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Stock carb - intake backfire

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  • Stock carb - intake backfire

    Hey guys,

    Before I ask any questions, I just wanted to say thanks. I've read so many useful posts that I haven't participated in, I sometimes feel like I know y'all better than y'all know me. Rejuvenating my 15 year old roadie has been an experience, and you guys have made it a significantly easier one. Much appreciation.

    So I've been in the carb 3 times since I got the bike. The bike is an 04. My uncle became the second owner in 05. He got a new bike about 2 years ago (Indian Darkhorse) and the Roadie sat under a tarp in the Arizona heat for about 18 months. I bought the bike back In September and have been slowly rebuilding it as time and funds permit. My uncle road about 2000 miles a year and kept the oil changed... that's about it.

    I was getting a heavy gas smell and figured I should dive into the carb - it smelled like it was running rich. The bike has a K&N RB-0700 cone air filter, and a Vance and Hines 2 into 1 exhaust.

    My first carb adventure involved a cheap (30 buck) oem rebuild kit and a lot of gunk. I replaced the jets with stock oem, the hardware, the gasket, the float bowl needle, the pms, various springs and o rings. The kit I purchased came with an oem needle, but I found (what I later learned was) a barons needle already installed. It seemed nicer than the oem so I kept it in. The clip is on the 4th groove down.

    Tearing into the carb the first time I found that the idle adjuster cable and the choke were both fucked. The coaster enricher cap had rotted out and the spring below had shot out.

    I did not dial my pms in correctly and the bike was riding like shit. I ordered a new idle adjuster, coaster enricher diaphragm, spring, and cover, and the air max braided stainless choke (which I really like, and was only 20 dollars more than a stock choke from partzilla).

    I opened the carb a second time, and the carb was much dirtier than expected after having just cleaned it out. Turns out the super old KN air filter (which I had also tried to clean) was falling apart and sucking into the carb. No bueno. Replaced the air filter immediately. The black vacuum cap that's found at the very top of the carb was also very gunky. I cleaned it out and ordered a freshie. I also ordered a fresh needle diaphragm after seeing the difference between the old coaster enricher diaphragm and the new.

    At this point I checked the OEM main jet, it was a 167.5. The one I pulled out the first time was a 182.5. I put the 182.5 back in. And had the pms at 2 and a half turns. Ran better than the first rebuild but still running rich (with that giant main jet) and I didn't feel like I was getting enough fuel in 1st and 2nd, riding a bit choppy. I ordered new mikuni jets from jetsrus.

    My most recent journey to carb land I installed the new needle diaphragm, vacuum tube, a Barons thumb screw pms, a mikuni 40 pilot jet, and a 172.5 mikuni main jet (I ordered 175, and 177.5 as well).

    After the most recent rebuild - the bike no longer smells gassy. It is running better than it has ever run - while warmed up, especially feels great in 1st and 2nd gears with that 40 pilot jet in there.

    Here's my concern, when the bike is cold, I get a fair bit of hiccuping if I give it any throttle. After the bike has warmed up, it doesn't happen. But when I give it some throttle without letting the bike warm up for about 3 minutes it'll often give me a little backfire up front (i assume that's what this is). Is this normal behavior? I know you're supposed to warm the bike up - I was giving her about 90 seconds before, I've had to about double that now. It also always requires I use the enricher (choke) for about 30 seconds to start up (dunno if this is relevant).

    As, I said, she's riding better than ever, I just wasn't sure about this in-take cough. With the after market exhaust I wasn't sure if I should be using a larger main jet. 182.5 seemed way larger than anything I've seen recommended around here though. As I mentioned earlier, I do have some larger sizes than 172.5 if need be. This air filter is also a touch smaller than the last one.

  • #2
    Air filter
    K&N RB-0700 - K&N Individual Round Style Stacks for inchEarly Type inch Fuel Injectors (Single Stacks) for Chevrolet, Etc. - Filters designed to fit with cut velocity stacks, or straight pieces of exhaust tubing.

    Comment


    • #3
      The 172.5 is the jet you need if I am not mistaken, Barons needle but I don't remember which groove and there should be a couple of spacers on the needle ( like a washer and a doughnut) There is a good write up on the carb in the tech section. 30 sec on the enricher sounds normal, if you didn't have to use the enricher there would be something wrong. The roadstar doesn't like to have the throttle "blipped" that will cause a cough. More knowledgeable guys will chime in here soon.
      Life is short, eat dessert first----Unknown

      Comment


      • #4
        Check out the following article, from the tech section, on Accelerator Pump Adjustment. I had the same problem, but after making the adjustments, it hardly ever happens now... FYI, once you move that Duration Screw, it has a tendency to vibrate loose, put a drop of *Blue* thread locker on the screw, otherwise you'll be wondering why the problem keeps returning.

        Comment


        • #5
          The 172.5 main jet and 40 pilot are correct with the Barons needle. The clip should be in the 4th groove on the needle with the plastic spacer and 1 silver washer under the clip. PMS should be 2 1/4 - 2 1/2 turns out. Now when starting pull the enricher to start, it will sputter after just a few seconds, when it sputters push it in to about half way and ride it for a few miles before pushing all the way in. This is the normal procedure and will fix your issue.

          Also make sure the idle is set at 900-950 rpm. A low lopy idle will also cause hesitation and backfire issues.

          Comment

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