1997 Yamaha RT 100

Discussion in 'Japanese Mini's' started by criggs, Jul 23, 2015.

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  1. Jul 23, 2015 #1

    criggs

    criggs

    criggs

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    Hey guys, finally get to post something in the Jap forum!

    Just picked up a 1997 Yamaha RT 100 as a first bike for my girlfriend. Not sure if it exactly qualifies as a "mini", but it is small, about the same size as the Suzy DS 80's. Since the lady is only 5'2", it fits her pretty well:

    [​IMG]
    [​IMG]

    It's a pretty basic little two-stroke. Air cooled, dual rear shocks, drum brakes... looks like something straight out of the 80's! As of right now it starts and runs for a bit, but will die if you give it any throttle, or all by itself after 15-30 seconds or so. I have no doubt the carb is totally gunked up, as the PO says it's been sitting for 4-5 years. This bike has Yamaha's "Auto-Lube" oil injection system on it, with which I have zero experience or info to go off of. I also know that he has pre-mixed gasoline in the tank, so the bike is most likely using way too much oil.

    So, can anyone explain to me how the oil travels through the system? I can see the line at the bottom of the oil tank that runs over to the right side of the engine and goes into the crank case, I'm assuming to the oil pump, and there is a small line that runs out of the same spot up to the bottom/side of the carb. So is oil fed into the pump and then distributed back up to the carb? How do I know if the oil is flowing like it should? I'm afraid to run straight gas in the tank in case the auto-lube system is gummed up. Also, do I just clean the oil passageway in the carb the same as the fuel passages? Do I have to bleed the oil system or anything? Probably a lot of dumb questions, but every other two stroke I have owned has always been pre-mix setups, so I just want to make sure before I go ramping this guy up and down the street.

    If anyone can point me towards a service manual for this thing that'd be awesome. I found a download for the owner's manual, but no service info whatsoever. Thanks ahead of time, guys, much appreciated as always. Lots more pics to come, as well. The GF wants to work on her own bike, so I actually have time to sit back and take some pics for once =P.
     
  2. Jul 23, 2015 #2

    my67xr

    my67xr

    my67xr

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    Once you've cleaned the carby out and put fresh fuel in and checked the oil level in the oil tank,
    start up the bike and run it without the oil hose connected (put the hose end into a plastic bottle etc) to the carby to bleed any air out of the line.
    Don't rev it while you are bleed the air out.
    It won't take much for it toi be straight oil coming out the hose.
    Then refit the hose and start it up and give it a couple of mins to warm up, and blip the throttle a couple of time's.
    You should see a bit of blue smoke as the rev's drop between blip's
     
  3. Jul 23, 2015 #3

    Cactus Jack

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  4. Jul 27, 2015 #4

    criggs

    criggs

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    So the lady and I spent some time on her new RT this week and got it running quite well, but not without a bit of drama.

    First off, I had her pull the seat, plastics, and airbox off to just get a general look at things. As soon as we removed the air filter from the housing, it fell apart in our hands. Then, upon further inspection, we discovered a nest of some fairly large spiders inside of the airbox as well, complete with egg sacs and all. So while she pulled the carb off the bike, I cleaned out the airbox (she told me she wouldn't touch the bike until the spiders were gone =P). After that, she pulled the carb apart (with my guidance of course) and found it full of green gunk, both jets totally clogged. I also noticed that the air screw was run almost all the way in, about 1/4 of a turn out from seated (more on that later). We gave everything a good hour long bath in carb dip, then sprayed everything through with Gumout, and finished everything up with compressed air. I let her re-assemble the carb, and told her to set the air screw to 1 1/2 turns out as per the carb specs I found online for the bike. We got the carb back on the bike, and I retrofitted one of my cheapy pit bike filters for the time being, and gave the bike a few kicks. After 10 or so it started up (although very reluctantly), and once it was warmed up it seemed to run quite well. Took it up and down the street a few times, and noticed that it revved quickly, but seemed to take a while to accelerate, as if the clutch were dragging or something. We left for a bit to take care of some things, and when we got back I checked the clutch adjustment out (which for some reason I didn't think of before), and found it was tightened up almost as far as it could possibly go. Backed it off and gave it a few mm's of play, then tried to start the bike again. Nothing. Gave it 20-30 kicks with different amounts of choke/throttle and nothing. I figured that maybe the pre-mixed gas was fouling the plug, or something still gunked up the carb, and called it a night.

    The next day we drained the gas (which did not look pre-mixed) and filled it with fresh 91, sprayed through the carb with cleaner and air one more time, and put a brand new plug in for good measure. Kicked the bike over expecting it to start pretty easy, and still nothing. After 20 or so kicks I got fed up and sprayed some carb cleaner in the intake and it fired right up, but died after 10 seconds or so. After that still nothing. So I sprayed carb cleaner again, it fired up, and I was able to keep it running if I revved the throttle on and off slightly. After a bit of this I tried to let it idle, but accidentally let it stall out. So, I sprayed a bit more carb cleaner, and this time it fired up and eventually started to idle. I warmed it up, rode it up and down the street a few times, and it ran great, like a brand new bike. So I called it a night and just brainstormed a bit on the weird cold start issue.

