how about 4 cylinder fuel questions


Information and questions on GL1200 Goldwings (1984-1987)
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koyote
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how about 4 cylinder fuel questions

Postby koyote » Wed Mar 02, 2016 11:10 pm



Doing "mixed" riding (some highway, some town) I tend to average about 37 on my 86 SEi. I noticed in the gl1500 fuel thread that people were getting some pretty big numbers.

Some of the reasons cited for drops in MPG are going over 3000 rpm, and modern government gasoline.

What's the magic number for the 1200? I admit I'm holding around 3500 out on the road quite a lot.

(And do people seriously go buy barrels of racing gas for their wings?)



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Re: how about 4 cylinder fuel questions

Postby flash1942 » Thu Mar 03, 2016 10:43 am

One thing that has always confounded me is why is a 1200 cc engine turning 3000+ RPM at hiway speeds. Cars turn much less RPM and have 2 more wheels to spin and more weight too. Less RPM means more MPG in most cases. I would think the 1200 could have benefited from a true overdrive from the factory, it's certainly capable in the torque dept, but I'm not an engineer.

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Re: how about 4 cylinder fuel questions

Postby koyote » Thu Mar 03, 2016 11:59 am

flash1942 wrote:One thing that has always confounded me is why is a 1200 cc engine turning 3000+ RPM at hiway speeds. Cars turn much less RPM and have 2 more wheels to spin and more weight too. Less RPM means more MPG in most cases. I would think the 1200 could have benefited from a true overdrive from the factory, it's certainly capable in the torque dept, but I'm not an engineer.


I dunno. I know that you can design an engine with any number of cylinders to run well at higher or lower speeds.

I have hanging out after some tires with my local shade tree mechanic and a few other guys (one wing guy, one harley) and Bill (mechanic. It's his retirement hobby and he's pretty good) was talking about a guy with one of the HD 6 speeds and making a local ride, but long enough for gas do it one way in 6th and lug the twin, one way in 5th and let it hum. (60 to 65 speeds).

Pretty much what you expect, about 7mpg running the revs where the harley likes it.

But that's still a lot lower than the rpms my sister's rebel 250 sips gas at.

Then there's my F250 with the old 460ci V8. that thing gets great mileage at 1700 rpm.....
What I don't know is where the sweet spot on the 1200 actually is.

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Re: how about 4 cylinder fuel questions

Postby julimike54 » Thu Mar 03, 2016 1:16 pm

I've averaged from 35 to 45mpg, that is solo to loaded 2 up. It also has been from '86. I used to count on 40mpg for calculating fuel refill, now I use 38mpg. Don't run racing fuel. I will run non-ethanol when I find it & the mileage goes up a little. The rpms don't seem to make as big of an impact as wind does. Example, a group of us came back from a trip (was 2 up & loaded) and the leader pretty much was running 80 (that's about 4K rpm), the fuel averaged 37. I think these are designed to operate efficiently in the 3000 to 4000 rpm range. Out on the highway there is not much time spent in the below 60 range, you just might get run over around here.
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Re: how about 4 cylinder fuel questions

Postby flash1942 » Thu Mar 03, 2016 3:24 pm

My point was: if a small car with about the same size engine is "loafing" along on the hi way at 2200 RPM then why couldn't the 1200 have been designed for that range. Engine speed makes a diff with cars and trucks otherwise overdrive, etc would not be needed. I'm not trying to be disagreeable here but rather making some kind of logic.

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Re: how about 4 cylinder fuel questions

Postby koyote » Thu Mar 03, 2016 5:06 pm

flash1942 wrote:My point was: if a small car with about the same size engine is "loafing" along on the hi way at 2200 RPM then why couldn't the 1200 have been designed for that range. Engine speed makes a diff with cars and trucks otherwise overdrive, etc would not be needed. I'm not trying to be disagreeable here but rather making some kind of logic.


I completely understand your logic and was attempting to answer by saying that different engine and transmission systems are designed for different speed ranges.

I would answer in part that the 1200 is a boxer and not an inline 4. Also, since we're in the GL1200 section, my answer would be that 5th gear was overdrive in very real terms at the time. (It's actually listed as OD on my display on the SEI)

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Re: how about 4 cylinder fuel questions

Postby pixel288 » Sat Mar 05, 2016 2:40 pm

Ah, similar displacement, but what about torque? Motorcycle engines dont have the torque values cars have, neither do they have as heavy a flywheel. So a 1.2 l car WILL loaf along easier, partly because of that. Final gearing today vs 25-35 years ago is significantly different too. Cars nowadays have quite tall finals, and the motors are cammed in such a way as to have a high, flat torque curve starting at very low rpm. My son has a 2000 Nissan maxima that pulls like a freight train from about 2500 right on up. No matter what gear it is in, including 5th (overdrive) this thing just pulls. Now granted, is is a 3 liter engine, but it is also a car that weighs 4+ times my Gl1200A
The point is, if we could re-cam and increase the final drive ratio, we could probably increase the mpg to 70. Not sure I'd want to spend the $$$ for the R&D and the machining.

