Honda GB500 thread

Discussion in 'Old's Cool' started by Spurlock, Aug 27, 2016.

  1. solidol

    solidol Been here awhile

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    Saw stock looking GB500 entering 101 northbound right before the junction to PCH. Sometime around noon today. Wonder if this is the same bike and gentleman I've been seeing around Hawk Hill.

    Went to see a buddy of mine and stumbled on another classic.

    IMG_20200524_190830.jpg
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  2. alvitdk

    alvitdk Adventurer

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    Small question to the people in the know. I bought the bike with the airbox removed and a clamp-on K&N in its place. All good thus far, however, the crankcase breather line is therefore removed and in its place is a small breather filter, also technically ok. However, I keep having to wipe down the engine of oil splatter in the area, pain in the neck. What do you guys with removed airbox do/solve the issue? I thought about attaching a tube instead of the breather filter and drill a hole at the end of the K&N air filter, sticking the tube in it so the fumes and oil get sucked back into the engine and get burned off. Does that sound like a good idea, or will the carb suck a vacuum out of the crankcase?
  3. Spurlock

    Spurlock Long timer

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    Interesting problem. Full disclosure: I'm not at all a fan of gauze and screen air filters for non-racing use for all the reasons explained here. And generally CV carbs work best with the stock engineered air box and inlet tube length. I also don't like noisy engines and especially the cow mooing intake noise of unenclosed air filters. So my first choice would be to reinstall the stock air box and filter. But my prejudices aside I would not want to feed raw crankcase vapors directly into the intake air without first at least passing through the stock oil separator tank so excess oil will end up in the stock drain tube. Then the separator tank outlet could be plumbed into the K&N, or else routed up along the frame to end at the rear fender. More info on crankcase breather recirculation here. Hope this helps!

    -Bill
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  4. XRLated

    XRLated Been here awhile Supporter

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    While waiting for smarter folks than me to respond, I believe a lot of folks in your situation put the filter on a length of tube raising the filter as high as possible, allowing oil vapor to condense on the hose and drip back down into the crankcase.

    I've read this never done it.

    A better idea might be adding in an oil separator.

    Or get an OEM airbox for $50 or so delivered to you from Yahoo! Japan Auctions.
  5. alvitdk

    alvitdk Adventurer

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    thanks guys, i will go with mounting it high and look for the stock airbox, would rather put it back to stock if possible. Thank you for the suggestions.
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  6. XRLated

    XRLated Been here awhile Supporter

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    Oops! Someone smarter than me beat me to posting by 60 seconds or so!

    But sounds like we agree.

    imageproxy.php(2).jpg

    If you absolutely don't want the stock airbox, install an oil separator and route the green hose up high with a filter on the end? Don't hook up to the carb at all. This way most of your oil gets back into the engine, not into the carb.

    Maybe a very tiny bit vents to outside. Or add a catch basin at the end that you clean occasionally.
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  7. alvitdk

    alvitdk Adventurer

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    Thanks, I don't mind getting a stock airbox...finding one is a different story. On that note, any recommendation on what oil operator to get? All I find are industrial not motorcycle specific....would probably look rather odd in there lol
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  8. XRLated

    XRLated Been here awhile Supporter

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    @alvitdk here is a goldmine:

    https://www.jauce.com/search/Gb400+air+cleaner

    Seing as 100 yen = a dollar more or less, you might get a box for a few bucks, plus a few bucks other fees, plus, $25 shipping. Done!

    Make sure whatever one you buy includes this that attaches to the front of the airbox;

    Screenshot_2020-05-28-18-19-14-1.png

    20200528_181717-1.jpg

    @Spurlock am I correct that this is the GB version of the oil separator? I'm mostly familiar with XR650L version that looks completely different.
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  9. XRLated

    XRLated Been here awhile Supporter

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    This one looks good with a buy it now price under $10, but then you have a ~$20 local ship charge, plus probably $5 fees, plus $25 or so shipping, so around $60-70 delivered.

    You might find cheaper yet.

