Low Fuel Economy - Running rich, not sure why

[ds1506]

Hello everybody,

So I bought myself a 1999 GZ250 a few weeks ago as my first bike. I got it for a steal since the previous owner left the prime valve open the night before I picked it up. After oil change and a new spark plug, I got the bike running again. While it seems to run fine, I'm getting absolutely terrible MPGs for this thing (I hit reserve about every 70 miles). Now since I've been working on it, I've been noticing that the bike is not very stock, so I've come to see if you guys could maybe point me in the right direction to maybe boost the economy of the bike.

As far as things that I've noticed are different goes: The bike has an aftermarket exhaust and the air box was taken out and replaced with a pod filter (which is kinda dirty, but still ok). I attempted to adjust the fuel mixture screw (the cap was already removed) and it seemed to be already screwed in all the way (that's supposed to lean out the mixture, right?). The bike is definitely running rich though, the plug is blackened. There's also a noticeable smell of gas when I'm sitting in traffic. I'm not entirely sure what my options are on how to get the bike to stop running so rich and I'm on a bit of a tight budget so I'm hoping it's not too big of an issue.

It also seems to be consuming oil, it smokes occasionally from the front, I'm thinking about where the exhaust meets the engine. I figure I can keep on top of the oil thing until I get the fuel issue resolved first.

I put a couple caps worth of seafoam in a couple days ago, but I'm not sure if that'll really fix my problem or not. The bike operates normally, runs fine, and gets me back and forth to school, but I'd like to do more than a weeks worth of commuting before I have to fill up again. Any help is greatly appreciated and I'd like to thank you guys for supplying the service manuals here, they've been very helpful so far.

Here's a couple pictures of the bike while I'm at it:
https://sphotos-a-mia.xx.fbcdn.net/hphotos-prn1/q81/s720x720/996877_10201182899368672_210622885_n.jpg
https://sphotos-a-mia.xx.fbcdn.net/hphotos-ash3/q84/s720x720/1095005_10201182900208693_1184764437_n.jpg
That's the condition I bought it in, and it's the same condition it's in now more or less (I moved the tail light and licence plate and got it running, that's about it).

[JohnC]

If it idles with the pilot screw all the way in there's something really wrong with the carburetor. (Leaving the petcock on prime shouldn't cause an issue unless the float valve in the carb is leaking).

A dirty air filter can also cause high fuel consumption.

If gas is getting in the oil your oil consumption will be high, too. Keep an eye on the oil level until you get a handle on things!

[jonathan180iq]

Looks like this guy put an aftermarket exhaust and intake on the bike and then WAY over compensated with his jetting.

If you're a newbie at this, you might feel a little intimidated by doing this, but you need to set the carb back to the stock setting and then rejet from there.

I agree with JohnC about something being really FUBARed if the bike runs with the pilot screw closed.

You need to at least pull the float bowl and see what size main jet he has gone with. It should be stamped somewhere on the outer rim of the jet, like this:
http://www.scootersoriginali.com/osc/images/Dell-1486_600x600.jpg
This would be a 103

For reference, no one on this forum has ever used anything larger than a 140 without eventually coming back down to earth. 145 is too rich for any setup that I can remember.

After that, check the needle setting and then we can get back down to the pilot setting.

[ds1506]

Thanks for the responses guys. I guess I'm going to take the carb off tomorrow and try to check on the float and the jets. I guess if at this point I managed to get everything back to stock settings, everything needs to be readjusted from there too. As far as the jets go, any idea of what kind of size I should be looking for and should I be returning it to the stock size if it isn't? Also, the pod filter/exhaust combination shouldn't be bring the economy down too much right?

[jonathan180iq]

You won't be getting 65MPG, but it won't be too bad. Guys with a full setup were still getting in the mid 50s.

You don't need to settle on the stock carb configuration; it will be too lean for your exhaust/filter system. Returning it to stock will just be your mental starting point when you start to rejet and adjust your setup. So you are right in assuming that you'll be making adjustments from there.

