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Messages - sgarnett

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1
General Motorcycle Discussion / Re: More Fun with Fuel....
« on: September 11, 2017, 11:03:21 AM »
I think you've hit the nail on the head, DD!  :gavel:

2
General Motorcycle Discussion / Re: More Fun with Fuel....
« on: September 11, 2017, 07:58:16 AM »
I have not measured the temperature of the Nighthawk engine.

You are right that modern water-cooled engines are by design running hotter than might be optimal for the engine because it changes the mix of exhaust gasses.

However, my point was that a modern water-cooled engine is operating in a much narrower range. Regardless of ambient temperature, the engine temperature is regulated to a fairly narrow range (ignoring extreme weather conditions).

I don't know whether a Nighthawk cruising at 70mph on a 70 degree day runs hotter or cooler than a modern water-cooled bike at the same 70 and 70. However, I'm quite certain that the air-cooled engine varies through a much wider range in normal operation. Ambient temperature, speed, RPM, and throttle are all going to have more effect without a thermostat to regulate the temperature.

As to how it would affect the idle, I suspect that is more about the mixture (including offsets by ethanol and/or oxygenators) and volatility (i.e. how well the fuel is vaporized in the carburator).

3
General Motorcycle Discussion / Re: More Fun with Fuel....
« on: September 10, 2017, 02:11:29 PM »
I used to compete in autocross with an LS1 Camaro. Those engines are extensively programmable. I did a lot of tuning work with a wideband lambda sensor.

The LS1 is quite efficient, and makes the most power with relatively lean mixture. However, even with a colder thermostat and aggressively programmed fans, I would get a 10-20 degree F rise during a competition run (roughly a minute). As a result, I had trouble with pinging late in the run. Retarding the spark did not help.

In the end, I had to add extra fuel as the coolant temperature rose just to quench (cool and slow) combustion. In other words, I was using excess fuel to increase the effective octane.

The stock Nighthawk tuning is reputed to be leanish anyway to meet emission requirements. I have not confirmed this yet, but it certainly is plausible for the era. E10 inherently runs a little lean in an engine without closed-loop control. I am also quite certain that the air-cooled engine temperature varies more than 20 degrees in normal operation.

Gasoline also varies not only by season and state but even by municipality. Besides ethanol content, some gasoline blends contain varying amounts of oxygenators, which may further lean the mixture. Then there's other variables like exhaust mods.

I was shocked by how much the LS1 tuning was affected just by changing the flywheel. There are no independent variables in an engine. Everything affects everything.

To me, it is entirely plausible that some carbureted bikes in some areas might run better on premium fuel, while others may not. However, I suspect that those that do run better on it would also benefit from rejetting.

4
Your Honda Nighthawk / Re: First time rider!
« on: September 01, 2017, 02:32:03 AM »
Hi, I'm less than two months ahead of you on the same path. I took the class in June, and found my 91 750 in July. The biggest problem was just getting the clutch working again after sitting for two years. Several hours and a lot of sweat later, I was making the long drive home much later than I had planned.

I've been impressed by how stable and forgiving the Nighthawk is.

5
General Motorcycle Discussion / Re: Placebo or Real? 87 or 92 octane
« on: August 30, 2017, 12:29:27 PM »
But still... Even in the same state at the same time there could be multiple local variants.... 
This could skew results on a ride where the bike gets different formulations even if they are from the same retail name and grade....
Yes, absolutely! Large urban areas can have different formulation standards than surrounding counties due to pollution levels. In my state, Kentucky, the standards are different for the Louisville and Covington areas.

7
General Motorcycle Discussion / Re: Placebo or Real? 87 or 92 octane
« on: August 28, 2017, 06:36:00 AM »
The slower burn rate of high octane seems to be dismissed as benign or even undesirable. I would expect that to be RPM-dependent. At lower RPM, slower burn could be an advantage.

8
General Motorcycle Discussion / Re: Placebo or Real? 87 or 92 octane
« on: August 25, 2017, 12:13:40 PM »
As mentioned earlier, there may be some difference due to ethanol content. Ethanol in the mix causes the engine to run leaner in an open loop (carb) system. Closed-loop control in a fuel-injected system can compensate for this; carbs cannot. That said, it's not a huge difference, but if the engine is a little lean already .... FWIW, stoich for gasoline is 14.7:1, while stoich for E10 is around 14.1:1

Higher octane fuel could conceivably burn at a different rate. Assuming (hypothetically) that it burns slower, that MIGHT improve idle and low-end torque. Whether there actually is a measurable difference, i have no idea. 

