is 40-45 mpg on gs450 right?

[sicnarf442]

Ever since I got the bike running, about eight months ago, I've been keeping track of the gas mileage on my 1980 GS450ST.

Here are some facts:
-Carbs rebuilt and synched.
-Idle set to 1100 RPM; creeps up to 1300-1400 once engine hot.
-Fuel/air screw at 2.5 and 3 turns (currently at 2.5)
-I use premium gas
-Stock airbox with new airfilter, new carb boots etc.
-Aftermarket exhaust (generic clamp-on megaphone, probably slightly less restrictive than stock but not by much I'm guessing).
-Stock tire size, kept at rated pressure

I mostly commute, 25 mi each way, riding at 75-85 mph on highway, with occasional episodes of bumper-to-bumper.

Have not yet done plug chops, although my guess is that I'm running a little rich. I've read it's better for the bike to run rich than lean. How real is the potential for damaging the engine due to excessive heating if I were to experiment leaning out the mix?

Any thoughts on what is going on appreciated?

Thanks,

Francis
Austin, Texas
1980 GS450ST

[Big T]

Experiment away - if you know how to do plug chops and read the plugs you'll be OK

You are correct that richer makes it run cooler

You are incorrect about running premium - that loss of power may be your mileage issue - try running 87, that's what it's designed for

But, your mileage should be higher - that's the mileage I get on my 1000

[BassCliff]

Hi,

To push that bike that fast takes fuel. Have you tried keeping it at 65-70mph? Are you using stock sprockets/gearing? You can try going up a tooth on the front sprocket.

The creeping idle makes me think "air leak". Is the airbox and air intake system tight with no leaks? Have you sealed the airbox side covers with new weatherstripping? Stock jetting? The aftermarket exhaust may require changes. Plug chops will tell you.

I agree, use regular fuel, 87 octane, the less ethanol the better. My buddy's 450 gets a little over 50 mpg.


Thank you for your indulgence,

BassCliff

[7981GS]

I agree with Cliff.
If you are using it to commute at 75-85, raise the front sprocket size by one tooth.

Eric

[pete]

I get between 33 and 47 MPG (calculated) on my 450.

My jetting is shocking, in that it's so rich it bogs off idle requiring me to open the throttle and slip the clutch too much to get off the line, and this means in commuting I do this an awful lot. Plus I tend to accelerate swiftly to attempt to stay in front of the traffic... I'm guessing an average of around 30 - 40kph during commuting.

If all I do is commute, I put just under 12 litres in at about 170km's, which I work out to be about 33MPG.

If I get out and about on a decent ride in the twisties without the stop start of traffic, I get up to 230km's in the same just under 12 litres before reserve, which I work out to be about 47MPG.

I'm going to guess an average of something like 80kph when out and about like that given the speed limits we have.

I use our standard 91 octane unleaded at the pump (no ethanol) and I expect Cliff and Eric's suggestion of different gearing will help, and Cliff is spot on about the higher speed on a 450 in that it will definitely start sucking the fuel down.

Watching RPM's on mine gives me the idea if I start going over around 100 - 110kph for any length of time it will start guzzling...

PS: I promise I will get around to tuning mine better one day... when I can bring myself to use some of my valuable riding time to not ride...

[sicnarf442]

I get between 33 and 47 MPG (calculated) on my 450.

My jetting is shocking, in that it's so rich it bogs off idle requiring me to open the throttle and slip the clutch too much to get off the line, and this means in commuting I do this an awful lot. Plus I tend to accelerate swiftly to attempt to stay in front of the traffic... I'm guessing an average of around 30 - 40kph during commuting.

Thanks for the feedback, Pete.

After reading in various places that the GS450 should get 55 mpg, I was starting to worry that there was something seriously wrong with mine. First thing I will do is stop using the premium gas. After that, do what you and I have avoided doing so far which is to take a serious look at the jetting. Reading other posts this seems to be the way to start:

http://www.ebay.com/itm/83-Suzuki-GS450-std-float-Dynojet-jet-kit-stg-1-3-/200571885065?pt=Motorcycles_Parts_Accessories&hash=item2eb3041609&vxp=mtr

take care,

Francis
Austin, Texas
1980 GS450S

[pete]

Thanks for the feedback, Pete.

