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Discussion Starter · #1 · (Edited)
70 Yamaha CT1 help

Anyone know of any sites to help with an old two stroke dirtbike. My 11 yr old son just bought a 1970 Yamaha ct 175 that has been sitting in a heated basement for 20 years. I don't know anything about a 2 stroke at all. Thanks
 

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Discussion Starter · #5 ·
Can you direct to a site that might tell me what to put in the gearbox for oil or if you know could you tell me? I have searched the net but no real success. I don't know jack about these at all. Its a bike and I know I can make it run for him but I don't even know what to mix for the fuel.
 

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I suggest you do more research on how the oil pump operates. Some are driven by different systems either by Rpms or by transmission. My suzukis pump is driven by rpm so that means it just relies on what rpm the bike is at to supply the oil. My Yamaha relies on the transmission, this means the pump is driven when the bike is in gear and moving. This is one of the downfalls of the Yamaha pump system because people who are not familiar with the pump will keep the bike in gear and sit at a stop light not knowing they are starving the engine of oil. Upon take off the engine usually seizes. You can probably run premix if you want since the oil is injected into the carbs, a lot of Yamaha guys eliminate their pumps.
 

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Remi's Dad
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One issue though with the oil injection bikes are if you are trail riding/low speed running you can actually have to much oil. Most that ride in those conditions often remove the pump (only if you block it off) and run premix.

I just use the oil bag and gas tank because it's more convenient for me and i usually run wide open or higher speeds
 

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Discussion Starter · #11 ·
So can I just not put oil in the system and run a premix or do I have to eliminate the pump totally. And thanks again. I didn't think there were a lot of guys on here that new so much about these old two strokers
 

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Well all pumps run off the crank (engine speed) and throttle position it's just how the Yamaha oil system is positioned on a huge transmission gear, which is also in connection with the clutch (they mounted the clutch on the crank in the early yamaha 2 strokes). The pump doesn't turn when the bike isn't moving with the clutch pulled in, just something to double check if that's the case. You can eliminate it by just plugging the oil lines.
 

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A lot of people delete the oil pump since if the seals go out, they can leak air into the crankcase, which is a big no-no for 2 strokes. While the pumps are generally reliable, it's not unheard of them failing which of course will toast the engine pretty quickly. Plus there's the issue of too much/too little oil. One thing you have to be careful of with 2 stroke bikes is coasting downhill for any time... the engine is revved up, but getting virtually no oil/fuel since the throttle is closed, you have to blip the gas now and then. You can "light seize" the engine from this. Usually once it cools down, or you kick the engine backwards it frees up and is fine, but can't imagine it's good for it.

If you choose to run premix, I would delete and then block off the pump...these delete plates are readily available and eliminate the chance of leaking air. With modern 2 stroke oils, 50:1 is fine, even if originally it might have spec'd 32:1 or 40:1.....oils are a lot better now than they used to be.
 

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Discussion Starter · #17 ·
Ok my boys 70 CT1 is drivin me nuts. We put new points and condenser in it still no spark. But after looking closer the old gent I got it from had removed a lot of stuff for racing in the 70's and I think this old girl still needs a battery but I am not sure? The other thing is that 3 out of the 4 wires from the magneto do not connect to anything? He had this thing wired to a toggle once upon a time. Any advise is great because I am at my wits end and my kid really want to ride it. Thanks all
 

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Remi's Dad
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the battery is for lights. Other wise it will run off the magneto for the coil.

i'm having the same problem with mine. I have no battery or wiring. I went out to start it up the other day and i didn't get any spark. I am 99% sure its the coil. I'm getting 12v from the "black" wire from the mag to the coil input side put nothing from ground to spark plug end. Even cleaned the factory ground then moved it to a different spot.

I'll let you know what i find.
 

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Discussion Starter · #19 ·
Thanks I will watch for a reply. Whats throwing me off here is that the old guy that owned it raced her years ago and stripped most of the wires out of it at that point. If I ohms the wires coming from the mag with points closed all 4 wires seem grounded together?
 

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CB350Cafe first build
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2 strokes are notorious for fouling plugs...don't know a thing about the bikes you are talking about but check maybe the spark plug caps? sometimes the coil wires can come loose, and if its a resistive type system, maybe the resistor in the plug wire cap is shot? Corroded? otherwise?
 
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