My GZ 's top speed seems low

[paulisnofun]

After a short amount of time practice riding in my neighborhood, I decided to actually taker her (2002 GZ250. 4500 miles) in to the real world. Yesterday was the second time I rode to work, and noticed that the bike doesn't seem to have the (for lack of a better word) balls that I thought it would. Reading on the forums, I saw that people had a top spead of around 70 miles per hour, and I am not close to that. I have about a half an our comute to work, no highway, just plain old suburban roads (mostly flat). The max speed limit on my route is 45, so I am not looking to go 75, but feel like maxing out at around 50 isn't right. That is 50 in fifth gear, with the throttle totally open.
Now, I am a bigger dude. I am six feet tall and weigh about 245 or so without my helmet and laptop bag. Would the fact that I am about as many pounds as my bike has CCs lower my top spead by that much? If not, where would be a good place to start looking to see where the lack of power comes from? I believe the person I bought the bike from said that a tune up had been done shortly before he sold it to me. Any help/advice would be great.
Thanks.

[northsidegz]

Even at your height and weight and laptop load, you should be able to reach 70 I would think (based on what I know from riding my GZ at my height of 5'10" and weight of 225). You're definitely taller and heavier, but you should still be able to go 65 still without too much struggle. Certainly much faster than 50 on an open throttle! It's going over 65 when other factors come into play (such as height, weight, wind resistance, road levelness, load, etc).

I don't know where the lack of power could be coming from, so I'll let the others chime in and try to help out there.

[paulisnofun]

Thanks Northside. I knew something didn't feel right. I something similiar in another post, but it turned out the rider was reading the speedometer wrong. I did check that I was reading it right before posting.

[dentheman]

I'm curious about what you mean by reading the speedometer wrong or right. Are you considering the speedometer inaccuracy? They generally read a higher speed than you are actually going. For example: When my Shadow's speedo is reading 70 mph I am actually going 66 per my GPS. This same inaccuracy also shows on my odometer and trip meters vs GPS mileage.

[paulisnofun]

I don't want to throw anyone under the bus, but when searching for anything similiar I found this. viewtopic.php?f=7&t=6063&hilit=speedometer (http://www.gz250bike.com/forum/viewtopic.php?f=7&t=6063&hilit=speedometer)
I thought that maybe I was doing the same thing as that poster, but I am not. I have not yet rode with a gps to see how accurate the speedometer is, but in fifth gear at full throttle (I even tried to upshift to make sure I was in fifth gear), the needle tops out at betweek 50 and 55 (actually it hit 55 when I was going down a decent sized hill).
I am new to riding, and don't know much (anything) about engine, and don't know where to start. I'm just looking for some suggestions on where to start looking.

[jonathan180iq]

Put the bike in neutral and blip the throttle.
If the revs hang up before coming back down, you have an air or vacuum leak somewhere that is limiting your overall power delivery.

Check the air filter for leaves or something similar glogging up the port.

There luckily aren't too many things that it could be, so we'll get through this.

Just by chance, have you checked your chain tension? A very tight chain will limit you there as well.

[paulisnofun]

Thanks for the advice Jonathan. I will take a look when I get home.

[paulisnofun]

The air filter was clean, and it didn't sound like the revs hung around. The chain is not too tight either.

[Water Warrior 2]

I wonder if the bike has ever had the valves adjusted. Do you have a history of the bike? You just may need to spend some TLC on the bike to make it happier on the road.
Tire pressures up, check for rear brake dragging, all controls lubed and working.
Oh, you said the air filter looked good. Did you take it out for inspection? The air filter has a reverse flow so you must look at it from the inside.

[5th_bike]

Mine goes up to 60 no problem, after that it's a matter of slope, wind and time. Maxing out at 50 is a bit low indeed.

[paulisnofun]

I don't have a history on the bike, but incan ask the guy I bought it from a few questions.
I took the filter out, and banged it around a bit and shook out any debris that was in there. I am going to pick up some some seafoam and dump it on the gas tank. I am also going to try to research a little more about vacuum leaks, and how to find them.

[jonathan180iq]

There are only a couple of hoses on the bike.
Someone correct me if I am wrong, cause I'm just going by memory.