9
General Motorcycle Discussion / Re: CB750 page at Wikipedia
« on: August 05, 2017, 12:31:56 PM »
My title says CB750, I believe, but that doesn't help with your main question. Besides peak power, have you found dyno curves to compare?

10
General Motorcycle Discussion / Re: CB750 page at Wikipedia
« on: August 05, 2017, 09:56:54 AM »
The last Nighthawk 750 was a CB750, but I've never figured out the suffix. Partzilla calls it a CB750A, but the A used to mean automatic. I've also seen CB750F2, but I think that was a European model.

11
General Motorcycle Discussion / Re: The Four Stroke Engine...
« on: July 30, 2017, 10:08:14 AM »
That has some seriously bizarre funkiness, no doubt!

12
General Motorcycle Discussion / Re: The Four Stroke Engine...
« on: July 30, 2017, 09:11:42 AM »
When I test drove a first gen RX7 years ago, the word that came to mind was "turbine", but I guess Leno already has that base covered.

13
General Motorcycle Discussion / Re: The Four Stroke Engine...
« on: July 30, 2017, 09:09:48 AM »
I have seen references to a Wankel MC, but haven't actually seen one. It seems about as far from American v-twin "potato potato potato" as you can get! :joker:

14
General Motorcycle Discussion / Re: The Four Stroke Engine...
« on: July 30, 2017, 08:50:25 AM »
Well, Wankels still go through all of those stages. They just do it all in a single revolution and burn more oil in the process!  brno

15
General Motorcycle Discussion / Re: What year is too old?
« on: July 27, 2017, 03:18:13 PM »
When I was looking for a Nighthawk (recently bought a 91, so no longer looking), there were several Dixon clones and quite a few bobbers and scramblers. If that's what you want, you could let somebody else take the loss instead of building it yourself. Even if you want to change a few things to make it yours, starting with one that's already built will give you a good head start.

OTOH, I had to drive several hours away to buy a relatively clean and unmolested Nighthawk. Seems a shame to start carving up a survivor if you don't need to.

The same goes for cars, really, and there's a few things I wish I could go back and undo on my Camaro.

16
Your Honda Nighthawk / Re: My new 91 NH 750
« on: July 27, 2017, 03:03:01 PM »
 :joker:

17
Your Honda Nighthawk / Re: My new 91 NH 750
« on: July 24, 2017, 12:50:39 PM »
I understand that there may be some debate about whether red or yellow is faster. For 1991 though, red was clearly the fastest  bnna+

18
Your Honda Nighthawk / Re: My new 91 NH 750
« on: July 24, 2017, 12:47:43 PM »
The rear fairing is notched for the sissy bar that came with it, and I think the muffler rivets have been drilled out and replaced (though it still seems quiet, so I'm not sure what was done). Other than that, mine is still stock (or repaired with stock parts) as far as I know.

19
Your Honda Nighthawk / Re: Black 1992 Honda Nighthawk CB750
« on: July 24, 2017, 12:16:32 PM »
Thanks! And yes, I'm new to the forum, Nighthawks, and motorcycles. I also have a gravel driveway ....

20
Your Honda Nighthawk / Re: Black 1992 Honda Nighthawk CB750
« on: July 24, 2017, 09:04:27 AM »
Today I installed an economical, black, aluminum kickstand enlarger with stainless steel hardware too, (as suggested by fellow NHF members).

Where did you find a kickstand foot enlarger to fit a Nighthawk?

21
Your Honda Nighthawk / My new 91 NH 750
« on: July 24, 2017, 05:19:42 AM »
I got this 91 a little over a week and 150 miles ago. It has 49xxx miles, but I chose it over some others with half the miles because it is well-maintained and in great condition. The previous owner had just had a lot of work done (forks rebuilt, wheel bearings, brakes, tires, xring chain, sprockets, etc) before accepting a job in Hawaii. It did sit for two years, started every now and then by his dad. I ran a healthy dose of Seafoam through it just "because", but the carbs seem fine.

The one thing that suffered from storage was the gummed-up clutch, which took us several hours to work loose enough to go into gear without dying. It was a long drive, so I wasn't giving up easily. It still drags a little, but maybe no more than normal for a wet clutch.

This is my first bike. I've already taken the MSF class, but still would have bought something smaller except I'm a big guy and live on a busy and hilly country highway. I had some reservations, but the NH has turned out to be easier to ride (for me) than the little bikes in the class.

Oops, I'm not sure I had the right side cover snapped all the way in for the picture. Oh well.



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