GS 450 HUGE Fuel Efficiency Drop

[Guest]

Hello all, I last asked questions about my chain, which seem to all be solved. Now I want to figure out my huge fuel economy drop. It dropped a while ago, and I just never got around to dealing with it. I recall thinking that It could have been winter fuel, but thinking it was probably a little too early for winter fuel, so my best guess is it dropped around September.

I was getting mileage over 50 (I calculated a 54ish once) for the back roads, 60 mph cruising with a buddy type riding, and high 47-50 for running the 40 mile ride to college. Then one day it suddenly dropped, and now I'm getting high 30s for the same exact ride. I doubt I'm riding any faster, and if I was, it would be less than 5 mph more. I ride 5+ over rather frequently and really always have.

I've read about fuel mix screws and jets and tires and chains and all sorts of things. None of which have changed on my bike. The only thing I can say has changed is that I checked my tire pressure and set it to recommended pressures, but i did that when I changed them immediately after purchase, so checking the pressure couldn't have been more than 2 or 3 pounds difference, which shouldn't drop me 15 to 20 mpg, right?

I got a new chain, but I didn't notice the drop in mileage until long after that.

Other issues that I've noticed that may help: the bike seems to not have enough power in the upper range sometimes. I feel like I used to be able to keep it over 70 in 6th with rider before, and I have since had times when I couldn't keep it over 65 in 6th with just me. Drop into 5th and it will wind right back up over 70. But when riding on a super (Read dangerously) windy day, I road all the way home in 5th (followed a car at 55 ish most the way) because it couldn't pull the wind in 6th. I realize that a huge wind drag requires much more power, but that seemed excessive. But I have also been able to run the bike up to the same top speed as I could before. It seems like whatever my power issue is, it's intermittent.

I also seem to have an intermittent fueling issue, like the petcock isn't flowing gas into the carb bowls. The bike can't sit at low idle for very long or it will start to die and require a high idle (3k plus) to get enough fuel to flow in to allow a nice idle again.

Is it possible that my fuel issue is causing my power issue sometimes? Limiting fuel into the bowl, limits fuel into the engine, but just enough to let it keep running but limit power? And why would the petcock not open enough? What might affect the vacuum that opens the petcock?

I'm at a loss here, hit me with everything you got, I've ridden down into the way cold, but I've got several things i need to work on, so service season is only a few weeks away and I can check anything.

Thanks in advance.

Bryce

[hillsy]

Clogged / dirty air filter.

[Nessism]

How long since your last valve adjustment?

[Bryce]

Testing replies since the last one didn't seem to work.... Sorry about this...

Ok, So this worked. It has pod type filters, which it has has since I got it, so it's not a pod vs airbox issue, however I haven't tried cleaning them. How often should they be cleaned/replaced?

I can't say that the valves have ever been adjusted. P.O. says he never really did any work on the bike, I have done much more than he ever did, never needed anything or he never knew it needed anything or whatever. How hard is it to check the valve adjustment? Can I do it myself? I am fairly mechanically inclined, but as far as I understand it, it would require opening the engine, and I am a bit hesitant to do that. Is this correct?

Thanks,

Bryce

[hillsy]

What sort of pods? The cheap EMGO style ones are notorious for being restrictive / not very good at filtering so they may either be clogged or you might have dirt in your carbs.

Running a fuel filter? Again, you may have crap in your carbs if you aren't.

And check your valves - probably not related to your current issue but it's just basic maintenance that you should have done when you first got the bike.

[Nessism]

Well Bryce,

You got yourself a 35 year old motorcycle with an unknown maintenance history. It's been modified and runs like crap. Time to check the Newbie Mistakes thread (linked in my signature). If it were my bike I'd park it in the garage untill all the maintenance is up to date. Failure to do so can damage the bike or worse, throw you on the ground.

[alke46]

Good advice here^^^^. Listen to what Ed is telling you----park the bike until you can check it out thoroughly.

You failed to mention how long you have owned the bike, what's the mileage etc. Sounds like it just needs some attention.

[Bryce]

Alright, Pods: Not sure what kind they are, I've never looked for a name on them, however, they are fairly dirty and I will clean that first.

Fuel filter: Added that about 3k ago. Had a tank rust issue that was my first issue on the bike and by the time I was all done with that I had shiny carbs and a new fuel line, pet cock, and filter installed.

Sounds like I'm definitely going to check my valves when I get it back home. Any one have a video or tutorial on that? I have a manual that I haven't checked in yet, but having a second source with different/ 100x better pictures is entirely likely to be helpful. I have looked for an inline twin valve adjustment video on youtube, but I didn't find anything terribly helpful.

And, my old girl is a 1980 GS450L. I bought her *Brand New* about 6 months ago with just a couple (Read 28500) miles on her. I have ridden right at 4000 miles since then. Which is a few more than I expected to get this year, due to the ridiculously mild winter we've had so far. I always figured it was well taken care of, however, I'm finding that it was taken care of to car standards, change the oil, put gas in, don't race it, and don't mod it. As far as I know, the only thing that has been changed is the pod filters, and I'm guessing that would be because someone decided to change the filter and couldn't get the right one from the local parts store and ordered the closest match and put it on.

I have since replaced defective parts and redone portions of the electronics including relay the lights, but that wouldn't affect engine performance.

And one more kicker, I just filled it up about 20 min ago and my apparent average over the last 90 miles was 41.some mpg. So now I'm just mad at her for being so finicky. I will check the valves probably next week when I get it home and see what happens from there.

Thanks All,

Bryce

[tkent02]

You probably burned a few valves due to not adjusting them for 30 years. Fix it, it's a lot easier than you might think.

[Nessism]

You probably burned a few valves due to not adjusting them for 30 years. Fix it, it's a lot easier than you might think.

Make that: it's easy to adjust the valves, but if they are burned already you have to pull the head to fix which is not trivial. Dollars to donuts there is no clearance on any of the valves.

[Bryce]

Alright, having read the newbie thread clear through, I have realized that I have way too much money in the bike for the amount of things I haven't checked. It was a starter bike, and after I check the valves, I will have a better idea if it remains a starter bike or gets a little more TLC and runs for years. How does one know if the valves are burnt? I've never really looked at a valve in such a way to decide if it was burnt or not.

Thanks.

PS: I've been on here enough, how does one get they signature set up?

[Crank]

A dry then wet compression test will tell you a lot about your valves!

[tkent02]

and after I check the valves, I will have a better idea if it remains a starter bike or gets a little more TLC and runs for years.

Don't be so quick to scrap it, even if the valves are burnt 450 heads are dirt cheap and very easy to replace. A complete 450 engine can be had for not too much money. Or replace the valves in the one you have, that's not a big deal either. First thing to do is find out exactly what you have, adjust the valves properly, ride it a bit then and check the compression again.

[Brendan W]

As said, unknown maintenance history baseline is going to be frustrating trying to troubleshoot.
If I had your symptoms on the side of the road I would pull the plugs. Are they sooty black?
If there were no signs of fuel leaks I would remove the two plug caps on the ht leads and check how clean the cores were. If corroded I would cut back about 1/4" or so to clean core and try again.
Have you checked for a dragging brake ?
If you leave the bike on prime can you smell fuel after a minute or two ? The floats could be staying open and over fuelling. Don't know if that carb has a drain screw. If it does I would drain fuel with the tap on prime for two reasons. One to let dirt out and two, to flush the float needle seats.
Are you on points ignition ? A failing condensor can cause these symptoms as well.