P series intake gaskets in it...is pretty foul.

 

I just ordered a set, with the right intake gaskets off amazon for 13 bucks, looks like it has the metal gaskets and not graphoil 

[lynnmor 7,813]

22 minutes ago, RED-Z06 said:

Gotta say...50 bucks for a gasket set only to have to put the old head gaskets back in because the new ones blew in 2 hours, not have the P series intake gaskets in it...is pretty foul.

 

I just ordered a set, with the right intake gaskets off amazon for 13 bucks, looks like it has the metal gaskets and not graphoil 

 

I learned a long time ago that the cheap imported gaskets are junk, particularly the intake gaskets..  You might get lucky.

[RED-Z06 2,567]

37 minutes ago, lynnmor said:

 

I learned a long time ago that the cheap imported gaskets are junk, particularly the intake gaskets..  You might get lucky.

I assumed the set from Isavetractors would be good quality...given the cost 

[lynnmor 7,813]

6 hours ago, RED-Z06 said:

I assumed the set from Isavetractors would be good quality...given the cost 

I assume that most of his stuff is from China, at least he may choose the best of the worst.  JMHO

[RED-Z06 2,567]

21 minutes ago, lynnmor said:

I assume that most of his stuff is from China, at least he may choose the best of the worst.  JMHO

Thus far, the governor spacer works amazing...but that gasket set is garbage.