CT70 117cc kit questions

A little back story to get started. This is the 5th CT70 I've owned. Second that I will be rebuilding the engine. The first was a 88cc that you guys helped me get through the first time, about 5 years ago. Had some money issues come up and I had to sell them all. During the time my friend bought a CT70 as well, and at some point ran it with out oil and it seized up. I remember opening it up and everything looking decent and was able to free it back up. Never ran again due to low compression and it sat in my back yard rusting for the next 4 years. Fast forward to now, I bought it off of him.

I've got all the paperwork straightened out, it's tilted, registered and insured. I've gone through it and bought new harness, tires, tubes, rubber gaskets, seat cover, shocks , exhaust and cleaned and painted the wheels. Just need bulbs and it will be 100% except the motor. It has the rough look that I'm going for and I'm really happy where it's at. Originally planned on putting a piranha 140 in it, but have since scrapped that and plan on putting that in a TRX70.

The 88cc kit I did on my original bike was a challenge at the time, but looking back it was pretty easy to do. This time around I got the 117cc stroker kit and I'm ready to throw it in. figured I'd ask some questions and get the final shopping done with some of your advice before I get it open so I can do it in one go.

1. I've read in some other post that a oil cooler is a must, is that true? People say the same about the piranha 140's but I've never had issues with out it.

2. My plan with the clutch was to keep the auto 3 speed and just do a heavy duty kit to the clutch, but I've read in other threads about a billet basket and I have not been able to find something like that. As far as the trans goes, I also have a 74 ATC 70 and 87 TRX 70 that I could pull from. Do those have the same trans, better options, or non compatible?


TIA, I figure I will have a bunch of questions and might as well start a thread.

If youre going to pull the trigger on that, TBparts is having a black friday sale all weekend.

Tripod said:

If youre going to pull the trigger on that, TBparts is having a black friday sale all weekend.

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Thanks! I've actually already bought the stroker 117 kit, but will definitely start a cart for all the things I got left.

Attached photos of the before and after.

So I just went ahead and did it. It wasn't that difficult to be honest, followed the video Kirby posted on how to bore the cases and it everything else went together fairly easy having done it before. Regardless I'm posting again because I'm not happy with the results. Now given that I'm trying to break it in nicely I'm not slamming on the throttle but I expected to get into the 50's relatively easily and I still have not in the 15 miles in put on it thus far. I'm topping out in the mid 40's giving it 100% for short spurts. I know I need to re-gear and tune to perfection but I figured that would be to get it from ~55 to what ever it maxes out at I'd assume ~65. So it's fair to say I am discouraged to say the least as how it sits it will not be sufficient for my plans.

Some info:
15/38 stock sprocket combo
VM26 (assume it's real since I got it from TB) w/ stock jetting
120/90-10 tires
Fresh points, condenser, plug

Currently 1st gear is pretty much useless, bucks like a horse and I instantly need to shift to 2nd. 2nd short as well, and all the work being done in 3rd. Any one got any advice to get this to the 60's with ease? I don't plan on cruising at 60, but I want to be able to get to it and stay at it for short periods as needed.

You're going to need to determine the diameter, and or circumference of the tires that you're running. We'll need to find the primary drive ratio of your 3speed...K0 engine? Then we can try to help you.
I think racerx recommended a mph per 1000 rpm for my 117cc "Recycled Cycle" in that thread. I can try to find it.
I think my bike is running 16/33 sprockets. But my engine and tires are different than yours.

I’m not sure a 117 can do much more than 62mph and that’s top speed and not useful for much. You should be able to get 55 mph for short bursts or a couple miles at best. Any resistance be it wind, inclines, ect will detract from top speeds. If you shoot for between 6 and 7 mph per 1000 rpms your going to be in the ballpark of all it can do. I run 15/33 on my 124 and sometimes I switch it up but always stay between 16/32 and 15/33. That’s 2.00 to 2.20 ratio. The 15/32 is buzzy but pulls to 69. The 16/32 is way more road friendly and I enjoy riding it more even though it can only top out around 64 mph. Both can do 55 for a few miles no problem. I’m running 120/90-10 tires. I think your gearing is way off.
Use the forum go to the rides other events. There is a thread NJ on the road. Start at post 25 and there is some good info

Running 15-38 is like running a 4:88 rear end gearing combo in a big block 4 speed Chevy Chevelle SS. Get the gearing dialed in. Most here had to buy many different combos at a great cost. You have just been spoon fed the right combo...

OLD CT said:

Running 15-38 is like running a 4:88 rear end gearing combo in a big block 4 speed Chevy Chevelle SS. Get the gearing dialed in. Most here had to buy many different combos at a great cost. You have just been spoon fed the right combo...

