Help with Carburetor

[Homebrew]

I'm hoping you guys can help me out. I'm not much of a mechanic and I'm trying to troubleshoot my PT425 w/ Robin engine. It started sputtering and now it won't start. I replaced what looked like a dirty fuel filter and fuel was flowing through that. I thought it might be the fuel pump, but after pulling the fuel line at the carburetor and cranking the starter, fuel seemed to be flowing fine from the pump. However, not much fuel is getting into the carburetor. I took the air filter housing off, and fuel appears to slowly leak into the carb if I don't turn off the inline fuel shutoff valve and let it sit. The PT will start for just a brief time then sputter out after all the gas in the carb is used up and very little appears to be pumped in. After reading this forum, sounds like I need to do some cleaning of some jets? But I guess I'm too dumb to figure out how to get the top part of the carburetor off. I've only had time to mess with it briefly, but I removed the 5 (or was it 6?) small screws, but it didn't seem to want to budge. I was afraid to beat on it any in case I was missing something. Any advice on how to get started?

 

[elderlyphart]

Check out this thread-> the saga continues... PT-425 engine problem at 10 hours?
I posted quite a bit of info on that carb there.
The top of the carb has a clearance problem coming off. You will need to remove one of the thru bolts (that hold the whole carb on). Can't remember which one or if it makes any difference. Then need to rotate it a bit as it comes off to get the linkage to not bind.
Anyway check that thread. I posted a lot of the info you are after.
Don't get all ham fisted.

 

[Homebrew]

Thank you! I'll report back after I've had a chance to work on it again.

 

[elderlyphart]

Back from town and more time to look at this problem.
It sounds like a bad accelerator diaphragm.
Reason I say that is...
You say you see gas slowly leak into the carb if you don't turn off the shutoff. You should NOT see any gas leaking into the carb at all. I am assuming you are seeing the gas dribble in the "throat" of the carb. You will not be sure how much gas is in the float bowl unless you get the top off.
A ruptured diaphragm will drain all the gas in the float bowl into the engine. NOT good!
When you start the engine it will run OK until the float bowl refills. Then gas from the normal jets PLUS the gas from the ruptured diaphragm will make it run way rich and stall the engine. Check your plugs. Black and wet/ black soot = way rich.

So it would be just the opposite of "sputtering out after the gas in the carb is used up". These freeking motors can fake a guy out! Been there done that a bunch of times.

Simple to check the diaphragm. Read my post in the other thread and pay attention to the parts diagram and which is the VACUUM line (which should never have any gas in it. Just vacuum air.) The other line is the discharge line the gas goes through when it's needed.

Info -That accelerator diaphragm is there to supply the engine with a momentary shot of extra gas when you slam the throttle open. If it don't work you will get a momentary bogging down when you try to accelerate.

Slow and steady. Pay attention to what you are doing and re read if necessary.
Gotcha all confused now?

 

[Homebrew]

Well, I could be a little confused. LOL.

A couple of things. When I see gas in the carb...it's shining a light down into the bottom. Is this the throat? It's all metallic shiny after it sputters out, but then I see stuff slowly seeping in.

When you say nothing should leak into the carb...I thought with a slightly dirty needle float and no shut-off valve (or an open one) that you'd see gas in the carb?

And finally, the oil level seems constant and doesn't smell like gas. Wouldn't this indicate no gas leaking into the engine?

In any case, thanks for taking the time to post more info. I will most definitely check out the other thread again and check all that you mention above.

Much appreciated!

 

[elderlyphart]

Yes you are looking down the "throat". You see the throttle valve at the bottom in the closed position. It opens as you open the throttle.
If you had the top off you would also see the float bowl where the gas is held and the float and float needle, jets etc.. That float needle would be the next place to check if the diaphragm checks OK. As well as the jets (discussed in the other thread.)
So if the top is on the carb you should see no gas. Unless the engine IS running. Then you would might see some spray down the throat.

Anyway, if the engine is not running there is no gas being pumped (unless you have an electric fuel pump).
So if you are seeing gas seeping in it will be coming from the float bowl.
The acceleration diaphragm sits next to the bottom of the float bowl.
If the diaphragm ruptures gas from the float bowl will go through the torn (ruptured) diaphragm into the vacuum side down the rubber tube into a vacuum port which is located right at the throttle valve where you are seeing stuff (gas) seeping in.
It will seep in till it empties the float bowl.
If you didn't close the shut off valve gas will gravity feed into the float bowl and on into the engine. I think you are closing the shut off when the engine is not running so you are not loading your oil with gas. What little you do get in there is probably vaporizing off when the engine is running.