    Yesterday I remembered how the air screw was run almost all of the way in. So I went back over there and adjusted it to 1/2 turn out. I turned the choke on, gave it one good kick, and it started up and ran for about 10 seconds or so before dying. I turned the choke off, gave it a few kicks, and it started up and immediately was able to idle. So at this point I knew that the one of the PO's had messed with the jetting on this bike and not properly tuned it.

    For now, the bike starts cold after a few kicks, if its warm it starts first kick every time, and it runs awesome. It actually has a lot more power than I expected, and the GF seems very happy with it. I'm really glad that I found a good two-stroke for her to learn on, since my RM is too powerful for a beginner (and too tall for someone who is barely above 5 feet tall), and the pit bikes are too uncomfortable for her to ride long distance on.

    Here is a pic of her with it:
    [​IMG]

    Here's a video of her riding it, as well (she over-revvs it a few times, she's still learning the two-stroke technique =P):

    There are still a bunch of things we gotta fix. The handle bars are bent, it needs new ones. The front fender sits low at the rear and it rubs over bumps or during hard braking. Also, the PO cut the old silencer off and rigged up the one seen in the photos, it's attached to the front pipe with a rubber hose and hose clamps. The bike is also missing more than a handful of nuts and bolts. I'll post some pics of all these things soon, I meant to today but I had too much fun riding it around and forgot about it =P. As always, thanks for reading, and thanks for all the help and advice =].
     
  5. Jul 27, 2015 #5

    my67xr

    my67xr

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    Yeah sound's like it has a pilot circuit blockage, or it has a smaller Pilot jet fitted.

    Look's like they use a #17.5 Pilot jet in them stock.
    1996 RT100H Yamaha Motorcycle CARBURETOR Diagram and Parts
    Did you clean out the hole at the bottom of the thread's where the Pilot jet screw's into in the base of the carby?
    And did you take the mixture/air screw out when you blew it all out ?
     
  6. Aug 2, 2015 #6

    criggs

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    Sorry for the late reply. Yeah, we removed every removable part from the carb in order to soak it in the carb dip. Then we sprayed carb cleaner through every passage, most especially through the pilot circuit in the base of the carb itself since I know how easily they are clogged up. Also sprayed through the jets themselves. Once all of the chem dip was cleaned out of the carb, we blew compressed air through everything as well. I double checked the markings on the jet, the Pilot still shows 17.5, but I can't read anything on the main. The PO told me that the PO before him installed a larger main jet, but he wasn't sure exactly what they did or how it was done. I think I'm going to get a new set of factory stock sized jets and set the carb back to factory settings.

    The reason that the PO said it was even re-jetted in the first place was for the aftermarket silencer that they installed. Not sure I follow the logic on that. I've had to change jets for different/aftermarket pipes before (I have an FMF "Fatty" pipe on my RM 125 that FMF recommended different jets for), but never the silencer. Not only that, but the way they installed said silencer is... interesting. They literally cut off the end of the stock silencer, and just attached the new one with a rubber hose and hose clamps:
    [​IMG]
    [​IMG]
    [​IMG]

    Not only is it ugly, but it causes some clearance issues with the rear tire, as well. If you compress the rear enough, it rubs on the side of the silencer and inlet tube just after the hose clamp. Ideally I'd like to find a stock one for it, or at least something that looks and fits better, but unfortunately aftermarket support for this bike is virtually nonexistent, and a factory replacement is $160, which is more than half of what I paid for the bike.

    Also ran into another problem. As I mentioned before, the air filter fell apart when we removed the air box, so I tried to order a new one last week. I called our only local motorcycle parts dealer, Cycle Gear, and was told that they didn't even list a replacement air filter for this bike. We then called the nearest few Yamaha dealers, who told us that they too didn't show anything for a 97 RT 100, but they had one for the earlier models that would fit. Since they were more expensive, we took the new info back to Cycle Gear, but the gentleman we talked to was able to find a replacement part for our exact bike from No-Toil. So we ordered it, was told it'd be there in 3 days. 7 days later it arrived. Went to pick it up to find out it was the wrong part, somehow. We double checked all part numbers, and it was the only one shown for our bike. So, we returned it, and after about an hour or so of searching online I was able to find a Yamaha PN for the factory filter, and used that to find a replacement on Amazon. Seems like finding parts for this little Yami is proving quite difficult.

