520-H won't idle

[Rock farmer 41]

My 1990 520-H runs fine above 2500 rpm's. but, under 2,oo rpm's it's starts to stall and rev. The vacuum gage goes up and down. I'm thinking manifold leak or, maybe grit in the carb low speed needle?

I took the air cleaner cover off. To no effect. Can't be fuel restriction because it runs fine at high rpm's?

My first onan. Maybe they just don't idle?

Joe

[JackC 617]

They idle.  Usually a good carburetor cleaning cures most problems, especially with today's lousy fuels  Good thing to know how to do. Maybe even have a spare carburetor so when it runs lousy you can swap it out and keep going.  Then clean it and be ready for the next time.

[RiverRat 0]

Sea Foam, Deep Creep sprayed directly into those 2 little holes in the carb while it was running cured my 16hp Onan......Took awhile but she purrs now.

[dbartlett1958 99]

Joe,

 

I will second what Jack says. Most likely the low speed orifices have some crud in there. A good cleaning will have things right. 

[Rock farmer 41]

They idle.  Usually a good carburetor cleaning cures most problems, especially with today's lousy fuels  Good thing to know how to do. Maybe even have a spare carburetor so when it runs lousy you can swap it out and keep going.  Then clean it and be ready for the next time.

I agree. I like to have an extra carb on hand. Just in case I screw up the one I'm working on! I see the carb kits for these are really pricey! So, I just won a spare carb on EBay. When that arrives I'll take out the carb for cleaning and put in the replacement. I hate to have a machine just sitting there, not running, and me waiting for parts!

Joe

[SAM58 30]

Last spring my 520H did the same thing after setting most of the winter, ran great around 2800 RPM's

sent to idle and surged like crazy.

You don't have to remove the carb, just take the top of it off and clean it out with spray carb cleaner.

Works every time...

[Rock farmer 41]

Last spring my 520H did the same thing after setting most of the winter, ran great around 2800 RPM's

sent to idle and surged like crazy.

You don't have to remove the carb, just take the top of it off and clean it out with spray carb cleaner.

Works every time...

So, today my new (used) carb arrived. I went to change it out. And, it seems you have to remove the intake manifold?

So, I just removed the top of the carb and sprayed it out good. And, that did the trick! Idles fine now!

Thanks everyone!

Joe

[zenithradio 1]

How I fixed engine idle hunting problem on 1996 520H.

 

 

I belived problem was a lean idle mixture problem. Problem has mostly gone at high

speed and better with choke on. Looking at Onan engine manual (on16_24h.pdf) page 7-4-2

figure 4a Carburetor middle drawing it shows a TAMPER-RESISTANT PLUG OVER

IDLE MIXTURE NEEDLE. I was sure the problem was with this covered idle needle

value.

 

The engine slows down do to lean mixture, then governor speeds engine up

so engine does not stop, then this repeats.

 

The fix is to remove idle needle value, clean, re-assemble and adjust.

 

Remove the muffler to gain access to the right side of carburetor. 

 

Looking at right side of carb on lower left is accelerator pump. Pump is round

and held on with 3 screws. To right of pump there is 2 temper resistant soft metal

round plugs. A larger one above a smaller one. The lower smaller plug is the

one we want to remove.

I used a small nail. Tap the nail into center of small plug making hole. Using nail,

bend to side and pull plug out. In my case plug was very soft and came right out.

 

Remove idle needle valve with small flat screwdriver. Using small spray tube on can of

carburetor cleaned spray cleaner into needle valve hole. Give valve hole several

good shots of cleaner.

 

Clean idle needle valve and re-install. Very lightly turn needle until it bottoms

in hole. Now turn back out (counter-clockwise) 2 turns.

 

The muffler has a bracket on bottom. The bolts for bracket go through part number

113874 Engine bracket (3318-524 Parts Catalog sheet 24). Install muffler, leaving off

the 113874 engine bracket.

 

With engine bracket removed we can run engine and still get to idle needle value

and make idle adjustment. 

 

Start engine. In my case idle was about 2200 RPM with NO hunting.

Let engine warm up. Using a long small blade flat screwdriver turn needle valve clockwise

slowly until idle is about 1400/1600 RPM.

 

Re-install 113874 engine bracket. 

 

I have made this repair on 2 model 520H Wheel Horse tractors, fixed both.