A leaking float needle will cause the engine to flood out and stall. But it would not cause gas to emerge down by that throttle plate. (Throttle valve) Or whatever Suburu calls it...
Thats why I think you have a bad diaphragm.

Slow and easy does it. Re-read until you have a good grasp of it. Make notes how things came apart. I still do if its something unfamiliar. Also if some jerk sez a good mechanic don't need no stinking book to fix something, run! I'm always looking in books. Clearances etc. I can't remember all that crap. I need my book!
Refer to that parts diagram in the other thread.

 

[elderlyphart]

Here is a picture that might help. After running the engine so the float bowl has gas in it, immediately pop that vacuum line off.
Gas? Ruptured diaphragm!

 

[Homebrew]

Okay, I may have made one step forward and two steps back. I got the top off the carb and there was indeed gas in the bowl. I took the little jet out and blew air trough it and through the hole it was threaded into. I took a look at the diaphragm itself and it looked intact (this was before I saw your last two posts). After reading your posts, I tried what you said. Note that the tractor wouldn't ever really start, but the bowl was full when I took the top off the carb, and no gasoline came out the vacuum line.

Perhaps my biggest problem is that I did get a little ham fisted perhaps. I thought I bent the little copper line coming out of the carb top as it had a slight angle on it. I believe it is the nozzle from the diaphragm. Well, I thought I'd put just a little pressure on it and see if it felt like it wanted to bend back straight. I broke it off.

I assumed the acceleration diaphragm would still spray gas, just maybe not optimally. I put everything back together and it still wouldn't start. Then I unscrewed the solenoid where it looks like the main jet is in the diagram. Some gas poured out, and I the little plunger on the solenoid seemed to move freely when I pushed on it. I put it back in and it didn't start the first crack. I sprayed a little carb cleaner into the throat and tried again and it started up. I let it run for 5 minutes or so while I put the air filter and housing back on. Then I ran it for maybe two minutes on a flat surface and it sputtered out. I got it started again, but the only way it would run was with full choke. After a minute of that, it sputtered out again, and I couldn't get it started.

So, now what? Is the accelerator diaphragm nozzle a big deal? I kind of thought it might sputter when I started forward if the nozzle wasn't spraying properly, but it didn't seem to.

And I'm not sure where to go from here.

 

[elderlyphart]

Oh boy, runs with choke on. That would mean way lean instead of rich.
See that wire coming out of the solenoid? That has power when the key is on. No power - no gas through main jet. Check power with a test light or meter and wiggle wires to check for an intermittent connection. Make sure solenoid retracts when key is on.
May have to tear the carb apart to find problem / clog.

I think you are talking about the bent copper tube that the rubber line from the diaphragm plugs into. The UPPER line. That is the line the gas shoots through when you apply throttle.
If it is broken gas is going to spray where it should not spray. FIRE- RUN FOR YOUR LIFE! Change the word optimally to internally. It will still spray gas, just not where it should be sprayed. Gotta fix that for sure.

Check the spark plugs. Black or more lite brown/white? Reading a plug is tricky but we are just interested in to little/to much gas going into the cylinders.

You say you started it on carb cleaner and it ran good for awhile then sputtered out.
That sounds like a bit of crud blocking the main jet and the other jet you blew out. You blow it out and the crud sits in the float bowl for awhile then wanders back into the jet. Not uncommon at all.
In that case you need to pull the float out to get into the bottom of the bowl and clean out any crud you see. The tiniest bit of crud can block that slow jet. Look at the hole with a magnifying glass. Be sure it is clear. Blow out the hole down to the main jet. Look in the bottom of the float bowl for any bits of crud and clean it out.
It can run good for awhile and clog up again. If it does run longer you know you are on top of the problem.
Hang in there.

 

[Homebrew]

Thank you so much for your help and encouragement. I learn a little something every time I dig in.

One thing I did do was lay the solenoid out and turned the key. I saw no discernible movement of the plunger, so you may be onto the culprit. I forgot to mention that, but wasn't sure if I'd be able to see any movement. Is it possible that it's dead (or no power as you suggest) and when I stuck it back in it stayed open for a bit before slowing creeping back out and sticking? I guess I need to test it out in any case.

Okay...so I need to replace the accelerator spray nozzle. It seemed like that copper tube might have been integrated into the top piece of the carb. Guess I'll have to dig around and figure out what to order to get that replaced.