The stock main jet size is listed in the service manual, which you can download here:
viewtopic.php?f=3&t=27 (http://www.gz250bike.com/forum/viewtopic.php?f=3&t=27)

IIRC, it's like a 115-117.5 or something like that. You will probably be in the 130 range. Since you have both an exhaust and a pod filter, then maybe a 135. ( But everyone's jetting is going to be slightly different. If you are going to buy some jets and try and sort this out and get this right. I would buy a 125, 130, 135, & 140.

You need to find the right main jet first, as it slightly affects all other jets, and then go from there. The needle and pilot jet you can simply adjust if you need to, along with setting your idle with the bike whit knob that is sticking out from under the carb.

One last thing, for guidance, do a search for Jaime's Rejet on his Marauder 250. It's very detailed and has photos. I also did one a long time ago called "Jetting: Part 1". There was also a part 2. It should at least have lots of good discussion and stuff about what you're getting into.

Sometimes talking about carbs may sound complicated, but they are really simple once you understand what you're looking at.

Keep us posted.

[ds1506]

Ok, update time:

I didn't accomplish as much as I would've liked to this weekend. Some work stuff came up and I spent way too much time adjusting and readjusting the chain (looks like I'm going to need to replace it soon) and I didn't really have the chance to give the carb much attention. I did get the chance to pull the float bowl briefly though, It looks like the main jet is a 125. I pulled the plug too, and it didn't look too dirty, a little blackened but not nearly as bad as it was before. Just as reference: the pilot screw is about 1/2 - 3/4 of a turn out from tall the way in. I'm assuming since the main jet is one of the smaller ones, that's probably not the cause to my economy issues anymore, right?

I also gave the filter a good cleaning. It was a lot dirtier than I thought. With that all in mind, I've made it to 83 miles since last fill up and I haven't hit reserve yet, but that'll probably happen later tonight.

Hopefully either Tuesday or later in the week I'll have time to pull it apart more and do some more inspection, but this thing's my main mode of transportation currently, so I can't really put it out of commission during the week.

[jonathan180iq]

125 isn't stock, so at least the PO tried to adjust the jetting. But it's a little lean for the set up that you're running of pipes plus intake... I'm sorta surprised the plug wasn't white. Oh, well. The results speak for themselves.

I understood your first post to mean that the pilot screw was all the way in. Having it out like it was an adjustment that the PO did, and again, if it worked, then let it ride.

A horribly dirty air filter would cause poor fuel economy. And it would suffer if your chain was too tight, so you're on a good path there. Find the tightest setting of your chain as you rotate the back tire and adjust it to that point. It won't all be uniform. But it's better to be slightly loose than to be slightly tight.

All the usual stuff? Air in tires? Condition of your oil? Clean fuel with some cleaning additive?

[ds1506]

In my first post I did mean that the pilot screw was all the way in. Although at this point I'm not entirely sure that was the case, I had a lot going on when I inspected it, so I could be remembering wrong. As far as the chain is concerned, I'm pretty sure I got the adjust right, the main issue ended up being that it needed some kind of lube action going on, but it was still out of whack. I'm thinking a new chain will be needed in the near future.

Otherwise I'm going to keep messing with the little things, as far as adjustments go. Oil was changed not too long ago, and it's slowly leaking, so I have to top it off every so often, so I'm thinking it's pretty clean right now. I put a little bit of seafoam in the gas a couple weeks ago, I may put a little more in tonight and see if that helps anything. I figure it can't really hurt.

I'll check the plug in a couple days too just to be sure of everything. I just filled the tank last night, so this is the first full tank since I started messing with things. I'll keep you guys posted as far as what happens.

