STILL getting crappy gas mileage with my GS450E

[prefect]

A few months back I posted about the terrible (28 MPG) fuel economy I was getting with my 81 GS450E. The general consensus then was that I was getting such poor fuel economy due to the PO putting on pods and increasing the jet sizes. I was running really rich and fouling plugs a lot, too.

Since then, I have replaced the carbs (not just the jets) with ones with stock jets that I bought from a fellow GSer, and I put the stock airbox back on. I am now getting an average of about 33 MPG with a high of 37 since then. This is ALL stop and go city driving.

The bike runs great once it is pretty well warmed up. I have to let it warm up for about 5 minutes with choke (if it's completely cold, that is). If i try to go without warming it up for at least 5 minutes, it dies on full throttle and hesitates very badly at all throttle positions up to full.

Known issues: I know of at least one pin-hole exhaust leak in my left pipe just before the "H." The bike seems to idle a little stronger if I turn the lights off (when it's fully warm). The head light dims noticeably when the turn signals are on. I get some back firing on deceleration, nothing really loud, just small pops.

The bike has a newer chain and sprockets (less than 500 miles) that I keep well lubed. I JUST put on new D404s (less than 200 miles). Spark plugs have less than 400 miles (haven't looked at them, though). The petcock was replaced about 400 miles ago with a brand new stock one, and it seems to work very well.

Any advice anyone can offer on what to check next to improve my gas mileage would be GREATLY appreciated.

Thanks,

-charles

[wrsimmons21]

Check your spark plugs again to see if they are rich. That's pretty much where you need to start at. If you are burning stoic then check valve clearances and look for a header leak on your exhaust. When you read those plugs let us know what you see.....

[prefect]

i'll check those plugs at lunch time...

I forgot to mention that I also replaced all the boots on the carbs, i.e. the engine side and the airbox side... I had a pretty bad intake leak when I first made the swap, but I'm pretty sure that everything on that end is tight and working properly...

[prefect]

ok, I looked at the plugs, and they look like it's running lean. The insulators are white, and the electrodes are kinda grey and ashy...

I ALSO forgot to mention before that the compression is good in both cylinders, about 140 psi in each.

[wrsimmons21]

Look for vacuum leaks anywhere there is a vacuum line. Make sure your crankcase is ventilating. I would make sure to check valve clearances. Make sure your air filter is clean. Check timing. I'm assuming you are on electronic ignition but if not then of course see if your points need to be tended to. The good thing about stuff like this is that it's usually not expensive. After you have gone through that and whatever else you can think of then I would put some new plugs in it and see what they read. If you are still lean then of course adjust the mixture on the carb. Sorry, i'm not too great a motorcycle mechanic but those are things I would check if I was getting crappy gas mileage.

[wrsimmons21]

Oh and you could easily have carb problems too. So I would put some carb cleaner in your gas and see if it clears up that backfiring. The headlight dimming isn't cool either. Test your VR.

[nabrams]

If you're running a bit lean then you're burning less gas, so that would improve gas mileage (though it's not good for the bike to be way too lean).
33-37 MPG in city driving sounds about right for a GS450 that's 20-something years old.
The dimming of the headlight while blinker is on is normal if the RPM is very low (below 2000), because the charging system doesn't kick in till you bring the revs up a bit. The charging system should be checked at 5000 RPM (you should have 13.6-14.9 volts DC) anyway just to be sure.
The idle being a bit stronger with the headlight off is also quite normal - more juice to fire the plugs.
Sealing that tiny exhaust leak will help gas mileage a bit, but not drastically (since you say the bike pulls strong otherwise, the exhaust leak can't be all that significant). A little popping on deceleration for a slightly lean bike with a slight exhaust leak is also to be expected.
If I were you, I'd do a two-hour highway ride (start with a full tank and set the trip-meter to zero) in sixth gear the whole time and then measure MPG (by re-filling the tank and seeing how much gas you needed for the mileage you covered). If you get about 42-47 MPG on the highway, I'd say you're doing about as well as can be expected with a 20-something year old bike.

[Road_Clam]

A few months back I posted about the terrible (28 MPG) fuel economy I was getting with my 81 GS450E. The general consensus then was that I was getting such poor fuel economy due to the PO putting on pods and increasing the jet sizes. I was running really rich and fouling plugs a lot, too.

Since then, I have replaced the carbs (not just the jets) with ones with stock jets that I bought from a fellow GSer, and I put the stock airbox back on. I am now getting an average of about 33 MPG with a high of 37 since then. This is ALL stop and go city driving.

The bike runs great once it is pretty well warmed up. I have to let it warm up for about 5 minutes with choke (if it's completely cold, that is). If i try to go without warming it up for at least 5 minutes, it dies on full throttle and hesitates very badly at all throttle positions up to full.

Known issues: I know of at least one pin-hole exhaust leak in my left pipe just before the "H." The bike seems to idle a little stronger if I turn the lights off (when it's fully warm). The head light dims noticeably when the turn signals are on. I get some back firing on deceleration, nothing really loud, just small pops.

The bike has a newer chain and sprockets (less than 500 miles) that I keep well lubed. I JUST put on new D404s (less than 200 miles). Spark plugs have less than 400 miles (haven't looked at them, though). The petcock was replaced about 400 miles ago with a brand new stock one, and it seems to work very well.

Any advice anyone can offer on what to check next to improve my gas mileage would be GREATLY appreciated.

