D600 lawnboy mower low idle/surging

[Brybo86]

So i found this on the side of the road. It runs but has low idle speed and surges.
I took apart the carb/airbox and cleaned everything,
The float looked like it had black flaky film coming off of it? The cork was jet black.
I cleaned and gapped plug, but it still sounds the same...?
The idle speed doesn't seem to change when I touch the throttle.



Any hints? Typically surging is accompanied by throttle moving back and forth.... With this surging the throttle isn't moving at all.

I'm thinking float is messed up? But this is the first 2cycle mower ive dealt with

 

[millerbl00]

Replace the float.

 

[xxch4osxx]

Id buy that from you right now if you lived close by!

 

[Panzerman]

I bought one similar at a estate sale for $5.00. I rebuilt the carb and put a new cork float in it. They actually still sell the cork floats. It still does the same thing. I cant figure it out either. All it will do is idle. The throttle must control the governor. I shelved the project for now and I ll tackle it again, when I am bored. The pull starter was broken, I fixed it, it was a nightmare. It was like some Indiana Jones tomb trap device. Make sure you are mixing oil with the gas.

 

[Brybo86]

yeh i have it at 32:1 now, with a little mmo, definitely smoky and some goo from exhaust, yours does the same low speed surging?

 

[hemitom]

Just a thought !
have you pulled the exhaust and cleaned out the ports? known to gum up over time.

 

[Mike72]

To check a cork float, put it in a container of fuel. It should be buoyant and float with just the brass arm tilting it down. If it sinks or is halfway under replace it.

 

[cmhj]

Sounds like it's starving for fuel.

 

[chestand]

In the second half of the video, the lever you're pulling on is the linkage from the governor to the throttle plate. Opening it as you're doing should definintely make the engine speed up. The fact that it doesn't causes me to suspect that that main jet in the carb is plugged up. The first thing I'd do is pull and clean the carb thoroughly including all jets and passages.
Lawnboy's website has a great amount of factory service information on many of their mowers through the years including your D 600 series engine.
https://support.lawnboy.com/portal/server.pt/community/product_center/217

 

[cmhj]

Originally Posted By: cmhj
Sounds like it's starving for fuel.


My how father time has left me sitting. I remember many years ago working on a similar unit with a similar problem for a customer. Problem was ignition, points would miss fire after a certain speed if I recall.

 

[Brybo86]

but this thing is solid state ignition. I adjusted the gap between magneto and flywheel, or whatever its called... didnt seem to make a difference?

 

[Quest]

If it's solid state, there's nothing you need to adjust other than maintaining proper air gap between the flywheel and the coil.

Work on the carb part first.

Q.

 

[PhilsSmallEngine]

The carb jet is clogged, there is too much water in the bowl or the float isn't doing its job and flooding the engine. You don't usually have to order seals when you rebuild Lawn Boy carbs. The only time I've ever had to replace them is through dry rot or I ripped them being careless.

The ignition isn't your first order of business when troubleshooting. The fuel system is. I make more money draining carburetor bowls full of water than I care to admit.

 

[afoulk]

If its surging, my guess is the crank seals are leaking and allowing it to suck air past the seals, causing it to run lean. Its pretty common on older lawn boys. The seals just dry out over time and start leaking.