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Off Idle Stumble

Discussion in 'Motorcycle Tech Talk' started by Gunnernate, Oct 20, 2011.

  1. Gunnernate

    Gunnernate New Member

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    Just installed SE-203 cams on my stage 1, 1450 Harley. SE-II exhaust with Big Mountain Thunder Baffles, Kuryakyn Hyper Charger. CV carb with 48 slow and 195 main jets. EZ adjust mixture screw. Sportster Needle, drilled slide 1/8" and SE diaphragm spring. Slight stumble at 1600-2000 rpms. Very annoying! Stumble is most noticeable when coming off coasting applying very little throttle. Under load, she does not stumble, even under 2k rpms. Other than that, she runs sweet! Took carb apart and cleaned everything. How can I tune that out or what do I need to change?
    Thanks
  2. JohnnyBiker

    JohnnyBiker Well-Known Member

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    Your problem right off the bat is that drilled slide!!!! That will cause your slide to flutter too much!!
  3. Gunnernate

    Gunnernate New Member

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    I drilled the slide 9 years ago. Never had the issue until installing the 203 cams.
  4. JohnnyBiker

    JohnnyBiker Well-Known Member

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    I have always heard that drilling the slide is a no no. You could also check the accel pump diaphragm...
  5. Gunnernate

    Gunnernate New Member

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    I changed the diaphragm a couple of days ago thinking that was it, but no change.
    Nate
  6. Lucifer

    Lucifer Well-Known Member

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    Was the carb set up the same as before and the only change made was the 203's??
    Could be that with the change in cams and air flow through the carb, the drilled slide could be opening too quick...
    A couple of things you can try first is dropping the pilot jet down a size with the N65C needle or putting the stock needle back in with the 48 pilot...
    Did you leave the stock spring in the carb unmolested when you drilled the slide or put in a lighter spring or clip a coil off the stock spring... drilling the slide can cause "hunting" or surging especially with a lighter spring or a clipped stock one....
  7. Gunnernate

    Gunnernate New Member

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    Yes, the carb is the same set up. The diaphragm spring is lighter and not a cut stock one. I will try the stock needle and spring to see if that is it! Will report back tomorrow with results. Thanks for the tips.
    Nate
  8. Gunnernate

    Gunnernate New Member

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    OK, I changed everything and I still have the stumble. Went to local Indy and he recommended that I get a new carb. He says at 90K, I am overdue! Of course, he wants to sell me an S&S carb! OH, I have my idle mixture screw out about 4 turns! Maybe I should go to the next larger slow jet! Any thoughts?
  9. HarleysLR

    HarleysLR Active Member

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    S&S makes a good carb but you don't need it, they are way over priced anyway.
    You can rebuild your CV to be just like new, or buy a new used one off ebay.
    Or Kenfuzed may still be selling CV's I'd ask him. But I would stay away from the S&S carb. Gas hogs, I've run them and the CV is a better carb for a street machine. JMO
    Lot of guys don't know how to tune a CV correctly so to them that makes the CV a bad carburetor.
  10. Lucifer

    Lucifer Well-Known Member

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    You don't need a new carb....it does need to be tuned though...4 turns out on the mixture screw is too much, backing it out indicates you need a larger pilot jet,but, you don't need a bigger jet than a 48 for your build...
    What changes did you make??you should only make one change at a time...
    When you set your idle mixture ,did you turn it in until it stumbled then back it out until it stumbles,the split the difference??

    Is it a Dyno-Jet kit you installed??
  11. Gunnernate

    Gunnernate New Member

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    I turned it in until it stumbled but could not get it to stumble turning it out. I did however turn it out just enough to keep it from hiccuping through the carb. That seem to help, but did not totally fix the just off idle stumble.
  12. Lucifer

    Lucifer Well-Known Member

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    Did you check for intake leaks??
  13. Gunnernate

    Gunnernate New Member

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    Did that by spraying carb cleaner around all the known areas for leaks. No leaks detected!
  14. Lucifer

    Lucifer Well-Known Member

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    OK...What about the accelerator pump??Do you get a good squirt of gas out of the nozzle when you twist the throttle??
    I still think you've got an awful lot of fuel in your idle circuit for an 88"er with mild cams....
    When you said you changed everything...What was everything?? What is your idle speed set at?? Should be 950-1050RPMs....
  15. Gunnernate

    Gunnernate New Member

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    I get a great spray from accelerator pump! It does not hesitate or stumble when I get on it! Just at a slight twist off idle. Once I get past that, she runs strong without any hesitation. So far, I put back the original diaphragm and needle. That was the last thing I did. Before that I replace the accelerator diaphragm and spring. The carb is clean, inside and out! Oh, when I rode it to Vegas (240 miles) she ran great and I got 44 mpg at 75-80 mph. Everything points to pilot circuit!
  16. Fatboy128

    Fatboy128 Well-Known Member

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    BTW, American Iron had a good article on carbs in the latest issue (December). Really explained them well!
  17. Copter MD

    Copter MD Member

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    Good evening gentleman. This my first post here so I hope it works.

