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Author Topic: 2-stroke newb with some questions!  (Read 3317 times)

Offline MotorbikeBruno

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2-stroke newb with some questions!
« on: Apr 17, 2012, 13:15:51 »
Well, I've had a myriad of bikes in my life thus far, but every two-stroke I've owned, has never had any problems and I ended up selling each one before they did.  So in all honesty I don't really know much about them.  I've got 2 new-to-me enduros and I'd like to actually learn something about them.

First one is a 1977 Yamaha DT100  It came to me without a magneto/electrics at all. It now has one and fires up nicely. It takes ONLY 1 wire to work, and thats from the magneto to the spark plug! Gotta love that!  It's in super rough shape and I'm going over it right now to see what all it needs to make it ride-able. This one I'm calling the "wife's bike" since she's never been out trail riding ever and I thought I would start her on something small for her first 2-stroke.

Second one I just bought the other day and it's a 1979 DT250.  It came mainly intact with the electrics, chain and headlight all in plastic baggies and clean.  It turns over with great compression and I just bought a battery today on my way in to work so I think I'll see what happens tonight if I hook all the electrical back up.

First off, is there anything specific I should be doing/looking at on these things? 
And when I need to rebuild the top end, how do I know what size they should be? I see 1st over, stock and 3rd, 4th over etc.  Seems stock is .25, 2nd over is .50 3rd must be .75 and 4th is 1.00.  Do you need new pistons with each set?  Does the cylinder need to be bored or anything, or do you just replace the rings going from first to second?  I tried to search on here, and I just joined Yamahaenduro forum too.  But I thought I would ask this amazingly talented group of individuals since it really is amazing how much so many of you know on here.  Thanks in advance.

I'll add some pictures tomorrow!

Bruno

Offline JustinLonghorn

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Re: 2-stroke newb with some questions!
« Reply #1 on: Apr 17, 2012, 14:01:20 »
If it needs to be re-bored, it will need a new piston/rings. However, it may not need it. It may just need to be honed and need new rings. If it has great compression, this is probably the case.

Does it still have a working oil pump? Either way, I would add at least a small amount of 2-Stroke oil into your gas when you first try to start it.

Good luck man, and welcome to the ever growing population of DT owners.
I'm going to eat your brains and gain your knowledge.

Into The Sunset, CB750 build

TT500 the Animal

Offline MotorbikeBruno

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Re: 2-stroke newb with some questions!
« Reply #2 on: Apr 17, 2012, 17:00:26 »
Thanks Justin.

Both bikes have good compression (from what I understand of two-stroke "good" compression)  The DT100 fires up with one or two kicks and doesn't idle right now because it didn't come with the original airbox so I took a pod filter I had and a 90 degree rubber pipe joint and it seems to work well enough.  I'll rejet it sometime soon when I decide it's ready to actually be ridden.  I took the oil pump out and cleaned it and it appears to be working just fine. When the engine is running it goes in and out and I can see some bubbles in the oil line moving.  I still put oil into the gas as you said (just in case!) so that's good.  I'll pull the line off where it goes into the carb next time I fire it up to make sure it is actually working.  Thanks for the heads up.

Tonight I'll go home and put all the electrics back on the DT250 and see if I can get spark etc... I sure hope so, as that would be pretty cool!  (I still have to clean the carb though and check airbox etc. 

As for the cylinder, I guess my question is: Can you just change to the next rings up, or do you HAVE to do the piston with the next size up rings like a matching set.  So if you have the stock piston, with a hone, can you ONLY put .25 rings on there, or will the .50 rings fit on the stock piston?  Sorry again, this is very new to me and I'm pretty excited to learn about it.


Offline SONIC.

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2-stroke newb with some questions!
« Reply #3 on: Apr 17, 2012, 17:32:04 »
Usually if there is no damage to the bore there is no need to fit .25 over rings just use stock (STD) sized rings.
Although you could get away with .25 over rings in the stock bore I'm sure

Offline JustinLonghorn

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Re: 2-stroke newb with some questions!
« Reply #4 on: Apr 17, 2012, 17:59:03 »
Yep. If no damage to the wall, I would hone it and run stock rings. That is of course if the ore is stock
I'm going to eat your brains and gain your knowledge.

Into The Sunset, CB750 build

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Offline MotorbikeBruno

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Re: 2-stroke newb with some questions!
« Reply #5 on: Apr 18, 2012, 11:07:27 »
Ok, I'll keep that in mind. Thanks gents!  Still learning..slowly.  :P  So there is a difference between .25 and stock...I wasn't sure.

Here's some pics. Last night I hooked up everything I could find wires for...and kicked it over and had spark.  The carburetor was completely stuck (slide was stuck) So I took a waste basket filled it with hot water from my basement laundry sink and loosened the cap on the carb.  Set it in hot water with the carb dangling from the cable and went back to work on the bike.  Was on to the headlight when I heard a splash and the carb loosened up and dropped into the hot water.  So I cleaned it up and when I bring home some gasoline and 2-stroke oil tonight, I should be able to fire it up!  Pretty stoked as I was a little worried the expensive and hard to find parts may be bad (ignitor unit) 

Offline SONIC.

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2-stroke newb with some questions!
« Reply #6 on: Apr 18, 2012, 11:12:28 »
Nice! First start is always fun!

The number designations for the ring are bore mm over stock. So .25 is .25 mm bored larger than stock. Etc

Offline MotorbikeBruno

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Re: 2-stroke newb with some questions!
« Reply #7 on: Apr 18, 2012, 15:01:06 »
I suppose that makes a ton of sense....ha! 

I'm stoked now! 3 hours before I get to go home and fire it up!!  8)
« Last Edit: Apr 18, 2012, 15:03:46 by MotorbikeBruno »

Offline spazzed

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Re: 2-stroke newb with some questions!
« Reply #8 on: Apr 19, 2012, 17:39:54 »
Oh man....  You're totally stricken with this!

(And I'm going to look at another old 2-stroke this weekend so I can't really judge.)

Looks like you're on the right path.  It doesn't sound like you need to but oversized rings are for oversized pistons are for oversized/bored cylinders.

Also -- you have read up on the new MN OHV registration, right?? You'll be able to put plates on both of these!!

Offline MotorbikeBruno

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Re: 2-stroke newb with some questions!
« Reply #9 on: Apr 20, 2012, 11:49:24 »
Oh yeah, I know the rules now...and since this was already titled as an enduro with tail light, head light, blinkers etc...pretty stoked as it fired right up the other night.  Can't really get it to idle though...is that a normal thing?  Winds right up, but then decides it doesn't really want to idle right, so I think it's getting too much air since the airbox filter was apparently non-existent.