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I've got 3 little Hondas, and have been working on, souping up and riding these for more years than I can count, and still cannot understand the obsession with top speed. If you gear it for top speed in top gear you're going to blow it up sooner or later and certainly risk destruction exceeding redline going down hill. I like to gear my bikes for nearly top speed in next to top gear and use top gear as an overdrive. For example, my 110 cc CT70 is geared to do max 45 in 3rd and barely 50 in 4th. With shorter legs, it would do 55 in 4th, but I like

Dkid said:

A little back story to get started. This is the 5th CT70 I've owned. Second that I will be rebuilding the engine. The first was a 88cc that you guys helped me get through the first time, about 5 years ago. Had some money issues come up and I had to sell them all. During the time my friend bought a CT70 as well, and at some point ran it with out oil and it seized up. I remember opening it up and everything looking decent and was able to free it back up. Never ran again due to low compression and it sat in my back yard rusting for the next 4 years. Fast forward to now, I bought it off of him.

I've got all the paperwork straightened out, it's tilted, registered and insured. I've gone through it and bought new harness, tires, tubes, rubber gaskets, seat cover, shocks , exhaust and cleaned and painted the wheels. Just need bulbs and it will be 100% except the motor. It has the rough look that I'm going for and I'm really happy where it's at. Originally planned on putting a piranha 140 in it, but have since scrapped that and plan on putting that in a TRX70.

The 88cc kit I did on my original bike was a challenge at the time, but looking back it was pretty easy to do. This time around I got the 117cc stroker kit and I'm ready to throw it in. figured I'd ask some questions and get the final shopping done with some of your advice before I get it open so I can do it in one go.

1. I've read in some other post that a oil cooler is a must, is that true? People say the same about the piranha 140's but I've never had issues with out it.

2. My plan with the clutch was to keep the auto 3 speed and just do a heavy duty kit to the clutch, but I've read in other threads about a billet basket and I have not been able to find something like that. As far as the trans goes, I also have a 74 ATC 70 and 87 TRX 70 that I could pull from. Do those have the same trans, better options, or non compatible?


TIA, I figure I will have a bunch of questions and might as well start a thread.

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Howdy, I've got 3 little Hondas right now, and have been souping up, and riding these things for over 40 years, and I still don't understand this obsession with top speed. I gear my bikes with long legs and use top gear as a cruising overdrive. For example, my 110cc CT70 is geared to top out at about 45-48, although it could have been geared to hit 55+. But It cruises nicely at 40-45 all day. If there's a hill, I just downshift going up, and going down, I know I won't blow it up going 55. Obviously, it's not as quick off the line, but to me it's a small price to pay in the interest of longevity. I also run 120/90-10 tires and my chain slightly rubs the sidewall of the rear tire. After several hundred miles, there's a pattern that has been etched onto it. I'd like to know if you run into the same issue. ( my rims are slightly wider than stock.)

I do not have any clearance/contact issues with my wheels. Is it possible that the shape of the sidewalls could be the issue? IDK. I’m running Michelin Boppers. I’ve tried others for many reasons and none of them had any contact issues. Wider rims is plausible

kirrbby said:

https://lilhonda.com/index.php?threads/new-jersey-on-the-road.22519/

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thank you Kirby. Also great video, it was a great starting point.

OLD CT said:

You have just been spoon fed the right combo...

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yes sir. I am very appreciative of the insight.

Old Guy Too Many Bikes said:

Howdy, I've got 3 little Hondas right now, and have been souping up, and riding these things for over 40 years, and I still don't understand this obsession with top speed. ... I also run 120/90-10 tires and my chain slightly rubs the sidewall of the rear tire. After several hundred miles, there's a pattern that has been etched onto it. I'd like to know if you run into the same issue. ( my rims are slightly wider than stock.)

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I have a specific trip in mind that requires a bit of speed for about 10 miles. That’s from the truck to the trail on a 2 lane highway, but other than that I am after your goals as well. As far as the tire goes, I have plenty of clearance and it doesn’t rub at all.

So after reading some on that thread it looks like I’m after a 16/33 combo. Did some chatting on the phone with Darrell as well and he recommended the same as well as gave some good advice on a bunch of things that need to be done and that should keep me busy for a while. Thanks all.

Deoodles said:

I do not have any clearance/contact issues with my wheels. Is it possible that the shape of the sidewalls could be the issue? IDK. I’m running Michelin Boppers. I’ve tried others for many reasons and none of them had any contact issues. Wider rims is plausible

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im curious what kind of oil cooler you’re running. I like the slick look

That’s a GCraft 5 row. It is bare minimum for here in the summer. More rows are better but I wanted the stock skid plate. I can run hard for 4 or 5 miles then have to let it cool down. It’s good enough to run a 75 mile loop I like as long as I keep it at or below 45 mph for most of it.

Dkid said:

thank you Kirby. Also great video, it was a great starting point.

