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Gas mileage >:-(

  • Thread starter Thread starter yamahafella03
  • Start date Start date
Y

yamahafella03

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does re jetteing a carb after you put 4 k&n pod filters and a 4 to 1 mac exhaust on a 78 gs750, make it have better gas mileage?? it runs as is now but only gets 23-27 mpg??
 
On the surface, it sounds like your mileage is quite a bit below where it should be right now - unless you're going 100mph wherever you ride.:shock:

Typically, any performance intake/exhaust modifications you make to an engine will lower gas mileage. The whole point in making such mods is to pump more power out of the engine and the only way to get more power typically is to pump more fuel thru it via better intake and exhaust methods in your case.
 
It should be re-jetted after those mods, but mileage may get worse not better. Those mods are about adding horsepower. I have a GS1000G that I don't have tweaked quite right yet that has pods and is jetted for them, and I get about 25 MPG. I think REALLY dialed in I might get 30. Where stock might get closer to 40.
 
There are guys here on the GSR who run with pods and headers, make plenty of power, and get in the 40s for fuel economy, so it can be done. I'm just vacuum-syncing and setting up my carbs on my 1979 GS1000, so I'm concerned about economy since I use the bike as a sport-tourer. From what I've been able to find, or was told in response to my question, the key lies in adjusting the fuel screws. I set mine originally at 2.5 turns out from lightly bottomed, and TKent02 recommended screwing them back in by 1/2 a turn at a time on all four carbs until it just starts to run worse, then turning them back out 1/8. That should give best fuel economy. After you do that, adjust the air screws for maximum rpm. You should also check vacuum sync after these steps. Now, this is what I was told; I haven't finished this yet, so I only speak from advice, but it makes sense when you think about it. I know Hoomgar had a lot of problems while rejetting his GS1000, but eventually got to the point of great performance AND decent fuel economy (unless you REALLY twist the throttle!).
 
Mark whiz said:
On the surface, it sounds like your mileage is quite a bit below where it should be right now - unless you're going 100mph wherever you ride.:shock:

Typically, any performance intake/exhaust modifications you make to an engine will lower gas mileage. The whole point in making such mods is to pump more power out of the engine and the only way to get more power typically is to pump more fuel thru it via better intake and exhaust methods in your case.
Click to expand...

Huh, so that's why I get like 25mpg... :)
 
GSBuilder said:
Huh, so that's why I get like 25mpg... :)
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No, that is because you ride too hard.:-D

Yes, pods and pipe will drop your mileage over stock. But the most important factor is the position of your right wrist. I get around 50mpg (imperial gallons, remember) with my 1100E cruising to work in traffic. That can easily drop into the high 30's if I am out fooling around and running it hard. It has pods and a Kerker canister system.

Mark
 
Hmmm, I've researched intake and exhaust over the years in relation to car motors and typically a more efficient intake and exhaust will increase gas efficiency if anything. I don't see why it would hurt it, since you aren't changing the internals of the motor. Why are motorcycles different?
 
jola said:
Hmmm, I've researched intake and exhaust over the years in relation to car motors and typically a more efficient intake and exhaust will increase gas efficiency if anything. I don't see why it would hurt it, since you aren't changing the internals of the motor. Why are motorcycles different?
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The only difference is that 4-1 pipes work best at high RPMs, which is not where you get the best gas mileage. I bet with a Tri-Y pipe the mileage could be better than with stock exhausts.
Also it's true that when you are able to accelerate faster, you tend to accelerate faster.
Properly tuned, and ridden sedately the mileage would be good. My GS1000 does well on gas with a 4-1 and stock airbox, about 45 mpg if I ride it in a mellow fashion... which I don't except when my wife is on the back.

I took the pods back off before I really got it tuned exactly, didn't like the fart-can sound when riding slow. But it was up to about 40 mpg at the time.
I would definitely use pods on a smaller bike that spends more of it's time wound out.

The main problem is that few take the time to adjust things correctly after putting on a pipe/pods. If it runs fairly well, most guys just call it good and don't do any more tuning.
A lot of people even think more gas makes it go faster. Compared with how well Suzuki set them up in the first place, they are usually not even close.
If the gas mileage isn't within about 10% or so of what it was with stock intake/exhaust this is most likely the problem.
 
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tkent02 said:
The only difference is that 4-1 pipes work best at high RPMs, which is not where you get the best gas mileage. I bet with a Tri-Y pipe the mileage could be better than with stock exhausts.
Also it's true that when you are able to accelerate faster, you tend to accelerate faster.
Properly tuned, and ridden sedately the mileage would be good. My GS1000 does well on gas with a 4-1 and stock airbox, about 45 mpg if I ride it in a mellow fashion... which I don't except when my wife is on the back.

