Onan Carb Cleaning

[WHX?? 50,037]

She likes to surge especially at low to mid throttle & needs choke to get fuel. Will actually snuff out at idle. 

Runs great at upper to WFO throttle. Gotta be a dirty carb.

Question is can a guy clean it without pulling it off the manifold? Just the top off? 

Don't wanna lay the tractor up too long supposed to get more snow. 

[Blasterdad 2,875]

I've "ghetto" cleaned carbs before, taken out the jets I could get to with the carb still on, sprayed carb cleaner with the straw through the passage, then dialed down my compressor & gave them a shot of air, last time I did a walk behind snowblower & it worked. I'm not saying that it will every time or that you should do it. Surging is usually the idle jet getting plugged up. 

[lynnmor 7,513]

Remove the hex plug on the right side and then remove the jet, then blast in there with a spray can of carburetor cleaner that has a straw.

 

Remove the brass piece with the screwdriver slot and blast it and the hole with cleaner.

 

Blast all other holes.

 

There is an idle mixture screw on the muffler side, gently turn it in till it stops while counting the turns, then remove it and blast in there.  Install the screw to the exact position it was in.  Be very gentle with this screw, turn it too tight and the carburetor will be knackered.

 

This should take care of issues maybe 90% of the time.

 

Edited February 14 by lynnmor

[cleat 6,884]

If you unscrew and remove this jet that the arrow is pointing at you will find it has several small holes in it.

If any are plugged your machine will surge and run weird at part throttle.

The one at the very bottom will usually be the culprit.

I clean the holes with a torch tip cleaner.

 

 

[squonk 42,037]

My 520 surged off and on when I had it at lower throttle. A heavy dose of Seafoam cleared it out.

[JCM 9,960]

I agree it's not the best time of year to get into it but after all the projects I have seen over the years you and Dan do this is a cake walk for you. Plus your retired, plenty of time on your hands. I keep a spare carb on hand ready for the occasion . If you have to pull the carb I use never seize on the new manifold gaskets on each side, makes them come right off  without scraping them off. Of course lightly sand the mating surfaces first. When I worked in Chemical plants we had hot oil pumps that we had to pull and bring to the shop to work on for maintenance . We used Mobil therm 603 heat transfer oil to heat the jackets on reactors . Then on the re install we coated the mating surfaces on the pump and housing with the never seize for future removal.    Good luck        Jimbo

[WHX?? 50,037]

2 hours ago, squonk said:

A heavy dose of Seafoam cleared it ou

I tried that in hopes of the easy way out but no dice. 

 

10 hours ago, cleat said:

remove this jet

My next plan of attack But wasn't sure if that could be removed or not. Thanks Cleat 

 

22 minutes ago, JCM said:

spare carb on hand ready for the occasion .

 I do have a spare carb off a 220 with bad jugs  that I could do that with Plunge. Was hoping to get by until the off season then pull every thing to check the valve lash and de-carbon the top end. 

I do run just hi test gas in these. 

10 hours ago, lynnmor said:

spray can of carburetor cleaner that has a straw.

I have a can of Sea Foam spray on hand. 

 

Manual says that idle screw 1 1/4 out. 

Edited February 14 by WHX??

[cleat 6,884]

9 minutes ago, WHX?? said:

I tried that in hopes of the easy way out but no dice. 

 

My next plan of attack But wasn't sure if that could be removed or not. Thanks Cleat 

 

 

It can be, just find a screwdriver that fits into the hole and properly fits the slots on top of the jet so you don't damage it.

I have a flat screwdriver with fairly straight sides that fits very well, hopefully you do as well.

 

[WHX?? 50,037]

18 minutes ago, cleat said:

screwdriver that fits into the hole and properly fits

I have some precision gunsmithing screwdrivers that are a perfect fit. 

[daveoman1966 3,772]

I had a similar 'surge' problem with my 520-H with the Onan engine.  Turns out, wasn't the carb at all....the intake manifold was leaking on the rear cylinder.  Replaced the gasket...problem solved. No more surge.  

 

[WHX?? 50,037]

The jet Cleat spoke of. Yes it was plugged at the bottom. I have a set of micro brushes that worked along with the torch top cleaner. A gunsmith screwdriver worked well. 

 I did not remove the main jet. A real bugger to get at on place but blasted it good. 

 

This stuff works very well. Came with the long flexibil straw. 

 

Back together and blowing 6 inches today. Surging gone for the most part. Still need to get it back in and check out the manifold. 

Edited February 15 by WHX??

[JCM 9,960]

I use Sea Foam products as well. They seem to work . Nice looking rigs there Jim.

[cleat 6,884]

I use Seafoam all the time.

If your carb is slightly clogged but still flowing fuel it may well clean it out.

However, if a passage or jet is completely clogged then the Seafoam can't flow through to clean it.

 

My 520HC was stumbling when working hard plowing a couple weeks ago so I dumped some seafoam into the gas.

 

After a couple of uses plowing out the driveway it is now running perfectly. 

[WHX?? 50,037]

I was never a believer in tune up in a can but it does seem to work. They have quite a few products I never knew about.

 

https://seafoamworks.com/