18hp Vanguard fuel issues

[jayreynoldsii5]

So I have been fighting this **** thing all summer, last year she ran fine all summer. So I keep having issues where it wants to surge and not stay running at low RPM. I have changed plugs, carbs fuel filter fuel pumps.

This is an 18hp Vanguard, it has the 23hp cam and high rev kit, everything else is stock including carb. What is going to be my beat bet to get this thing running right??

[slonomo]

Lots of variables here.

What type of fuel are you using? If you are using ethanol fuel like E10 or E15 pump gas then you could have some ethanol related issues inside the carb.

How old is the fuel? I've had water in my fuel before and didn't know it. Try emptying the fuel and get brand new clean ethanol free fuel.

How old is the engine? Hours? It could be something internal like valves or an intake gasket leak.

How old is the carb? If the carb is older or original it could have some dirt in it. I typically remove the carb, disassemble, soak, and clean all the passages out with small tools for that purpose. Bad fuel, old fuel, dirty fuel can all clog up a passage or two.

Air filter housing? Could have a leaky gasket to the air filter assembly. If the air filter assembly has been changed to aftermarket that can affect things too.

[KOZ45]

Adjust the idle screw to bump it up a tad?

[jayreynoldsii5]

So the fuel is fresh, I have changed plugs, carb (more than once), fuel lines, pick up tube, fuel filter and fuel pump. it will start and idle but at low RPM it spitters and sputters and at high rpm seem to run ok. It has stock carb and air cleaner. I have been thinking of upgrading to either the 2bbl carb or a mikuni.

here is a video of it running.

https://youtube.com/shorts/6h6n0ks1C...SPQTRkNzAjm8-5

[KOZ45]

How do the plugs look when you remove them?

Rich? Lean? Fouled?

[slonomo]

Idle rpm quality is adjusted by the idle air/fuel jet screw. Typically you'll want to get the engine to operating temp. Adjust the "idle speed screw" so it's idling about 1000 rpm or so. Then adjust the "idle air/fuel jet screw" 1/4 turn at a time, give it 30 seconds, see how it sounds. You're looking for it to smooth out and raise in rpm slightly. Keep adjusting until it gets better then gets worse, that's where you adjust it back to where it gets better. Once that's done, adjust the "idle speed screw" until in reaches the desired rpm.

On some carbs, the "idle air jet screw" is hidden by an EPA plug. You may have to remove that plug to get access to the adjuster.

If that doesn't work, you might have some gunk in the idle air jet. It can be cleaned with a small piece of copper wire, it's pretty small. It's common for that to get plugged up.

Also, if you aren't using the original carb that came with the engine, that could be your issue. Amazon and Ebay carbs are crap.