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  • 1600 Gravity Feed Mods

    I have a 1999 Roadstar 1600 that has been bobbed (picture attached, I call it my Yamahog). It doesn't have a fuel pump anymore, and I'm trying to sort out some minor carb issues. I bought it two days ago. Short story goes: 1. Test rode bike, seemed good, bought it for a steal. 2. Tried to ride the bike home, died on me about 3 miles from sellers house. 3. Kept dying on me until I got halfway home, then it finally wouldn't restart. 4. Figured out that I could basically keep a high idle if I kept one hand on the choke (enricher) and one hand on the bars. 5. Idled the rest of the way home using only 1st and 2nd gear! (and one hand on choke).

    Anyway, pulled the carb yesterday and cleaned it up as best I could. Runs dependably now but I have a bad stumble when trying wide open throttle. All normal riding seems fine, no big hesitations or anything unless I go WOT. I have no idea what jets are in the carb now as no markings could be ID'd. Previous owner had the bike for 8 years, and the bike sat for the last 6. Carb was pretty crudy. I have a few plans and need some advice. The bike appears to have an aftermarket, K&N style air filter and VERY short, open exhaust pipes.

    1. I plan to buy a Baron's jet kit
    2. It sounds like I need a larger pilot jet (37.5?) from reading other posts on this forum.
    3. I'll be replacing a damaged starter jet (It almost snapped on me when trying to get it out during cleaning)
    4. My rubber intake is cracked on the outside, but felt smooth and solid on the inside. Will be replacing it a some point.
    5. THE QUESTION: Do I need a larger float/needle setup for a gravity fed carb? Again, I have no idea what is currently in the carb, and I'm happy to spend a few bucks to know what I have in there is right for my application. I think when I hit WOT I'm burning fuel faster than the bowl fills back up, leaving to my stumbling engine. Just a thought at this point.


  • #2
    from Conway, SC. Nice looking bike. I am not an expert, but I will agree with you when you said it seems the carb. is starving when you go WOT. If you don't have a pump you may have the wrong float needle. Also you may need to adjust the float. You should also run some sea foam in the tank. It will help cleaning up any junk that is in the fuel system. Good lock with your new purchase and ride safe.
    I will not apologize for being white, being straight or for loving this country.


    • #3
      Check the Tech Articles section about changing the needle and seat, and going pumpless. The number is there for the larger grizzly gravity flow needle and seat. Normally, unless somebody was bargain shopping because they’d save a couple of $’s buying an off brand Main jet, instead of Mikuni’s, the size is stamped on top. The pilot jet will be stamped on the side. Make sure and get a Mikuni 37.5 pilot.
      If you didn’t get the starter jet out, just leave it alone. If you did, put it back and don’t worry about it. You only need to be sure about the main and pilot.
      Pick up a 16 ounce can of Seafoam, some Techron or Marvel Mystery Oil, add it to a full tank of gas and ride the bike.
      Make sure the idle is between 850 and 950 rpms, and it’ll help when rolling on the throttle from the closed position.


      • #4
        DAMN!!! I saw that bike on craigslist. I recognized the bike, it was in a magazine several years back. . I have a pic of it saved in my favorite road star folder on my computer. I was going to buy it until I saw it didn't have a phone # , but only an email so I figured it was a scam... good buy and congrats on the new bike.

        owning a motorcycle is not a matter of life or death, it is much more important than that


        • cike
          cike commented
          Editing a comment
          that's weird that it shows the back of the bike in the small photo, but shows a different picture when opened

      • #5
        Thanks for all the help so far! I found the tech article on the needle valve and seat:

        Definitely answers my question. Sorry I didn't catch that already.

        Yeah, the bike came with the V-twin magazine article (March 2006). It has a lot of nice attention to detail that I would never have done, but time hasn't been very kind to it. It looks awesome in pictures but up close the satin paint job is really sun faded and chalky, the seat cover is worn through, and shows some other signs of aging. But, I love it! I will focus on the mechanical needs right now and maybe someday I'll get the visuals back to build-time glory...

        This is my first big cruiser. I've had a lot of standard/universal bikes, sport bikes, cafe racers and dual sports. This is my second V-twin (last was a Suzuki SV1000), and my first bobber/chopper. Most of my sport bikes were in the 1200CC size range, so I'm glad for the torque this thing delivers. I'm used to having more power than necessary on my rides, but have fun on all of them (even the slow ones!).


        • #6
          If it sat for 6 Years, the fuel system would be a bunch of gel. Did you clean the tank, fuel pump, fuel filter, fuel lines, etc. then run some Seafoam in the fuel.


          • #7
            Big V-Twins don't respond well to rapid throttle movements. Try just rolling the power on rather than snapping it open. Snapping works fine for sportbikes but not for single carbed V-Twins. That's one big hole with two bigger pistons sucking through it. Things take a little time to develop.