    In the mean time, I rigged up the intake tube and a pit bike filter as a temporary replacement until we get the new one in the mail:
    [​IMG]

    Ugly, but it's better than nothing. I have no doubt that it's contributing to the cold starting, as it will be running a tad leaner without the slight restriction of the stock air box and filter.
     
  7. Aug 3, 2015 #7

    criggs

    criggs

    criggs

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    Finally got around to fixing the uneven front fender. As you can see in some of the previous photos, the fender was sitting low in the back, only an inch or so from the front tire. So, if you brake hard or hit bumps, the tire would hit the fender and rub quite loudly. We pulled the fender off, and found the bracket that attaches it to the bike was quite badly bent.

    [​IMG]
    [​IMG]

    Hard to tell in the picture, but the two side bolt holes on the bracket were twisted rearwards, which tilted the fender back quite a bit. Hammered them flat again and tweaked them back to the right angle, and it's all fixed:
    [​IMG]

    Looks much better, now =P.
     
  8. Aug 3, 2015 #8

    my67xr

    my67xr

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    Yeah i agree with it looking much better.

    You might be able to buy new aftermarket longer fork spring's for it too, just to give it a little bit of a lift ?
     
  9. Aug 4, 2015 #9

    criggs

    criggs

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    Thanks =]. Yeah, we talked about trying to find some longer/beefier shocks for the rear (they're pretty soft) to bring the seat height up a bit. The idea was actually inspired by your DS80, I only wish our RT had a linked mono shock in the rear instead of the dual shocks. If I could find a decent set of fork springs I'd be very interested in that, as well. The bike is a really comfortable height, but a few more inches of travel would really help with the rough, rocky terrain of our high desert, here.
     
  10. Jan 26, 2016 #10

    criggs

    criggs

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    So I just wanted to update everyone on the only issue we've had with this bike that we were finally able to sort out. Since we've had this bike it has always been difficult to start cold (mentioned in detail in my second post). I'm talking 20 or so kicks to start it if it's been sitting longer than an hour or so. This entire time we've just had the air screw adjusted in to 1/4-1/2 turn out to compensate for what we assumed was incorrect jetting. Well a few weekends ago we went out on a riding trip with the family, and when we tried to start up the ol' RT, it would not fire no matter how hard we tried. After maybe 50 or so kicks, with varying degrees of throttle/choke/air screw settings we finally managed to get it to start, but it would not idle and would bog terribly unless throttle was applied very slowly. Unfortunately it didn't get better and we didn't get to ride it that day.

    Later that week we got around to pulling the carb off and checking everything out. Didn't see anything obvious, so we decided to clean everything extra thoroughly. This time, we ran some threading wire through the pilot jet just in case. Afterward, SIGNIFICANTLY more light could be seen through it. Seemed as though it was clear, but not quite clear enough. Shortly after that, I found the fuel passage from the bowl to the choke was also completely clogged, which we must have somehow missed the first time around. Once it was all clean again we re-assembled and re-adjusted everything, gave it a few kicks, and it started up strong on the second kick with no choke. Still starts in one kick warm, and now it only takes a couple no matter how cold it is. Looks like our cold-start issue was just a partially blocked pilot circuit this entire time.

    Also, not only does it start way better, but it also has a lot more power right off the throttle. Way more snap down low. Did a few wheelies by accident, even =P. Just goes to show that any problem can be caused by the littlest silly thing. Hope this helps someone somehow.
     
  11. Jan 26, 2016 #11

    my67xr

    my67xr

    my67xr

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    Glad you got the starting issue's sorted,
    there's nothing worse than kicking a bike over, and over and over with it not starting.
    The only thing i'd be doing to it now is swap that mesh filter for a decent foam filter like a Uni Filter (use foam filter oil on it too)
    If you are ever going to park the bike up for a while,
    turn the fuel tap off with the bike still running and let the carby run dry and allow the engine to stall, this should help you from having problem's starting it with dried gum etc in the jet's so it's ready to go next time you take it out

    Oh and use a strand of copper wire from some old automotive wiring for cleaning the jet's, less chance of it damaging the bore of the jet etc
     
  12. Feb 1, 2016 #12

    criggs

    criggs

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    Yeah, we ditched that mesh pit-bike filter a while ago, just used it temporarily because we had a hard time finding a quality replacement. There are virtually NO aftermarket parts for this bike, but I was able to google the part number and found a factory replacement on Amazon. Basically all that we need/want to do with this bike now is get a factory silencer to replace the ridiculous aftermarket one the PO hacked into place, and get some taller shocks/springs to bring the bike up a few inches.
     
    Last edited: Feb 1, 2016
  13. May 29, 2020 #13

    aletocalvin

    aletocalvin

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    Does anyone know what plastics would fit the 1998 yamaha rt100? Thank you.
     
  14. Jun 17, 2020 #14

    michaelgfutch

    michaelgfutch

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    What was that part number?
     

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