Confirming my proper jetting configuration

[gs500ey]

Hi, I'm new on the board, but I've been reading a lot on jetting. i didn't know how cold blooded these bikes are till I just got one this weekend. My old old Rebel 250cc seemed to have gotten on the road a lot better.

One interesting thing is that when I'm going 35mph + and pull in the clutch to wait for the rpms to go down, it would eventually stall. Usually I am at some speed and just pop the clutch to jump start it. Also it takes forever in my book for the bike to be happy, I would say at least 5min warming up from a 35-40F morning and then a 10-15min city drive (25-35mph) before its really happy.

So I'm going to go ahead and rejet. Its a 1999 GS500 with a uni filter (non pod), and no other modifications. I'm mainly commuting in the city with this bike, so my concern is gas mileage, and driveability; its getting pretty inconvienant to have to constantly fiddle with the throttle and choke in the morning.

Having (2) x #125 main jets (part# N100.604/004-190)
and (2) x #40 pilot jets (part# N151.067/004-609)
with 1-2 shims on the needle for each carb

Again, not looking for power, just want the bike to be not so cold blooded in the morning, so I'm more interested in keeping the bike from stalling.

Any advice or experience would be helpful.

Maybe I should put a stock paper filter instead of the foam to give it less air?

Thanks

[Cal Amari]

Since you're going to rejet, you have some options; you can install a stock air-filter until you rejet the carbs, or you can let the bike sit until the new jets arrive. I see nothing wrong with your basic jetting choices (larger pilots and mains with a shim under each needle), but don't forget to drill out the covers on the air bleeder screws. Once those screws are uncovered, turn one clockwise until it is LIGHTLY seated, then back it out three full turns, and repeat for the second screw. Three turns out will give you a baseline starting point; if you notice that the engine is too rich at idle, turn each screw in one-half turn to lean out the mixture. If you notice that the engine is too lean, turn each screw counter-clockwise a half-turn.

Keep in mind that your Uni-Filter is less restrictive than the stock air filter, so if you tune the carb to work properly with a stock air filter, you'll probably have to do some minor rejetting / fine tuning if / when you reinstall the Uni-Filter.

Good luck; hth

[gs500ey]

CalAmari,  thanks. The Uni foam filter was replaced by the last owner, I guess it would be pointless to go order a paper filter at this point since they cost about $30 after shipping. I do agree that the foam filter allows more airflow and will require rejetting. The last owner already drilled out the screw caps since I was able to mess with the mixture settings on both carbs.

I'm going to go ahead and call Sudco and order the jets. I wonder if I could get away with just using the #40 pilot jets and keeping the main stock at 122.5. I'm only interested it having it start,idle nice. As for the flat spot in the power band, it doesn't really bother me. Well since i have the carbs out, I might as well do it.

[scratch]

One interesting thing is that when I'm going 35mph + and pull in the clutch to wait for the rpms to go down, it would eventually stall.

Idle is set too low.

Also it takes forever in my book for the bike to be happy, I would say at least 5min warming up from a 35-40F morning and then a 10-15min city drive (25-35mph) before its really happy.

What rpm does it idle at when it's happy?  1200-1300rpm's?

Maybe I should put a stock paper filter instead of the foam to give it less air?

A paper filter will flow more air.  Just leave what you have, but maybe clean it.  Buy the foam air filter cleaning kit.

[neilson]

A good idle speed is right around 1200rpm's, right?

[Cal Amari]

The owner's manual lists 1000 to 1300 RPM; I prefer to shoot for 1300...

[Cal Amari]

... I'm going to go ahead and call Sudco and order the jets. I wonder if I could get away with just using the #40 pilot jets and keeping the main stock at 122.5. I'm only interested it having it start,idle nice. As for the flat spot in the power band, it doesn't really bother me. Well since i have the carbs out, I might as well do it.

I agree; since you're removing the carbs anyway, you should rejet, but that isn't the only reason.

You should als rejet the mains because the GS is already too lean, which makes the engine run hotter than it should. IOW, you're slowly cooking the oil while you ride. Extended exposure to heat breaks the oil down much quicker; I'm a strong believer in keeping engine components as cool as possible. The oil has two main jobs; first, it lubricates moving parts. Secondly, it carries heat away from the combustion chamber as it flows back to the oil pan and filter to be cooled and recirculated. Anything you can do to bring temps down in the hottest areas (the piston crowns and exhaust valves) will help extend the life of the oil, and that will help extend the life of the engine itself.

I understand the concern some riders have for maintaining good fuel economy, but that has to be balanced against running the engine harder or hotter over time. The effects of heat-soaking cook your internal engine components along with the oil long after you shut the engine down; rejetting means the engine will run cooler, and the benefits will carry over to longer usable life for the oil, which in turn will help protect the engine internals from metal-to-metal contact during normal and high-speed operation.

