Jetting problem: 2 smokes

Discussion in 'Old's Cool' started by Drif10, Sep 26, 2004.

  1. Drif10

    Drif10 Accredited Jackass

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    Got an 82 RD350. Been trying to get this thing to run properly, and been doing a lot of this :baldy Figured I'd post here because I need some old skool thinkin'.

    Redline is 9.5. If I give it more than half throttle above 4k, it starts to break up, and won't pull. If I'm gentle on the throttle I can get it to rev out, but there ain't much power. It gets worse as the motor warms up. Plug is medium to dark brown. Sounds like it's too rich, doesn't it?

    But the more I lean it out, the worse it gets. :dunno And the plug doesn't appear to change color. Checked the float level, it's bang on spec.

    I'm outta ideas, guys. Cleaned the carb out a couple of times, synched the cables, made sure the airfilters were clean and properly oiled.

    Help. :scratch
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  2. AnnieGS

    AnnieGS Namasté, bitches!

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    #2
  3. Mully

    Mully Kineticist

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    Anything above half throttle is likely due to fuel restrictions in the main jet circuit. You say you've cleaned the carbs, so if you're confident in that, I'd next look at the petcocks for restrictions due to trash clogging the filters. Higher loads also increase ignition load, so I'd confirm plug cap resistances. Beyond that you'll have to post some additional info.

    mully
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  4. Drif10

    Drif10 Accredited Jackass

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    Thanks, Annie! Will review and see if there's something that'll help.

    Mully: Plug caps are new. Fuel lines, filters, float valves, all flowing properly. What other info? Plugs have been changed 3 times, and in any case the bog is even, as in both cylinders, not just one cutting out.
    #4
  5. a_k_nicholls

    a_k_nicholls Been here awhile

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    Have you thought about checking the compression & the reed valves too. If everything electrical & in the carb's checks out ok this may be worth a shot.
    #5
  6. Mully

    Mully Kineticist

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    Helpful info. Petcocks on those relied on a manifold vacuum signal to open the petcock and supply fuel. Manifold vacuum decreases with throttle opening, hence, a loose connection between petcock and manifold could affect fuel supply at higher throttle openings. Fuel tank vent may also be a factor: check that whatever hose or vent is present is clear and unrestricted. Finally: is there any indication that at the time the engine loses power/breaks up that there is an increase in exhaust smoke? If so, crank seals may be a factor.

    Keep feeding more info and we'll keep trying to get closer. :thumb

    mully
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  7. Flash

    Flash Sand Boxer

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    Hiya Drif

    You say it runs worse as you lean it out. What are you doing to lean it out? Smaller main jet? Adjusting the needle clip?

    Plug color is good, indicating reasonable spark and mixture. Leaning it out doesn't change the plug color, but its hard to get a good plug "chop" if it won't run over 4 grand. Whack the throttle and it blubbers. Feed it slow and it revs gingerly.

    She's sat some time during ypur Middle East vacation.

    My bet would be a clogged main jet. Replace 'em with new ones. Just for giggles, go up one size. Leaner hasn't worked, right?
    #7
  8. Drif10

    Drif10 Accredited Jackass

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    Hokay,

    Petcock is not vacuum fed, so no leak there. Reeds and cage are good. Motor recently rebuilt, with all new seals. The guide that Annie linked shows what the base setting were for this motor, gonna use that as a start. Have changed jets, so no problems there, and prior to parking it I had drained everything and disconnected the battery, so that shouldn't be an issue. Have taken the carbs apart since to check, all is good (cleanliness wise, anyways).

    Changed the head out last night for one that has been shaved 0.030". Runs a little better, and then tried a bit leaner on the main, think you're right about richening it up.

    Info I should have included before: Motor is an 85 RZ, so that means with the power valve, which is working to spec. Shaved head currently. RD 400 carbs, which make them 2mm larger. Individual air filters. Stock RD pipes, but will probably trim the baffles once I get a good baseline going. Fresh rebuild, 0.25mm over (first overbore).

    Gonna try richening it up tonight, starting with the baseline settings in the jetting guide, and see what it does.
    #8
  9. Flash

    Flash Sand Boxer

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    Hmmm...individual air filters...more air. Bigger carbs...more air. Higher compression...needs more octane. Larger displacement...needs more fuel.

    And we're leaning it out?

    :lurk
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  10. Drif10

    Drif10 Accredited Jackass

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    Yeah, cause the plug is so dark. I agree with what your saying, should need to be richer, but the plug says different. So do the pipes, pretty sooty.

    Oh yeah, oil injection is set up and working properly, so it's not that causing the dirty plugs.

    I'll see what happens tonight. Gotta fix the wife's car first though, damn thing wants a new knock sensor, got lucky with the part, local Subaru dealer had one in stock. NAPA wanted $540!!! OEM cost $103. :scratch
    #10
  11. AntWare

    AntWare Lost In Translation

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    Is the choke sticking open?
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  12. Drif10

    Drif10 Accredited Jackass

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    Nope, choke isn't sticking on.

    Trying to figure why I misread this thing. Plug was telling me it was rich, and the specs in a manual for this motor said that the stock main jet was a 115. But it bogged when I got below a 260. Last try was at 160, and I'd tried richer before, without noticable change.

    Kudos to Annie for that link, as it gave base set up numbers for 240 to 250. Like Fast said, we should be going richer. But I thought I was fairly rich, based on the manual I had here stating the 115 was stock. Fucking Haynes manual. So based on what was in that link of Annie's, I went to a 270 tonight.

    Can you say wheelie? I know I can. :D :ricky

    Not finished yet, still a a bit of bog at 4.5, gonna go to a 290 and see how that works out. If good, then some work with the needles. Got this bike when it was mostly modified many years ago, but it spent 6 years in storage while I was in Europe, then got rebuilt in the past year. Buddy gave me a whack of stuff for it, including a jet board from 85 to 420, and some needles of various tapers. Too many choices is not a good thing, at least this time.

    Thanks to all for their input, it was all good as it confirmed what I was doing, and pointed me in the right direction. :thumb

    I love this place.
    #12
  13. Wayne Weber

    Wayne Weber why are we stopping?

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    Drif, I've run into this before on 2 strokes. It looks like it's running rich because the plug is too cold. I use an NGK B7ES. With too cold of a plug, you can actually lean seize a motor, but the plug still looks rich. I had this problem, running a NGK B9ES (not seizing, just the rich look).

    The only danger of two hot of a plug is that it will overheat and the electrode will vaporize at higher RPM's (not a good thing either...) but not so bad.

    I've run the 7 in my KTM550 at continued high rpm use, no problem ever, and I've only fouled a plug once in 10 years on it.

    And, it sounds like just the main is too lean, easy fix!!! But do the plugs first so the reading is accurate.
    #13
  14. Drif10

    Drif10 Accredited Jackass

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    Good point. Running an 8, which is stock, but the motor ain't. What is it, smaller number is hotter? Can't remember. :scratch
    #14
  15. neduro

    neduro Addict Super Moderator

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    One other thought- pipe spooge, and to a certain extent plug color, will be heavily affected by oil mix ratio. In the case of the pipe, more so than by jetting in my experience.

    What kinda oil you running, and at what mixture? Just curious, won't actually have anything to add, as my experience w/ 2T jetting is all on KTM 300's and Jap 250 MX'ers...

    :thumb
    #15
  16. Flash

    Flash Sand Boxer

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    Lower number, hotter plug.
    #16