Robins 25 HP Surging

   / Robins 25 HP Surging #1  


Jul 18, 2016
Fort Dodge, Iowa
PT 425
Took out the 425 to acreage today to spread out two trucks of gravel on my mud road. Before I left, I greased it up, cleaned the air filter and topped off fluids. I used it yesterday and it ran, it was constantly surging unless I was using the treadle in forward or reverse???? When I blew out the air cleaner, I didn't wash it or oil it up and since it was pretty dirty, I noticed some dirt drop into the carberator so I got the vacuum out and vacuumed it out hopefully. At the acreage, I double checked the engine oil and noticed that it was overfilled so I hit up the neighbor for some tools to drain some out. I PUT a small amount in before I left and obviously read the dip stick wrong. I drove back into town for dinner and googled mower engine surging and saw there were a bunch of things that can cause this and am racking my brain to figure out what I did to screw it up. I oiled up the air cleaner element when I went back out, I checked the gas cap (looked OK.... is there any way it can go bad). Anyhow, short of taking the carberator apart (which I have never done), I'm not sure what to do next. Any suggestions?
   / Robins 25 HP Surging #2  
I double checked the engine oil and noticed that it was overfilled so I hit up the neighbor for some tools to drain some out. I PUT a small amount in before I left and obviously read the dip stick wrong.

You didn't necessarily read the dip stick wrong. When the engine is off, if the carburetor float sticks or debris clogs a jet, the carburetor bowl will overflow and gasoline will drain down the crankcase ventilation tube and dilute the motor oil in the crankcase.

Robin specifications require a shut-off valve between the fuel tank and the engine to prevent this, but Power Trac chose to ignore that requirement. Many people on this board have reported having this problem.

I would drain and refill the oil, hit the carburetor with some carb clean while it is running; if that doesn't solve the problem, then you need to clean the carburetor the old fashioned way.
   / Robins 25 HP Surging
  • Thread Starter
I bought mine early last fall so it has the shut off valve at the gas tank.... I haven't been using it lately cause I have been using it almost every day and assumed this was more of a storage feature. Now that you have told me this, I will start using it daily. I need to change the hydraulic filter for my 50 hour so I will go ahead and change oil and filter on the motor also. I missed Terry's call Friday about changing the hydraulic filter. I was very confused from the diagram's in their book because they don't look like the components on my newer model. I found a valve with a cap on the end of it and I am assuming that is what I hook my hose to but wasn't sure.
I was planning on disconnecting the spark plug wires, wrestle the old filter off and put new on, hook up the supplied hose to the place I found the cap, put the opposite end of the hose in the hydraulic tank, cranking it a few times making sure fluids were shooting into the tank, and then capping it and replacing the spark plug wires. I have never bled anything in my life with the exception a few of my limbs requiring stitches so I want to make sure I do this right the first time. For those of you that have done this several times, it sounds like it is fairly simple.
Any pointers in getting the old filter out, how you deal with leakage (cardboard where) and anything else in this process would be appreciated. I have a lot of hours to put on it this weekend and I am sitting on 49.5 hours on it now.
   / Robins 25 HP Surging #4  
MR did a get write up on the filter change a while a search on this forum to find it......I got a vinyl covered strap wrench to remove the filter as it's the only thing that worked for me......for spillage I put a couple of paper towels down and a plastic bag underneath it to catch the oil but I think I have more room to work inside the tube then the low boys do.......I did find that I do need to crank the filter on tight and periodically check it as it has loosened up on me a few times.........Jack
   / Robins 25 HP Surging #5  
Try these suggestions.

Surging is indeed a symptom of lean running. Make sure you didn't disconnect any tubes that might create an intake leak. If you pull the carb be careful to mark the float bowl orientation before you remove it. Before you take the float bowl off drain the fuel from the carb, connect a piece of tube or hose to the fuel inlet, and blow in it with the carb upright and inverted to see if the needle valve is working. You should be able to blow into it with the carb upright and should not be able to blow into it with the carb inverted. Be aware the needle valve will fall out when you pull the pin holding the float. Pay attention to how it fits together before you pull that little pin. If you unscrew the main jet to clean it get a screwdriver that fits it as perfectly as possible. They are made of brass and are easily damaged. Turn the carb upside down and check the float level before you pull the pin. The top of the float should have an even gap all the way across and be even with the gasket surface for the float bowl. If it isn't and it has a metal float you should be able to bend the tab and correct it. If the float and tab are plastic it is not adjustable.

I am not familiar with this machine or engine but I recently put a carb on my son inlaw's Robin in his golf cart. It had the wrong carb put on from a previous repair and had always run rich. The new generic carb was running lean and had the float adjusted wrong.

