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Thread: '80 Yamaha Tri Moto 125 - Yanks Back on pull start (Backfire? Timing?)

  1. #1
    Join Date
    Jul 2017
    Location
    Chicago, IL
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    Angry '80 Yamaha Tri Moto 125 - Yanks Back on pull start (Backfire? Timing?)

    I want to first start by thanking everyone for reading and viewing my post.

    I will let you know that where I am NOT new to engines, or fixing them, I am new to this site (although I have been browsing it for years) this ISSUE I have never seen before and I am very curious how to fix it - this machine WILL NOT beat me!

    So to explain, I used to ride this trike many years ago, when I was a kid we had one and there are still many family stories about how I rode it into the Mississippi River (I just cleared up the facts on the telling of this story last year). So I had driven by this guys house for 3 years (at least) and had seen this machine sitting in their yard. I finally got up the courage to pull into there driveway and ask the guy if he was looking or willing to sell it. Obviously, I bought it from him ready to knock a small project, clean it up, getting her back in shape and ride the hell out of her.

    I have to admit, where at first I was disappointed because it seemed to be a simple fix (head bolt stripped) of drilling out and installing a heli coil, and reinstalling the head and orginal copper head gasket. I had 120 psi compression, spark at .040 on the gap (moved the gap back to factory or .028), ultra-sonic cleaning the carb & reinstalled.

    I discovered the pepcock was stuck on (open) so I removed, broke it down and cleaned and lubed, tested and reinstalled = fuel flowed good, and shut of completely on OFF.

    After reinstalling the carb (air box off/exhaust pipe installed) I pulled to start it, took a couple of pulls but she fired up at a high idle - not reving out but high. I turned to pick up the screw driver to adjust the AirFlow intake and she died on me.

    HERE's where it get's sticky....

    I try to restart it and the engine kicks back on me yanking the starter cable out of my hand, I figure "fluke" pull on it a couple more times and same damn thing, except this time it breaks the old rubber handle in half!

    So off with the starter, at this point I am thinking >timing< right? NOPE-> I recalled that these are 2 stroke and non adjustable stators (fixed).

    So it has to be the sheer key right? NOPE->sheer key was fine, intact: I removed it to inspect it, not a mark on it. reinstalled and retorqued the flywheel nut to specs. I did notice that the starter wheel was mangled and broken. I did some repairs and reinforment with the small welder; basically I used thin gauged flat metal sheet cut into 7/8in strips, by 1in folded in half and insterted on the pully engaged side of the starter wheel. Spot welded them into place, ground smooth = starter get's it right now!

    So it has to be the Trigger Coil right? NOPE-> Trigger coil test at 10.4 ohms (little high but good enough)
    So it has to be the Charger Coil right? NOPE-> Charger coil test at Brown Wire = 283.9 ohms (right in range)
    So it has to be the Ignition Coil right? NOPE-> Ignition coil test at: Primary = 1.0 ohms (right in range), Secondary = 5642 ohms

    Out of ideas, I am back at the crank case, maybe there is TOO much fluid (oil, gas, water) in the crank case causing it to back fire? I used an electric fuel pump and 1/4in line to suck out the crank case. Got to tell you, there wasn't alot in there, maybe 10oz, although there was some, but I wouldn't think it was enough to cause this "backfire."

    So back to the Carburator: it has to too much fuel... I remove the carb, remove the plug (run another compression test just to be sure = 120psi: still holding strong). I removed the carb bowl, nothing out of the ordinary; no dirt, sand, tank debris, gas smelled clean. For all intent and purposes the carb still looked clean. I checked the float adjustment; shuts off at level with carb: I re-adjusted it a little tighter to close out just A LITTLE SOONER.

    So I had read some where that a clogged exhaust pipe >might< be the issue, So I uninstalled the pipe and reinstalled the carb, gas line on=check and away we go ....

