(hush hush) Tweaking the Robin Subaru 35 for faster speeds

Discussion in '4-Stroke Engines' started by bamabikeguy, Jul 8, 2009.

  1. bamabikeguy

    bamabikeguy Active Member

    Last night Mr. Cantor called, he's the 80 y.o. with 2 artificial knees, who chased me down on the last day of my NC trip. He ordered a 21 speed with RS 35.

    He was thinking of ordering a second bike, selling the first one to a friend of his. But he wanted to know about getting more ooomph out of the Robin.

    Then, about 6 pm, Jimmy Burke called, he's a MB.com lurker. He dropped off a Jaguar the same day as Mr. Cantor picked up his, test road Mr. Cantor's bike, and since April, he has 2,000 miles on his bike. He has a GPS installed on the Jaguar, to check everything to the 0.00001 decimal.

    A friend of his also put a Robin on a Jaguar, both are superMB addicted.

    Then they started tweaking.

    When they finish analyzing the results, they will give me all the specifics, including item number.

    But I thought I'd put up this preliminary thread, to get the ideas out there.

    I talked to Denis at GEBE to discuss them this morning. He can't do this to his kits, because of warranties and such, but says "it works".

    First, (AND I DIDN'T TELL YOU TO DO THIS) Jimmy removed his catalytic converter. He didn't touch the baffles, but used a dremel stone to clean it up, inserted a 3/8" nipple (locktited).

    He says the increased compression could be felt 3 feet away from the exhaust, upped them both by 2 miles per hour.

    Then they contacted, discussed and ordered two bigger carburators. This is where I'll get the product # later, but they cost $57 plus shipping (Denis said $55, I guessed $ 60 ).

    The short story is, when they told the representative which carb was on the R/S, the rep. replied that size "acted like a governor".

    We will wait for the road test results from Jimmy, but they are expecting more speed from the upgrade, with maybe a small decrease in m.p.g.

    I spoke to my buddy Jack this morning, we MAY duplicate this on my recumbent soon.

    (note the typographical error in my ad, I got a free week for their mixup)....

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    Last edited: Jul 8, 2009

  2. Happy Valley

    Happy Valley Active Member

    Interesting. I didn't know they had a cat converter. Where is it?
  3. Mountainman

    Mountainman Active Member

    cool ads there -- god eye catchers !!
    been wanting to get a little more from my R/S
    looking forward to hearing more about those carbs
    going to take a look at my muffler -- if you know what I mean ??
    thank you
  4. RMWdave

    RMWdave Member

    and by take a look i bet MM means remove, inspect, analyze and tim taylorize
  5. loquin

    loquin Active Member

    I believe they're inside the muffler... IOW, a combination muffler/cat converter.
  6. Old Bob

    Old Bob Member

    Why would Robin Subaru put a cat/con on an engine that already meets Tier 3 standards with out it?

    More likely they removed the spark arrestor.
  7. bamabikeguy

    bamabikeguy Active Member

    I haven't explored mine yet, if it is just a spark arrester (screen), that really is no biggie. I know there is a collar to hold that screen on the Zenoah's and Tanaka's, that must me what he used the drimel stone on, to push in the nipple.

    Carb upgrade, maybe this Diamond Fire plug I noted in another thread, and a 14 tooth (not recommended) belt drive gear, I might get the recumbent in the 35-36 mph range.

    Last edited: Jul 9, 2009
  8. AndyT

    AndyT Member

    Any word on the carb upgrade? Part number or venturi size? I may have a carb sitting here that will work. ;)
  9. mlcorson

    mlcorson Member

    This might be a Sasquatch sighting.
  10. AndyT

    AndyT Member

    Could be! I know that switching to an adjustable carb is easy. Which one is the question. I may have to go digging for info myself.
  11. Old Bob

    Old Bob Member

    The biggest carb that will work on 35cc robin is 10.5mm, unless you can increase valve lift.(tightening lash does nothing to speak of)
    Simply browse the WYK listing at Walbros website until you find one.
    You want a WYK rotary carb not a butterfly carb.Most WYK have an adjustable needle, it makes it easy to adjust but in reality you can get a fixed jet carb to work better.
  12. mlcorson

    mlcorson Member

    Definitely a Sasquatch sighting! Too bad, I wanted to goose my Robin.
    Bama, What happened to this thread???
  13. Goosing the Robin.

    I'm using a Robin 33.5 on my bike and want to give it just a little more zip. I will get a one or two step larger Walbro diaphragm carb(similar to stock) and grind the intake port out in a cone shape to match the carb outlet. I would like to find a reduced back pressure exhaust pipe/muffler that points the exhaust down towards the ground and doesn't increase loudness an obscene amount. I could build one but I am afraid I'd screw the engine up. Does anyone know of an after market supplier with such a pipe and muffler?
  14. bamabikeguy

    bamabikeguy Active Member

    I got a gd Vendor Infraction for the funny ad attachment. Ain't that a crock??

    The only thing I tried to buy on this site was an $8 wrench, mailed him cash and a SASE, and he never sent it.

    The only thing I've sold were 2 predrilled steel mounts and 8 metric bolts, and that guy didn't even mail the $15, $5 which was postage.


    Anyway, what was the question??

    The modifications?

    Pull out the screen, that spark arresstter. You'll need a dremel. Then put a copper elbow, exhaust extension pointed to the rear.

    Quieter, more power, nothing else you can do except increase the drive gear to 14 teeth (I use 12, I'm in no hurry).