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CT3 - start problem

  • Gallotti
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CT3 - start problem was created by Gallotti

Hi guys, I need your help.
I have practically finished the restyling of my ct3, I had to fix the carburetion, because according to me it was fat.
Well, the bike won't start anymore and I don't understand why. The spark is there, gasoline is coming into the carburetor, I also believe it is not a compression problem because I replaced the piston rings.
I rebuilt the engine completely, opened it up, cleaned it, replaced the bearings, gaskets, oil. Once I closed it up it would always start on the second kick. I replaced the idle jet with a smaller one but no dice. I put the original one back in...but nothing. It must be said that every time I replaced the jet I reopened the engine head to make sure the piston was clean.
What do you think it could be? I replaced the ignition system with a VAPE system. New 12v battery (checked and fully charged). I fit a new Polini CP 17.5 carburetor and K&N air filter.
Thanks for helping me solve this nightmare :)
I apologize for the English but I had to use an automatic translator
 
09 Mar 2023 13:38 #1

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Replied by RT325 on topic CT3 - start problem

Just a guess, but if the crank seals are in place & spark is at about 1.8mm btdc, has compression to feel on the kickstart, fuel in the carb, then should run!!. So has the flywheel moved. Is the motor just flooded up so choke only makes it worse. Bit of a guessing game. Be shure the throttle slide is in place & going fully down--& up, then get help to push it with no choke & full throttle. If it doesn't fire up in 20-30 meters then--umm--have a cuppa tea & a lie down.
The following user(s) Liked this Post: Sneezles61
Last edit: 12 Mar 2023 01:02 by RT325.
09 Mar 2023 15:33 #2

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  • Gallotti
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Replied by Gallotti on topic CT3 - start problem

Thank you very much for your reply.
Something occurred to me when you told me about the spark (1.8mm btdc). The measurement is correct because I checked it again, however, I wondero....does it have to be done with the vape ignition system as well? In the assembly manual they indicate "Bring the piston into ignition position." What do they mean? As stated in the bike manual (1.8mm btdc) or place it directly to the TDC (so without the 1.8mm gap)?
I made the cup of tea in the meantime :)
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09 Mar 2023 22:52 #3

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Replied by Gr8uncleal on topic CT3 - start problem

Wouldn't do any harm to check that the tiny jet in the float bowl is clear.

 
09 Mar 2023 23:36 #4

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Replied by Gallotti on topic CT3 - start problem

Any other advice or answers to my question? :(
12 Mar 2023 00:15 #5

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Replied by RT325 on topic CT3 - start problem

I'm not familiar with the Vape ignition. But i guess that when they say ignition position they would mean 1.8 btdc in your case. I'm also guessing there must be a firing mark on the flywheel & stator plate to align at 1.8, then it's ready to run. Hopefully someone that runs the Vape system will tell me i'm right [or wrong] as i don't want to put you wrong. If you've had it running then something went wrong, did it stop while running or just didn't want to start the next day. I'm thinking two unlikely things--did it blow a crank seal out while running. Or did it flood with fuel overnight due to a fault, in which case it could force a crank seal out with pressure just from kick starting. Also if it's a complete cdi magneto system it won't require the battery to run. Someone correct me please?.
12 Mar 2023 01:14 #6

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Last edit: 12 Mar 2023 01:38 by RT325.
12 Mar 2023 01:26 #7

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Replied by RT325 on topic CT3 - start problem

I must say 17.5mm carb sounds very small [or am i misunderstanding] but no reason why it wouldn't work so long as you have it jetted about right. Why did you go so small. I'm running a 28 on mine which is a bit larger than normal. Mine isn't a true CT3 but a bit of a mixture AT1 with a 175 top end. Polini carb 'looks nice'.
speed-line.com/carburetor-polini-cp-175mm
12 Mar 2023 01:48 #8

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Replied by AirborneSilva on topic CT3 - start problem

I have the Vape 12v conversion on my DT400, as in the picture that RT325 posted you line the marks up but only after you have set the proper BTDC as noted in your service manual.
2023 Tenere T7
1976 DT400C
1975 DT400
1981 DT175H
1972 DT2 250
1980 GT80
1972 JT2
12 Mar 2023 06:38 #9

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  • Quartermaster35
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Replied by Quartermaster35 on topic CT3 - start problem

Vape Installation

This video does a nice job of explaining the installation process, if you want to double check your work.
1973 Yamaha CT3 175

Prior Bikes:
1973 Suzuki TS90
1977 Yamaha IT175
1978 Suzuki 390SP
1980 Yamaha 175 Tri-Moto
1969 Yamaha DT1 250
1981 Yamaha XS650 Special
1982 Suzuki GS550ES
1982 Honda 250R
1984 Honda Nighthawk "S"
2005 Kawasaki KLR650
12 Mar 2023 08:35 #10

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