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1973 Yamaha CT3 - starts and revs full throttle

  • Jogar
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So before I start disassembling everything , I know there are people here who have forgotten more about these bikes than I’ll ever know. 

i started my resto project for the first time today, and I nearly blew out my ear drums when it started . 

it went right to full throttle, and I had to shut er down. I’ve tried it again a few times, still the same result. Air screw is where it’s supposed to be, carb was cleaned, and I’m fairly certain the throttle cable is in the right way. 

edit: with the choke engaged , it runs around 4000 rpm, with the choke disengaged, revs up to 9000rpm

slide seems to be sitting properly. No leaks around the manifold intake. 

help? Haha

thanks in advance, 

Jogar 
Last edit: 11 Aug 2022 15:02 by Jogar.
07 Aug 2022 15:30 #1

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  • AirborneSilva
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Replied by AirborneSilva on topic 1973 Yamaha CT3 - starts and revs full throttle

Did you put the slide in the carb wrong, that will do it - don't ask me how I know! 

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1976 DT400C
1981 DT175H
1972 DT2 250
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07 Aug 2022 16:11 #2

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Replied by Northern hunter on topic 1973 Yamaha CT3 - starts and revs full throttle

One thing I noticed with mine is with the gas shut off try and open and close the throttle and see if you can feel/hear the slide going up and down or pull the boot of the intake and peek in. i had this happen on my bike it got stuck at the  top and would just over rev tell you shut it off, or you could just pop off the slide on the top and just double check if its stuck there.
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07 Aug 2022 17:18 #3

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If the bolts to secure the carb to the intake flange are over tight ,
the carb body warps and the slide can stick open , or not fully closed .
Best checked from behind intake .
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07 Aug 2022 18:47 #4

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First thought is slide is wrong way around so sits on the guide pin & is well open, maybe not full open but i'm sure it seems like it when starting. If you're feeling like throttle is operating then likely just feeling the oil pump spring pulling throttle back but would feel half strength. Check the slide needle is down the jet too. I'm sure it's been said but those old carbs go out of shape tightening the flange bolts. Bottom line is if you grap the cable at the carb top does the slide feel under spring tension & can you move it up & down. Down as in bottoming out with speed screw backed off. & up as hits the cap. With it down do you have minimal cable cleance or lots of clearance like slide is stuck up somewhat. Did you have the exhaust on?, it's damn scary eh!!. She's run in now & ready for a ride.
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Last edit: 07 Aug 2022 19:23 by RT325.
07 Aug 2022 19:23 #5

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  • Jogar
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I did not have the exhaust on, popped my ear holes lol. Still hearing ringing , especially frightening  because I wasn’t expecting it to start!

so it only sits around 4000 rpm now when it’s started . Hmmmm 
07 Aug 2022 20:03 #6

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  • Jogar
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I’ll give this a look tomorrow !
07 Aug 2022 20:04 #7

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  • Jogar
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I’ll have a look inside tomorrow , and I’ll report back ! 
07 Aug 2022 20:04 #8

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Yes can imagine the noise. When i was young & stupid--now old & stupid lol--at work in mid "60's i had the exhaust off a suzuki s32--150 twin & touched the start button to which it lit up. Guy on his knees at the bike in front was very p--sed off with me. Said--My high frequency hearing better not be damaged--in not so kind words!!.
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07 Aug 2022 20:58 #9

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Loosen both carburetor fasteners. It might snap back to idle position.

a
YAMA-LAND RESTORATION,
( 818 ) 521-2109 This email address is being protected from spambots. You need JavaScript enabled to view it. 1971 CT1-C ( BRANDY ) 1970 DT1-C
( MONICA ) 1972 AT2M ( ZIFFLE) 1970 CT1-B ( HULK ) 1971 DT1E
( GINA ) 1970 CT1-B ( CLIDE ) 1968 DT1 ( WILSON )
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09 Aug 2022 22:11 #10

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