If the engine has a fuel shutoff solenoid those can fail and cause the float bowl to overfill when sitting. The overflowing fuel actually goes into the cylinder and past the piston ring end gaps to cause the engine oil to become diluted and overfilled. A stuck needle valve can do the same thing. This usually causes a rich condition and flooding. As the oil becomes diluted it runs past the valve guides and into the combustion chamber.

It's always been a mystery to me how it gets in or past a fuel filter but I have found bugs stuck in needle valves on more than one occasion.

I have a lawn tractor that I have put 3 different gas caps on and despite using ethanol free gas the gaskets deteriorate and fall into the tank. That can clog the tank outlet and prevent the carb from getting enough fuel. Another possible cause for a lean condition and surging.
   / Robins 25 HP Surging #6  
When you do your purge with the spark plugs disconnected and hose submerged, you crank the engine with the key.... most people know but I'm gonna say it anyway, don't crank it for too long at a time, like maybe 5-10 seconds at the most, then shut it off and wait a good 4-5 minutes, then crank again, wait, crank, wait, etc.... till no bubbles coming out of the hose in the tank. You don't want to crank the starter too long or too often to avoid heating the starter up too much. Other than that, I think you mentioned everything.

As for the oil filter on the engine, all bets are off as to the mess. There shouldn't be too much of a mess at all on the engine oil filter, because it drains down when you shut down the engine. Just put a wad of paper towels under it before you loosen it and observe any leaks as you slowly loosen it. You can try putting a plastic baggie around it once you break it free, but again, there shouldn't be too much on that filter.

The hydraulic filter, I've had great success with putting paper towels under it, cracking it open just till it's free, slip a quart-sized zip lock freezer bag (the heavier plastic) over the filter from the bottom, then remove the filter the rest of the way. Works great!
   / Robins 25 HP Surging #7  
I just bumped up a 422 oil change thread in the PT forum. Might be some good info in there for you, too.
   / Robins 25 HP Surging
  • Thread Starter
After a quick rundown from Terry, I changed the hydraulic filter today with some help from my son. He told me to connect the supplied hose to the gold hex cap on a tee on the left side of the main hydraulic pump hooked to the motor. Only problem was that mine wasn't a tee and had a silver colored cap so he said that must be the right one. I REALLY didn't notice much for any air bubbles in the reservoir so I cranked the motor at 5 second intervals about 6 times resting before each try. It all works so must have done it right. My son took the carburetor off and cleaned it up with cleaner so no more surging.....yehhhhhh. We did end up having to put a self adhesive cork tape around the filter to get the 1/2" socket wrap wrench to bite. Without the tape.... the nylon strapping just kept slipping. I can really see how much easier it will be from now on with the learning experience we had today. The gallon zip lock bag also was a blessing.....not a single ounce of oil was spilled.
After that, I decided to take the covers off and grease the steering zerts. Only problem is there wasn't a front one and there was grease all over. Not sure if it vibrated loose or it never had one....anyhow, picked some up on the way home from work. They are one thread longer so hope the will work fine on the PT. The other thing I found after taking the covers off was that one or more of the hoses coming down that center behind the steering wheel are leaking. I pulled the cover off the front of the PT steering wheel and found where to tighten them but need some advise how to do it. There sure isn't a lot of room in there and taking it all out by removing the 4 bolts on top look like a real PIA. Does this require specialty wrenches like shorties and crow foot wrenches or even something else? Thanks for all the input are great.
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   / Robins 25 HP Surging #9  
Glad you got the engine surge resolved.

As for the leak from a hose at the steering valve..... good luck. Seriously, it's about the most confined space there is. I took it out once and I had to start at the front, label a hose and location, remove that hose, move on to next hose. Repeat, repeat, repeat, repeat..... until I got to the last hose.

As I recall, I tried removing the top plate and lifting it out from the steering wheel side, but the hoses were too short to let the valve come out from the top enough to get to the bottom of the valve to remove/tighten the hoses.

Just clean everything really well before you start. I'd also suggest you DISCONNECT THE BATTERY at the battery terminals before you start, because, with any luck(like I had), you'll touch the hot terminal on the ignition switch with a wrench while squeezing around in there and that big spark is always good for a busted knuckle as you yank your hand out of there. ;)
   / Robins 25 HP Surging #10  
X2 on the steering hoses being the tightest fit. I have a set of offset wrenches from HF that are 15degrees or so off from each other, so by judicious baby steps, I can get the hose tightened. I have only had to do it three times; once just after I bought the tractor, once again about a month later to replace the broken fitting (Terry was kind enough to replace it under warranty), and one more time as the replacement hose settled in.

And it is not just that the knuckle space is tight- there is almost no comfortable position to be while working on it.

Oh, yes, x2 on the battery tip. I have done it twice, and it scared the daylights out of me both times.

All the best,