Latest updates on progress of the C70 commuter

Apologies in advance but this is a bit of a cross post with one of the Yahoo groups but I'm not sure how much overlap there is between this group and the Yahoo C70 group. I took the bike out this weekend for a longer ride -- two 20 mile circuits with an hour rest in between. I'm in Seattle and even planning to stay on roads with max 40mph speed limits, had to run at WOT for really long stretches without a break. To boot, a good 20% of each ride was on 4-6% minimum grades for long stretches. The bike with the long duration cam works great on the flats, but on the long grades the bike looses all oomph and downshifts to 2nd and then ultimately to 1st just to keep moving. In 1st or in 2nd it I either had to run at the top end of the throttle (again WOT) or else I just couldn't keep moving forward. Compounded with that was a fair amount of either pinging or pre-ignition, it sounds like the piston is just rattling around in the bore. Pulling over and just letting the bike rest for 5 minutes helped things, but this is not a good long term solution for a commuter bike.

Just to recap the bike -- it has the Dr Atv long duration cam and his aftermarket head with the 25mm intake and 22mm exhaust valves. For sprockets i'm running a 14/37 which gives me just about half the increase over the move to a I5t front.

Any thoughts here? I had a huge amount of fun doing this but I still feel like i've lost the ability to hold a solid 20-25mph on a hill and also be able to get up to 40mph. Am I just expecting too much of the bike? I may throw on an 88cc jug just for giggles, but I'm suspicious at this point that my timing is off slightly and trying to get that dialed in and continuing to work on my fuel mix and jetting may help more

hal

whereshaldo said:

a good 20% of each ride was on 4-6% minimum grades for long stretches.

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That's a BMF variable. Minimum is one thing, what about the maximum & mean average? Add a headwind and the power requirement can go off the proverbial scale. Then, there's the gearing, especially on long grades. On a 10% grade, I'd expect to see ~70-80% of top speed potential, sans headwind. That assumes a completely healthy engine that is tuned & geared optimally. As long as the engine can make a certain hp number, the only effect of cam profile would be the rpm at which that occurs...you'd match the gearing to allow this. That said, something here isn't right. If you end up downshifting to first gear and the motor can't pull that, let alone without overheating (and that's the sense you're giving), horsepower is down...way down. 20mph should only require ~1/3 the power needed to reach 40mph. In stock trim, it should be damned near impossible to overheat one of these motors.

You've introduced some interesting variables: head, carburetion & gearing. Having a 4-speed tranny would be helpful, in that crucial midrange. But that isn't going to solve the overheating/pre-igntion & power loss. First thing I'd want to know is why you're getting pre-igntion. In stock form, 87-octane should suffice...at sea level. Does running pump "premium" (91-93 octane) make any difference? What's the static compression ratio of this engine, as fitted with the aftermarket head? Is the air:fuel ratio near the rich limit? What kind of oil temps are you seeing? That would speak volumes. I could see adding a high volume oil pump and, possibly an auxiliary cooler to bring down both oil & head temps.

If you're considering going back into the motor, a stroker crank will add more oomph than any other mod...and the longer the better.

Ha! Over 3 miles the grade ranges from 2.5 - 5.9% Its all uphill, and I'm in the gravelly bike lane trying to avoid the families out for a drive in their F250 dually. http://www.bicycleclimbs.com/Default.aspx?ClimbId=20

Going the other way i was stuck on this route which gets up to an 11% grade. http://www.bicycleclimbs.com/Default.aspx?ClimbId=392

Hal

"2.5 - 5.9%" contradicts "4-6% minimum". Sitting behind a desk, a couple thousand miles away, this is clear as mud...so far. I'm not being argumentative, far from it. What's needed is clear, detailed & accurate data; otherwise, it's blind guesses, with a good chance of being dead wrong...at best. 11% is going to be a challenge for stock displacement but, I'd expect 20-25mph and the engine at, or near, its power peak.

Seriously, I just came back from riding in an area where there are a few extended 10% grades, along with several steeper, but much shorter, ones. 8-10% over a 3-mile span was enough to slow a 60-65mph bike into the low 50s, with a modest headwind. There were a couple of shorter but steeper grades which, combined with a stiff headwind, slowed proceedings into the mid-to-high 40s. Over an estimated 30% grade, I had no trouble pulling 30mph (didn't even try going any faster, the speed limit was 15mph, as it was)...we're talking 50-80% of top speed, minimum. Now, this is with a bone-stock, long-stroke 110cc Honda motor and, the higher speeds involve substantially more aerodynamic drag. The main point is the percentages...from an engineering standpoint. The other issue is what one can reasonably expect from an "unstressed" engine and why you're not seeing that, as things are.