[raul10141964]

I runing
filter mod
2.5 turns pilot
140 main
needle mod
get 62MPG

[ds1506]

So, I pulled the carb off the bike today and I think I made some headway.

http://i.imgur.com/OhMhNiMl.jpg?1
Here's the pilot screw being almost all the way in. Adjusted it out to 2.5 turns, it doesn't smell any richer when I went on a quick ride, but I'll check the plug later after I get some more riding in.

http://i.imgur.com/b9lWb75l.jpg?1
Here's the float needle, I pulled it out to make sure it wasn't worn or damaged. Didn't look too bad.


http://i.imgur.com/qU9uB5Rl.jpg?1
Here's the jets inside. PO really did a number on the float pin screw. Go figure. Anyway, I pulled all the jets and cleaned them. I was talking with my father and he suggested that I check and make sure that the float actually worked properly. I dropped it in float bowl full of gas and it floated fine at first and then one side sank a little bit. So I'm thinking that the float might be at least partially responsible for all the gas consumption issue. Although, I did forget to check to see if it was just a float adjustment issue, so I'm going to check that a little bit later as well.

[Water Warrior 2]

Don't know if this would apply to the GZ carb but a mechanic friend told me this years ago. If the float itself is a piece of material that is supposed to float it can sometimes start to absorb gas and result in it starting to sit lower in the float bowl.
Might be worth throwing a new float in there if you can get one without having to acquire a whole carb.

[ds1506]

Well, I checked out the float height adjustment, ande. it was WAY off. I just finished adjusting it to somewhat close to what it should be, I don't really have any of the tools to do the fine tuning. But with the amount it was off, I think this should help at the very least, let's see if that solves the problem.

EDIT: The bike seems to be bogging down when I let off the throttle. I might try to adjust the fuel mixture in the morning to see if that helps.

[JohnC]

Some of the jets have tiny holes on the sides of the "holder". If they are plugged it will run real rich.

If the float is hollow, submerge it in a pan of hot water. If it is leaking you will see bubbles.

Not sure what you mean by "bogging down when I let off the throttle." I'd say that's what it is supposed to do...

[ds1506]

I'm not sure if the float actually has to be replaced at this point, I checked it again and it floated fine, then I checked the adjustment of it and saw that it was way off.

As far as the bike "bogging down," maybe that's not the right words for it. The bike idles fine, accelerates fine, but when I get off the throttle, the bike jerks a bit as it slows down. Deceleration is not smooth.

[Water Warrior 2]

Does the bike jerk more than once or just once when you let off the throttle? Did it jerk prior to making the carb adjustments?

[jonathan180iq]

Smooth acceleration and the smooth feel of a bike on the road are dependent on maintaining speed. If you're just letting go of the throttle and it's whipping back into the zero throttle position, I would think it's normal for the bike to feel like that. These are really basic machines and they don't coast the way a car or a fancier bike would (unless you've pulled in the clutch or something)

Maybe I'm not understanding, but feeling like you are lurching forward a bit on decel is normal.

[ds1506]

Smooth acceleration and the smooth feel of a bike on the road are dependent on maintaining speed. If you're just letting go of the throttle and it's whipping back into the zero throttle position, I would think it's normal for the bike to feel like that. These are really basic machines and they don't coast the way a car or a fancier bike would (unless you've pulled in the clutch or something)

Maybe I'm not understanding, but feeling like you are lurching forward a bit on decel is normal.

Ok, I think this might be the jerking issue then. I wouldn't say I'm whipping back in to zero throttle, but this would explain it. I guess I just didn't notice it as much before I started messing with things and looking for something wrong.

Anyway, on my ride from my house to campus, the gas smell was definitely stronger than before, so I guess I'm going to have to lean the mixture out again when I get back home.

[jonathan180iq]

With open carbs and a straight exhaust like that, you're going to naturally smell more of the combustion process... It shouldn't be overpowering but it won't be as toned down as a factory set up would be.

That is another option, by the way, should you want to go that route. You can put the stock parts back together, reset the carb to the factory setting and go from there. But I'll tell ya the exhaust is expensive unless you find someone who wants to part with theirs.

