72HK1 For CJ

cjpayne

cjpayne

Well-Known Member
I ended up riding by myself yesterday, but it was nice to finally go ridding again. Bike is running great, but I'm beginning to think I finally need to change the back sprocket to a 36 or 38. She is just a little over geared. The 14/35 combo works o.k, but I think a 38 should be tried. 4th is basically acting like an overdrive gear and acceleration is a little slow in forth. I don't want to go with the original 14/45, because I really dont want the engine screaming itself to death on the open road, which is 95% of the kind of driving it does.

Here it is just unloaded from the truck in my brothers back yard.
IMGA2268.jpg

Pulled off onto a gravel road to relax a bit. That house in the background is an Omish farm. Was great to ride out again where there are tractors and horse and buggies out on the road. A couple of them recognized me and waved.lol
IMGA2266.jpg
 
6

69ST

Well-Known Member
The bike looks great, none the worse for the ordeal.

I've seen 14/44, 14/45 & 15/45 listed as stock sprocket combos. That ranges from 3.0:1 to 3.21:1...take your pick. 14/35 = 2.5:1, that's one huge increase (~21%) over stock. 16/44 effectively splits the difference...2.75:1 and the larger C/S sprocket not only buys you some extra chain clearance, it'll extend chain life. (15/41 would be slightly, but not significantly, taller.) Frankly, I'm surprised that the motor pulls your existing final drive ratio but, it if works it works. Fewer revs-per-mile is a goal worth pursuing, especially for a road bike.
 
cjpayne

cjpayne

Well-Known Member
racerx said:
Frankly, I'm surprised that the motor pulls your existing final drive ratio but, it if works it works.
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I am too.lol
I can carry 3rd over 35mph without it revving to high, but it still tops out at 48mph on the flat. I tried it once just to see if it still would, then tried it going down a steep grade, it will fly over 50.lol
I usually cruise it 40-45, but mostly 40. I'm really in no hurry.
To extend the chain life, what about a 15/41(do they even make those?) or 15/44. I'm wondering what a back sprocket number would be for the 15CS that would resemble a 14/38 combo. Is that the 16/44 your talking about?
 
6

69ST

Well-Known Member
Easy to figure out what wheels sprocket to use...multiple the C/S sprocket tooth count by the ratio you want and, voila! Just round-off to whole numbers, sprockets with fractional teeth...not so good.:ROFLMAO:

14/38=2.714
2.714 x 15 = 40.714

16/43= 2.6875
43 tooth sprocket

Unfortunately, there's not much call for 41t wheel sprockets. So, it comes down to importing one or having one made, both of which are pricey options.
 
cjpayne

cjpayne

Well-Known Member
Got the correct air filter put in and put the rubber K1 end caps in too. They're SO much easier to deal with than the rings. Going to fiddle a little with the carb too. See if I can fine tune her a little better if I can. I think its pretty well dialed in, but will see.

Yo Bob! Last weekend, my brother and I went back roading. To my surprise, the new forks didn't like the brief encounter with the gravel. It got unstable quick.lol. I just slowed way down. Hopefully we will go today later(weather permitting) and I can tune the forks a little like you messaged me about. I don't have a CC measuring cup, so I'm going to use a small mL cup(from a DayQuil bottle) to measure with. I think first I will drain 5mL(5cc) from both the forks before heading out. I remember you telling me, after draining, to loosen the top bolts, extend the forks to get the volume of air in there, and then retighten the top bolts.
 
OLD CT

OLD CT

Well-Known Member
That sounds like compliments to the chef, special gearing may be required. I do remember my HKO came with a 14-44 as a kid. The fastest the thing went ''back then'' was 42 and it was screaming.
The Rupp 3 1/2 hsp TCI-1 ''torque converter'' equipped Tecumseh Scrambler would kick it's butt till 35 or 40 mph. It was nice having two bikes to tool around on. And racing my brother.
 
