Robin Subaru Cutout Possible Fix

Discussion in '4-Stroke Engines' started by bird_e, Jul 27, 2009.

  1. bird_e

    bird_e New Member

    Hello all,

    Last year I built a friction drive/ Subaru 35 setup and had about 600 miles on it and started to experience frequent engine cut outs at full throttle. It seems that the engine would starve for fuel when at maximum RPM. If I let up on the throttle just a little it seemed better. Well, after messing around with cleaning the carb and fuel filters I still couldn't solve the issue. So I sold the motor and bough a new DAX Titan 50, which works mint by the way.

    Anyway, my Dad just recently built a similar setup with a new robin Subaru engine and is experiencing the same cut out issue that I was having. After checking several things and nothing seemed to fix it. So, just by chance, he wanted to see what would happen if he clamped off the return fuel line from the carb to the gas tank. BINGO.... he said it has completely solved the issue and that the motor runs better then ever. So, if you have a similar problem and want to try something simple, just clamp off the return line and take it for a ride. Please post back your results.

    I believe what may be happening is that the return line is causing bubbles in the tank which is then picked up and sent to the carb causing fuel cutout problems at high RPMs.
    let me know!

  2. Happy Valley

    Happy Valley Active Member

    Bill there is also a fine mesh screen filter fitted into the carb where the fuel intake enters. This has caused some problems with clogging for people in the past being overlooked in maintenance. You have to open the carb to get to it. I think using the return line bypasses this screen though by doing so you're not getting that final filter.
  3. loquin

    loquin Active Member

    I would think that blocking the return line would force all fuel pumped, through the carb screen.

    If this carb inlet screen is what was blocked, eventually, it'll get blocked even more... eventually leading to the same problem even with the return line blocked (and maybe to diaphram pump failure:icon_cry:)
  4. Happy Valley

    Happy Valley Active Member

  5. Silvaire

    Silvaire Member

    Your "fix" of blocking the fuel return line shows that you have a lean run condition, but blocking the fuel return line is not a permanent solution.

    For what it's worth, you can suck in a lot of air with the fuel and still have the carb function properly and not run lean.

    Diaphragm carburetors can be a bit of a mystery if you are only familiar with float type carbs. I won't try to provide an explanation of how they work here, but I will say that there are several very small passages and a fine mesh screen, and some one way valves in these carbs that are easily crudded up. There are also two flexible diaphragms in the carb - one which is a fuel pump and one which (along with a spring) provides steady fuel pressure to the metering jets. When the valves in the fuel pump portion of the carb get crudded up, they can no longer maintain the required fuel pressure. When either of the diaphragms gets brittle, they no longer flex easily and do not work properly.

    When any of these situations occur you will have a malfunctioning carb, and this most likely results in a lean condition. Your plugging of the return line has overcome an issue of some sort, but you no longer have the steady regulated fuel pressure that is required for the carb to work properly under all conditions.

    I have encountered similar issues with these carbs more an more frequently in recent years, and I strongly suspect that it is due to the increased amount of alcohol in the fuel.

    The carb on your Subaru EHO35 is a Walbro WYL series carb. This is a very common series of carburetor that is used on many weed trimmer engines.

    Here is a link to the Walbro Service Manual for the WYL:

    I would suggest familiarizing yourself with this manual, and then purchasing a gasket/diaphragm kit for your WYL carb. These kits are available online in the $5 (plus shipping) range. Your local small engine shop would likely have this kit on hand too. (You could also purchase a full repair kit instead, but unless your carb has a lot of time on it you won't likely need anything other than what comes in the gasket kit.)

    You MAY be able to just go through the carb and clean it and not need any parts, but I would want to have the gaskets and diaphragm on hand just in case.

    There is also a possibility that you have a partially clogged or pinched fuel line or filter. Check this out before getting into the carburetor!
    Last edited: Jul 27, 2009
  6. Zev0

    Zev0 Member

    Hmmm wonder if a good dose of "SeaFoam" would help. I put an ounce in my gas about once a month and have over 2000 miles on my robin with no cutouts.