Scag Rough Idle

[Green_Will]

I just bought a 48" Scag hydro W/B. It has Velocity deck which makes it at least an '06 if my info is correct. It ran great first few times I ran it, but I started it the other day and the idle has turned rough. Almost a repeating "surge", not a steady idle. When I throttle up the pattern happens faster. I changed plugs, fuel filter and hose.... No change. I'm seeing some black smoke puffing out on start up also. Plugs were dry, but obviously old. Could you guys help me out?

[weldondl]

When posting a thread about the problems you are having with your equipment:

Please give a full and accurate description of the problem you are having and what you have already done to correct the problem. It will also benefit you to post all model and specification numbers off your equipment.
Machine problem - machine numbers.
Engine problem - engine numbers.
This will aid in letting everyone know exactly what equipment you have and to give you a quicker and more accurate response to the problem at hand. We do have some Service Technicians here on Lawnsite and some have Technical Support at their fingertips but need model numbers to access proper information.
Thanks For Reading.
Good Luck

[Patriot Services]

Not knowing how long it sat around, I would bet a thorough carb cleaning will fix your problems. Check the mounting gaskets and intake block too for possible vacuum leak. Black puff on startup is normal especially if you have the choke on.

[Green_Will]

Copy that! Thanks for the input. I'm just getting started with a commercial mower and the deal turned out to be a little shady. I just don't want to get it out mowing and make a potentially small problem into a big (expensive) one. I appreciate the feedback very much. I will provide serials next time.

[Green_Will]

I don't have serials for the engine unfortunately. Mower is SWZ - 48V17KAI. Serial is C1000... . I bought the mower from a private seller, and it showed signs of having sat... Hydraulic filter had flaked paint and rust, tires slightly dry rotted, etc. What confuses me is that it started, idled and ran nice and smooth. I ran it at idle twice on and off for thirty minutes during the week to adjust the tracking, neutral, etc. and the following week the rough idling started.

[Green_Will]

Could you go into a little more detail on what you mean by "carb cleaning", Patriot Services?

[Patriot Services]

Originally Posted by GreenWillowLandscapes

Could you go into a little more detail on what you mean by "carb cleaning", Patriot Services?

Sure. I have the 19hp version of that engine on a Cub. Just unbolt the carb and disassemble it. Chances are the float bowl will be full of a sandy grit. Use spray carb cleaner to flush out every passage. Replace the float, needle and seat. Reassemble and reinstall. Should run like new. Carbs really dont like to sit with todays fuels for extended periods of time.

[Green_Will]

Great! That helps a lot. Thank you very much!

[The Lawn Ranger CT.]

I agree with Patriot on checking the "mounting gaskets and intake block too for possible vacuum leak".~ While the engine is running on idle and surging spray some carb cleaner around the intakes where they enter the head , if the idle increases then its the intake mounting gasket... I had a few of these go and cause the same issue~

[Green_Will]

Copy that. Thanks Lawn Ranger.