After reading in various places that the GS450 should get 55 mpg, I was starting to worry that there was something seriously wrong with mine. First thing I will do is stop using the premium gas. After that, do what you and I have avoided doing so far which is to take a serious look at the jetting. Reading other posts this seems to be the way to start:

http://www.ebay.com/itm/83-Suzuki-GS450-std-float-Dynojet-jet-kit-stg-1-3-/200571885065?pt=Motorcycles_Parts_Accessories&hash=item2eb3041609&vxp=mtr

take care,

Francis
Austin, Texas
1980 GS450S

I don't think I even got 55MPG when mine was stock when I first got it, pretty sure it was still around the 230km's out of a tank.

The big difference is that didn't change much between around town and out and about riding, and that's what's killing me at the moment.

That jet kit is a no-go for your bike I'm afraid, the '83 and on use completely different carbs.

There's an E3305 stage 3 kit for our bikes but is listed as UK only. I emailed them and it will work for my Aussie model, not sure about a US model though. I can't imagine why it wouldn't although it might technically be illegal perhaps?

I believe the description is something like 1980 - 82 GS450 external main jet.

I was given a Morgan Carbtune Pro and Gunson Colortune for Christmas and aside from a one-off sync with the Carbtune I haven't been able to use them properly yet. It's hard to find time when I can make a lot of noise in the garage these days...

[gearheadE30]

I didn't realize that 450's took that much fuel. I beat the crap out of my old CM400 because it didn't really have enough power, especially on the highway, and I still got a tad over 60 mpg calculated.

[tkent02]

I would have thought it better, maybe the alcohol in the fuel effects them more than the bigger bikes since they are running harder or something.

I don't know how they would have sold them originally if they didn't get decent mileage.

[pete]

I could easily see mine going to 55MPG (highway riding) or higher if I tuned it right and went easier on the throttle... in stock form I could definitely see it.

Guarantee it would still be a little quicker than a stock CM400 though

[old_skool]

Yeah, I'd expect much higher, my 1100 gets 44-45 almost everytime if I don't twisty da throtle

[pete]

Yeah, I'd expect much higher, my 1100 gets 44-45 almost everytime if I don't twisty da throtle

Haha yes well... I like to twisty da throttle... so yeah... if I had an 1100 I may not have a license... hahaha

[sicnarf442]

Clarification on my riding speed

Ever since I posted the original post, I've been bothered by the idea that I am actually riding that fast. Speed limit in TX is 70 and I am not riding that much faster than others. So, I compared the speedo readings against GPS over the weekend and the GPS was showing 6-8 mph slower than the speedometer. So riding too fast is probably not the complete explanation for the poor mileage.

I also realized after Pete's warning that I was about to buy the wrong jetting kit (I had added a link to a DynoJet kit for an '83 GS450L), that I am using a pilot jet from my parts bike (an '83 gs450L) on the assumption that the carbs for the two bikes are exactly the same. I synched the carbs using one-of-each pilot jets. Wondering if this means the carbs are out of synch at higher rpm, that is when the other jets kick in?

Francis
Austin Texas
1980 GS450S

[pete]

Ever since I posted the original post, I've been bothered by the idea that I am actually riding that fast. Speed limit in TX is 70 and I am not riding that much faster than others. So, I compared the speedo readings against GPS over the weekend and the GPS was showing 6-8 mph slower than the speedometer. So riding too fast is probably not the complete explanation for the poor mileage.

I also realized after Pete's warning that I was about to buy the wrong jetting kit (I had added a link to a DynoJet kit for an '83 GS450L), that I am using a pilot jet from my parts bike (an '83 gs450L) on the assumption that the carbs for the two bikes are exactly the same. I synched the carbs using one-of-each pilot jets. Wondering if this means the carbs are out of synch at higher rpm, that is when the other jets kick in?

Francis
Austin Texas
1980 GS450S

Bikes generally read faster than they're actually going, so that doesn't surprise me. I calibrated my Acewell with a GPS and I made it so it reads 2 to 3kph faster than I'm doing to give me some buffer, but I'm glad I know how accurate it is now.

Are you sure you have a pilot jet from an 83 450L in there? Going by the fiche, they're a complete different series of jets (17.5 vs. 45) so I don't know how the 83 type pilot would physically fit into the 82 carb...

Does the pilot screw down into the float bowl or up into the carb body?

[nejeff]

Years ago I read somewhere that the car companies (and assuming the MC companies too) based the optimum MPG ratings at the maximum speed limit. In 82' I believe the speed limit in the US was still 55 mph so like Cliff said, pushing your bike another 20 mph faster is very likely whats sucking your gas down so fast. I am in agreement not to use the ethanol blends but where I live the premium 91 is no ethanol so not sure that's your issue.