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Awesome! Thanks for letting me know that the video was helpful. That's what it's all about. Hopefully once you get that bike geared a little closer you'll finally be impressed by the stroker, and the extra 9cc that you got by boring the cases. I like my 117 a lot. The whole bike. Basically stock... suspension, brakes...makes for a bike that's quick, light, and nimble. Mine will zing right up close to 60mph...then maybe gain 5 more on the flat. But hills don't really seem to phase it much at all...even in 4th gear.

I'm sorry that I forgot to come back and reply to your first post in this thread... after you first posted. But your trx70 engine has a good 4speed transmission in it. That is the same trans that's in MY 117...a 4 upshifting trans. The TRX70 engine CASES are the 12volt type too.
In case you ever wanted to build a 4speed, that would be a good one.

kirrbby said:

I'm sorry that I forgot to come back and reply to your first post in this thread... after you first posted. But your trx70 engine has a good 4speed transmission in it. That is the same trans that's in MY 117...a 4 upshifting trans. The TRX70 engine CASES are the 12volt type too.
In case you ever wanted to build a 4speed, that would be a good one.

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It is what it is at this point, and probably already too late by the time I asked anyways. But I do regret it for many reasons. 1. I'm blowing bulbs and I can already tell what a goose chase that's going to be. I feel like the 12v systems are more resistant to those type of issues, and not having to deal with points/ignition would have been nice. 2. The 3 speed transmission is driving me crazy, I keep shifting from 2nd to 1st out of pure habit and getting slung onto the bars like a fool. 3. The TRX cases I have for some reason have a 49cc cylinder on it and low compression so that's needs to change anyway, and also the nicest looking cases of the 3. I will probably end up getting a 70cc cylinder on it and selling it for future project funds. It has the foot brake instead of the kick starter and I read these are sought after for ATC projects since they don't have foot brakes.

Well anyways, yesterday I notice a single drop of oil under the bike and figure either the case bolts were either too loose or more likely too tight. So I loosened them and the plan was too torque them to the correct spec, but of course that was more damaging. The new engine bolts I got on eBay are slightly shorter and were only engaging on a couple threads so torqueing them with my HF torque wrench cause them to strip out. I was dumb/smart enough to only do this twice. So I reinstalled the OEM JIS type back in the 2 holes and since they are a bit longer I was able to get them to bite back into the threads farther into the case but who knows the condition of the case threads now. Actually I know, they're f'd. But anyways I ditched the torque wrench and retightened the way I always do ( as tight as I can one handed with the stubbiest 3/8 wrench I own) and it seems to be fine for now, no leaks so far.

But now I don't want to split the cases and here is the problem I need to solve. Until Darrel let me know about the upgraded kick starter I didn't know that would be an issue and I didn't upgrade the kick starter. Now every time I kick the thing over I'm fearing for the snap that I assume is inevitable. I remember being able to push start my old 88 semi-auto, but that one had a stock clutch and with this HD clutch I don't think that is an option as it doesn't unengaged between shifts as much as I remember. So given that I don't want to split the cases due to issue just mentioned, I'm thinking off throwing an ATC pull starter on there. Is this a reasonable approach? Or will it pull my arm out of the socket trying to crank over the 117. Even though I do have one on my ATC 140 piranha and it's a non issue, but it's aftermarket. I have the side cover and flywheel from a 74 ATC so all I would need is a good recoil right? I see these pop up on eBay from time to time, and it would cost as much as the kick start upgrade but be significantly less work. It might look a little goofy, but I don't care about that if it'll work.

Thanks guys.

So today I put the 16/33 combo on and the ATC flywheel. Huge difference and happy to see the ATC flywheel works. Still not getting the top speeds I'd hope for but I hit 51 today so that's progress, and I'm coming to the realization that I'll be happy with it getting to 40 in a hurry and being able to cruise at 45 with no problem. So maybe how it is now will be the final form, although I do need to figure out the carb. I went to a 175 main jet from a 190 as recommend by Darrel and its runs a lot better with the exception of the shift into second. I need to let of the throttle all the way or it will bog out on me.

Few other things I got to work out still. I need to cut the side cover so that I can put my chain guard back on. I need to find an insert for my exhaust, it's too loud for me, and I'm sure my neighbors aren't thrilled that I got another one. I need to source a complete recoil(or parts) as the one that came with my ATC only had the housing and wheel. And lastly I need to cycle some oil through it and give it a proper break in.

I've included some pics so you can see my exhaust and the hackjob shifter I made. Haven't decided if I should get a proper ATC shifter or leave it as is since it works well, and hell it fits the hackjob theme of the rest of the bike.

PS: Sorry for what has essential become a build thread in the TECH section.

did you order that exhaust recently? I ordered a fmf pipe almost 2 months ago, still waitin.