I am stumped. I have an Echo SRM-225 string trimmer. Issue is that under full throttle, the engine would start to get bogged down and ultimately quit. This only happens if trimmer is held as if trimming grass (fuel tank down and engine up). If you rotate trimmer as if edging (fuel tank is up), runs fine. Even if it was bogging down, you rotate, it will clear up and run fine. Also, if its bogged down, you open the fuel cap, all good. Also, if its bogged down and you remove the vent off the tubing, all fine. Seems like a classic case of plugged vent. This is the 3rd or 4th vent I tried. At least 2 of the new vents were part of a new refuel kit (fuel lines, grommet, vent, fuel filter etc..).

I even tried a couple of other carbs. Chased down orientation of gasket between carb and engine block. Checked exhaust screen (ran without muffler on but still bogs down eventually).

Typically on cold start, I can get it to run at full throttle for a few minutes (hold the machine with engine is up and gas tank below) before it bogs down. I can then either rotate the machine, open the fuel cap or even remove the vent off the line to get it to run fine. I then rotate back and bogs down in 10-15 seconds.

Not sure what else could be the problem. Any thoughts/ideas would be appreciated.

 

Could be a weak fuel pump or partially plugged filter. Did you put new carbs on it to test or just some used jobs off the shelf?

 

Brand new card - OEM (ie Zama) as well as a cheap knockoff from Amazon (Hipa). Same results. The fuel filter was replaced many times with the change of the fuel lines/ grommet.

Does not seem carb related.

Drilled hole in one of the vent filters and runs fine, except of course now gas can leak out of hole. Took a vent filter apart as well an only a rubber check valve. Not sure if issue is build up of pressure or if creating vacuum in tank. Have to check more.

If leave gas cap loose, remove vent filter, or rotate upside down all fine. I thought i might be fuel pump due to upside down so that is why chased gasket between carb and engine. It can go on two ways and different holes cover over. No change either way.

 

Is it possible it doesn't have the right fuel cap or the cap is not venting. Have a good one. Geo

 

Thanks. It isn't cap related. Venting is not done through cap on these. There is the vent filter.

 

The vent lets air in but not out. Can you draw air through the vent yourself?

 

Yes verified on the last one before installed that I can suck air through to let air in. This last one is the 4th brand new one as well.

 

I have a blower in the shop I have not looked at yet, complaint was it was blowing fuel out. First look noticed the grommet to the fuel tank and lines blown and leaking so I ordered a fuel system repower kit. Echo #90028... I think.
Since the vent lets air in, the cap or some other must be able to let air out...this is my thinking at this point but will update once I have a look at it. The vent should actually work both ways on these so the tank is not constantly under pressure from Priming.
It is also possible the vent is meant to let air both in and out and could be a defective run of filters, you might try a regular fuel filter in place of the vent filter and see what that does.

 

Nope, it's just meant to let air in, nothing to let it out. It's a duckbill rubber check valve. You can actually pressurize the tank a little by priming quite a bit but as the engine uses fuel, it will soon return to a vacuum situation (not really a vacuum, but a lower pressure than atmospheric).

It sounds like either your port that operates the fuel pump diaphragm is partially clogged with carbon and not pulsing pressure enough to operate the pump well or that pulse pressure is leaking out due to a gasket problem or bad intake insulator, or there is a design flaw.

 

Hi Cheese. I was thinking along those lines (obstruction to proper operation of fuel pump diaphragm). This may also explain why when I rotate the trimmer essentially getting fuel tank above the engine (carb), it now runs fine - fuel pump does not have to work as hard to get fuel into carb - gravity is taking care of this. This is why I was chased down the gasket between carb and engine. There is one small hole on the intake insulating block but does not seem it lines up with anything on carb. I believe the correct orientation of the gasket simply covers this hole up. I rotated gasket to line up a hole in gasket with this opening (nothing lines up to this hole on carb side though) with same results.

What/where does the fuel pump diaphragm get powered from?

I have had this trimmer for about 5 years and its worked fine so have to rule out design issue. I have tried many of the vent filters (different sources) so have to rule out a bad batch of vents. Tried 3 different carbs (borrowed one off another functional echo machine, brand new OEM and brand new knock off) with all the same results so have to rule out anything on carb.

 

I assume the pulses from the engine to operate the fuel pump diaphragm are are coming through the intake insulator. This has one small hole and is not symmetric to the rest of the insulator. I flipped the gasket to match the hole with no change. Next up will be to flip the intake insulator so that the hole is on the bottom (spark plug above). I have a SRM230 trimmer and the intake insulator has 2 holes and they are symmetric so can not use this machine as a point of reference. I do not recall taking off the intake insulator but at this point anything is possible - and this is the only thing that makes sense. I am typically careful about disassembling and making sure clear on how it came off, but if I did take this off and I do not remember then no hope in that I did remember the original orientation.

 

Good news and bad news.

First the good. I am definitely not losing my mind/memory. There is no way I had previously removed the intake insulator and flipped. The gasket against the engine is stuck to it and based on the size of the gasket, this is the only way to orient insulator. The hole on the carb side basically goes to a other side of insulator, but is sealed off by gasket so this hole does nothing that I can tell.

Bad news. Issue still there. Depending on how full the tank is, the issue shows up sooner (full tank) or later (emptier tank). The vent is also not necessarily the issue. I removed the top off one vent so that I have access to the duckbill check valve. I ran engine to point it started to sputter, and then inserted basically a leaf stem through the check valve. This forces the check valve to open. No change. Overall issue may be a flow/volume of air that can get into tank. Maybe tee off vent line and add a second vent?? Again, if I crack the fuel cap, remove the vent or even rotate machine, it clears up.

Any thoughts?????

 

Did you replace the fuel lines? I think that you have a pin hole and it is sucking air.

 

Yes. 3 new refuel kits (has the fuel lines and rubber grommet for tank.

 

The fuel pump is pulse driven off the crankcase pressure which varies with the piston up/down. That pressure is flap checked in the fuel pump diaphragm.

 

What kind of compression do you have?

 

Does not appear is due to restriction to fuel pump diaghragm since path is all contained within carb. Three different carbs tried with no change. I thought source of pulses may have come through insulator block

 

Check your compression and maybe if you can vacuum leak on the engine. Since you have seemed to eliminate all external components maybe check out the internal...???

 

Maybe the insulator is cracked, try spraying some carb//brake parts cleaner on it while the engine is idling, if the engine tempo changes there is a leak. Have a good one. Geo