chainsaw won't start and I'm running out of ideas

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If you have not monkied with the OEM carb settings check them and set your new carb to the same.
You might consider re-installing your OEM carb for a test. If it's worse consider installing a kit in the OEM carb if the kit can be had at reasonable cost.
Was the new carb a $10 with free shipping China clone type??? (just curious here)
Chaina is getting better at cloning carbs but I still don't completely trust them YET.
I'm getting ready to go fill the tank with fresh 40:1 to test rupedoggy's settings with a full tank. If I'm still having issues I'm going to put the OEM carb back on and give it a go. The OEM carb has both needles open about 1.5 turns.

I ordered the new carb off of Amazon, it is Chinese made. I went for the most reviews with the highest ratings. I have a carb from this manufacturer on my mower and trimmer that have been working great for over a year so I'm comfortable with them. However, that doesn't mean I couldn't have a bad one. We'll see.
 
yeah I'm also curious on the carb. What part did you use, and was it an exact OEM clone, or slightly different, etc?

when I fixed this P4018WT, the replacement carb had decent reviews on amazon and was cheap, was in a kit with other little goodies that got this saw up and running. everyone said you had to trim the top cover for the throttle linkage. totally true, and it fired right up, tuned easily. the throttle linkage isn't as smooth as the OEM Zama carb, though. I rebuilt the OEM carb later on and may slap it back on, but I gave the saw to my BIL who knows nothing - he hasn't used it much but did just say he "adjusted the screws" so who knows..... maybe he'll destroy it.

Yep, Chinese clone from Amazon. Has good reviews and I've used this brand before with good results. I did have to trim the cover for linkage clearance just as you said.
 
The latest. It will start run and idle with rupedoggy's settings and a full tank of fuel. However, after I shut it down it will not start right back up. It goes back to the flooded condition where I have to pull it 10-20 times with the throttle open to get it going again. This is with the aftermarket Chinese carb. As soon as it cools back down I'm going to put the OEM carb back on and try again.
 
sounds like the new carb may have a stuck or leaking needle valve, allowing fuel to flow in when it's not supposed to.

If it's an OEM Zama carb, rebuild kits should be readily available pretty cheap, and it's easy to do.
 
yeah I'm also curious on the carb. What part did you use, and was it an exact OEM clone, or slightly different, etc?

when I fixed this P4018WT, the replacement carb had decent reviews on amazon and was cheap, was in a kit with other little goodies that got this saw up and running. everyone said you had to trim the top cover for the throttle linkage. totally true, and it fired right up, tuned easily. the throttle linkage isn't as smooth as the OEM Zama carb, though. I rebuilt the OEM carb later on and may slap it back on, but I gave the saw to my BIL who knows nothing - he hasn't used it much but did just say he "adjusted the screws" so who knows..... maybe he'll destroy it.

I know your BIL per your description.;)
 
This thing is going to make me crazy. The chainsaw acts exactly the same with both the OEM carb and the replacement. As soon as I shut it down it goes back to a flooded condition. I need to leave it for a while then come back and give it 10-20 pulls with the throttle wide open. Is there something besides the carbs that can cause it to flood? I did replace all of the fuel lines. They are hooked up exactly like below. The only difference is there was a tiny plastic plug at the end of the fuel return line the appears to narrow that outlet a bit.

Also, I have found that I can't get it to fire at all when the air filter and housing is back on. Seems to me that extra vaccuum created by the filter is causing it to continue to pull too much fuel. I've only been able to get it to run with the filter and cover off.

1592588073042.png
 
This thing is going to make me crazy. The chainsaw acts exactly the same with both the OEM carb and the replacement. As soon as I shut it down it goes back to a flooded condition. I need to leave it for a while then come back and give it 10-20 pulls with the throttle wide open. Is there something besides the carbs that can cause it to flood? I did replace all of the fuel lines. They are hooked up exactly like below. The only difference is there was a tiny plastic plug at the end of the fuel return line the appears to narrow that outlet a bit.

Also, I have found that I can't get it to fire at all when the air filter and housing is back on. Seems to me that extra vaccuum created by the filter is causing it to continue to pull too much fuel. I've only been able to get it to run with the filter and cover off.

View attachment 836922
Have you tried a new tank vent? I have an MS360 that was filling with fuel when sitting after shutting it down. I could see fuel pouring into the carb when the saw was shut off. I removed the vent and it quit. Put a new vent on it, and haven't had the problem since.
 
Have you tried a new tank vent? I have an MS360 that was filling with fuel when sitting after shutting it down. I could see fuel pouring into the carb when the saw was shut off. I removed the vent and it quit. Put a new vent on it, and haven't had the problem since.
Is the tank vent in the cap? I did notice that when I unplugged the supply line from the carb that it squirted fuel.
 
