2 stroke carb question

bertsmobile1

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I did an overhaul on the carb tonight. I had a spare matching carb body that I knew was in good shape so I cleaned it again and swapped it out. I put in another new diaphragm and both gaskets. I replaced the fuel lines. I started it up and again it ran strong at first but quickly started to choke out. When I pointed it up in the air it would run good again. So based on that I'm confident this is not a carb issue.

I'm guessing now that perhaps the rubber grommet that the fuel lines pass though is not sealing well. When I tilt the blower up the grommet is submerged in fuel and that's when it runs smooth. When I lower it the grommet is exposed to air inside the tank. I haven's seen any fuel leaking from the grommet but I can't imagine what else it could be. I have replaced that once before. It's a three hose grommet with the third hose going to what I guess is an air check valve. I'm going to replace that and see what happens. It looks in good shape though.

Side note...when I was cleaning out this second carb body I blew out the small screen on the flip side of the needle valve. I was going to replace it with a spare I had but I forgot. If I leave it out am I asking for trouble or would it be alright to run it without it. I've pulled that carb apart about a dozen times now and I'd really like to avoid doing it again if possible. I'm pretty cautious about clean fuel and I've never seen a dirty screen in any of my equipment. I was going to leave it and if the carb fouled up because of it I would just pull it off and clean it then, hopefully a long time from now. Am I crazy for even thinking that?

You bet you Charlie you are asking for trouble without that screen.
You have seen how fine those holes are.

As for the problem, good chances you have a split in the hose just where it goes through the grommet.
OR
You have the feed & return tubes transposed.
The return hose goes about 1/4" into the tank past the grommet.

Take the tank cap off and pump the primer.
You should hear the returning fuel "peeing" into the fuel tank.
If not, or you hear it "blowing bubbles" then the intake and return lines are on the wrong carb spigots.
Don't feel silly, we have all done it before.
 

arch252

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You're right, guess I'm breaking it down again tomorrow to put that screen in. I have double checked the hoses, the one closest to the primer bulb is venting back into the tank, the other is connected to the fuel filter.
 

bertsmobile1

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You're right, guess I'm breaking it down again tomorrow to put that screen in. I have double checked the hoses, the one closest to the primer bulb is venting back into the tank, the other is connected to the fuel filter.

That sounds right so looks like you have a hole or split in the fuel pick up hose.
They tend to go hard & crack just past where they exit from the tank grommet inside the tank.
Echo make a complete replacement set, both hoses, the filter & grommet which is the easy & safest way to go.
If the fuel line is hard & cracked then the grommet will not be pristine either.
If you are not intending to replace ht grommet then do not remove it as old ones rarely reseal properly.
Use Tygon fuel line, should cost $ 2 to $ 5 for the 6" length you will need.
Just make sure it is the right size.
Supply tube is heavy walled to prevent the tube collapsing onto itself.
Return tube is thin walled.
 

Lawnranger

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I have an Echo PB-2100 leaf blower that I've had for a LONG time, she's been good to me.


The fuel lines are in very good condition, replaced not long ago. It has a new fuel filter and spark plug. I've blown air into the lines to see if the lines were cracked or had a pin hole but found no leaks.

Since you have had this machine for a LONG time, you will need to perform a few advanced diagnostic tests to verify the integrity of the fuel lines, carburetor and crankcase seals. Using a pressure pump and vacuum pump test each fuel line and the vent itself. Test the fuel lines by plugging one end off and install the pressure/vacuum pump in the other end. Pump up to at least 5psi and watch pressure gauge for any drop. Repeat with vacuum. Test the vent by applying pressure - pump to 5psi - should drop to about 1.5psi and hold. Repeat with vacuum and should not hold any vacuum. I'm not saying this is the problem because nobody knows at this point but you need to test & verify the involved systems.

Since you said the fuel hoses have been replaced not long ago, I don't suspect them but I do test and verify everything. Do not assume the fuel lines are good just because you replaced them not long ago.

Look up Joe Pace on youtube, he has some good instructional videos on how to pressure/vacuum test the entire system. Use "Joe Pace pressure test" in the search box - more than one Joe Pace on youtube

When it comes to chainsaws, sometimes the engine will die when turned on its side and this is usually a leaking crank seal. If you watch all the videos you will learn how to test primary compression and vacuum to verify crankcase integrity. When dealing with an engine this old anything is possible and you need to verify every aspect of the machine.

If you don't have the necessary test tools and/or you can't acquire them, it may be time to retire your blower and purchase new - your decision. You could spend the money on a new carburetor but if that isn't the problem then you are throwing good money after bad.
 

arch252

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I haven't considered all that, and that's a little more advanced than I'm capable of. I have a local small engine shop where I buy a whole lot of parts and I'm pretty sure I could get the to check that for me. Thanks for the info
 

arch252

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Those are great videos. Time to buy a tester.
 

arch252

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I have it running fine now and I hate to disappoint but I can't give you clear feedback on exactly what the problem was. I bought the fuel line kit which contained the fuel cap gasket, new primer bulb, new fuel filter, new check valve, new lines and new grommet. That solved the problem. It already had a fairly new primer bulb and a new fuel filter and lines so the problem was apparently a bad seal in the fuel cap, check valve or grommet. I appreciate everyone who chimed in with suggestions. I learned a lot with this. Enough to reaffirm my disdain for two strokes!
 

arch252

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On the bright side, I now have a REALLY clean carb!
 

Lawnranger

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Most likely a leaking fuel line. Pressure & vacuum testing the lines would show you the leak. Good for you that the blower is running again.
 
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