25HP Robin engine surging on PT425

[bol4fun]

I ran out of gas last week, filled it up and it immediately started to surge. I opened the hood and noticed I forgot to put the cap on so that I discovered the problem but that didn't help. I called young son who told me to change the fuel filter. I cussed through that job and finally removed the metal firewall to get my hands in there to change. It has a lot of air in the fuel filter so not sure how to get that out. Son came over and was pinching on gas line from the pump to the carburetor and it started running smooth but the next owning, it was back to surging. I drained some gas out of the tank and blew back into the tank while watching it inside and saw some crap shoot out so it appeared maybe I solved the problem but that didn't help either so am now at a loss. Is the air in the fuel filter causing problems....how to remove it? Don't understand how running out of gas caused the issues??? Any help would greatly be appreciated. Thanks

 

[Tinhack]

Is this fuel injected or carb? Sounds like there's junk in the carburetor--A clogged passage or jet. Or perhaps water that has caused corrosion in the carb. Surging is almost always a fuel supply problem.

 

[marrt]

I've had two of these Subaru-powered PT's. On the first one, the fuel solenoid at the carb leaked or failed and filled the engine with fuel. I took out the engine and threw it away (should have kept it for parts)...replaced with another brand. Filling the engine with fuel is a fairly common occurrence with these engines and it can cause a lot of damage.

I decided to try and save the second one. I rerouted the fuel line and installed an electric fuel pump with an electric shut off valve. I highly recommend this mod. Bought the parts on Amazon. It may save your engine someday. At the very least, it runs better when hot. I can provide part numbers if interested.

As to your specific problem, was the tractor running perfectly before the problem? There are a lot of potential causes for this issue...water in the fuel, dirty carb, air leak, governor out of adjustment, etc... Try adding a little choke and see if it helps. I would normally suspect a dirty carb (I hate ethanol). If you decide to take the carb off and clean it, order the large gasket that separates the carb into two pieces. It will almost certainly need to be replaced. I just cleaned my carb a couple weeks ago and it's a very easy job.

 

[m5040]

If you pinched the fuel line (cut off the pressurized supply) and it ran good, then it might be the needle and seat in the carb, or debris holding it open.

 

[2manyrocks]

My first reaction is that this process dislodged some dirt in the fuel system that went into the carb and is causing the surging, but you also say the surging stopped when your son pinched the fuel line. It could be that your fuel line is shot and leaking air into the fuel line. Pinching might have temporarily helped it.

 

[m5040]

It could be that your fuel line is shot and leaking air into the fuel line.

This could only be possible if it was on the suction side of the fuel pump.

 

[2manyrocks]

Or the gas used to refill was bad.

 

[bol4fun]

I played around with gas supply and blew back into the tank and dislodged some crud from the outlet.....didn't help yet the next day it ran perfect. A week later it started again and removed the gas tank, cleaned out some more crud at the outlet and changed out the tubing but nothing. I finally had my son come over to clean out the carburetor and he found one of the secondary's was plugged some, so put a needle down it and carb cleaner shot it right out. Evidently, some crud got through the fuel filter when I ran it out of gas a few weeks earlier. WHAT A PAIN IN THE BUT. ANYHOW, PROBLEM SOLVED. THANKS FOR ALL THE HELP