    First I’d just like to say that I am in no way claming to have an answer to the problem we are talking about; I’d only like to throw a few things out to possibly (FUEL) another train of thought. Gunnernate, I feel for ya! These things will drive you crazy!

    Ok, just need to ask: you said that this stumble is most pronounced after a coast down and then rolling the throttle on just a tad. Does this mean that it does NOT do it when accelerating from a stop? Or, is it just worse after a coast down? The only reason I ask is because I’m thinking of spark plugs possibly loading up after a long de-cell from high RPM. I would think that your new cams, along with the bigger primary jet, will be pulling in a lot more fuel on a hard de-cell. If your plugs or wires are getting a little tired they could be loading up. When you say “stumble” does that mean “rough running”? Or, does it seem more like you just turned off the key for a split second and turned it back on? In my experience, a rich condition will cause an engine to act like it has an ignition problem “rough running.” Whereas a LEAN condition will seem more as if you just plain turned the fire off for a split second and then it bursts back to life. Sometimes it can be hard to distinguish between the two.

    This next thought is just that, A THOUGHT. Did you install the cams, or did you have it done by a shop? Does it have adjustable push rods? If someone got one a little on the tight side, it could cause havoc when the engine gets hot. I own an 02 FLHT and do all my own maintenance, but I also maintain an entire fleet of BMW R1200RT’s and the #1 complaint I get from the guys is an off idle stumble. It ALMOST always turns out to be tight valves combined with throttle bodies being out of sync. NO, I’m not in ANY way comparing BMW’s to Harleys. As I said, just throwing some stuff out there.

    If the carb was working well before the cam install, you just might not be having a carb issue. Even though that’s where MOST of us, including myself, would look at first.

    Thanks for listening and I wish you the best of luck with your problem.
    Regards…
  18. Gunnernate

    Gunnernate New Member

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    Very good questions Copter MD. the stumble feels like I am running out of gas. Give it a little twist of the throttle and she jumps into action! As the bike warms up, the stumble is less noticable. As I coast to maintain a reasonable speed while spitting lanes, is when it is really annoying!

    Yes, I too do my own work! Besides the cams, I installed the hydralic cam tensioned kit about 10K miles ago. This after loosing one inner bearing which took out the oil pump. This was at 30K. And another time, it was one inner bearing. Same results!

    Thinking like you, I readjusted the the push rods. No change! I replaced the spark plugs and wires. No change! I swapped out the coil. No change! Of course, all to rule out these as causes!

    If not for the stumble, she runs great! I would say that in the plus 2K rpms range, she runs smooth and strong!

    I have a new rebuilt carb coming in a couple of days and will swap it out to verify or rule out that! Thanks for your thoughts on this.
  19. Copter MD

    Copter MD Member

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    Darn, I guess great minds think alike…

    Sorry to here you have had to go through all that and still have not found the problem…
    I do agree with Lucifer in that you should not have to have a bigger primary than a #48, but have you jumped up to a #50 yet just to try it? I’m guessing you probably have already…

    I have felt your pain on the cam bearing issue. I bought my bike about a year and a half ago and it’s my first Harley. I road it for a week before I did an oil change and found the oil drain plug looking like Tina Turners hare from 1987! It was the forward inner cam bearing; and yes, it did waste the oil pump and everything else on the right side of the engine. It sat in my garage for almost eight months while I tried to decide what to do. I only paid $8,500.00 for the bike with 25k miles on it. Being strapped for cash, a good friend hooked me up with some lightly used parts and a bunch of NEW parts as well. It’s still all stock with the exception of the Ness filter and mufflers. I hope to do some bigger cams and a 2 into 1 exhaust next year. It’s been 2k miles since all the cam stuff and it still is running well. I’m only 5’ tall and a buck fifty, so it pulls me around quite well.

    Good luck and I’ll keep thinking about your issue. Hope the new carb works for you! If I have any brilliant ideas I’ll let you know…

    Take care…
  20. Lucifer

    Lucifer Well-Known Member

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    I think it's down to the drilled slide causing the problem,raising a little too quick allowing too much air and not drawing enough fuel in light throttle situations...
    Let us know how the new carb works
    When you're setting the fuel mixture have the engine up to operating temp,then turn your idle up to a fast idle(1300 RPM's or so)that makes it easier to detect a change in idle...
    I think a 46 pilot is a good starting point and with the N65C needle should take any transition stumble out....
    Good Luck:D Keep us posted...:):devil:

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