High-Performance Carb For Mitsubishi Engines

Discussion in 'Performance Mods' started by 5-7HEAVEN, Apr 5, 2009.

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  1. 5-7HEAVEN

    5-7HEAVEN Guest

    Has anyone used a high-performance carb on a 43cc Mitsubishi engine?

  2. What is on it now?
  3. 5-7HEAVEN

    5-7HEAVEN Guest

    The TLE43 has a stock two-barrel carburetor and filter with no adjustments except idle speed.

    I installed ADA S1 expansion chambers on both engines of The Dragon Lady". They could use better-performing carbs and air filters to make use of their improved exhaust.

    The front engine bogs a little at high sustained speed, which I think might be a fuel delivery problem from the reserve tank. Both engines have 1.5" friction rollers and WOT is maybe 9400rpm at 39mph. I'm up at that speed for just a few minutes enroute to and from work. On the boulevard stop and go traffic, engine speed gets up to 8900rpm and 35mph.

    Front engine has 39.37" of rubber exhaust tubing connected to the bleed port. The tubing leads to the silencer/muffler strapped below the frame near the crankset. The smoke would blow directly into my face, so I had to reroute the front engine's fumes.

    The exhaust tubing is so effective at silencing the front engine that most times I disconnect it from the muffler.

    The rear engine has the normal silencer/muffler connected by four inches of rubber exhaust tubing.
    Last edited by a moderator: Apr 5, 2009
  4. I was referring to the Walbro # on your stock carb (it's on the side)
    There are a few options.
    1. WYK-58 is great, barrel carb, high/low/idle adjustments.
    You might have to make an adaptor plate to line up the pulse hole.
    2. WT-603 or 668 (almost identical), h/l/idle but this is a butterfly carb.
    Both would be optimal for that motor.

    I use both on my 39-50cc 2 strokes, and they do very very well.
    You just have to learn how to tune them well if you don't know how,
    or you'll be in big trouble.
    The butterfly version has a bit more throttle response,
    and on the WT series you can tap a fitting into the bottom plate of the carb and engine's cases to do an external pulse line,
    which makes lining up a pulse hole on the mani's a moot point.
    Like this...

    Bogging is dangerous on this motor without a tunable carb.
    You are most likely running very lean at WOT.
  5. 5-7HEAVEN

    5-7HEAVEN Guest

    The WYK-58 carb was also mentioned in a thread on pocketbikeplanet.com. It was also installed on a hopped-up Mitsubishi engine.

    Thanks, I'll keep researching.

    davesmotors.com sells the WYK for $39.
  6. 5-7HEAVEN

    5-7HEAVEN Guest

    What's a pulse and why does carb and crankcase have to be connected?

    Is there a carb that'll bolt on without fabrication?
  7. loquin

    loquin Active Member

    The 'pulse' line is a small pressure port running from the crankcase to a diaphram on the fuel pump. As the piston moves down, the pressure rises in the crankcase, which moves the diaphram in the fuel pump 'out'

    Then, when the piston rises, the pressure drops, which in turn allows the fuel pump diaphram to move back 'in'.

    On the other side of the diaphram there's a small chamber with an in and out port, with one-way valves on both (one pointing in, one pointing out) along with the priming bulb.

    As the diaphram moves in/out, it alternately pulls fuel into the chamber, then pushes it out. The chamber also acts as the fuel reservoir for the carb.

    I believe the second 'barrel' in this carb is only used to provide filtered air (no fuel) to the engine during the initial scavenge stage of the cycle, when exhaust gases are purging out of the cylinder
  8. 5-7HEAVEN

    5-7HEAVEN Guest

    Thanks for explaining, loquin.

    The new Walbro wyk-58 carb arrived. I'll see how it fits.

    Right now I'm having engine stumbling problems with the rear engine. Maybe this carb will cure my troubles.
  9. 5-7HEAVEN

    5-7HEAVEN Guest

    Well the new carb bolts onto the Mitsu's dual-port(air/gas) manifold, but the carb's larger port doesn't even come close to matching the manifold's gas port. :detective:

    I definitely need a new manifold.

    Now to find one!:detective:

    capturedbyrobots, I replaced the sparkplugs. Both engines are running lean due to the expansion pipes.

    Stumbling problems probably due to poor fuel delivery from the reserve tank. I probably will have to prime the engines' tanks manually until I come up with a permanent solution.
    Last edited by a moderator: Apr 18, 2009
  10. 5-7HEAVEN

    5-7HEAVEN Guest

    Well, the WYK carb needs an adaptor to mate to the Mitsubishi intake manifold.

    Will a G43L or GSR40 carb spacer fit my manifold?

    Does anyone know if there's an aluminum or insulator adaptor that'll work for me?
  11. 5-7HEAVEN

    5-7HEAVEN Guest

    I worked on my WYK-58 install yesterday.

    An adaptor for a WT-butterfly-style carb was ordered from partsforscooters.com It is a simple .125" thick aluminum plate with intake port, pulse hole and bolt holes. It included two paper gaskets and two bolts, cost me $16 with shipping.

    Darn, the adaptor won't work on the TLE43 engine, even if I used the WT carb.. This engine's manifold is dual-port/over-under like a shotgun rifle's barrels. The adaptor bolts directly onto the mani, but its port and pulse hole don't line up with the engine, not even close.

    The manifold's top port feeds gas mixture to the engine thru a single reed valve. The bottom port is a straight shot of air thru the engine block to the piston.

    :idea:I need to fabricate a TALLER thicker adaptor and drill it to match carb, pulse hole and manifold. The adaptor will also block off the lower port completely.