    Again, a few pulls to start and the thing fires up! I give it gas and it throttles up nice, then back down to a high idle. AGAIN, i turn to reach for the screw drive to adjust the idle with this beast screaming at the top of her lungs and it shuts off. I go to start it again, and she yanks BACK hard and here the backfire out of the exhaust port. I remove the plug and it's oiley wet with a tinge of gas smell.

    Now here are the new waters for me - I am not sure that excessive OIL would cause it to backfire, whats more - I'm not sure how to adjust the oil delivery (if it can be adjusted). So again - taking out the plug (NGK-R=BR8ES) and taking a shot in the dark to replace it with Manufacture recommended Champion Copper Plus 801cN3C (replaces N10Y), to no avail - still BackFires and yanks the pull starter.

    SO in conclusion - I have ruled out EVERYTHING that I can possibly imagine. If I am missing something - please let me know. As a last ditch effort, I have already ordered a new CDI praying that this MIGHT fix it. I can not think of anything else that it could be. Thoughts?

  2. #2
    Join Date
    May 2010
    Location
    Wichita, Kansas
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    1,359
    It sounds like an issue with the CDI. If wire incorrectly, or from the wrong machine, this can happen. A blaster uses a similar set up for the CDI, but the curve is different. They could have swapped it out with this. A recoil stator assembled backwards could do this too. I don't know if that is possible though.

    Can you take a picture of your stator as its bolted on the motor, and the inside of the flywheel? Incorrect stator position or a modified flywheel (reglued magnets out of time) could cause this. I doubt either of these would be the problem though.
    Last edited by RubberSalt; 07-21-2017 at 04:00 PM.
    I just wanna go fast. If your not first, your last!!
    Reproducing the Tecate CDI. Contact me if you need one. I'm most accessible on FaceBook. You can find me on the 1984-1987 Kawasaki Tecate KXT250 Group.

  3. #3
    Join Date
    Sep 2010
    Location
    NEPA
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    7,048
    Recoil could be wound backwards. Very popular on these.
    Please help those who cannot help themselves.

    ALWAYS buying Museum quality machines,3 and 4 wheels. And any and ALL ,NOS parts,EVERY brand.

    I am turning my PM's Off,my Email is billsracing@hotmail.com,put 3WW in the subject. Thanx!

    Gun laws do not stop criminals. BULLETS do.

  4. #4
    Join Date
    Jul 2017
    Location
    Chicago, IL
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    9
    RubberSalt, thanks for the reply, i'd be happy to take pics and upload them when I get home this afternoon. J

    ust as a "Hail Mary" I'm also planning on removing the carb intake block and removing the reeds: they are the ONLY thing I haven't cleaned yet, and see what that does, but I am leaning toward CDI, perhaps won't one!?!

    I don't know...
    Last edited by Akhenra_Tri125; 07-21-2017 at 08:32 PM.

  5. #5
    Join Date
    Jul 2017
    Location
    Chicago, IL
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    Quote Originally Posted by atc007 View Post
    Recoil could be wound backwards. Very popular on these.
    You know, I never thought of that....

    Anyone have any idea the direction of rotation of the engine?

    The engine (as you are sitting on it) the winding of the recoil pulls the engine: stator on left side counter clockwise (on mine ... FYI)

  6. #6
    Join Date
    Jul 2017
    Location
    Chicago, IL
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    9
    STATUS UPDATE: Issue resolved:

    RubberSalt -> so I got home this evening and started to remove the starter cover to get to the flywheel, so that I could take pictures of the stator. I didn't get past the starter cup, as what ACT007 had said, stuck out in my mind: I noticed that all the clips that I installed were on the right side of the holes, which meant that the starter was engaging and turning the engine "CLOCK WISE" and NOT counter clockwise as I had earlier speculated. Click image for larger version. 

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    So, after reinstalling one of the clips that had popped it's welds and running the engine rotation in my mind over and over - I was convinced the issue was the recoil and I had been trying to start this engine in reverse!?! (see attached picture). The guy that I had gotten the trike from had reversed the starter and I had just assumed that the direction was correct as it was working... or not.
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    I completely disassembled the recoil, flipped the coil spring, moved the engagement clip over to the opposite hole, re charged the spring, fed the cord around the inner pulley and installed the handle (see attached picture). Once installed, I reinstalled the muffler CONVIENCED this was the issue, and ready for a test start.
    Click image for larger version. 

