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Old 12-02-2012, 11:49 AM   #61
JerryH
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There is a device called a Dial-A-Jet that works on some carbs, including the Mikuni CV on the XT225. I have not tried it yet, but everyone who has seems to like it. Don't know if it would work on the C70 or not.

I just found out about the TAT. I wonder if a properly modified XT225 would make it. Sure would like to try if I could find a way.
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Old 12-02-2012, 01:03 PM   #62
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In '97 rode my wife's '92 XT225 for a few days in Colorado with a fatter pilot jet and the mixture screw readjusted but otherwise stock. Anytime I went over about 10,000 feet it fouled plugs and quit running. It definitely needed leaner jetting. This was in September with cooler temperatures and denser air. At the time I never thought about something as simple as the wire trick.

Short of fitting nitrous oxide to a bike--or anything with an internal combustion engine--once you get up where the air is thin you're going to lose power. At that point all you can do is reduce the amount of fuel going into the engine to compensate for the lack of air.

I read somewhere that the Luftwaffe was the first to use nitrous oxide to compensate for the lack of air at high altitude. I'm kind of surprised no one has adapted an NOS kit for this use instead of just for performance.
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Old 12-02-2012, 06:35 PM   #63
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I live in the desert at around 1200 feet. My XT is jetted slightly rich to compensate for the drilled stock muffler (PO did it, but didn't rejet) and to avoid engine seizure while running in 115 degree temps. I have ridden it up in the mountains close to 10,000 feet, and it is blubbery as hell, but still runs. If I lived up there, I would have to down jet it, but as things are I just have to live with it.

The problem I see with nitrous on a bike, even if it is just there for high altitudes, people are going to use it for performance, and quickly blow their engines. I am an amateur drag racer, and run a small block Chevy in an '89 S10. The engine is well built, but built more for durability than absolute max power, as I can't afford to keep rebuilding it. Seems like every time I go to the track, someone running a Japanese car using nitrous blows an engine. Stock engines are built to barely handle stock power.
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Old 12-03-2012, 12:29 PM   #64
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Using the same sort of computerized technology that determines how much fuel to feed our vehicles' engines could the same thing be used to automatically feed NOS into engines to compensate for altitude and temperature?

It would be awesome to have the same performance at 14,000' as we have at sea level.

The only NOS system I ever dealt with was one we put on an outlaw figure-8 car. It was turned on via a button on the steering wheel and triggered with a microswitch fitted to the carb linkage. About the only way you could control it was to adjust where it came on in conjuction with throttle opening and what jets were put into it. Stone ax simple!! Unfortunately it was also pretty uncontrollable to drive and according to the driver it was kind of like letting go of an inflated ballon--at least until the head gaskets got blown out a few laps later.

My thinking is that computer control of NOS might eliminate some of it's liabilities and might make it usable for altitude compensation. There again my experience with it was a total of about one day so I really don't know all that much about it. Fascinating stuff, though and it really makes power!!
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Old 12-03-2012, 03:23 PM   #65
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I might be able to throw a bit of light on the NO2 use possibly. I'm also a drag racer like Jerry, and have used it for 20 years on different stuff.
NO2 is a really cheap way to get HP our of an engine. That's it. It's cheap. Becasue of this most people get greedy and want more, don't tune it in properly (fuel/NO2 mix ratio MUST be right) and a loud bang follows. Get the mixture right and most engines can take an enormous amount of power, get it slightly off (when your close to the limit) and get a new motor.
I put 50HP into a Kwaka 1600 cruiser, because it was the CHEAP way to get enough HP to qualify (I need to run at least 11's) to run at my National drag meets.
I put 40HP into my S4R Ducati, coz it was the CHEAP way to get the thing to run in the mid-9s at the track and put the wind up the Busa's!
I threw 150HP at my Supra years ago.......shit I can't remember why, but I'm sure I had a good reason at the time!

Anyway, I also have found out over the years that when the HP level gets too small, the orifice that meters the NO2 can, as a combination of extremely small size (less than 0.010") and extremely low temps (NO2 will instantly frostbite anything on contact, VERY cold) actually freeze shut. The size seems about the 0.008" or less mark. This is at around the 8HP level roughly. Since with most engines, stock or modded, a safe NO2 HP level is around 30-40% extra, this means that it is very difficult to tune or get reliable NO2 use out of engines with less than 20HP.

