Carby dual carburetors, one gas, one e85, suggestions?

Discussion in '2-Stroke Engines' started by jatgm1, Apr 24, 2016.

  1. jatgm1

    jatgm1 Member

    i replaced the cork gasket in my carb so it wouldnt get eaten away(made one from some autozone stuff that seemed good) thinking i could either use something like this

    with two carbs , and two tanks, or add a splitter and second fuel cutoff switch to another gas tank, but then i would need to screw with the carb every time i switched from one to the other. suggestions? and with all due respect, everything can be done, so telling me otherwise will just make sifting through posts more difficult, thank you very much!

  2. 45u

    45u Active Member

    My opinion do not wast your money just put a bigger better carburetor. Have you ever sink two carburetors? I do it all the time as I work on motorcycle as a living and now that I am retired I am still working on them as many will not take their bike anywhere else.
  3. butre

    butre Well-Known Member

    syncing carburetors is a huge pain in the ass and not even a little bit worth the effort on a single cylinder engine. just get a mikuni VM18 and a manifold that fits. it won't save you money but it will save you a whole heap of headache and 2 or 3 weekends of trying to get that junk tuned right.

    that 30mm thing is false advertising anyway, the area is only equivalent to a 20mm carb. they got 30mm by adding the diameters, not the area, and the vm18 has better flow characteristics and an idle circuit to make up for that 2mm

    you would also have to have airtight blocker plates in both plenums if you were to run one for one fuel and one for another. it's easier to just have a carb with seals for e85 and swap jets if you're changing fuel types.

    I also presume you didn't change out the main seals to cope with the e85 either.
    e85 is useless as a fuel in anything without forced induction anyway, the dynamic compression ratio even with the smallest chamber aftermarket head of 5.3cc is only about 9:1 or so depending on your primary compression ratio and port timing

    don't bother with e85 until your dynamic compression is 16:1 or greater
    Last edited: Apr 27, 2016
  4. 45u

    45u Active Member

    I agree I would never run e85 in mine. Everything I have read says 91 octane or more. As far as setting twin carbs not a big deal to me as I have been sinking carbs on old British bikes for years but not on a single cylinder as they only run one as one is more then enough. The dual carb for these bike are more for show and not riding. Stock compression is 6 to 1. The stock wrist pin bearing will not handle much over 7 to 1 and many mess up at stock 6 to 1. The Chines know the quality so they do not have a very high compression or rpm.

    About all these engines stock will turn is 6K rpm which most 2 cycles turn 10K or better other then yard equipment.
  5. butre

    butre Well-Known Member

    stock static is 6:1, stock dynamic after factoring in crankcase compression is probably 5:1 at best. my engine runs a static of 14.4:1 and dynamic of 13.5:1 after factoring in crankcase compression. all made possible with the help of a bronze bushing instead of a bearing. upgraded studs probably helps too

    even in my engine, the 105 octane rating of e85 is unnecessary, I get by just fine on 100 octane avgas, and make more power doing it because ethanol has about 33% less energy per gallon than gasoline.
    Last edited: Apr 27, 2016
  6. 45u

    45u Active Member

    So the bushing holds up fine? The reason I ask is I was told on two cycles they will not hold up running a bushing and is why they use a bearing. In all my 40 plus year of working on motorcycles most of the time for a living I have never seen a bushing in a two stroke. I have seen the bushings for sale but not sure about them. How many RPM s do you turn? Mine runs fine on pump perineum.
  7. butre

    butre Well-Known Member

    holds up fine, but you can't run plain bronze, you gotta run oilite. old 2 strokes, older than either of us, that didn't spin very fast would run plain bronze bushings without problems, but 2 stroke technology advanced quicker than bushing technology and the switch to roller bearings was made. now days the use of roller bearings is mostly down to hard-headedness.

    it's also very necessary with a titanium wrist pin, the hardened steel bearings chew through titanium like it's nothing.

    they don't last as long as needle bearings but the failure mode isn't catastrophic and it shows signs of impending doom a couple dozen miles in advance which gives ample time to go ahead and replace it before it does fail.

    my engine tops out at 11500 rpm but being as that's cresting 60 miles per hour it rarely hits that.
  8. butre

    butre Well-Known Member

    there was one online store selling aluminum bushings for these engines. now that there was ill advised.
  9. 45u

    45u Active Member

    I have worked on quite a few of OLD 2 cycle motors talking 40 and 50s and none of them revved very high. What held back 2 cycles for years what leaning about the exhausts system and when the got that right things changed quick. Would love to see a video of yours turning 11 grand. You must rebuild yours often. Might just have to make a rode trip to see this beast.
  10. 45u

    45u Active Member

    See a seller on eBay that sells brass or bronze ones. When I post a link I do not make anything and is not mine I am just trying to help others with pictures.
  11. butre

    butre Well-Known Member

    making a trip just to see my bike might be ill advised, I'll probably have blown it up by the time you got here.

