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Discussion Starter · #1 ·
I bought this bike for $100 about 5 months ago. Needed a new stator kit and wiring. I have enjoyed cruising on it for the past months but ive been having some engine issues. Sometimes it wouldn't idle after warming up and would also have trouble starting it up. Went through did all the adjustments + maintence. Took a before and after compression test. Compression dropped alot when warm. Now! We are onto the fun. I am rebuilding the stock motor.
Currently on my bike I have
CT90 rear shocks
Trailbuddy luggage rack
New aftermarket dratv bars
Led headlight
Stock 72cc engine
120/90-10 Michelin Reggae tires

My motor build will consist of
Dratv 4speed + shift drum conversion
88cc big bore kit
Dratv race cam and hd valve springs
HD clutch (keeping semi auto)
Oil cooler
Ct90 Carb
High Volume oil pump
And also going to regasket and seal the entire motor.
And while not engine related... a new seat cover+foam

Now I can already hear people who say I am better off going with a chinese motor.. well I like my honda motor and I am looking for a cruising speed of 40 which I believe will be very doable with my engine build. I have rebuilt many engines before so this should be very enjoyable for me. One thing I did not want to loose is the offroadness of the bike. I love using it for driving around the yard and offroad trails and as AG equipment on a buddies farm. Another thing is I want to keep the look as stock as possible, this includes the airbox. As for keeping semi auto.. For me its much easier than a manual and anyone can hop on and enjoy the bike without to much introduction. The 4 speed im going with is a 4 down setup. Should be a fun build!! Whats everyones thoughts?

Current photo of how she looks.


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Discussion Starter · #3 ·
Coworker waa moving and was going to scrap it... luckily he had it on the back of his jeep. Threw it into my crown vic and took her home.
Thanks for the welcome. I hear there are many knowledgeable people here!

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1970 CT70, 2019 Super Cub 125, and five or six other basket cases
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MAN YOU GOTTA STREET TITLE THAT THING! Go through Vermont. These bikes are the best "run around town" bikes. Just the right size! cant wait to see how she ends up. Use THIS GUIDE and THIS FORM. Just got a plate for my 81XT ;)
 

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Good lookin bike, and welcome to pm. I like your plans and think you're on the right track. I do HAVE to mention...you could add a TON of power by adding a $150 stroker crank...and a exhaust (which I think you need either way), and a oil cooler. It's a big jump in power...but if you don't really need it, your current plan should be pretty foolproof.

@WarnerSteel has a video where he shows how he easily modifies those cheap Chinese exhausts to flow better on bigger engines. Might be worth a look.
 

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Discussion Starter · #6 ·
I absolutely plan to make this street legal!
Now since im going so deep into the motor im not opposed to stroking it. Im using tbparts basic 88cc kit as im doing head mods myself. Could I run their 51mm stroker kit on my engine?

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Discussion Starter · #7 ·
Good lookin bike, and welcome to pm. I like your plans and think you're on the right track. I do HAVE to mention...you could add a TON of power by adding a $150 stroker crank...and a exhaust (which I think you need either way), and a oil cooler. It's a big jump in power...but if you don't really need it, your current plan should be pretty foolproof.

@WarnerSteel has a video where he shows how he easily modifies those cheap Chinese exhausts to flow better on bigger engines. Might be worth a look.
Is there a specific stroker crank u reconmend? The exhuast I have is a cheapy ebay one but seems to perform rather well. I will probably swap it to a trail buddy thumper exhuast eventually. Is the stroker really worth it considering im using a stock head and intake box?

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1970 CT70, 2019 Super Cub 125, and five or six other basket cases
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It all depends on what you want. Usually the strokers make it so you can have more torque at a lower rpm. If you’re not convinced you need highway speeds you might actually be ok without it. Also the thumper exhaust is in fact a China exhaust modified to flow better.
 

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Discussion Starter · #9 ·
It all depends on what you want. Usually the strokers make it so you can have more torque at a lower rpm. If you’re not convinced you need highway speeds you might actually be ok without it. Also the thumper exhaust is in fact a China exhaust modified to flow better.
Fastest road I plan to take is a 55... and im perfectly happy doing that road at 45 lol. Use this bike off and on road. If when I tear into the engine and see any crank damage (shouldnt be) then I can decide on doing the stroker crank.

