Soot from drain hole in exhaust question

[Graydog]

When my bike is warming up in the driveway I always find a black (soot) spot on the gravel under the drain hole (pin hole) on the exhaust. No smoke from exhaust under load or just idling. I am also getting poor gas mileage (about 55mpg). Plug is not brown as should be...it is slightly black but not built up black and not white at all. I recently plugged the eight holes the previous owner drilled in the exhaust. I dropped from the 58-62 mpg I was getting to the 55 mpg I am getting now. I have run several tanks to make sure of mileage. Bike runs much better with the holes plugged. I have read here about re-jetting the carb after plugging the holes but talking to two Suzuki mechanics at dealerships they both say the same thing....no. Both looked at the carb and agree it has not been "broken down" and is still original condition. (one did the make ready when the bike was sold to the first owner, knows the first owner, and assures me the carb has never been tampered with. He also did the break in procedure after required mileage on this bike for the first owner and the make ready for me when I bought it.) I have not questioned either of them about the black spark plug (I looked at it after they had looked at the carb and suggested I take it out and inspect it). both agree sometimes valves need adjusting after break in but that is very rare.

Bike has 1500 miles on it and is an 07. Before I call one of them Tuesday and tell him the plug is "sooty" but not crusty black I wonder what your opinion is on the poor gas mileage? Normal speed for me is 45-55 on country roads. Bike runs great.

Thanks,

[primal]

Are you riding the bike hard? I get 65-70 MPG, but when I first got the bike (and liked to accelerate as quickly as the bike could) I had one tank that got 57 MPG.

[5th_bike]

How long do you have it "warming up in the driveway" ?
You should always try to minimize use of the 'choke', it enriches the mixture, which could be the cause of the soot - when hydrocarbons burn only partially, it's the carbon (=soot) that doesn't get burnt. Hydrogen goes first.

Start the bike and drive off, when you are driving the motor warms up faster than when it's just moving some air and mixing some oil, on the driveway. After half a mile, turn the choke down, and after one mile you should not need the choke anymore. With warm weather, half a mile total should be enough.

[primal]

I manage to only need to use the choke for the amount of time it takes for me to gear up. As long as its running fairly smoothly with the choke off I don't use it. I'm sure that will change this winter, of course.

[Easy Rider]

Bike has 1500 miles on it and is an 07. Before I call one of them Tuesday and tell him the plug is "sooty" but not crusty black I wonder what your opinion is on the poor gas mileage? Normal speed for me is 45-55 on country roads. Bike runs great.


If you haven't cleaned it already, save to old plug to show the mechanic.

All your symptoms point to running VERY rich.
It won't really hurt anything but the plug will eventually foul out so it should be fixed.

Two things you can do: Check the air filter. If it is plugged with oil or dirt it has the same general effect as leaving the choke on all the time. With the bike warmed up, ride it a block or two with the air filter OUT. DO NOT do this in traffic. A stock GZ will run like CRAP with the air filter out. If yours still does OK with it out, you will know that the carb is too rich for some reason.

Second, you can run some carb cleaner through with a tank of gas. I don't usually recommend SeaFoam but in your situation it might be good enough. Gumout or Berryman's B12 are really better cleaners.

If the air cleaner is OK and the carb cleaner doesn't help, then it's off to the shop.

One last wild idea: Maybe the previous owner's tampering with the muffler broke something loose and now it's restricted more than it should be ????? Not likely though since it seems to run OK.

[Graydog]

Guess I should have clarified some things.

Seldom use choke in this hot weather. Bike starts and idles great without using it.

By warm up I mean while I put helmet etc. on. It doesn't actually just sit and idle for several minutes.
Well less than a minute I would say.

I drive it easy. A few fast starts but only when needed to get into traffic.

Air cleaner is spotless.

I'm sure it is running rich. I'm confused because both mechanics say no adjustment should be necessary.
Leave it set at factory settings (because the carb has not been touched.)