Cutting to the chase, I rode ~400 miles over three days; 330 of that was covered in two of them. Between the hills and stiff headwinds, I'd estimate at least 30% of that was at-or-near WOT. Oil temp maxed-out at 102C, once...with a tankful of lame fuel. That, along with speeds that came up short of what I'd have preferred, is the absolute worst of it, period. The engine doesn't know the difference between running at 85-100% output over inclines, declines, level road or facing 20-35mph headwinds. Over the years, there have been a few members here with totally stock CT70s that were run wide-open for miles...at speeds that exceed your minimum requirements...with similar results. IOW, no obvious signs of weakness, mechanical stress or overheating/detonation. The money question is what combination of factors is holding you back. Even if 11% grade is overwhelming, the bike should be able to maintain speeds close to, or meeting, your reasonable minimum(s). Getting this sorted is going to take clear & accurate data, no way around it.

Thank you. This forum is the most technically informed group i've ever been involved with and every time I come away smarter and with 20 more questions to ask.

hal

No worries, that's why we're here. Ask all the questions you need to solve your issue. Given sufficient time, information and persistence you'll get the desired result.

Since he has a cub scooter ,I wonder if the much taller tire diameter is hurting him ,how does the gearing match up with a ct70 ?

The taller tires actually work in his favor...less rolling resistance and better angulariy for dealing with uneven pavement. The requisite sprocket combo must, of course, be matched to the tire diameter. Once that's been done, revs per mile are the same as is the gear spacing.

I made some small incremental tweaks today to continue to hone things.
First i put in new rear shocks. Quite a bit stiffer but lots less bouncing down the street, which actually seems to help with maintaining momentum forward! There aren't many options for the '80-81 bikes, but these seem ok. Also, i got some grease into the front suspension grease points. This also seems to help with the bounce.

Second, I checked, re-checked, and re-re-checked my points gap. It is now set between the .3 and .38 mm feeler gauges that are in my set.

Third, I re-checked my point gap. It was a little wide, but not terrible. I think the plug looks ok, though there were a few small crusty bits starting to build which may be indicative of what I suspect was pre-ignition, but I'm not sure.

Overall, there does seem to be some improvement in initial low end torque and in holding speed on grades. I took a nice little trip today which included 1.5 miles up a pretty consistent 2.6% grade. Not steep, but its a good indicator since i ride up it a bit. I seemed to be able to actually increase speed in 3rd even if it took a long time -- accelerating is better than not. Also, it seemed like the engine just ran a bit smoother overall and was a bit quieter.

All good progress. I won't get to ride much this week but I'll put another 200 miles on before making the next change.

h

Sounds like a win. You most likely advanced the timing now to the optimal range. That is not the first time on here I have seen this white crusty build up. Kirby's plug looked worse. Must be the new norm for the goat piss we call gas. I am better off sticking with corn syrup free 100 octane Cam2 unleaded. I have not had this crusty build up happen to me yet. I would keep an eye on that. Good idea to keep some new plugs in stock.

OLD CT said:

Sounds like a win. You most likely advanced the timing now to the optimal range. That is not the first time on here I have seen this white crusty build up. Kirby's plug looked worse. Must be the new norm for the goat piss we call gas. I am better off sticking with corn syrup free 100 octane Cam2 unleaded. I have not had this crusty build up happen to me yet. I would keep an eye on that. Good idea to keep some new plugs in stock.

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FWIW, I share this concern. That said, consider that the first time I ran across plugs that looked like this was circa 1973, well before 21st century goat piss fuel...the engine was a 273 Chrysler V8, in a first-gen Barracuda.

Fast forward to 2018, the original, factory-installed plug in my red bikes engine didn't look anything like this...after 23,000+ miles, when I checked it at the start of the season. Consider that kirrbby's truck engine had but one out of eight plugs that looked like this. That, IMHO, casts doubt as to what the exact cause of those deposits are. For the moment, I'm thinking that it's more to do with oil control than anything else. I hope I'm right or, at the very least, it's spotty fuel quality. Racing fuel is not only a witches brew of its own...it's also a damned short tether for a road bike.

There is ethanol free gas in my neighborhood, I may give that a try too. I know it's an issue for 2 strokes, but probably also for any older era engine.

Hal

The main issue is what it does to rubber parts, like fuel lines, seals and...for 2-strokes...carburetor diaphragms. With the carburetors on our 4-stroke Hondas, the worst impact is on petcock packings, the rubber washer/seal with all the holes. They'll shrink and turn brittle if allowed to dry, after being exposed to current formula gasoline. Draining the fuel system and coating the packing with a little grease, immediately after draining the fuel, will keep a packing viable for years. They still shrink a little, over the winter but will reconstitute and swell back to full, original, size within a matter of hours, once you refuel...cometh the spring.

Those issues are true for almost any old vehicle -- the rubber compounds just were not made the same. With old cars, the first thing to be done is to replace the fuel lines with ones of a more modern rubber composition. A pain in the ass, but less so than a fire.

There are other issues as well. Ethanol fuel removes the oil buildup on cylinder walls and in bearings and can cause premature wear. I have also heard that I makes engines run hotter, which may be a contributing factor to my pre-ignition. I'll post back after I get some non-ethanol gas in the bike.

