Author Topic: Echo 590 (Read 7342 times)

1manband · « **Reply #10 on:** April 24, 2014, 07:41:35 pm »

note: this is the process i used. the holes were too large and too many. since then have plugged and got closer to a working result. so, don't use these hole sizes or hole count!!! will post what ends up being the best i found, but have not reached finding that point yet. note: also trimmed off 0.020 inch off of the stock butterfly indent. the saw ran great, but had too high of idle rpm, (clutch engaged), an idle was unsteady surge. the mid to high rpm were quite a noticeable difference better.

1manband · « **Reply #11 on:** April 24, 2014, 07:47:52 pm »

1manband · « **Reply #12 on:** April 24, 2014, 07:50:56 pm »

1manband · « **Reply #13 on:** April 24, 2014, 07:53:13 pm »

1manband · « **Reply #14 on:** April 24, 2014, 07:57:55 pm »

note : on pic 0012 ..................this "L" shaped tab on the throttle shaft was bent down even to the the point of the idle speed screw.

going to mention this an additional time, this is not the final result, just the process i used.

-joe

Cut4fun . · « **Reply #15 on:** April 24, 2014, 08:14:02 pm »

Wow super nice how to's with pics. Thanks for sharing info.

1manband · « **Reply #16 on:** April 25, 2014, 06:18:14 pm »

Quote from: Cut4fun_ on April 24, 2014, 08:14:02 pm

Wow super nice how to's with pics. Thanks for sharing info.

if it does not help, easy to change back to what it was. three dollars in parts. right now, it's not helping.

currently stick expoxied two of the 3 additional holes shut. leaving a single 0.060 inch hole and 0.020 inch indent. this made the saw idle too slow, (with throttle butterfly completely shut).

as the holes were closed off, the effect of better mid-range to better high rpm operation decreases. disappointing.

to try to get some of that back, increases single 0.060 inch hole to 0.073 inch. testing this change tonight, the idle speed is just below clutch engagement. runs pretty well at mid to high rpm. but again, it's not nearly as good as with all running all 3 additonal holes. you win some and lose some.

another thing to mention is the sudden stalling lack of fuel after idling for about 30 seconds, after test cut.

don't like fiddling with metering springs to get more fuel delivery. anyone have some ideas?

gotta think about this over a beverage.

-joe

will post some pics of this.

sharkey · « **Reply #17 on:** April 25, 2014, 08:59:20 pm »

Hi Joe,
Be careful with the B12. That stuff is known to melt the check valves inside the high speed nozzle. Walbro HDA-268 doesnt have a replaceable nozzle fwiw so if you melt it you will need to make some other arrangements. I may be telling you something you already know? There are two kinds of check valves in the H side of the walbro carbs. i. is a capillary seal type and ii. is a mechanical seal. The reason that the check valve is needed is to keep the baro pressure from getting down inside the metering chamber of the carb. Symptoms of a leaker is an idle mixture that wont tune. One moment lean the next rich and so on. Wont accelerate from an idle (bog).

The black plastic 'scoop' that is in the air filter is a spit back plate. In a piston ported engine, the piston skirt closes off the intake. When this happens any speed that has accumulated in the intake track slams into the skirt. Air itself doesnt really have a whole lot of impact, but once mixed with fuel is heavy and thick. The inertia of the fuel bounces off the skirt and splashes out into the air filter. The spit back plate is there to catch this and keep it out of the atmosphere.

Thanks for the pics on the throttle plate adjustment. I could see where this would make a big difference on the high speed hit.

sharkey · « **Reply #18 on:** April 25, 2014, 09:26:16 pm »

The other thing that crossed my mind about transition fuel delivery is the 'idle' holes which are drilled into the throat of the carb below the welsh plug. Usually there are 3. The 1st one should be visible from the throat with the plate closed looking into the throttle bore. #2 is directly beneath the plate, at the cutout, with the plate closed. #3 is on the venturi side of the plate.

Im trying to post the drawings for the 268, the hole sizes are in the narrative. I dont know how much larger I would go with those holes unless you want to start running alcohol instead of gas.

***Keeps saying the file is too large, let me try something else***

sharkey · « **Reply #19 on:** April 25, 2014, 09:28:40 pm »

Schematic of HDA-268

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