6

69ST

Well-Known Member
That'll work, Chett. I doubt that you'll end up draining more than 15cc, max. The adjustment range, via fill quantity is small. I would keep track of the total quantity drained, in any event. I've never even heard of the kind of instability you experienced. Thus, I'm wondering if the 15W oil is the "X" factor. If it turns out to be, knowing how much oil was drained will make quick & accurate work of the refill with 10W or the OE-spec 7W.

FWIW, when I ran K1 fork legs on my red bike, they were "tuned" exactly as your were/are. I was surprised by how stable the bike was. It'll be good to learn what's going on here.

OLD CT said:
The Rupp 3 1/2 hsp TCI-1 ''torque converter'' equipped Tecumseh Scrambler would kick it's butt till 35 or 40 mph.
Click to expand...
In this part of the world, Lil Indian and Ruttman were locally manufactured & marketed. The Ruttman bikes were particularly well-crafted, as lawnmower-type minibikes went. I built one from a bare frame, powered by a 5hp "130000 series" Briggs engine and one of the first TAV99 "Torque-A-Verter" kits to hit the market. With an effective "low gear" ratio around 15:1, the thing could pull stumps. You had to be careful, overenthusiastic throttle application, below ~15mph, would send the front end skyward. I managed to get that machine inspected, passed, titled & plated...got pulled over for lic & reg check almost daily. It was a lot of fun being able to out-drag just about anything across an intersection, before it started running out of horsepower, around 40mph. The thing was a death trap, for anyone beyond 16 years of age. Below that age, wasn't everyone immortal and in possession of "all the answers for everything"?
 
cjpayne

cjpayne

Well-Known Member
racerx said:
That'll work, Chett. I doubt that you'll end up draining more than 15cc, max. The adjustment range, via fill quantity is small. I would keep track of the total quantity drained, in any event. I've never even heard of the kind of instability you experienced. Thus, I'm wondering if the 15W oil is the "X" factor. If it turns out to be, knowing how much oil was drained will make quick & accurate work of the refill with 10W or the OE-spec 7W.

FWIW, when I ran K1 fork legs on my red bike, they were "tuned" exactly as your were/are. I was surprised by how stable the bike was. It'll be good to learn what's going on here.
Click to expand...

I'm pretty sure the "X" factors are me only weighing about 160 and the fact that the gravel was pretty loose and the road rough. I'm thinking 5cc's should do the trick. On the other roads, it was perfectly stable. The tires also have 30psi in them, so the bike rolls easier.
 
6

69ST

Well-Known Member
Yeah, that's pretty high inflation pressure and could be a significant factor. I run Trailwings ~24f/28r, that's sufficient for riding 2-up.
 
cjpayne

cjpayne

Well-Known Member
I am surprised how well the stock Bridgestones work for these bikes. They are great for on or off road. I do wish they were a little harder compound, just for the wear factor of pavement in the summer time.
 
6

69ST

Well-Known Member
50mph, from 72cc is rhumboogie'n! From a bone-stocker, that's outright impressive. "She's tuned" is an understatement...good job, CJ.(n)

BTW... tread life is the inevitable tradeoff, road grip or longevity...choose not more than one. What's a new rear tire every 3-4k miles, if it's working well for you?
 
cjpayne

cjpayne

Well-Known Member
racerx said:
50mph, from 72cc is rhumboogie'n! From a bone-stocker, that's outright impressive. "She's tuned" is an understatement...good job, CJ.(n)

BTW... tread life is the inevitable tradeoff, road grip or longevity...choose not more than one. What's a new rear tire every 3-4k miles, if it's working well for you?
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After I got the correct element in, I played with the carb settings. I eventually had to set the idle down a little. Changed the plug too. I haven't removed the baffle pipe yet, but I don't think its really necessary at this point. It sounds so smooth as it is.
I sent the vid to kirrbby and asked him to send it to you. I sent it to others too.
 
cjpayne

cjpayne

Well-Known Member
Deoodles said:
Cool video, that’s as good as it gets for stock. Hats off to you!
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Yeah, I dont think it will go any faster on a straight.lol. Wish I could upload the vid, but I cant seem too. Maybe you can since your phone isn't ancient like mine and will transfer.
The vid quality is pretty lame and I had a hard time holding things steady. I'm definitely not a professional.lol
 
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