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First post to the forum, I have no idea if I’m putting this in the right spot, if not I apologize. 
Anyways, I have a yamaha Blaster frame with a yz490 84-86? Motor in it. 
when I picked it up I knew I was getting into trouble but not nearly this bad. 
Motor would NEVER kick start, so off I went.

Had a smeared piston from a base gasket leak, no big deal. Replace the entire top end, have the head mod done to prevent the dreaded pinging issue, reassemble it. starts first kick! Shut it off, won’t start. Kick it a million times, won’t start. Would pop start fairly easy and run like a MF but idle would fluctuate like crazy so I figured I had a vacuum leak. 
was out riding and it ran away on me, had to pull the choke to kill it. Since then it has refused to start at all again except for the occasional major backfire and now the clutch slips when I try to pop start it. 
New tm38 mikuni flatslide carb, New CDI, new coil, Brand new reeds, compression is 150, timing was verified to be correct, plug is new. Cannot get it to start. 
only thing I have not done is a leak down test and replaced crank seals. At this point I am grasping at straws. The ONLY other thing I can think of is that the ends of the reed cage have slight pitting to them and have a minuscule gap on them when held to light but slight pressure closes them up, so I would figure case pressure would shut them easy. This is my first 2-stroke bike project as I have always built jetski for the last decade. Carb is jetted to factory spec. Still won’t start with OEM carb. I have way to much money into this thing to sell it now. Any insight would be appreciated. 

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Leakdown tester for sure is a good idea, followed by new crank seals.

That's a pretty crazy machine!

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6 minutes ago, smirmeister said:

Leakdown tester for sure is a good idea, followed by new crank seals.

That's a pretty crazy machine!

I’ll have to get one ordered and make up some block off plates I suppose. I have never replaced seals on a quad/bike motor, Im assuming you have to use some sort of puller and slide hammer since the case splits vertically instead of horizontally? 
Yessir it is insanely fast, when it runs haha. 

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Chances are it's like every other Yamaha; the seals are installed from the outside so it's an easy job. To remove them, punch or carefully drill a small hole in the seal (there's a metal backer) and put in a wood screw. You can then yank it out with pliers. 

I think there is a thread in the Honda 2 stroke section with DIY tester plans.

Edit:

 

Edited by smirmeister
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46 minutes ago, smirmeister said:

Chances are it's like every other Yamaha; the seals are installed from the outside so it's an easy job. To remove them, punch or carefully drill a small hole in the seal (there's a metal backer) and put in a wood screw. You can then yank it out with pliers. 

I think there is a thread in the Honda 2 stroke section with DIY tester plans.

Edit:

 

I’m going to throw seals at it and inspect the clutch plates while I’m there, guess it wouldn’t hurt to replace everything. 
Any thoughts on the clutch slipping all the sudden? All I did between then and now was change the fluid (Gtx 10w-40 no additives) and throw new back tires on it. I’m not familiar with wet clutches so I’m not sure if it’s a possibility that they were on their way out already and the change made it more obvious? 

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hello there I went through all the same troubles your going through 4 years ago. the not starting is scary check your woodrif key I have a 2000 blaster with a 1980 it 425g motor and was having a hard time starting it one day well it kicked back on me and I broke my "F_____ing foot the crank seals are easy, you may also check for porosity on the flywheel side sometimes the cases have pin holes epoxy fixes that.

the only thing with mine is I have to take off the foot peg on the kick start side for cold start after that it will start with the peg on

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6 hours ago, DIY IT 425 said:

hello there I went through all the same troubles your going through 4 years ago. the not starting is scary check your woodrif key I have a 2000 blaster with a 1980 it 425g motor and was having a hard time starting it one day well it kicked back on me and I broke my "F_____ing foot the crank seals are easy, you may also check for porosity on the flywheel side sometimes the cases have pin holes epoxy fixes that.

the only thing with mine is I have to take off the foot peg on the kick start side for cold start after that it will start with the peg on

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Haha sweet blaster dude, I’m sure you’ve been through almost all the same troubles I have squeezing the motor into the frame! 
I would have sold it already if they were so much fun. 
I have checked the key and timing several times now but I’m going to do seals so I’ll check again! 
Everytbing points me toward timing but it seems to be spot on, and I’ve replaced all the electrical components short of the stator plate.. 

I would have it running but it seems I need to replace my clutch plates!!!