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Re: how about 4 cylinder fuel questions

Postby Rednaxs60 » Sat Mar 05, 2016 10:25 pm

I have noticed a difference in fuel economy between my 1800 and the '85 LTD. The '85 gets far less fuel economy than the 1800. Was out today for a ride and two up. Lots of power and torque with two on board. Didn't notice the fuel gauge going down any faster. Cheers.
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Re: how about 4 cylinder fuel questions

Postby pixel288 » Sun Mar 06, 2016 12:00 am

Forgot to mention that the fuel injection of today is also a major contributor to increase fuel economy. Carbs can be set very well, but with the ability to control fuel mixtures very tightly, current fuel injection computers with their o2 sensors can and do maintain an almost perfect air fuel ratio. :mrgreen:
Makes me wonder if a up to date standalone ECM and a better fuel injection system (pump, pressure, injectors) wouldn't create a 1200 that would be virtually perfect even by today's standards.
Anybody want to give it a try? :ugeek:

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Re: how about 4 cylinder fuel questions

Postby koyote » Sun Mar 06, 2016 10:41 am

So, I understand the frustration with a motorcycle designed for touring during the NMSL era, when 55 was the limit and 65 was about what you would expect people to do out on the road.

It's true, the GL1200 was not adequately designed for cruising at 75mph at 2000 rpm.

I'm not sure this is a *defect*, given the time of the design.

They do (or mine does) actually handle cruising at 75 quite well.

I suppose my main question really is "what's the ideal rpm range for economy?" Where does the engine sip gas and produce power? I'm certainly not having a *problem* at 75, but if I was on a 45mph road, do I want to be in 4th or OD? Is lugging a problem?

ECM and drop in injection would be pretty sweet on a lot of older bikes.

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Re: how about 4 cylinder fuel questions

Postby twocams » Sun Mar 06, 2016 2:04 pm

I have owned a 1970 Datsun Roadster ( SPL311) for about 10 yrs now. They use a pushrod engine or overhead cam (SRL311). They use SU Carbs. Point being that some of the guys put an O2 sensor in the exhaust to see when they are running lean and rich. I dont know much about it.....U would have to read up on it yourself. So if you want to know what your carbs are doing at a given RPM this could tell you.

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Re: how about 4 cylinder fuel questions

Postby pixel288 » Sun Mar 06, 2016 10:07 pm

Right. That is what is known as a wideband sensor. You need an o2 sensor, a small ecu (engine control unit) to read what the sensor is doing, and a digital gauge to display the actual fuel ratio. The ecu isn't actually controlling the engine, it is just used to read what the carbs are doing.

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Re: how about 4 cylinder fuel questions

Postby Rednaxs60 » Sun Mar 06, 2016 10:56 pm

koyote wrote:So, I understand the frustration with a motorcycle designed for touring during the NMSL era, when 55 was the limit and 65 was about what you would expect people to do out on the road.

It's true, the GL1200 was not adequately designed for cruising at 75mph at 2000 rpm.

I'm not sure this is a *defect*, given the time of the design.

They do (or mine does) actually handle cruising at 75 quite well.

I suppose my main question really is "what's the ideal rpm range for economy?" Where does the engine sip gas and produce power? I'm certainly not having a *problem* at 75, but if I was on a 45mph road, do I want to be in 4th or OD? Is lugging a problem?

ECM and drop in injection would be pretty sweet on a lot of older bikes.


I find that the gearing for the 1200 is similar to the 1800. At 3000 rpm, both bikes are 95 to 100 Kms/hr. At approximately 3200 rpm on the 1200, I'm doing 105 or so Kms, and the bike is quite smooth at that rpm. The 1800 does get better fuel economy though. I also find the 1800 has enough torque that you can cruise around town in 4th without a problem, not so with the 1200. Having said this, is there a need for a higher gear ratio? My son-in-law is always on me for "lugging" the bike when I ride it. He is a proponent of keeping the rpm such that you are in the power band all the time.

The other thing I've noticed about Honda is that all its bikes seem to have the same type of gearing. My son-in-law had an older CB600 and it too was geared quite low, you could ride around town in fourth as well.

I haven't enough time and Kms on the '85 to have an idea as to the ideal rpm for max fuel economy. If it is anything like the 1800, 3000 rpm may be the magic number. The 1800 starts to drink more as the rpm goes past the 3000 mark, and I think this may apply to the 1200.

Cheers
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Re: how about 4 cylinder fuel questions

Postby WingAdmin » Mon Mar 07, 2016 1:30 pm

Keep in mind, if you change cams in a bike to produce more torque, you may also need to adjust the size/materials of the transmission gears and the clutch, in order to keep them strong enough and reliable to handle that torque. I used to crew on a GT1 racing car. We changed cams to change the torque curve one one of the engines. First thing we had a problem with was valves impacting pistons - the springs weren't strong enough to close the valves fast enough at higher RPM's, because of the higher cam profiles. So we replaced the springs with stiffer ones. The next problem was broken valve springs - the stronger springs had a very limited life, the solution was to replace them every other race.

Next we had transmission failures. The helical-cut gearset in the Tex Racing T-10 transmission couldn't handle the torque, so we changed to straight-cut gearing. I still have a souvenir T-10 input cluster in my garage, with a chunk of teeth sheared off.

Once the transmission was strong enough, we started shearing driveshafts. We switched from the hollow aluminum driveshaft to a solid steel one (severe weight penalty there). I again have a souvenir piece of sheared aluminum driveshaft in my garage.

Next we started going through rear ends. We switched to a stronger rear end.

Then we started winning races. :)







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