There should be 2 lines running between the gas tank and the carb. And 1 or 2 between the crankcase and the air box.
That's it, unless I missed one. So you basically just check that those hoses are connected and snug and that the rubber isn't degrading.

That being said, if you aren't getting any rev lag, popping on deceleration or crazy bucking while trying to accelerate, then you are most likely ok. It's good to give them a once over every now and then though.

Try the seafoam. These carbs can be persnickettey with even the tiniest amount of debris in there.
Also, slosh the gas tank around a bit. I know this sounds ridiculous, but those petcock screens can develop a varnish that will impede gas flow.

Lots of little things to try.

[paulisnofun]

Last night when I started the bike, it would run for a second, then stall. I think the rpms were a little too low. I turned...ummm...screw thing that changes the idle speed and increased the idle a bit. I don't have a tach so I was kind of listening to how mine sounded against what other GZs sounded like on Youtube. After increasing the idle, the revs were hanging up for longer than they were when the idle was set lower, and I have been hearing popping.
I will check the hoses and see how they look. I watched a few videos, and read a few posts, that said to spray WD-40 on the carb and the connections and to listen to the rpms to help find the leak. Is this good advice, or is the internet lying?

[fatoldfool]

If there is a vacuum leak the engine will rev up a bit when the WD40 is sprayed there. It gives the engine more fuel.
My GZ runs great, no missing or popping but it will only run 65 on level and drops to 60 or 55 quickly on a grade.

Be sure and check that tire pressure, and with your weight, I would run about 2 psi above the recommended pressure on the front

Good luck!

[paulisnofun]

I checked for vacuum leaks. It looks like all of the hoses and clamps are new. I sprayed WD-40 on the hoses and boots and the rpms did not change. I poured some seafoam in the fuel tank and took it for a quick ride (have not checked tire pressure yet), but didn't get it over 35 mph due to speed limits (25) in my borough.
I wasn't able to find any vacuum leaks, but I recorded two short videos of my bike idling, with a few revs. I hear some popping, but you guys probably have better mechanical hearing than I do. Can you give me your opinion on if you hear any rev lag and/ or popping when the rpms decelerate?
Also, does it sound like my idle rpm is high, low, or about right?

Video 1
http://www.youtube.com/watch?v=Rg7i5ug4epY&feature=context-cha

Video 2
http://www.youtube.com/watch?v=PRrEZyCVPNk&feature=context-cha

Thanks again for your help everyone. I really do appreciate it.


Sorry...couldn't get the videos to embed.

[vikz250]

Mine can go 40 to 45 mph on 3rd gear and can easily hit 50 to 60 mph in 4th but I have only done it once on a highway but typically I stay on 3rd most way and have no problem hoing 40mph..

[raul10141964]

open the choke a little if the power increase install a bigger main jet

[Kcarvajal]

One suggestion... Check your throttle cable to make sure it's not too loose to the point where it isn't opening the carb enough. Another thing is your clutch cable. Make sure you have enough slack. You can adjust his from the lever. Make sure the lever has a gap about the space of a dime.

I had a similar experience before a long ride and thought I'd have to back out. Come to realize I tightened the cable too much and wasn't getting all of my clutch.

Try those out and let us know.

Ken

[b1pig]

Paul,

my wife's GZ goes much faster than 50. medium saddle bags, a small windscreen and my 5-10, 215lb self can see 70+ on flat ground. fastest i've riden her bike was an indicated 75-ish. her carb gummed up the first winter we had it. i removed it and cleaned it, but it still had idle issues with some loss of power. i adjusted the pilot screw and its a whole different animal now along with the new front sprocket.

you should read this thread:
viewtopic.php?f=8&t=617 (http://www.gz250bike.com/forum/viewtopic.php?f=8&t=617)

my thread where i had a similar issue
viewtopic.php?t=3888 (http://www.gz250bike.com/forum/viewtopic.php?t=3888)

[paulisnofun]

Thanks for the advice Kcarvajal and B1pig. I will take a look at the throttle and clutch cable, and make sure they are just right. I dumped some carb cleaner in the engine hoping to clean the carb up a bit. Since I am not mechanical in any way, I probably shouldn't take the carb off and clean it.
One other question. When I ride to work and I am going around 45 or 50 and need to stop at a traffic light, when I stop the bike the revs seem really high. I mean really high. I don't have a tac, but it sounds like the engine is still running does when riding at a higher speed. That's not good, right? What could be causing that?