H

Owners of old cars face a number of fuel-related problems. Things like fuel pump diaphragms and inlet needles with neoprene tips become Dixie-cup-disposables. Two-stroke motors, such as those used in chain saws and commercial landscaping equipment, are a pain in the arse to keep running. In this area, landscapers and tree services all buy their fuel at marinas; not everyone has that option.

Viewing your plug photo on a real screen, I don't see any metallic artifacts...good news for you. I do wonder if those thick deposits on the side electrode start glowing, as in red-hot...literally. That could easily result in pre-ignition. I'd want to retest the bike using a new plug, or at least after giving this one a good cleaning. It's a simple test that could give you a definitive answer and point toward the real problem.

Funny you mention the wear & heat issue. On the wear side, ethanol has an insignificant impact...it's almost like LNG (methane/natural gas), or propane, clean & high octane. Methanol is a whole different story. Gasoline, itself, is a dirty fuel but it has its positive aspects, to which most engines have been adapted. IMO, other additives that have come into use (the "goat piss" in pump gas soup) are more worrisome. Back in the day, ~45 years ago, there were detergent gasoline formulas, to which chemical "scavengers" were added and they could result in fouled plugs with deposits resembling what your bike...and kirrbby's truck...have exhibited. Of course, electronic engine management has really cleaned-up combustion, from cold-startup to idle to WOT, rendering the pre-PC era "Mexican tuneup" mostly obsolete. One thing that hasn't changed is oil control and once that becomes an issue, nothing short of a mechanical correction can fix it; that doesn't necessarily mean a major overhaul. As for increased engine temps, that's largely a result of leaner mixtures...a major goal of "reformulated" pump gas, largely realized by the addition of oxygenates. Alcohols, including ethanol and methanol, are both oxygenates. And they do result in leaner mixtures.

When E10 first hit the pumps, it became necessary to upsize the main jet by one number in many, but not all, situations. A year, or two, later I started seeing leaky petcock assemblies and, for those with VM22 carbs, problems with the main jet well O-ring shriveling to the point where it would no longer seal. Our own kirrbby went through the proverbial meat grinder trying to jet one of these carbs, unaware of this underlying problem. I also noticed, during testing/tuning sessions, that engines would rev-out cleanly with A:F ratios that were significantly richer than the rich limit had been previously. With A:F ratios sorted, to compensate for the "revised" pump gas available in this area, things mostly returned to normal, minus a few mpg...until relatively recently. Going back at least 5 years, I've gotten the occasional tankful of lame fuel...manifesting as reduced power, higher oil temps and a ~5-15mpg+/- decrease. As of this year, that's almost become the "new normal" (ugh)...~5C increased oil temp and ~5mpg less. On the surface, one could easily and logically conclude that the engine is getting a little tired. That said, if this were true, the results would be more consistent than they are. When you ride, say, 350 miles in 3 days, there will be plenty of fuel stops along the way, each one a chance to check fuel consumption, while the numbers are still fresh in memory. With ~85 mile range (per tankful), I'm usually hitting "reserve" at 62miles...with a tank top-off verifying actual consumption. When that comes up at 52-58 miles, then returns to the expected 62 with the next tank...clearly it's something other than engine health causing this. Another clue, refilling the tank at home, from a 6-gallon container then topping-off the tank (same day), at a pump, after it's been run low, consistently shows mpg in the expected range. Consistent mpg when using known fuel, random variations over the road, refueling from unknown sources. IMHO, this is not the kind thing that most folks would even consider, let alone make a systematic effort to decipher. I mean, WGAF about ~1/2 gallon of fuel burned at the rate of, say, 87mpg vs 94mpg? That's not enough pennies to even impact the "sofa cushion piggybank" That said, consistently topping-off the fuel tank and a little basic math can be an effective early warning system/diagnostic tool. When fuel consumption takes a sudden dive, that should tell you that something is amiss.

I thought I would just post an update on where I'm at with the bike. In short, it is running like a top now. I now feel like a lot of the small issues I was having with idle cutout, poor performance on hills & pre-ignition were all timing related. Now that I have the timing correct -- and this was largely points gap -- the bike runs like a champ. I am getting close to 93mpg riding it like I stole it. It really is a superb piece of machinery.

So, I want to mess it up. I'd been thinking about going to 88cc but that's not going to do what I want. What I'm more interested in is getting another gear. Is there another Honda with the same semi-auto clutch and a 4 speed transmission that can be put into a stock 6v 70cc engine?

Thanks for the ongoing support.

H

The clutch and transmission types are independent of each other. All you need to source is the complete 4-speed tranny assembly (gear clusters w/shafts, drum & forks, shift star & pins) and swap-out the 3-speed.

racerx said:

The clutch and transmission types are independent of each other. All you need to source is the complete 4-speed tranny assembly (gear clusters w/shafts, drum & forks, shift star & pins) and swap-out the 3-speed.

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What bikes had 4 speed transmissions?

CT70H, SL70, CL70, XL70, TRX70 (some years)...along with non-US-spec C70 and C90.

4 speeds come in 4down, 4up, and 1down 3up.

1down 3up isn't recommend with a semi-auto clutch.