    @Spurlock does this one also look good to you? No damage or defects?
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  10. XRLated

    XRLated Been here awhile Supporter

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  11. alvitdk

    alvitdk Adventurer

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    So, GB400 and GB500 using the same airbox? There is a GB400 airbox including the oil operator for sale for 900.-, with all fees it's 65.-, not too bad
  12. alvitdk

    alvitdk Adventurer

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    Thanks, bought it for the 900.- yen, will be great to put it back to the original condition. Thank you so much for your help, guys!
  13. XRLated

    XRLated Been here awhile Supporter

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    Late reply, but yes, you are golden. 500 = 400 in almost all respects except some engine parts, centerstand, dual seat on some models, grab bar on the dual seater, and maybe a very few other things?

    Again, though, AnNoGBer, Bill, Clay, etc. know better than me.
  14. XRLated

    XRLated Been here awhile Supporter

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    Bill: this surprised me in Mike Nixon's article:

    Screenshot_2020-05-28-19-29-01-1.png

    Is Mike saying remove or block crankcase recirculation? Or maybe just don't feed it into the airbox. Vent to the rear of the bike?

    I'm guessing Mike talks in more detail about this somewhere. Just need to try to dig it up.
  15. XRLated

    XRLated Been here awhile Supporter

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    Airbox goes in from the rear, by the way. At a minimum, the rear tire needs to come off, the front plastic fender piece, the battery box, and the shocks need to be unbolted from the swingarm so that the swing arm can drop way down, allowing you to slide in the airbox from the back into position on top of the oil tank.
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  16. wiguzziman

    wiguzziman Adventurer

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    My 1990 GB500 still has the stock air box on it, but I have 2 other big singles that do not have the stock air boxes. One is a 1978 Yamaha SR500 and the other is a 1982 Honda FT500 Ascot single. On both of these bikes I'm running a motorcycle specific PCV valve and gauze filter. The PCV valve is attached via short hose close to the motor, and then a longer hose runs from the PCV valve up and to the rear of the bike with the gauze filter at the end of that. No issues with oily discharge at all. Be sure to get a motorcyle specific PCV valve. One from the local auto parts store wouln't hold up very long. I used one from a KTM 950 SuperMoto; part #60030090300 (about $45.00). They call it a back pressure valve. Mikes XS also has a reed valve type PCV valve that has a built in oil separator, but it's been out of stock since January. Part # for that is 1-50677, and it's about $28.00. Hope this helps some. wiguzziman
  17. Spurlock

    Spurlock Long timer

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  18. Spurlock

    Spurlock Long timer

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    Yeah, he recommends not routing CC fumes into the intake. But I've never ever seen any residue buildup on CV slides myself. I leave everything hooked up as original. I drain the two drain hoses (one from the air box and one from the separator tank) at each oil change and they rarely have more than 1/2 tablespoon in them, so I have a hard time imagining they would ever fill clear up.

    -Bill
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  19. AnNoGBer

    AnNoGBer 89 GB500, 85 VF750S, 84 V65 Sabre, 85 V65 Sabre

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    Heard of one GB500 owner fairly local to me who removed the oil separator and simply connected the crankcase breather outlet to the valve cover ditto and plugged the air filter box stud. He even claimed the engine ran smoother, at least idling where he could hear and feel it. Never got to see it, and dunno how bright a hint, guess the pulsation in the lower and upper parts more or less equalled out or just had a larger room move in. Anybody having tried that on a RFVC or an other large single cyl.?
  20. XRLated

    XRLated Been here awhile Supporter

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    Not sure how much a topic of interest this is, but my understanding is the Honda RFVC engines has an oil separator as OEM equipment, but not a PCV valve.

    There was some discussion years ago about the possible benefits of adding a PCV to thumper here:

    https://thumpertalk.com/forums/topic/649696-pcv-valve-bennifits-fact-or-fiction/#comments

    But that discussion concluded that adding a PCV is not of measurable benefit.

    The oil separator on the other hand is OEM equipment on our engines, and the wide concensus is it does no harm while delivering great service.

    I do understand Mike Nixon's reasons to remove the carb intake from the oil separator (vent out the back instead), but I also respect Bill's knowledge from experience that, in the GB'S case anyway, the oil separator does not have an adverse effect on the carb, so I'm sticking with the OEM setup with the separator connected to the airbox.

    (My wild guess is that anyone getting excessive oil in the airbox via the separator may be overfilling the oil tank, or has some other less-than-optimal engine issue going on.)

    Again not sure how interesting a topic this is for anyone. I can probably dig up more information if if there is interest though. There has been lots of discussion over the years.
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