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Fastest road I plan to take is a 55... and im perfectly happy doing that road at 45 lol. Use this bike off and on road. If when I tear into the engine and see any crank damage (shouldnt be) then I can decide on doing the stroker crank.

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Stroker crank is great, if you can find one :(
 

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TB parts has them instock


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I believe the stroker crank you need for your 70 CT70K0 3-speed engine is the TBW0622, which is out of stock. The stroker crank Upgrade Kit (TBW9090) that TB Parts used to have listed on their site consisted of the following parts for the '69-'79 3-speed CT 70 and the '73-'80 ATC 70:

108cc Stroker Crank Upgrade Kit – 3 Speed Models Only –

TBW0622 - TB Stroker Crankshaft, various 3-speed models
TBW0365 - TB Piston Kit - 88cc and 108cc, stock and race head
TBW0225 - TB High Volume Oil Pump, K0-81 models
TBW0287 - TB Crankcase cover gasket, right - All Models
TBW0334 - TB Crankcase Center gasket
TBW0206 - TB 52mm (88cc) Head Gasket Kit
 

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The TB Parts Stroker Crank that is in stock (TBW0713) is for All 4-speed CT70H, SL 70, and XL 70. It is also for the '81 and up ATC 70 and the '80-'81 3-speed CT 70.
 

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Discussion Starter · #14 ·
I bet you need the race head to clear the extra stroke of the motor. And since I already have plans (and parts on order) to rebuild my stock head with a cam and valve springs I guess the stroker kit probably isnt worth it currently.

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The configuration of the stock CT 70 head is such that you can still use the the TBW0365 piston with either the stock or race head and the stroker crank. I have done the same thing to a stock CT and ATC 70 head using a "street cam" and wide-coil valve springs and a stroker crank - to retain that "stock" engine appearance...:cool:
 

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Discussion Starter · #16 ·
The configuration of the stock CT 70 head is such that you can still use the the TBW0365 piston with either the stock or race head and the stroker crank. I have done the same thing to a stock CT and ATC 70 head using a "street cam" and wide-coil valve springs and a stroker crank - to retain that "stock" engine appearance...:cool:
That is awesome! Howd it perform?

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What I did was use the 51mm TB Parts stroker crank after having a stock 47mm cylinder from an XR 70 bored to 48mm and used a Wiseco piston, an ATC 70 4-speed trans, and a TB Parts ShengWay 20mm carb. When you do the math, it comes out to 92.287cc of low-end torque and 2nd gear holeshots all day long. All from a stock looking engine that has "a pipe and a carb" on it...
 

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Discussion Starter · #18 ·
That sounds wicked. My bike currently tops out at 33mph witb 16/36 gearing. Im hoping with 88cc and 4 speed I can get atleast 45. If I do 16/36 I think a cruising speed of 45 is easy and have enough power to hold it.

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The crankshaft that you'd need is the one for a 3speed semi-auto. Reason is...because it will work with the STATOR AND FLYWHEEL that is on a 3speed semi-auto.
There are 2 other versions of the tb stroker cranks that are made to work with the 4speed manual type STATOR AND FLYWHEEL, and the 12volt type ...FLYWHEEL.

So...another option...cause I know you like options...
If you want to upgrade your old 6volt points type ignition and lighting...to a spiffy new 12cdi setup...many of us have done it. Lots more options with lighting...brings your old CT right into the 21st century...eliminates those pesky points and condenser...maybe the 12v style crank IS available..?
Just sayin...options...

I think the stroker crank is worth waiting for...for a guy like you. It's a big jump IMO. No regrets and all that. You're splitting the engine, and you're lookin for more power.
A basic BB kit adds 16cc. A basic stroker kit adds 36cc including extra low end torque. A BIGGER stroker kit...54mm cylinder requires the cases to be bored, but adds another 9cc for +45cc... 117cc total...go anywhere power.

But...the 88cc kit is super easy and reliable :)
lol
 

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Discussion Starter · #20 ·
I work with vintage tractors so points is something I am very comfortable with and for that reason I will be keeping them lol. Im going to call TB and see what the time frame is on a stroker crank. I think im gonna go ahead and do it.

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