            • #8
              I pulled the tank and emptied it completely. There was some gunk in it, but not terrible. There is also some rust in it. Oddly enough, the petcock has NO nozzle or strainer of any kind on it. It's like someone cut them off with a hacksaw. So, my "Run" and "Reserve" positions both pull from the same point, directly on the bottom of the tank. That, coupled with the lack of fuel filter, probably explains the amount of crud I found in the carb.

              I have no idea if the original builder vented the gas cap or if the overflow vent is enough. It was put together by Speed City Cycles in Indy in 2006, so hopefully they knew what they were doing.


              • #9
                With the bike being pumpless you need to make sure the tank has very good venting. I'd go with the Grizzly float needle & seat if your doing any performance riding. I've went to using only one filter for the gravity feed, and removed the filters off the petcock and the carburetor inlet tube.


                • #10
                  Duke, that's a very compact and efficient looking filter setup. Thanks for the ideas. Maybe I can put a tube on the petcock like yours to get my normal and reserve tank functions back. Thanks for the ideas. I'm pretty sure I don't have the strainer on the carb fuel line inlet (at least, there is nothing external on the tube). When I pull carb again I'll double check. I saw that on the carb breakdown in the manual but didn't find anything on the carb I was working on that looked like a strainer.

                  I ordered some carb-service parts and will be getting back into the carb as soon as they show up. I didn't get the Baron's kit since it was on backorder where I was buying everything else, so I have 3 Mikuni main jets on the way (167.5, 170, & 172.5), a 37.5 pilot jet, new starter jet, and bigger float needle valve & seat on the way. Will try using the stock slide needle for now. This way at least I'll know what my jetting is, which knowledge should help me if I still have to troubleshoot anything down the road.

                  Father Pobasturd, I'll test your roll-on advice next time I get the bike out.


                  • Duke
                    Duke commented
                    Editing a comment
                    Inlet tube on the petcock is stock, strainers taken off and tube cut down. Petcock outlet is threaded 1/8" NPT and has a close nipple threaded into to it.

                • #11
                  Great riding weather has come upon me and the bike has been running so well that I"m reluctant to tear into the carb at the moment. I got all of my jets and the larger needle/seat, but will probably be doing other maintenance before I get back into the carb.

                  A future question, however, about the intake manifold and jetting. I'm perfectly fine installing my new OEM manifold without porting and then just jetting it appropriately for the K&N intake and very open and short exhaust. Is that shooting myself in the foot? I don't really care about power (it has plenty) but want the best reliability, which I think running a little rich is better than running a little lean. Is porting the intake manifold just a performance thing or does it have some other benefits?

                  When I read about porting the manifold it said my jetting size might DROP afterward. So, does that mean if the 172.5 main and 37.5 pilot are correct for my stock needle and stock manifold that I need to drop the main size for a ported manifold? Just trying to understand. THANKS!


                  • #12
                    IMHO, porting the manifold, doesn't require any changes in jetting. On the stock CV carb, if the airflow increases, so does the venturi suction. Ergo, more fuel when you need it.

                    Use the 37.5 Mikuni Pilot, and the 170 main. No need to go richer then that on the main. A 167.5 main, is often sufficient. The 170 will give you more pull at the top end. The 170, is a great choice when running the Dyna 3000 ignitor, or the stock 04 thru 07 ignitor(plug and play on a 1600), which raises the rev limit on the 1600's.

                    Put the clip in the 4th groove from the top of the new Barons needle, and use the stock stack up configuration the way it came off the stock needle.
                    The PMS, can be set at about 2 1/2 turns out, and then leave it alone. It main purpose is to set the air/fuel mix at idle when the throttle is closed. Other then making you feel like you're a super tuner, tweaking the PMS beyond that if the bike is jetted correctly, is a waste of time.

                    If you don't port the manifold(or if you do), at the very least surface the flanges so the faces are nice and clean and even. I recommend soldering the AIS port shut. Unlike sealing it with a rubber cap, soldering is final. No more worries.

                    Use some Hylomar or Permatex's Permaseal around the outside of the orings on the flange. When tightening the manifold fasteners, finger tight on all the bolts. Then alternating side to side and top to bottom, tighten them about a 1/4 turn at a time until the are tightened correctly.

                    I also recommend some washers under the heads of the bolts for the manifold, to help spread the force further out from the bolt head(s).


                    • #13
                      I have a stock needle, not a Baron’s. Just bought genuine Mikuni jets. Does that change any recommendations?


                      • #14
                        My bad. I saw “Barons kit”, and skipped right over the rest.

                        The stock needle is fatter and has a slower taper then the Barons. It also only has one groove. The Barons will have five. Coincidentally, it won’t supply the fuel you need for a proper transition from the pilot to the main, without a stack of shims under the clip. Maybe not a stack, but an undetermined number.


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