[Water Warrior 2]

Thanks for the advice Kcarvajal and B1pig. I will take a look at the throttle and clutch cable, and make sure they are just right. I dumped some carb cleaner in the engine hoping to clean the carb up a bit. Since I am not mechanical in any way, I probably shouldn't take the carb off and clean it.
One other question. When I ride to work and I am going around 45 or 50 and need to stop at a traffic light, when I stop the bike the revs seem really high. I mean really high. I don't have a tac, but it sounds like the engine is still running does when riding at a higher speed. That's not good, right? What could be causing that?
Likely a vacuum leak or the carb is hanging up. Does the throttle grip close smoothly by itself? The cables may need lubing.

[paulisnofun]

I checked for a leak and couldn't find one. Checked all of the hoses and sprayed some WD 40 on the boots and connections. The throttle grip does close smoothy by itself.

[fatoldfool]

Sure sounds like she is running lean. Check the plug color.

[raul10141964]

I am 6' 2" 230 lb my have similar problem before i mode the carb now I can cruse at 75mi and with good conditions 80+
my settings
main jet 140
pilot 3 turns
16T
mode air filter ( do not mode the filter without change the main jet )

http://s18.postimage.org/rl4jnh1f9/IMG_20120830_110644.jpg (http://postimage.org/image/rl4jnh1f9/)

[jonathan180iq]

Thanks for the advice Kcarvajal and B1pig. I will take a look at the throttle and clutch cable, and make sure they are just right. I dumped some carb cleaner in the engine hoping to clean the carb up a bit. Since I am not mechanical in any way, I probably shouldn't take the carb off and clean it.
One other question. When I ride to work and I am going around 45 or 50 and need to stop at a traffic light, when I stop the bike the revs seem really high. I mean really high. I don't have a tac, but it sounds like the engine is still running does when riding at a higher speed. That's not good, right? What could be causing that?
Likely a vacuum leak or the carb is hanging up. Does the throttle grip close smoothly by itself? The cables may need lubing.

Agreed. Something is sticking....

Or

People have also complained of the carb boots (the rubber things that connect the carb to the engine) not being tight enough and letting in way too much air.

[mrlmd1]

You said a number of posts above that you turned "that screw thing" and increased the idle because your biker stalled. You probably adjusted it too high, and that wasn't your initial problem anyway. That idle adjustment screw is only to be used when the engine has fully warmed up, and then set to about 1300 rpms, then you don't touch it again. Ride your bike, warm it up, and turn down that white knob until the idle sounds right, then leave it alone.
And make sure you are also not riding around with the choke on.
You may need the choke to start the bike after it sits a while and this is normal and may be why your bike would only run for a second and then stall, being up in cold Pennsylvania. As you ride and the engine warms up, slowly turn it down 'till it is off after a few minutes or about 1 mile of riding.

If you haven't yet, read the owners manual and it will answer and solve a lot of problems before you start making new ones. It can be downloaded off here if you don't have one.

[bourbonjohnson]

I am 6' 2" 230 lb my have similar problem before i mode the carb now I can cruse at 75mi and with good conditions 80+
my settings
main jet 140
pilot 3 turns
16T
mode air filter ( do not mode the filter without change the main jet )

http://s18.postimage.org/rl4jnh1f9/IMG_20120830_110644.jpg (http://postimage.org/image/rl4jnh1f9/)
I just picked up my GZ a week ago. I just got it over 65 for the first time and I have to admit I was a bit anxious. About how long are you able to hold 70+?

[Vegas Street Rider]

I installed a 16 tooth front sprocket and can reach 80 mph on my GZ barring any wind or hills, but with the stock 15 tooth front sprocket you should easily cruise at 60 mph for extended trips with the same caveats. Just remember that you are creating a lot of wear and tear on that single cylinder engine at those higher revs. Safe riding.