Echo cs3400 starts easily and dies quickly; new coil/old coil; new carb/old carb

[Arborist0064]

Push the primer bulb 3-4 times, set the choke, pull the cord; this saw has always fired right up and run strong for what it is. No more, now it fires up and I can keep it running for a while by playing with the choke; choking it when it starts to die and then opening the choke; but 30 seconds is about all I can get it to run. Same result after replacing the coil. Same result after replacing the carb. Initially I replaced the fuel filter, gas cap, air filter and checked the exhaust screen. I'm no mechanic, but recently succeeded in getting the newer of my 026's to run with a new coil. This cs3400 may be 30+ years old, but it hasn't lost power. I'm 70 and she and I haven't seen a lot of action for many years, but it seems we end up renting a lift once a year to do someone a favor for kicks and old times sake to prove we've still know how. But this year I had to borrow a Stihl 201t from a young whippersnapper I know. Every year I rent the lift I think it's the last tree, and then..... So I'm hoping to get my sidekick running again, just in case.
I'm all ears. TIA

 

[Lawless]

I have a 3450 that I really love, we have done a lot of cutting together.

It sounds like the carb is gummed up. You can seat the screws making careful note of where they are set (like 1.25 turns) and then remove them. Spray some carb cleaner in the bore the screws came out of a few times and let it dry. Reinstall screws and try it.

If it is worse it may need to be disassembled and cleaned.

 

[Arborist0064]

Thanks for the suggestion. I took the old carb apart and cleaned it; though not the adjustment screws. That didn't change anything. It now has a new carb installed and that doesn't change anything either. I'm going to replace the plug next, though the present one looks fine. I think I'll start it then pull the plug after it diesto see if it has any fuel on it. Then I'll replace the rest of the fuel lines, ugh!

 

[isawben]

If you have a pressure-vac tester you might check for an air leak around the crank seals, especially clutch side.

 

[Lawless]

I wonder if the reed valve is bad?

https://www.ebay.com/itm/164056913081

 

[cdherman]

If it runs just 30 seconds, then dies, and can be "babied alone" for a while longer, then its a fuel issue. Your primer bulb is getting enough fuel in the right places to start, but then something is awry with the continuing fuel delivery. That's what I think I know, but what your next step it, beats me.......

 

[Arborist0064]

I wonder if the reed valve is bad?

If you have a pressure-vac tester you might check for an air leak around the crank seals, especially clutch side.

I wonder if the reed valve is bad?

https://www.ebay.com/itm/164056913081

Thanks for the suggestion. Thankfully I don't "need' this saw desperately. This may turn in to a winter project in the backroom of my garage. I never felt bad when my Homelite XL's or Super @'sgave up the ghost. They just went in the spare parts bin. But this saw has been so reliable I'd like to put it my will still running.
https://www.ebay.com/itm/164056913081

If you have a pressure-vac tester you might check for an air leak around the crank seals, especially clutch side.

Thanks, I appreciate the input. I've tried YouTube and those vid's always seem to be about straightforward issues.

 

[mowerman]

I've seen small wood chips get stuck in the reed valve, holding it open. That might be all that's wrong.

 

[samaritan]

I've seen small wood chips get stuck in the reed valve, holding it open. That might be all that's wrong.

If you have a pressure-vac tester you might check for an air leak around the crank seals, especially clutch side.

Also, check or just replace the gas tank vent

 

[samaritan]

Here's something that might help you

 

[Old2stroke]

Sounds like your fuel pump isn’t working. How does the impulse signal get to the carb?

 

[leaf]

Yuh, Old2stroke would seem to be providing the most likely suggestion. You get gas in the carb with the primer bulb, but the impulse line isn't taking over and getting gas into the carb after that. Impulse lines come from the lower cylinder (where there is heat) and often cross the "anti-vibe" setup. Definitely look for pulses on the impulse line (and do a pressure/vac test). Thus, they easily crack. Cracks in impulse lines can be hard to see.

 

[lone wolf]

Thanks for the suggestion. I took the old carb apart and cleaned it; though not the adjustment screws. That didn't change anything. It now has a new carb installed and that doesn't change anything either. I'm going to replace the plug next, though the present one looks fine. I think I'll start it then pull the plug after it diesto see if it has any fuel on it. Then I'll replace the rest of the fuel lines, ugh!

You can pressure test the fuel line .

 

[leaf]

Not exactly. There are basically two lines that go to any chainsaw carb: 1) fuel line 2) impulse line. The fuel line can be tested just by determine whether fuel is going through and not leaking out. The impulse line operates what is called the "pump diaphragm" on the "pump side" of the little cube block which is the carb. It just moves little bits of pressure to flex the diaphragm. It has to be "leak" / "pressure" / or "pulse" tested.

 

[lone wolf]

Not exactly. There are basically two lines that go to any chainsaw carb: 1) fuel line 2) impulse line. The fuel line can be tested just by determine whether fuel is going through and not leaking out. The impulse line operates what is called the "pump diaphragm" on the "pump side" of the little cube block which is the carb. It just moves little bits of pressure to flex the diaphragm. It has to be "leak" / "pressure" / or "pulse" tested.

Presure test them for leaks the check pulse with vac testor.

 

[mowerman]

The cs3400 does not have a impulse line. The carb is attached to an insulator block(which has a reed valve on the inside) that is attached to the engine. Leaking gaskets will mess with the impulse signal. Many times I've seen similar problems with things keeping the reed valve open. If you take the carb off, then the insulator block you can check both gaskets and the reed valve. The fuel check valve can be bypassed by cracking open the gas cap carefully to see if that makes any difference. I don't think I've ever had a problem with crank seals. Sometimes The exhaust port gets restricted with carbon buildup. That is easily check by removing the muffler. You can also see the condition of the piston rings then. This saw is one of my favorites, there are many versions but all have the same fuel design. I hope you get it figured out. I'm betting its something in the reed valve that just need cleared.

 

[Old2stroke]

Are you getting a lot of spit-back from the carb? That's a good indication that the reed valve isn't closing properly but even so, since the saw fires up and runs good briefly (just long enough to drain the fuel chamber), it should continue to run if the chamber was being filled by the fuel pump.
Too often on saws that conduct the impulse through the carb base, I have seen the base gasket in wrong and blocking the hole that the impulse comes through.

 

[Kenskip1]

Seeing as how this is winter how about making adjustment for the colder conditions. As we all know from our reading that cold air is more condensed than warm air. If the air is now condensed then we need more mix to compensate. simply richen up both high and low sides of the carburetor.