    I'm tired of these chintzy junk heaps anyway, next time it blows it's getting a DeNardis, maybe a 60cc model, I haven't seen one of those on a motorized bike yet.
    HeadSmess likes this.
  12. jatgm1

    jatgm1 Member

    what gaskets would you want to use if making your engine e85 safe? im actually not concerned with power, more so with emissions.
  13. butre

    butre Well-Known Member

    if you're concerned with emissions, get a 4 stroke. 2 strokes pollute far worse than 4 strokes.
  14. skyash

    skyash Active Member

    I don't think you need to change everything gaskets will be fine
  15. HeadSmess

    HeadSmess Well-Known Member

    oh no, alcohol in the fuel is going to dissolve your alcohol proof gasket materials!

    hang on... no they wont.

    leave the gaskets alone.

    leave the twin carbs alone. only one bike i know of ever had two carbs on one cylinder and it had a reason for it. good old honda XR 200, if it had just one BIG carb, of the same total would die when the throttle was opened wide too fast. no air speed through the venturi, no fuel gets sucked up and mixed with air, engine dies.

    being on one cylinder, they did not require synching. one carb was "untuneable" one wasnt. both throttles were locked together, with no adjustment necessary. or even possible, from memory.

    then someone developed the CV carb and the twin carb concept was thrown out on the rubbish heap where it belonged. no matter how fast or wide you open a CV carb, its slide will only lift as high as the engine requires.

    adding a bigger carb is going to do nothing for performance unless you have opened all the ports up to suit the increased breathing capabilities. if the hole behind the carb is only 16mm across, sticking a 20mm carb on is going to do what? somehow squeeze extra air down the 16mm hole? reality says no, it wont.

    but, some people wont listen to logic, its your money, so if you think two carbs is going to make a huge difference, and want to stuff around with different fuels that also make no difference... go for it :)

    now, if you were running straight methanol and needed one carb setup for the extra fuel flow...maybe. easy way to get double the power. buying drums of methanol isnt exactly cheap when youre using four times the amount of fuel! definitely not the way to proceed if mileage and economy is your desired outcome.
  16. HeadSmess

    HeadSmess Well-Known Member

    this i have to see!

    i would be happy with the 40cc denardis... though the 50cc seems to have more parts available? more common i guess :)

    found one! takes a bit of searching for the china ones to pop up on ebay... fairly cheap though and i know they DO get up and go! far superior to the poxy 49cc things with the carb at the back of the case.

    china direct...

    radiator required...
    Last edited: Apr 28, 2016
  17. butre

    butre Well-Known Member

    I just like the idea of a fully liquid cooled engine on a motorized bike. I'm sure a 50cc would be more than fast enough for me, but go big or go home.

    I mean, if I don't want to go 60 miles per hour, I just don't crack the throttle quite so much. not too hard. I've already got one of the faster bikes around but rarely crack 35 anyway. I'm too starting to get old for that shit, I don't spring back like I used to. I only have a couple bones left that I haven't managed to break yet, and I'd like to keep them intact as long as possible.

    but having the option to do 60 is sure fun when it's on a closed course and you're in full race gear.
  18. HeadSmess

    HeadSmess Well-Known Member

    hows about one of these engines?


    might cost a bit though!

    look at the poor rider..."aw cmon, let me on it!"

    100MPH from a lil fiddy! and look at the front brakes! caliper/rim brakes! oh yeah baby!

    hard to believe its a four banger... and it took how long for the gx25-35 to start being manufactured? um...50 YEARS?!?!

    im thinking of a denardis 50-60 myself...suitable for an ICV or "individually constructed vehicle"... has to be 50cc and has to hit 50km/h... for nsw, au road registration...
  19. butre

    butre Well-Known Member

    as much as I love the sound of 20000+ rpm, I don't have the cash to support it's hunger for parts. or buy it in the first place.
  20. skyash

    skyash Active Member

    I have seen pocket bikes for sale 2 hand with 8 and 10 hp warter cooled for $200 the hole thing but it's a jump I don't know if i can get spare pats