Do you have bike buddies who could give it a ride and see what they think? I don't know how much of what you are experiencing is an issue or if it's a result of overthinking due to lack of experience, and I don't say that negatively. Sometimes it's just better to have a second set of eyeballs...noses...whatever :)

[ds1506]

With open carbs and a straight exhaust like that, you're going to naturally smell more of the combustion process... It shouldn't be overpowering but it won't be as toned down as a factory set up would be.

That is another option, by the way, should you want to go that route. You can put the stock parts back together, reset the carb to the factory setting and go from there. But I'll tell ya the exhaust is expensive unless you find someone who wants to part with theirs.

Do you have bike buddies who could give it a ride and see what they think? I don't know how much of what you are experiencing is an issue or if it's a result of overthinking due to lack of experience, and I don't say that negatively. Sometimes it's just better to have a second set of eyeballs...noses...whatever :)

Alright, I think the gas smell is a bit strong, I'm going to give it some time and see if it's really an issue.

I would like to restore some of this stuff to stock, but that's going to take some time while I save my pennies and locate the stuff I need.

As far as bike buddies go, I've been the one leading the charge on the motorcycle thing as far as my friends go and unfortunately out of all my friends nearby I'm the most mechanically inclined. So I'm a bit out of luck until I can get this thing down to Fort Lauderdale where I do have a couple sets of experienced eyes and noses to show the bike to.

As far as the lack of experience thing goes, I wouldn't really take that negatively, I know it's just a matter of me getting out and learning and doing. You guys have been super helpful and patient with me and my lack of knowledge, and I know it's hard to troubleshoot anything over the internet. So thank you all for helping and dealing with me. I'll keep you guys in the loop if I have any updates or questions.

[jonathan180iq]

It's all good, man. Each of us started somewhere.

[Water Warrior 2]

Just noticed in an earlier post. You said you spent a lot of time adjusting and readjusting the chain. Might be your problem with jerking right there. With worn sprockets and chain you will get a jerking sensation as the power is turned of and the chain repositions itself on the worn sprocket teeth.

[ds1506]

Ok, so I just went through another tank since I adjusted the float, and it's still about 80-ish miles until reserve. So it would seem that the adjustment did nothing. Back to square one as as far as figuring out why I'm running rich I guess.

[JohnC]

These comments are made without going back and re-reading everything...

You said the PO left the petcock on "prime" and that caused trouble, presumably gas in the oil. This should not be a problem unless the float valve leaks. If it leaks then adjusting the float is a waste of time. How bad it leaks determines how much extra gas the bike gets. It could be very significant. Is the oil level increasing? Does the oil have gas in it?

Have you verified the air bleeds in the sides of the jets or jet holders are clear? They are vital to getting the correct mixture.

Lastly, remember Lucas' Law: 90% of all carburetor problems are electrical in nature and 90% of all ignition issues are carburetion.

[ds1506]

When I changed the oil last originally, there was a very strong smell of gas, so I'm fairly sure that there was gas in the oil. However, since then, the oil level has not increased (in fact I seem to be leaking oil slowly, I'll address that issue once I get past the gas thing). I was under the impression, because of the gravity feed, being left on PRIme would over flow no matter what, even with a good float. Back when I was first messing with it and figuring out what did what, I set it to PRIme and I watched gas come out of the filter, so it would seem the float wasn't stopping it then either.

The jets are all clear, I'll check the holders again this weekend, but everything else seemed really clean. The float needle seemed fine as well, so I'm guessing that the problem lies with the float itself as far as that's concerned. Feel free to correct me if any of this is wrong. I was planning on doing a more intensive dive into the carb this weekend to try to see if I can find anything broken, but I'm not sure if I'm just overlooking the issue or not.

[JohnC]

When the valve is on "prime" it is simply open even though the engine is not running. the float valve should still stop the flow of fuel once the bowl reaches the correct level. If everything is working correctly, you could leave it on prime indefinitely and no gas would flow. (Not recommended, though, as things seldom work correctly forever...)

Watched gas come out of what filter?

[ds1506]

Ok, so it sounds like the float should definitely be looked into.