I took the pods back off before I really got it tuned exactly, didn't like the fart-can sound when riding slow. But it was up to about 40 mpg at the time.
I would definitely use pods on a smaller bike that spends more of it's time wound out.

The main problem is that few take the time to adjust things correctly after putting on a pipe/pods. If it runs fairly well, most guys just call it good and don't do any more tuning.
A lot of people even think more gas makes it go faster. Compared with how well Suzuki set them up in the first place, they are usually not even close.
If the gas mileage isn't within about 10% or so of what it was with stock intake/exhaust this is most likely the problem.
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Those points make excellent sense. Thanks for clearing that up some!
 
The stock set up is the most fuel efficient. Adding pods, exhaust and rejetting will lower your efficiency. But even your milage is lower than should be expected, you should get somewhere around 35-40.
But then you could be flogging it all the time too.
 
jola said:
Hmmm, I've researched intake and exhaust over the years in relation to car motors and typically a more efficient intake and exhaust will increase gas efficiency if anything. I don't see why it would hurt it, since you aren't changing the internals of the motor. Why are motorcycles different?
Click to expand...

Guys, he's right.

Consider that K&N filters, Frams Air Hogs, and anyone else selling high flow air filters all advertise that you will increase your mileage (truck, car or motorcycle). This is because you will be able to make more power at a lower rpm and the lower you can run the engine, the less gas you will use.

Free flowing exhaust systems work the same way. Although, as someone all ready stated, a tuned system may be tuned to a higher rpm range and that would have a negative effect on your mileage.

But pod filters and rejetting for them, should give the same or better mileage. And the only way it would go down is if you went faster than before. As far as the exhaust is concerned, it all depends on what rpm range it was tuned for.
 
zig06 said:
Guys, he's right.

Consider that K&N filters, Frams Air Hogs, and anyone else selling high flow air filters all advertise that you will increase your mileage (truck, car or motorcycle). This is because you will be able to make more power at a lower rpm and the lower you can run the engine, the less gas you will use.

Free flowing exhaust systems work the same way. Although, as someone all ready stated, a tuned system may be tuned to a higher rpm range and that would have a negative effect on your mileage.

But pod filters and rejetting for them, should give the same or better mileage. And the only way it would go down is if you went faster than before. As far as the exhaust is concerned, it all depends on what rpm range it was tuned for.
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What you say makes logical sense. However, in my nearly ten years on this board, I know of NO ONE that has installed an after market pipe, pods and rejetted and realized a gain in gas mileage. Without exception, all that have calculated their gas mileage have reported a decrease.

Earl
 
Water cooled vs air cooled. You can lean out a gas engine a lot and it won't burn up, increase intake flow, increase exhaust flow, but do you change the venturi/jet configuration, most likely not. So you will see an efficiency increase and a power increase. On a bike, if you put pods on or run velocity stacks and a free flowing exhaust (open pipes) you cook the engine. There is not the cooling capacity built in. So you have to stick in bigger jets, more air=more fuel=more power=less efficiency.
 
Mark M said:
No, that is because you ride too hard.:-D

Yes, pods and pipe will drop your mileage over stock. But the most important factor is the position of your right wrist. I get around 50mpg (imperial gallons, remember) with my 1100E cruising to work in traffic. That can easily drop into the high 30's if I am out fooling around and running it hard. It has pods and a Kerker canister system.

Mark
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That's what I meant actually, I should've only quoted the 100mph part.

Mileage is all about tuning. An efficient engine runs better and will WASTE less fuel. Being able to freely breathe reduces pumping losses (pods, free flowing exhaust), but with inhaling more air, you do need more fuel, ofcourse the biggest thing that needs to be tuned is that stiff wrist. I can get 36mpg in my van or I can get 20 mpg. Same van, different pedal positions (gentle, barely depressed or to the floor constantly)
 
I only make 50 mpg on my 1100G stock everything, I was wondering does K&N make a replacement filter not the pods so i can keep the air box, i have heard that pods make the bikes a cold natured B1T(h. just wondering since i am new to this
 
ok i understand that k&n pods and 4 to 1 mac exhaust will reduce gas mileage but increase performance and rejetting helps gas mileage a little bit but it just makes me curious on why a stock but much bigger engine can get 50 mpg while i'm lucky to get 25. 1100G 50mpg > '78 gs750 25mpg. why does this happen lol
 
I don't know but that is the math I am getting, and I run this bike very easy possibly that is why I get better milage... I don't know, but I'm not going to lie about something like gas milage...
 
yamahafella03 said:
ok i understand that k&n pods and 4 to 1 mac exhaust will reduce gas mileage but increase performance and rejetting helps gas mileage a little bit but it just makes me curious on why a stock but much bigger engine can get 50 mpg while i'm lucky to get 25. 1100G 50mpg > '78 gs750 25mpg. why does this happen lol
Click to expand...

Because your 750 isn't even close to being tuned right.
They can get 50.
 
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