onan p220g engine

[kawimaniac2145 6]

i had a topic on another post, and have a new issue, what would cause the engine to run fine with the air filter off. when i run it at high rpm with the air filter off it runs fine, but once i put the black, or the chrome air filter on it surges at high rpm. and runs fine at idle. it also sort of runs on one cylinder when going downhill.  i know i need an air filter and pre filter i am ordering one. p.s. how do i get to the carb adjustment screw. cause the muffler is in the way. pictures of air filter and carb adjustment screw. thanks for anyone who is able to help, i appreciate it alot.

[lynnmor 6,762]

Don't do a thing till you replace the extremely over-used air filters.  The air filter light should have come on, is the hose still attached?  Your engine does not have an idle mixture screw, if it doesn't run right after doing the air filter maintenance, pull the carburetor and clean it out.  It may need an accelerator pump and a float adjustment or replacement.   Has the valves ever been adjusted and how many hours are on the engine?

[kawimaniac2145 6]

no the air filter light is not on, what hose are you talking about? the carb was cleaned and adjusted. float was adjusted and yes the beginning of this year i adjusted the valves. the plugs are always black when i remove them still havent found out why. heres a video of how worse the engine sounds now.

 

 

[kawimaniac2145 6]

taking the air filter off doesnt help.

[lynnmor 6,762]

 

There is to be a hose from the bottom of your air filter housing to the sensor behind the instruments on the left side.  See the hex shaped fitting in your first photo.  The hose often breaks off the sensor nipple.

You really need to do the carburetor right, my guess is that the float is way off or faulty.

[kpinnc 10,669]

I don't want to hijack this thread- but I will add this to the good responses already posted:

It is always a good idea to seal the intake manifold. Of the three Onan engines I've had, all those two peice manifolds required sealing up to stop the surging of the engine, and did away with running half choked. Opinions vary on what to seal them with, but I've used high temp silicone gasket RTV and never had to go back. 

Edited May 26, 2021 by kpinnc

[kawimaniac2145 6]

i cleaned the carb last week elverything was fine. let me try sealing the intake manifold. thanks guys for helping. i will keep you posted.

[lynnmor 6,762]

A leaking intake seam will not cause the black smoke seen in the video, excess gasoline is the issue.  While checking the intake is always a good idea, most never have a problem.

[kawimaniac2145 6]

lynnmor so how would i get the engine to run better?

[Tuneup 1,416]

Man, that certainly is a black smoke generator! Assuming no electric pump was installed that is overcoming the float, that carb needs to be re-opened. Float setting and checking that it is free of obstruction. If you turned off the fuel, I bet it would start running sweetly for a minute or so before it dies as that level drops.

[lynnmor 6,762]

1 hour ago, kawimaniac2145 said:

lynnmor so how would i get the engine to run better?

 

Fix the carburetor.

[WheelhorseBob 1,548]

Agree with every one else. New air cleaner and carb cleaning. It was running like the choke was full on.

[kpinnc 10,669]

Just thought of one other thing- while you have the carb off, check the crankcase breather and tube that goes into the breather pan. I've had one get nasty and clogged up, so all of the extra crankcase pressure goes through the fuel pump. It can force extra gas pressure into the carb. Mine was too much for the float to stop.

[kawimaniac2145 6]

thanks guys i will do just that thanks.

[kawimaniac2145 6]

i will keep you guys posted desperatly want to get this engine running well again and will do anything. thanks

 

 

 

 

[lynnmor 6,762]

1 hour ago, kawimaniac2145 said:

i will keep you guys posted desperatly want to get this engine running well again and will do anything. thanks

 

Take photos as you disassemble the carburetor, there are some tiny parts in the later models that have the accelerator pump.  I believe that is what you have.  pump kit

[kawimaniac2145 6]

i will try it

[kawimaniac2145 6]

I got it to run but now it’s failing out plugs Compression is 120 psi on both cylinders new air filter gasket’s are good in carb was rebuilt and works correctly what would cause black around the plugs every time I put in a brand new plug and what can I do to fix it

[lynnmor 6,762]

1 hour ago, kawimaniac2145 said:

I got it to run but now it’s failing out plugs Compression is 120 psi on both cylinders new air filter gasket’s are good in carb was rebuilt and works correctly what would cause black around the plugs every time I put in a brand new plug and what can I do to fix it

 

If you are saying that the spark plug is black at the end where the bent electrode is welded on, then you need to find the reason that your carburetor is supplying too much fuel  Do you have new air filters?  Is the choke opening completely?  Did you inspect or replace the accelerator pump?  Is the float good and adjusted correctly?  Did you do the carburetor work or have others involved?

 

If you are saying that there is black outside the engine around the spark plug, then you have an issue with the threads.

[kawimaniac2145 6]

yes i bought new air filters, the choke does open completely, yes i inspected the accelerator pump and everything looked fine, the float is adjusted fine, and the float is adjusted correctly, i rebuilt the carb myself, i do small engine repair in my freetime. i hooked my vacuum gauge up to the inlet of the carb. and right side up, it wont pump up. but if i flip it upside down it holds 10 psi steady. there is some damaged threads on the intake block side the screws will not tighten down. i am getting a hellicoil kit and im going to helicoil it. but for the time being. i want to figure this out. all help will be appreciated thanks.

[lynnmor 6,762]

The original vacuum (horsepower) gauge connects to a nipple installed in the intake manifold forward from the carburetor.  A vacuum gauge does not display psi, it displays the amount of vacuum.  If you are talking about checking fuel pressure, then 10 psi is way too much and might be the cause of your problem.  Are you using the stock oem fuel pump?  I have no clue what an "intake block" is.  If you stripped the threads in the engine block where the intake and exhaust mounts, some of those can be tapped deeper and longer bolts use, there isn't much room to increase the hole size for heli-coils.  It is a good idea to use the longer bolts, regardless of the condition of the threads, to better mount those parts.

[kawimaniac2145 6]

The vacuum gauge I put 10 psi in it

[kawimaniac2145 6]

I am pretty sure it is a stock fuel pump how can I tell

[kawimaniac2145 6]

How do I get it to stop fauling out my plugs. The electrode is completely black

Edited June 11, 2021 by kawimaniac2145

[lynnmor 6,762]

A vacuum gauge displays a negative pressure, not 10 pounds per square inch of positive pressure.  Some gauges can do both.

 

Photos of the components might help, for example the carburetor, fuel pump and the "vacuum gauge."

 

To fix the black spark plugs, you need to fix the carburetor.  With good compression, the engine appears to be sound but it may be possible that the spark plugs are being oil fouled from bad rings or valve guides, but I doubt that is the issue.