Watched gas come out of what filter?
The air filter. It's an aftermarket pod filter with no air box so I was able to watch the gas come out of the filter.

[jonathan180iq]

...That's a lot of gas...

[JohnC]

Watched gas come out of what filter?
The air filter. It's an aftermarket pod filter with no air box so I was able to watch the gas come out of the filter.

When the engine is running, all that gas is going into the combustion chamber. Definitely the float valve is not working. Something might be preventing it from closing, it could be assembled incorrectly, the needle or seat may be bad, or the float doesn't float.

Also, make sure the float bowl vent is working correctly. I'd expect fuel out of there, too.

[ds1506]

Well I took the carb apart again this weekend and I'm fairly sure the float itself is ok. I'll check my assembly and the float valve again tonight. After this weekend it would seem that the seal for the float bowl is bad now. Whenever the bowl fills up, gas leaks out of the seam between the bowl and the carb. I'm wondering if the seal could've had a lesser leak prior to this week that wouldn't have noticed, as even with this one only a few drops every couple minutes are obvious.

[ds1506]

Just an update: sealed the bowl up with some liquid gasket and messed with the float a little bit. Made it to 114 Miles before hitting reserve (used 2.7 gallons). Possibly could've made it to 120 before switching over, but either way it's an improvement. Not completely fixed, but considerably better than it was before.

The new thing that's been happening now though is when I shut of the engine it seems to have a small backfire(afterfire?).
Plug currently looks like this:
http://i.imgur.com/PZci9OZ.jpg?2
Doesn't look like it's running overly rich, but I'm not entirely sure what else I can really do to mess with the mixture at this point.

[JohnC]

That plug is pretty black. Can you adjust the (slide) needle down at all?

[5th_bike]

That plug is pretty black. Can you adjust the (slide) needle down at all?

I agree, way too black. The bike should get about 200 miles out of a tank, until reserve. The carb's float needle/seat combo is still leaky.

[JohnC]

One thing you can do is to connect a piece of clear plastic tubing to the float bowl drain. Fold it around until the open end points up, hold it up against the side of the bowl and open the drain valve. Stand the bike up, turn the petcock to "prime" and observe the fuel level in the bowl, equal to the level in the tube. IIRC, it should be about where the seam is for the bowl gasket, mid way for and aft along the seam. More importantly, it should not continue to rise to the point where fuel overflows.

If you are careful, you can even check the level this way while the engine is running.

[Water Warrior 2]

One thing you can do is to connect a piece of clear plastic tubing to the float bowl drain. Fold it around until the open end points up, hold it up against the side of the bowl and open the drain valve. Stand the bike up, turn the petcock to "prime" and observe the fuel level in the bowl, equal to the level in the tube. IIRC, it should be about where the seam is for the bowl gasket, mid way for and aft along the seam. More importantly, it should not continue to rise to the point where fuel overflows.

If you are careful, you can even check the level this way while the engine is running.
WOW, is that a neat way to check the float and fuel level.

[JohnC]

Here's a photo. It's not a Mikuni carb, but you get the idea...

[attachment=0:3gzcwcor]P6060249.JPG[/attachment:3gzcwcor]

[Water Warrior 2]

Here's a photo. It's not a Mikuni carb, but you get the idea...

[attachment=0:1jgggg56]P6060249.JPG[/attachment:1jgggg56]
:2tup: :2tup:

[jonathan180iq]

Follow this link to see John's idea on a GS500, which is the same carb as the 250, just times 2.

http://www.gstwin.com/float_height_check.htm

[Ultimx]

Not to thread jack but I have the same problem. I just bought this bike and the po said he adjusted the carb. I need to open it up but was wondering does anyone have the factory manual? The forums one in the sticky doesn't work. I would like to see the parts in the manual before I go opening it up. I am hearing little backfires in the exhaust but my bike is completely stock. Thanks guys.

[jonathan180iq]

Ultimx, we have a temporary fix on the service manuals. Try them now.

http://www.gz250bike.com/forum/showthread.php?t=28