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    First pull: it sputtered and wanted to start then died.
    Second pull: (after turning the idle screw up 1 full turn) fires right up and comes straight to idle.

    So back on go all the covers and over to the hose for a bath (remember: this thing has been sitting under a tree for 3 (+) years). (*See Picture )
    Towel dry her off and OFF WE ROLL, shifts nice in all 5 gears, though it does have an issue staying running in 1st at stop. I imagine that is going to be the carb fine tweaking to get it where I want it.
    Click image for larger version. 

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    Thank you guys for giving me a second set of eyes and helping me see what I could not. I appreciate you guys and your words of wisdom.
    Last edited by Akhenra_Tri125; 07-22-2017 at 01:09 AM.

  7. #7
    Join Date
    May 2010
    Location
    Wichita, Kansas
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    1,359
    Yeah, after reading what ATC007 said... i dunno why i didn't think that lol.

    Kick ass on getting it going. There is quite a bit you can do for power with these. The YT175 jug/piston/head/exhaust flange/pipe fit these. This gives these machines a whole lot more power. Much much more fun.

    The stock reeds on these are metal petals. All the OEM ones I came across where perfectly fine in sealing and response. Several of the 125s/175s I picked up still had the oil injection system in use, they where on the original bore too. Under a stock set up, it sounds like the injection isn't a bad thing.
    I just wanna go fast. If your not first, your last!!
    Reproducing the Tecate CDI. Contact me if you need one. I'm most accessible on FaceBook. You can find me on the 1984-1987 Kawasaki Tecate KXT250 Group.

  8. #8
    Join Date
    Jul 2010
    Location
    glendive, montana
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    1,822
    so I see you have a suzuki waterbuffalo, never let that baby just sit , or you will be looking at a complete tear down to replace a inner crank seal
    rectum nothin damn near killed them
    feel free to leave feed back for me here. http://www.3wheelerworld.com/showthr...06#post1119306

  9. #9
    Join Date
    Jul 2017
    Location
    Chicago, IL
    --
    9

    Cool

    Quote Originally Posted by RubberSalt View Post
    Yeah, after reading what ATC007 said... i dunno why i didn't think that lol.

    Kick ass on getting it going. There is quite a bit you can do for power with these. The YT175 jug/piston/head/exhaust flange/pipe fit these. This gives these machines a whole lot more power. Much much more fun.

    The stock reeds on these are metal petals. All the OEM ones I came across where perfectly fine in sealing and response. Several of the 125s/175s I picked up still had the oil injection system in use, they where on the original bore too. Under a stock set up, it sounds like the injection isn't a bad thing.
    Yep - RubberSalt - it's been awhile, after I got the YT125 going I picked up another 1980's project; 83 pick-up/Dump truck with a seized 351 engine.

    the oil inject set-up is still in place and functioning on this YT125. That ol' girl hauls ass. I opened it up on the street the other day just as a reminder of the good ol days when we used to ride on the sand dunes of LaGrange, MO right off the ol Big Muddy: Mississippi' River. Ah, those were the days

  10. #10
    Join Date
    Jul 2017
    Location
    Chicago, IL
    --
    9
    Quote Originally Posted by muthey View Post
    so I see you have a suzuki waterbuffalo, never let that baby just sit , or you will be looking at a complete tear down to replace a inner crank seal
    I Wish I had a "WaterBuffalo" that's a 1980 GS550 project bike that I might work on this comming winter and see I can get it refinished for next spring. Yes it was left sitting for 5 years and yes the MAIN seals on the stator side are already shot (it was laying on its right side Stator up for a good 3 years after the center stand sunk into the mud/dirt and the bike fell over - previous owner just left it sit).

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