Is the tank vent in the cap? I did notice that when I unplugged the supply line from the carb that it squirted fuel.

Some are, I am not familiar with your particular saw though.

Try to unflood it like you did before, start it up like before and run it for a few minutes, everything you did before, but then turn it off and open your gas cap for a little while, put the cap back on,, and then try restarting it again. If it it starts, I would bet tank vent.
 
Some are, I am not familiar with your particular saw though.

Try to unflood it like you did before, start it up like before and run it for a few minutes, everything you did before, but then turn it off and open your gas cap for a little while, put the cap back on,, and then try restarting it again. If it it starts, I would bet tank vent.
Okay, I'll try that. The OEM cap has a tiny hole in the center with a thin rubber stopper on the inside. I noticed the saw was leaking a bit of fuel through this hole. When I got the replacement carb it came with a new gas cap which I started using. It doesn't have this hole in the center. You may be on to something here. The tank seems to be under a little pressure after running. When I swapped carbs the intake line squirted fuel until I unscrewed the cap.
 
Okay, I'll try that. The OEM cap has a tiny hole in the center with a thin rubber stopper on the inside. I noticed the saw was leaking a bit of fuel through this hole. When I got the replacement carb it came with a new gas cap which I started using. It doesn't have this hole in the center. You may be on to something here. The tank seems to be under a little pressure after running. When I swapped carbs the intake line squirted fuel until I unscrewed the cap.
Good luck. Keep us posted.
 
Don't blame the tank vent, it is supposed to let air into the tank but not OUT of the tank. It is perfectly normal to have pressure build up in the tank and that's why the carb has to be tested to see if it will withstand this pressure. If you pressure test the inlet to the carb, it should hold at least 7 to 8 psi without the inlet valve opening, if it doesn't you are going to have flooding issues.
 
Don't blame the tank vent, it is supposed to let air into the tank but not OUT of the tank. It is perfectly normal to have pressure build up in the tank and that's why the carb has to be tested to see if it will withstand this pressure. If you pressure test the inlet to the carb, it should hold at least 7 to 8 psi without the inlet valve opening, if it doesn't you are going to have flooding issues.
Don't blame the tank vent, it is supposed to let air into the tank but not OUT of the tank. It is perfectly normal to have pressure build up in the tank and that's why the carb has to be tested to see if it will withstand this pressure. If you pressure test the inlet to the carb, it should hold at least 7 to 8 psi without the inlet valve opening, if it doesn't you are going to have flooding issues.
Is there any simple way to test this? If this is a normal condition that means I've got two carbs that are malfunctioning exactly the same way. One is the OEM and the other is an aftermarket replacement.
 
This thing is going to make me crazy. The chainsaw acts exactly the same with both the OEM carb and the replacement. As soon as I shut it down it goes back to a flooded condition. I need to leave it for a while then come back and give it 10-20 pulls with the throttle wide open. Is there something besides the carbs that can cause it to flood? I did replace all of the fuel lines. They are hooked up exactly like below. The only difference is there was a tiny plastic plug at the end of the fuel return line the appears to narrow that outlet a bit.

Also, I have found that I can't get it to fire at all when the air filter and housing is back on. Seems to me that extra vaccuum created by the filter is causing it to continue to pull too much fuel. I've only been able to get it to run with the filter and cover off.

View attachment 836922
Stupid question... Are you absolutely positive that the hose connections are correct? The purge bulb should pull fuel through the filter and then push it back into the tank. You should be able to test this on the bench.

The other thing to check is that the fuel inlet on the carb will hold 7-10 PSI pressure indefinitely. If not you have a needle seat issue. If you don't have a Mity-vac you can use a sports inflator with a gauge.
 
Is the tank vent in the cap? I did notice that when I unplugged the supply line from the carb that it squirted fuel.
With modern saws the tank vent is designed to let air inot the tank but NOT let vapors out so the tank will be pressurized by the fuel. This is why the carb needle and seat must hold against this pressure or it will continue to force fuel into the saw and flood it
 
Stupid question... Are you absolutely positive that the hose connections are correct? The purge bulb should pull fuel through the filter and then push it back into the tank. You should be able to test this on the bench.

The other thing to check is that the fuel inlet on the carb will hold 7-10 PSI pressure indefinitely. If not you have a needle seat issue. If you don't have a Mity-vac you can use a sports inflator with a gauge.
No, not a stupid question. I've gone back and checked and rechecked that as well. It's connected exactly as in the picture.

1592616575823.png
 
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