Thanks,

-charles

All your engine behavior symptoms are telling me you are running a bit too lean. 33-37 mpg seems reasonable considering you have pods. Pods are a gas milage KILLER. I average about 38-41 mpg on my 1100.

[prefect]

All your engine behavior symptoms are telling me you are running a bit too lean. 33-37 mpg seems reasonable considering you have pods. Pods are a gas milage KILLER. I average about 38-41 mpg on my 1100.

I got rid of the pods for the stock set-up. I assume my city mileage should be better, but now that I read Nabrams' reply, I'm thinking that i'm pretty OK...

Once I move into ma new house with a garage or at least some place to work, I'll go ahead a tear the engine apart and rebuild it...

[REDDY]

I think that the part about idle speed when the lights are on is your best clue. I fought a " carb " problem on my hot rod VW for two months. I changed from electronic ign. back to points. Problem solved. The loss of rpm indicates weaker spark. I would ckeck and clean all elect conns, especially grounds, to the igniter box. Check voltages TO the coils and FROM them. The age of a piece of machinery is not important to its performance. Its the condition that makes the diff. You can not have a spark that is too hot.

[Nessism]

How are you checking the mileage?

One thought: If you are taking lots of short trips where the motor is cold, you will have to run with the choke ON quite a bit since as you noted, the carbs are on the lean edge. Running with the choke ON will flow quite a bit of gas through the motor thus the poor mileage.

[nabrams]

I think that the part about idle speed when the lights are on is your best clue. I fought a " carb " problem on my hot rod VW for two months. I changed from electronic ign. back to points. Problem solved. The loss of rpm indicates weaker spark. I would ckeck and clean all elect conns, especially grounds, to the igniter box. Check voltages TO the coils and FROM them.

Yes, the electronic ignition will indeed draw more juice at low RPM when the bike is not charging - which is exactly why the bike will idle a bit stronger with the headlight off - so we are, in effect, in agreement. I don't think the switch to points is worth the effort for a bike that's running fairly well with a charging system that works as it's supposed to.

The age of a piece of machinery is not important to its performance. Its the condition that makes the diff.

Yes, of course, but his machine IS old and therefore is most likely NOT in tip-top condition. Until everything is verified he must assume that the bike is somewhat worn and imperfectly tuned - which will result in degraded performance and gas mileage. I'm trying to be realistic - most bike owners do not maintain their bikes attentively/regularly/properly, and unless he's the original owner he has to go under that assumption.

To prefect/Charles: You say you'll perform a full tear-down soon. Now, I enjoy tinkering with bikes - I've restored at least five non-running bikes over the years to daily commuters. BUT, don't go messing with a perfectly good engine if you need that bike for transportation. If you're just talking about a valve adjustment, then I'm all for it. Otherwise, leave that bike's engine alone unless you've done a tear-down before - you're bound to mess something up. Not that it couldn't be fixed, but sometimes the effort to attain a perfectly running bike is simply not worth it.
By the way, I see from here http://www.thegsresources.com/_forum...highlight=pods that we gave you extensive advice when you first started fixing up the bike - and it looks like you've made significant progress since then - so keep at it, you'll get there!

[prefect]

How are you checking the mileage?

One thought: If you are taking lots of short trips where the motor is cold, you will have to run with the choke ON quite a bit since as you noted, the carbs are on the lean edge. Running with the choke ON will flow quite a bit of gas through the motor thus the poor mileage.

Thing is that it WON'T go until it's warmed up, even if I leave the choke on. I usually let it idle for about 5 minutes before I take off. It usually takes that long for the bike to warm up enough so that it will idle without choke.

When the bike is cold, if I give it full throttle (choke or no choke) it bogs and dies. If i open up the throttle slowly, it will rev up, but not very well.

Could my warm-up times affect my fuel economy that much?

-charles

[prefect]

To prefect/Charles: You say you'll perform a full tear-down soon. Now, I enjoy tinkering with bikes - I've restored at least five non-running bikes over the years to daily commuters. BUT, don't go messing with a perfectly good engine if you need that bike for transportation. If you're just talking about a valve adjustment, then I'm all for it. Otherwise, leave that bike's engine alone unless you've done a tear-down before - you're bound to mess something up. Not that it couldn't be fixed, but sometimes the effort to attain a perfectly running bike is simply not worth it.
By the way, I see from here http://www.thegsresources.com/_forum...highlight=pods that we gave you extensive advice when you first started fixing up the bike - and it looks like you've made significant progress since then - so keep at it, you'll get there!

I don't plan on pulling everything apart until I get settled in a new house and actually have another bike to ride. I'd like to make this bike my little "twin cafe tuner on the cheap," but not until i get a new bike, a new job, and a new house .

[Nessism]

Thing is that it WON'T go until it's warmed up, even if I leave the choke on. I usually let it idle for about 5 minutes before I take off. It usually takes that long for the bike to warm up enough so that it will idle without choke.

When the bike is cold, if I give it full throttle (choke or no choke) it bogs and dies. If i open up the throttle slowly, it will rev up, but not very well.

Could my warm-up times affect my fuel economy that much?

-charles

Hi Charles,

It seems stange that the bike clearly is running lean but your mileage is so poor. Again I say, if you are running the bike a high percentage of the time with the choke on, you are going to burn a lot of gas. For example, lots of short trips where you don't get a chance to turn off the choke. Honestly, I don't know what's going on for sure. This is just a guess.

Good luck.

Ed