So I just pulled the clutch apart, the fiber plates measure at 1.2mm thickness and the basket has about 1mm grooves worn into it. Any chance I can get away with filing them flat? Thanks!

Edited by Dylan7936

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1mm grooves?? No way. Sounds like you got a crank seal issue if it is running away and barely running. I would go through that motor, if you found it in a quad god knows what it has been through.

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18 minutes ago, JustinXR said:

1mm grooves?? No way. Sounds like you got a crank seal issue if it is running away and barely running. I would go through that motor, if you found it in a quad god knows what it has been through.

I’ve been through everything shy of splitting the case at this point and up until now the clutch. It’s a nightmare. 1mm is a rough eyeball estimate but it could be less, I’ll check with a micrometer. It isn’t pretty though. 

BF878BBA-5084-4ECC-AE97-2EDAEA1CB270.jpeg

Edited by Dylan7936

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11 minutes ago, JustinXR said:

That looks very bad, i would replace. My CR500 clutch is nowhere close to that and i even want to replace it.

Ok, I’ll see if I can source one. I guess I might as well spend the money to do it right now and not let the issue to the next guy. I think the baskets are interchangeable on a few of the different motors..

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On 1/9/2021 at 6:14 PM, Dylan7936 said:

I’m going to throw seals at it and inspect the clutch plates while I’m there, guess it wouldn’t hurt to replace everything. 
Any thoughts on the clutch slipping all the sudden? All I did between then and now was change the fluid (Gtx 10w-40 no additives) and throw new back tires on it. I’m not familiar with wet clutches so I’m not sure if it’s a possibility that they were on their way out already and the change made it more obvious? 

If the clutch started slipping suddenly I would change the oil and put motorcycle oil in it. It does make a difference! And yea, get a Henson clutch basket.

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Oh yeah...you want motorcycle oil for sure, the friction modifiers you find in automotive oil are gonna hurt clutch performance. I have used ATF, it works good but will break down faster and turns very thin in extreme temperatures. Yamalube probably cannot go wrong.

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I had an issue with a bike once. It ran great then it lost spark. Check your flywheel to insure the nut didn't back off and let the flywheel slip back just enough to not let it fire. Just a suggestion to go along with all the rest so far.

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I've filed worse than that but it will only get beat up that much sooner. I doubt any aftermarket baskets exist for the 490.

If you find that the woodruff key keeps shearing then get valve grinding compound. You can then lap the crank and flywheel tapers together for a perfect match.

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finished replacing both crank seals and new clutch plates(filed basket down), was giving it a slow kick and heard the reeds hissing. Took the cage off again and I noticed some pretty bad grooves and pocking that could have made the seal bad. Sanded the entire cage down and made it all flat, but unfortunately backfiring has chewed my 3rd set of brand new reeds up again. Hissing is slightly better, still a problem. Normally on a electric start this isn’t as big of a deal when it comes to starting but I’m assuming on a kick start it makes it almost impossible to get it fired cold. Going to order another set and try it, I’ll pop stsrt it tomorrow and go over everything with a spray bottle to check for vacuum leaks. Cheers.

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Edited by Dylan7936

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Bike starts when I put fuel in the cylinder, first kick. Runs only off of the fuel in the cylinder then shuts off, I’m not getting fuel from the carb for some reason.. 

no more backfire, think my new crank seals solved that. 
Anyone have any clue?

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Are the carb and petcock in good condition? If the carb has a few hours on it and the needle and seat are worn they sometimes don't operate smoothly.

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28 minutes ago, smirmeister said:

Are the carb and petcock in good condition? If the carb has a few hours on it and the needle and seat are worn they sometimes don't operate smoothly.

Brand new tm38 flat slide carb and needle.. once it’s cold it refuses to start but once I put a little fuel ontop of the piston it fires now and runs fine. I think there was a decent ammount of nasty fuel laying in the case and once it cleared up it started to idle fine when the mixture screw was adjusted. Once it’s warm it runs good but needs some tuning. Fires first kick warm finally!!! As far as cold starts... not so sure lol. My jetting might be way off, I’m sure the tm38 factory needle and seat aren’t even close to the right size but I couldn’t find the right set. 
Can’t keep the front end down 1/4 on the throttle haha, thing is insane. 
going to list it for sale here soon, thank you for the help guys!

Edited by Dylan7936
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