I rekn gearing is a MUCH better way of multiplying torque at the tyre.
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Old 12-08-2012, 05:21 PM   #66
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Another idea...

I plumb forgot about the fact that the Passports use the same primary gearing as the majority of the 50's. Using the primary gears from an XR/CRF-70 would lower your cruising RPM's on the road substantially. I don't have the numbers here in front of me but the difference was substantial enough that changing to the 50 primary gears was a hot rod trick I did to the 70 motors to give them more accelleration. By contrast using the taller 70 primary gears would give you a more relaxed engine feel on the road.

The changeover requires the front and rear primary gears from the 70 plus the gear that goes inside of the clutch and takes maybe a half-hour to complete.
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Old 12-18-2012, 04:37 PM   #67
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sorry to hijack, but I'm wondering if Trail 90/110 wheels will fit on the C70 Passport (is the hub a direct exchange?)
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Old 12-19-2012, 09:23 AM   #68
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Factory engineers labor greatly to seek reliability and performance in proper proportions. Modifying is fun but when alone a long way from anywhere and the computer geeks In the comfortable suburbs have moved on to the next modification project, a stock bike inspires confidence in the person riding it out there on the road. Confidence in your ride will get you through and will increase relaxation which multiplies pleasure. Very best of luck and look to the Third World where reliability trumps expensive modifications every day on appallingly bad roads.
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Old 12-19-2012, 07:00 PM   #69
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Sorry it's been a while since I updated this thread. Work on the engine is progressing slowly. As usual what starts out as a simple reseal quickly turned into a top end rebuild. I found what was probably the main cause of the top end oil leak. It appears that the replacement cylinder that I installed many miles ago had a casting flaw in the oil return passage. The passage is way offset from the hole back into the case, so much so that a section of the O-ring collapses into it instead of sealing against it. So a new cylinder was a must and has been ordered. Also the area of the head where the cam rides is scored pretty badly as well as the bearing area of the cam itself, probably from the same incident that burned up the piston, cylinder, and crankshaft which I had to replace, courtesy of a previous owner. The reasoning behind me not inspecting the head during the original rebuild has been lost to the passage of time. The engine has run well for about 25,000 miles with the cam bearing surfaces all scored up, but this trip will be hard enough on the little engine, even in top shape, so I want a fresh cylinder head for the journey. The OEM Honda head has been discontinued so I ordered a complete aftermarket (Lifan, I think) cylinder head. The cam in this head rides on ball bearings, which is nice. Upon disassembling the oil pump, it was pretty rough inside as well. Again the bike ran good enough, but I don't want to reassemble it with a marginal oil pump. After a little internet searching, I found a new genuine Honda oil pump. I also got a new Honda piston, wrist pin, and piston rings as the cost was minimal and its already this far apart. Amazingly the cheapo $50 aftermarket crankshaft assembly that I installed years ago in the original rebuild has held up fantastic. I also ordered new clutch plates and springs for the little bike. Right now I am just waiting on the parts to arrive to begin reassembly. On a side note, I finally got my other ride, a 1980 Honda CB125S, running well enough to make the commute to work on, so that has been exciting.

Conchscooter your words are wise. I am just going to keep it simple. Really the only thing I changed performance-wise are the front and rear shocks. That was mostly because I didn't want to ruin my NOS Honda rear shocks that I had acquired after several years of searching. Honestly the stock shocks are a little on the weak side all around with just me on it, let alone with another 50 pounds of stuff.

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Old 12-26-2012, 02:55 PM   #70
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Today I rebuilt the Honda's clutch assembly with new friction disks and springs. Then I disassembled the gears and spacers off the worn transmission countershaft and reassembled them onto a new one.

Half way through the clutch rebuild.


The countershaft gears reassembled onto the new shaft. Its hard to see in the picture but the splines on the old shaft are very worn out where the front sprocket for the chain rides. This allowed the sprocket to rock back and forth on the splines every time I shifted gears which was wearing a deep grove into them. I doubt it would have survived the trip.

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Old 12-27-2012, 02:00 PM   #71
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Quote:
Originally Posted by conchscooter View Post
...Modifying is fun but when alone a long way from anywhere and the computer geeks In the comfortable suburbs have moved on to the next modification project...
Well, if this was aimed at me I'm afraid you're sorely mistaken. I can barely operate these damned things but I have worked on motorcycles for the past forty plus years and I'm far more comfortable with a wrench than I am a keyboard.

