What's the secret to better gas mileage? By jster (Read 2,859 times)

[jster]

I have a MC-54-250B and got 50 mpg's when I first got her. I replaced all fluids, fuel filter, rear tire, adjusted valves, and now get 56 mpg's. I want more mpg's. What are some of the things I can adjust, replace, or clean in order to get better gas mileage?

[jalat]

Hmm.. are you sure your electric auto choke is working? It may be on all the time. Your mpg should be something like 60-75mpg.

[jster]

I don't know if the auto choke is working. I will do some research and see if I can find out if it is working.

[Jeff]

Burn 87 grade fuel. Your scooter will love it, it will perform better and your mpg will go up to the mid 60s. You didn't say how many miles are on it, but the mpg will be better when she is fully broke in too.

[jster]

I have 1750 miles on it and put 91 octane or higher gas in it. I want to play with the air/fuel mixture screw on the carb, but cant figure a way to get to it. Do I need to take off carb to adjust it?

[Alleyoop]

No you do not have to take the Carb off. But most likely on yours the Fuel Ratio screw is UNDER THE FRONT of the carb which is a PAIN to get at. But use one of the little interchangeale screwdriver TIPS like this:
Alleyoop

[jster]

Thanks Alleyoop. Do I just hold the screwdriver tip with some long nose pliers and adjust the screw that way? I can't seem to reach the screw with a normal screwdriver because of the postition of the screw.

[speedracer]

That is the worst screw to get at. You will burn your hand trying to adjust with engine running. What I did was loosen both c clamp screws, turn the carb slowly towards the kick stand side. Put scooter on kick stand and from the muffler side you can get at the screw with a long screw driver. Turn it all the way in and then back off 2 1/2 turns. Should not run rich or lean at that setting. I use 90 octane and my scooter gets over 70 mpg with almost 8,000 miles on it.

[Bashan]

OK, I've did extensive reaearch on this and here's how it works with gas vs. octane. You can believe me or not but this is the way it is. Higher octane fuels have more potential energy per unit of volume than lower grade fuels. So that sounds like a no brainer, run higher octane, get more energy per unit, and get more mileage. WRONG! High octane fuels need a higher compression ratio to generate the heat necessary to release the energy contained in the fuel. If you run high octane with a low compression ratio engine, like most of our scooters, you simply do not "harvest" the energy contained in the high octane fuel and actually get less energy than if you run regular. Scooter engines and others that run a compression ratio of 9.3/1 or lower will actually get more energy not running high test since the engine cannot utilize the available energy. If you happen to have a FI scooter that has a compression ratio of say 10.5/1, yeah, you better use high octane. Here's an article that explains this in detail, it's worth reading and has some scientific references. I've checked the compression ratios on all of my engines and it's 87 octane for me all the way. Rich

[jster]

Interesting Bashan, very interesting. So from what the article says, only high performance vehicles(auto's, moto's, and scooter's) that can produce enough heat from a high compression ratio will benefit from high octane gasoline? Who knew? Thanks for passing that on. Now I can go about saving myself some money by buying 87 octane.

Wait just a minute. Before sending this response, I checked my owner's manual, and my scoot's compression ratio is 10.3:1 . So, being the newbie that I am, what does this mean? Is this ratio high enough to warrant using high octane fuel? What is a high ratio compression rate? You mentioned 9.3:1 is on the low end and 10.5:1 may want to consider high octane. Is 10.3:1 close enough to warrant using high octane? Thank you in advance for doing the research on this for those of us who are too lazy to.

[Bashan]

There was a great chart bumping around the web that listed specific octanes for certain compression ratios. Unfortunately it seems to be lost to the ethers. I did find this chart by a reputable source called Daytona Sensors. They provide this handy little chart although you have to figure about where your compression ratio falls.

You can see that with scooters that have about a 9.3 they're coming in at around 87 octane. You've also got to remember that the Chinese figure their octanes different so what they recommend in their owner's manuals is probably incorrect. I think we can trust them to figure a compression ratio, they're pretty good at math. So if you have a scooter with a 9.3 compression ratio and your using high octane gas, your engine simply cannot harvest the energy contained in the fuel and your wasting money and losing mileage. Many scooters now have higher compression ratios and would be able to properly utilize a higher octane. You will have to look in your manual and check your compression ratio. If you feel your scooter runs better on high octane even with a low compression ratio...hey, knock it out, it's your scooter. According to the experts, low compression equals lower octane. Rich

[speedracer]

Just what I said. If I follow your scale up I should be using 90 octane fuel which I have been using since day one. Not wasting any money and gas mileage is great at over 70 mpg. Plus the graph is wrong a 427 Chevy engine with a 10.5 to one compression can only use 93 octane.

[neallyb]

I have not tested this yet, but I've recently learned there is a huge difference between "ethanol" added gas and "real"gas. While researching gumming in my 250YY carb, I learned that gas with ethanol additive is much less efficient. Also the rapid evaporation of the alcohol increases the probability of gumming quickly (my carb gummed up in two weeks of sitting).

For instance - my friend filled up his SUV in Austin with ethanol flavored gas and drove to Oklahoma CIty. It took 1 1/2 tank of gas. Because real gas was available in OK - he filled up with real gas in OK and drove home -- it only took 1 tank to get back with the real gas.

I'm sure yet, but that sounds like a substantial increase in efficiency.

[jct842]

not so much for scooters but for cars and trucks, don't use your brakes. allow some distance so you do not need brakes when following other vehicles. when you brake slowing down then you need extra gas to get back up to speed. It makes me wonder when you see some cars running on the highway brake light flashing on and off, hard starts and stops kill mileagewith drivers feet one on gas one on brake how they make it to the next gas station.

hard starts and stops kill mileage. john

[royldoc]

E.F.I.! At 90+mpg I'm not to worried about it. I am interested to see what what kind of performance I get when I install a E.F.I system on the magnum.


Roy