    :idea:THENNN, instead of fabbing an external pulse line, I groove a passage from the adaptor's pulse hole to the 13mm(?) air port that matched the original carb's 13mm(?) air port.

    That way the original manifold is left intact in case I reinstall the stock carb.

    It SHOULD work.:detective:
  12. loquin

    loquin Active Member

    I would think that if you don't care about the scavenging aspect of the TLE43, you could provide the fuel-air mix to BOTH the IN ports.

    According to Mitsubishi's documentation, the TLE43 allows air-only to enter the cylinder during the initial intake portion of the cycle; this air gets pulled through the engine and exhausted with the remainder of the burnt gases. By only allowing air in the early portion of the cycle, it cuts down the unburnt HC emissions. By a LOT. (20% to less than 5%)

    If you wanted to keep this (it also improves fuel efficiency, if you're not tossing unburnt fuel out the exhaust) you could probably add a separate air-only tube (filtered) at the air-only port. Either route this tube around the carb to the air filter, of add a second air filter. (this one wouldn't have to be as big, I wouldn't think)...
  13. 5-7HEAVEN

    5-7HEAVEN Guest

  14. 5-7HEAVEN

    5-7HEAVEN Guest

    I wish they made intake manifolds for this engines, but I can't find any.

    Unsure if this BladeZ mani fits, but it accepts the carb I have. The pulse hole lines up and should be no problem drilling the 1/4" aluminum plate to match.

    The 1/4" aluminum plate will mate the BladeZ mani to the engine block. The stock manifold has a single reed, which I will try to bolt onto the 1/4" plate.

    The BladeZ mani has a 15mm carb hole and hopefully under that is an open plenum. First I'll drill the plate to 15mm, near where the engine's original manifold's top port is located. If that doesn't work well, the 1/4" plate can be hogged out to match the BladeZ's plenum.

    Here's crossing my fingers that everything works well.:sweatdrop:

    Why am I making such effort to add high-performance carbs? Well, ADA S1 expansion pipes were installed for more power. However this resulted in a lean condition which needs a richer gas mixture.:detective:

    Sadly, the Mits engine original carbs are not adjustable, That is why high-performance carbs with low/high speed mixtures are necessary.
    Last edited by a moderator: May 10, 2009
  15. One other option is to just run a WT-603 and then tap the case/carb to run the pulse
    Much easier, imho.....
    You tap the case anywhere you like,
    then tap the bottom of the carb with 10/32 threads and connect hose barbs to both, running tubing between them.

    This way, all you have to do is get the carb attached
    and you're done!

  16. 5-7HEAVEN

    5-7HEAVEN Guest

    Not quite, captured.

    I have the WT/WA carb adaptor with a pulse hole.

    HOWEVER, the TLE intake manifold is not like any normal intake. It has two 12mm intake ports, over/under like a 410 gauge shotgun.

    There is NO way any adaptor for the WT/WA carb or any carb will match ports with the TLE.

    I've brought that up at least twice.:confused:
  17. Can you post a pict of the setup?

    I meant that it doesn't have to match exactly......as long as you block off
    a section with a blockoff plate or epoxy it closed, you'll be set.
    It would be similar to adding an HP carb to a Zenoah Geo motor.
    Those geos have the same style ports.

    The modding folks used block off plates and removed the reeds
    to use the larger carbs.

    Sorry if I was misunderstood.
  18. augidog

    augidog New Member

    hi 5-7...

    most of this topic is over my head...but, have you looked at any of the intakes used on the mitsubishi clones? i think the one on mine would fill the gap you're trying to bridge, because one of your attached pics seemed to be the exact carby i have. maybe i'm wrong, trying to help is all: http://www.motoredbikes.com/showthread.php?t=19457

    you can go to the regular scooter-parts sites to get some good pics.
  19. loquin

    loquin Active Member

    the port setup is exactly as 5-Heaven mentions. One port over the second one. Almost like the number 8

    One port admits nothing but clean air to the engine - it's used in purging the burnt exhaust gasses. The second port carries the fuel-air mix, and starts entering the cylinder a little after the clean purge air.

    With 2-stroke engines, a fair amount of the air that enters the engine during the first 5 to 10 percent of the exhaust cycle gets exhausted along with the burnt gasses. IF there's fuel mixed in with this air, then it gets exhausted from the engine, unburnt. This process, of air going straight through the engine, is known as a short-circuit, as the fuel-air mix doesn't get burnt. it 'short circuits' the combustion phase. This, of course, raises the unburnt hydrocarbons to high levels. By allowing air (only) in the first part of the air intake, the unburnt HCs are much less.

    This is the reason for the dual ports in the Mitsubishi engine.

    Now, you could follow two approaches to adding a HP carb to this engine, I would guess.
    1. Run two, separate feeds to the engine. One with the carb, and one that's just a pipe to the air filter. (or, use a separate filter.) This approach will maintain the design integrity of the engine, and keep the pollution down and the fuel eficiency up. It IS a more complex design, though.
    2. Ignore the benefits of the clean-air purge, and have the carb supply both ports. Yes, it will cause the motor to emit more HCs, (and, will drop fuel efficiency by about 10%) but, it should work, and it is certainly the simpler approach.
    You may still need to supply a separate pulse line from the crank, though.
    Last edited: May 11, 2009
  20. 5-7HEAVEN

    5-7HEAVEN Guest

    captured, no apology needed. :grin5:

    There would be major restriction if I just bolt the carb and adaptor onto the stock manifold. It would be similar to center an "o" directly over an "8".:detective:

    Like most experiments, ya just gotta try it.

    augidog, thanks for the tip. Lou, thanks for the explanation.

    Does anyone have a picture of the clone's intake manifold?