I think the key thing to remember is that I was getting 10 mpg better mileage before the holes were plugged in the exhaust. No driving habits have changed since then. The soot marks, the rich smell, and the lower gas mileage all appeared after the holes were plugged.

I may take a couple of the screws out just to see if it helps or makes a difference. Also I think I will try some carb cleaner before removing the screws and see what happens.

[Sarris]

Are you sure someone hasn't moved the e-clip up on the carb needle? Usually people that drill the muffler raise the clip to richen the mixture to make the bike run properly. It does sound like you are running too rich.

Check this thread http://www.gz250bike.com/viewtopic.php?t=617&start=0 and it explains how to raise the clip. You may want to check yours and reverse the procedure if it has been done.

:tup:

[Graydog]

Thanks Sarris for that link.

One of the mechanics did mention there is an adjustment screw I can get to but would be sealed off with solder on bikes sent to America.

After looking at Jaime's step by step I went outside and found the screw he describes to adjust the mixture in the first stage.

It wasn't sealed off with solder and looked as if it had never been plugged so you couldn't get to the adjustment screw. (I used a dental mirror to see the bottom of the carb).

I made a minor adjustment in the direction Jamie suggested and the soot was not as bad. I made one more minor tweak to the screw and bingo....no soot and the rich smell was gone. I had to use a tiny screw driver that would fit into the small space you have to work with.

As soon as I fill the tank again I will track mileage and see how she does. She does seem to idle a little better.

[Easy Rider]

As soon as I fill the tank again I will track mileage and see how she does. She does seem to idle a little better.

Don't expect too much. That only comes into play at idle.
I think I'm going to have to open mine up and tweek it the other way.

Starts fine with a little "choke" but then idles WAY down without the choke until it's been run a good 15 minutes and gets really warmed up. Then it idles fine. OR If I set the idle speed within that first ~15 minutes, then it idles WAY fast when it does get warmed up.

[Sarris]

Yeah EZ, mine does that too, so I just leave the choke (enrichment lever) a tad open until the little iceberg heats up.
When mine is good and hot I set my idle to about 1200 ~ 1250 rpm on my tach.

Greydog, that's a pressed in cap. Just carefully drill through it (don't damage the screw below!!) and then just pull the cap out to expose the mixture screw.

:)

[5th_bike]

[re: expected mileage improvement from tightening the 'idle' jet]... Don't expect too much. That only comes into play at idle.


Hm, is that so ? I thought the idle jet is *always* on...
Please enlighten me, thank you.

[Easy Rider]

Hm, is that so ? I thought the idle jet is *always* on...
Please enlighten me, thank you.

OK, I guess I deserved that. :blush:

Let's rephrase, OK?

The fuel provided by the idle "jet" is only a small portion of the fuel consumed when running above idle so,........whatever you do to the idle circuit is not likely to make a significant difference to your overall fuel consumption. Unless, of course, something is out of whack other than just a simple needle adjustment. The idle mixture adjustment doesn't normally have enough range to make much of an overall impact.

Did I say it right that time? I think so.

[Easy Rider]

Yeah EZ, mine does that too, so I just leave the choke (enrichment lever) a tad open until the little iceberg heats up.


Yep. I used to do that too but lately it's been sputtering just a bit when I leave the "choke" operated for more than 30 seconds or so. Somethings not quite right. May be due for another shot of Gumout.

[jonathan180iq]

Your miles are getting close to mine and I'm considering doing a vavle adjustment around 5500 miles. You might want to do the same, if you think it's warranted.

[5th_bike]

The fuel provided by the idle "jet" is only a small portion of the fuel consumed when running above idle so,........whatever you do to the idle circuit is not likely to make a significant difference to your overall fuel consumption. Unless, of course, something is out of whack other than just a simple needle adjustment. The idle mixture adjustment doesn't normally have enough range to make much of an overall impact.

Did I say it right that time? I think so.

Yes, thank you ! :tup: