X575 Hesitation

[psdx]

I have searched using a number of different key words and had no luck in finding anything to help me. Obviously the question is broader than just this tractor, but I found nothing.

The x575 I bought recently has about 300 hours on it. I noticed that the transition from idle to full throttle results in a momentary stumbling - a near stall - unless the throttle is advanced very slowly. This is with the engine warm. I also notice that if I advance the choke lever about 1/3 of the way, that the transition from idle to full throttle is totally smooth - no stumbling or hesitation.

Would this carburetor have a pump that squirts fuel in when there's a big change in fuel delivery? Or does it have a secondary jet that kicks in? Or if not - does it sound like it's running too lean? Or what else should I be looking for?

Everything I have owned for work around the house has been diesel for the last 25 years so I guess I'm a little out of touch on this aspect of maintenance. Any assistance is appreciated.

 

[tomd999]

Hiya,

Not having the machine in front of me this is all speculative.

Most carbs on small engines are 2 circuit non-accelator pump types. (Yes, some have pumps on them but they are the exception)

In order to provide a smooth transition from idle to main circuit the idle mixture needs to be slightly rich to compensate for the fuel falling out of suspension when the throttle is opened and the vacuum falls in the intake system.

Since your has some hours on it, I would suspect your carb has some deposits in the jets and passages and this is causing a slightly lean condition. I suggest that the carb be freshened up by taking it apart, soaking in digestive carb solution and a rebuild kit installed. If you don't have the soaking type solution, spray cleaner works but is not as good and a bit more messy.


So as to what happens during the "stumble" is as the throttle plate is opened rapidly as the hand throttle is opened, the fuel in vapor during idle forms large drops as the intake vacuum level falls and these drops fall to the lowest parts of the intake system and the intake charge entering the cylinders for a second or 2 is very lean, causing the stumble, then as the governor system closes the throttle plate, the engine is able to provide enough vacuum to again suspend fuel vapor in the intake air, the engine recovers and the governor opens the throttle plate slowly to the set point of the hand throttle lever and the engine runs to set RPM. The reason you see black puffs out of the exhaust when the engine recovers is that when the throttle plate was closed and the engine was providing enough vacuum to support fuel in vapor, all the fuel that fell out as drops initially is again changed into vapor, carried into the cylinders as a very rich charge making the black soot out the exhaust.

My 2 cents,

Tom

 

[psdx]

This all makes sense to me. I rebuilt a carburetor in my college car - a Toyota Celica. Let's just say it didn't go quite as planned, but I'm wiser and more thoughtful now, I don't think it will be a problem.

I will take a good light out and hunt for a manufacturer and model # on the carburetor. Maybe someone else could chime in with a good source for a rebuild kit and instructions - or at least a set of exploded diagrams?

 

[beenthere]

You may be one of many victims of the CA carb control regs, as my 425 tech manual shows a change made mid-way through production that in short makes the carb not adjustable except for trained technician. There are limiter caps put on the carb adj. screws.
But good luck with the carb overhaul.
Getting the tech service manual for your tractor should be very helpful. In my 425, 445, 455 manual it shows the parts breakdown clearly. Also has the footnotes about a trained CARB tech necessary if done in CA. We should have buttoned up that group a long time ago. IMO

 

[Gittyup]

JD should have a rebuild kit for it. Just ask them at the parts counter.

You might also try running a can or two of seafoam through it. This might clean it out without the trouble of a rebuild. Might run rough until the seafoam is all burned out. The refill and try again.

Ethanol is ruining carbs all over the country. Everyone should be using an additive.

 

[psdx]

I got the manual. The removal and disassembly look pretty straightforward. I'm a little surprised that the radiator and fan have to come off though. I'm not familiar with seafoam but I'm about to read about it. It's low risk and low cost, so no harm in trying it. I'll let you know how this works.

 

[jenkinsph]

Seafoam may well solve your problems as mentioned above, I would try that first. I use it frequently on my outboard and gas mowers. Marine Stabil goes in all of my gas motors too. Everything else is diesel and I use Power Service with these.