New to this. Could someone tell me what I have here before I sink a bunch of money in it?

Discussion in 'Projects/Builds' started by TOLO, Jul 8, 2020.

  1. racerx

    racerx Administrator
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    There is no "lean mix" screw. The two adjusting screws are the throttle stop and pilot airbleed. That second one adjusts the amount of air entering the pilot (idle) circuit. Out/CCW increases the amount of air in the pilot circuit, leaning-out the mixture. It's only effective from about 1/2 turn to ~3 turns out from seated. Less than 1/2 out, the airflow is cutoff and the pilot circuit goes dead...no fuel or air. But the important issue is that pilot (idle) circuit operation...and by extension all adjustments to it...are only effective up to about 1/8 throttle opening. Beyond that, it's all up to the main metering circuit. So, if you're expecting those two adjusting screws to have any real impact on normal riding, you're going to be disappointed.

    What you need to do is figure out why the main metering circuit isn't delivering enough fuel. There aren't many adjustments on this type of carburetor. Float height is fixed and, I believe that jet needle height is also. Basically, the carb has to be in perfect working condition, or the engine goes lean; that was the emission-compliance solution. It's kinda lame, imo. Surprisingly, these emissions-era carburetors do seem to respond well to a proper cleaning. If you're sure that the emulsion tube orifices are all flowing equally, there aren't many other places to "look". It is possible to adjust jet needle height in a non-adjustable carb; use thin washers as shims. I'd expect total usable adjustment range to be not much beyond 1/8". You'll know if you go too far; the mixture will go pig-rich.

    How rusty is the inside of the tank? There's plenty of garbage in pump fuel. Rust flaking inside the tank can clog up the works. You've not mentioned the internal fuel screen on the carb...and there should be one, unless this carb is different from the earlier and later versions.

    You can always throw a new reproduction carburetor at this. The early style, from trailbikes.com is a faithful copy of the early Keihin, has all the adjustability and uses OEM parts. But...before doing that, I'd want to know that the engine itself is healthy. If it isn't, carburetion won't correct the problems. How's the compression? Do a cursory compression check, crank the engine by hand...you should feel strong resistance via the kickstart arm. Make sure point gap hasn't narrowed, that can really degrade performance. Is the intake port clean? If it's blackened, the intake valve is leaking and the reversion is wreaking havoc on the incoming air/fuel mix.
     
  2. TOLO

    TOLO New Member

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    Ok. I’ll get the pilot screw for idle circuit correct and get idle right afterwards because it was set way lean.

    Unfortunately this carb has a round bowl and has no screen! I added a mini fuel filter to reserve circuit and only run it on reserve figuring I will eventually get the small stuff out that way. Only riding around my 2 acre yard for now. Tank is not bad. Maybe I’ll add a filter to normal line too.

    Engine is healthy. Healthy as far as I can tell. Intake pipe is clean. Orifice openings are all clean from spraying carb cleaner through them and blocking one end. Will clean carb again and then see if I can shim needle up a little. Boot above carb from throttle cable is torn but I taped it up for now.

    No leaks as far as I can tell. Sprayed ether all over it at idle and no surges.

    If it is still fighting me then I’ll just buy a Keihin copy carb from early years with the square bowl. Don’t like the lack of adjusting in the one I have.

    I do appreciate all your input. Really. Thank you.
     
  3. racerx

    racerx Administrator
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    If you haven't run a wire through every single emulsion tube wall orifice, there's a high probability you're shortchanging yourself on the carb cleanup. I don't know why those orifices are so hard to clean, brass is a stable material, but they often are. And, it only takes a slight restriction of one or two of them to cause grief.
     
  4. TOLO

    TOLO New Member

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    Ok. I’ll get the pilot screw for idle circuit correct and get idle right afterwards because it was set way lean.

    Unfortunately this carb has a round bowl and has no screen! I added a mini fuel filter to reserve circuit figuring I will eventually get the small stuff out that way. Tank is not bad. Maybe I’ll add a filter to normal line too.

    Engine is healthy. Healthy as far as I can tell. Intake pipe is clean. Will clean carb again and then see if I can shim
     
  5. TOLO

    TOLO New Member

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    Well. Took the carb all apart. Cleaned every hole with torch tip cleaners. Took main jet out of orifice tube. Sprayed carb cleaner through all passages. All 10 orifice tube side holes are clear. Needles all look fine. Put new orings in. Found that the gas cap wasn’t venting. Fixed that.

    Bike starts and idles fine. As SOON as I start to give it gas it dies. Or if it doesn’t it backfires. No air leaks for sure. Hosed it down all over top to bottom from both sides with carb cleaner and no change to idle.

    Maybe points slipped and got too narrow? I don’t know. Not really sure what now.
     
  6. Tripod

    Tripod Active Member

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    Are you starting it with the choke on? My 79 needs choke and about five minutes of runtime(idle) before i can ease off the choke and give it gas.
     
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  7. power6994

    power6994 Member

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    Replace your condenser.
     
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  8. kirrbby

    kirrbby Well-Known Member

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    Torch tip cleaners are actually files. You may have oversized your jets and such..?
     
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  9. TOLO

    TOLO New Member

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    Lol. I used the only smooth torch cleaner tip. :)

    FINALLY!!!!!! Runs awesome. Ripped around the yard 20x and I have to lean forward going up my berm in first to not wheelie. All smiles now. Got it up to 40mph on the road.

    Between the tank not venting (fixed) and advanced timing (points gap too tight) no wonder it only ran on choke.

    So now to clean and paint since it runs well. It’s actually a nice looking bike under all that dirt. I’ll post photos later.

    Thank you all for bearing with me. Thank you thank you thank you.
     

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