I have a huge appreciation of the design of the horizontal Honda design and it's ability to absorb abuse. I've worked on these fine little motors since my earliest days riding motorcycles and only recently (about nine years ago) got back into them, first through a late mid-life crisis on a heavily modified XR-50 in backyard pitbike racing and more recently bringing a Honda Passport back to life. Currently I'm building up my "Ultralight Adventure Bike" using a CT200 chassis and an OHC cam motor for long-distance adventuring. I also carefully set up my ex-backyard-racer-turned-street-legal-runabout and did a 450+ mile dual-sport ride on it so I know a thing or three about setting up these littles bikes for stone reliable performance over the long haul.

I've also ridden on the Trans-Am Trail several times, twice with it's creator Sam Correro and probably half of my motorcycling has been done off-road.

slowlane asked for real-world suggestions for taking a C70 on the TAT. Yeah, he could take a box-stock C70 on the trip and probably survive but there are lots of things he can do to the little bike to make it more reliable, easier to ride and in general a better long-distance adventurer.

But typical of most forums there's always people with no real-world experience other than their own opinion and that's why I'm always hesitant to offer my suggestions knowing that it often turns otherwise good threads into on-line arguements.

Good luck on your trip, slowlane. I believe you're on the right track with your careful preparation and I hope you have the adventure of a lifetime.
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Old 12-27-2012, 02:16 PM   #72
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On the issue of NOS there is also maintaining street legal status. Assuming one wants to do more than ride off road legally the bottle has to be off and disconnected from the engine on public roadways.
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Old 12-27-2012, 06:46 PM   #73
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Many of the ricers around here have it hooked up on street cars (these are the same guys who blow their mostly stock engines at the track), cops don't know or care, but you can't use it. If a cop so much as hears you squeal the tires leaving a light, you are going to get busted for reckless driving.

In 45 years of riding and working on motorcycles, I have yet to find anything better than stock. When you make engine modifications to a bike, it seems you always lose way more than you gain. I did go up one tooth on the front sprocket on an '07 Ninja 250, that bike was seriously undergeared. Some went way more than that, but I found that the 15T sprocket (instead of a 14T) made it perfect.
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Old 02-26-2013, 07:30 PM   #74
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Wow, it's been two months since I updated this. Well, the little C70 has been up and running again for about a month and 500 or so miles now. It was funny when I took the old piston out I noticed that I had installed the second piston ring upside-down when I first rebuilt the engine about 6 years ago. The little mark on the side that faces up was almost microscopic on these piston rings. The crazy thing was it had been running like that for over 25,000 miles and it ran no different than any other Cub I have ridden. I made extra sure that the new rings went on right this time.

However, I am now in a mental dilemma over whether to even use the Cub for the trip. The length of my upcoming ride has increased dramatically from my initial plan. I originally was going to transport the C70 to the beginning of the TAT and then attempt to ride it to then end. Then I would transport it back to Texas. The more I think about it, I really want to ride a bike on the entire trip and will probably skip a lot of the western TAT, because the more I look at ride reports from the western half, the more I doubt that I currently have a bike that is truly capable of handling it. I want to ride from Texas to Georgia for the Vintage Japanese Motorcycle Club Rally, which is only about 100 miles from the start of the TAT. After the rally I'll start the TAT in Tennessee to about midway through OK, then head north into Kansas to go visit a friend up there. I also want to go back to some of my old favorite riding destinations from when I lived in Kansas. Then I am most likely just going to wing it all the way to the west coast, probably ending up in Oregon or northern California. On the way back to Texas the only thing I want to visit for sure is the Grand Canyon and then head for home.

That brings me to bike choice. In addition to the C70, I also have a '80 Honda CB125S that runs very well, but would need some more work like wheel bearings, fork seals, and a few other things before I would consider it ready for a trip. I have all these parts, I just need to install them. The 125 can run 50-55 easy where the C70 will struggle to hit 40mph with me and my stuff. This still relegates me to state/county roads, but I think with the better speed of the 125 I will be able to enjoy the actual trip a lot more, verses constantly worrying about what sort of vehicle is bearing down ready to run me over.

Either way, the Honda got some needed attention and will be more ready for it's upcoming additional duties as a farm run-around vehicle when I go to New Hampshire.

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Old 02-26-2013, 08:09 PM   #75
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Post a build of the CB as well.
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