Consider this for a minute: oil wears out most quickly from the effects of heat, and use under pressure. If you heat clean, fresh motor oil to ~300F in a pan on the stove, it will be ruined just as if you'd done it inside the engine, even though the oil in the pan was NEVER used inside an engine. Now think about that point; UNUSED oil is ruined by heat alone, regardless of any other factor. It is also ruined from the breakdown of long-chain polymers present in the oil (caused by squeezing the oil between metal parts, such as transmission gear teeth), and the byproducts of the combustion process. Though you can't control the shearing of the long-chain polymers (caused by the transmission gears), or the effects of combustion byproducts (until you replace the oil), you CAN help to control the heat the oil is exposed to simply by rejetting the carbs properly.

The shear resistance of those long-chain polymers decreases over the life of the oil; the heating and cooling cycles of normal engine operation take their toll, as does using the oil as a load-bearing surface inside the engine. As those long-chain polymers break, they become less effective, and there is nothing (that I'm aware of) that you can add to the oil to put the broken polymer chains back together again.

Plain-bearing engines (such as the GS engine) need oil to keep many parts from making metal-to-metal contact; in essence, the GS camshafts and the crankshaft (along with many other components) constantly ride on a thin cushion of oil, which makes the condition of the oil critical to engine life. A roller-bearing crank does not put such a severe burden on oil, though there are at least a few major drawbacks to the use of roller-bearing cranks (durability at high RPM over extended periods being one of the main concerns), which is why most (if not all) Suzuki engines are now the plain-bearing variety. Time has proven the plain-bearing design to be better suited for high-revving motorcycle engines, but again, the condition of the oil is critical to the durability of the engine, since the oil itself acts as a load-bearing surface to prevent the dreaded metal-to-metal contact that destroys major engine components, such as cranks and cams.

The bottom line is, fuel economy and better performance are only two of the things you need to take into consideration when you're deciding whether or not to rejet your carbs. Rejetting offers less obvious benefits that you shouldn't overlook, and hopefully, I've been able to make you more aware of them by taking the time to write this.

Keep us posted on your progress...

[scratch]

Better to burn gas than oil.  Gas is supposed to get burned anyway.  There's a dragbike racer that always exclaims, "Eat GAS!!", when he launches.

[Wrecent_Wryder]

[e

[gs500ey]

Thanks for the great responses everyone.

CAL AMARI: I will go ahead and rejet the main along with the pilots, will having a #125 be good enough with the stock system and the uni filter? I dont mind going back to paper, it just came that way when i bought it.

SCRATCH:

Quote from: gs500ey on March 08, 2006, 07:48:26 PM
One interesting thing is that when I'm going 35mph + and pull in the clutch to wait for the rpms to go down, it would eventually stall.
Idle is set too low.
RESPONSE - I actually had the idle set around 1500rpms, how it stall at high speeds when I pull in a clutch seems to be weird, all actuality no one really does this unless they were braking suddenly to a stop. I'm going to check my float levels, maybe it's too low.

Quote from: gs500ey on March 08, 2006, 07:48:26 PM
Also it takes forever in my book for the bike to be happy, I would say at least 5min warming up from a 35-40F morning and then a 10-15min city drive (25-35mph) before its really happy.
What rpm does it idle at when it's happy?  1200-1300rpm's?
RESPONSE - From what i've read 1200rpms. The other symptom is that if i'm going from like 35mph to a stop light and stopping somewhat aggressively, idle will drop to about 1000rpms and then slowly come back up to about 1500-2000rpms during when FULLY warmed up. Just to make sure its not lean, i put in the choke and it bogs down.

Quote from: gs500ey on March 08, 2006, 07:48:26 PM
Maybe I should put a stock paper filter instead of the foam to give it less air?
A paper filter will flow more air.  Just leave what you have, but maybe clean it.  Buy the foam air filter cleaning kit.
RESPSONSE - The UNI foam filter came new with only 500mi when I got the bike

[scratch]

I will go ahead and rejet the main along with the pilots, will having a #125 be good enough with the stock system and the uni filter?

Even though you directed the question at Cal Amari; yes.

RESPONSE - I actually had the idle set around 1500rpms, how it stalls at high speeds when I pull in a clutch seems to be weird, all actuality no one really does this unless they were braking suddenly to a stop. I'm going to check my float levels, maybe it's too low.

I concur, check your levels; use the clear tube method to see what the level is in the floatbowl

[Quote from: gs500ey on March 08, 2006, 07:48:26 PM]
Also it takes forever in my book for the bike to be happy, I would say at least 5min warming up from a 35-40F morning and then a 10-15min city drive (25-35mph) before its really happy.

What rpm does it idle at when it's happy?  1200-1300rpm's?
RESPONSE - From what I've read 1200rpms.  The other symptom is that if i'm going from like 35mph to a stop light and stopping somewhat aggressively, idle will drop to about 1000rpms and then slowly come back up to about 1500-2000rpms during when FULLY warmed up.  Just to make sure its not lean, I put in the choke and it bogs down.

Again, this is related to float level (maybe too high)

[Quote from: gs500ey on March 08, 2006, 07:48:26 PM]
Maybe I should put a stock paper filter instead of the foam to give it less air?

A paper filter will flow more air.  Just leave what you have, but maybe clean it.  Buy the foam air filter cleaning kit.
RESPSONSE - The UNI foam filter came new with only 500mi when I got the bike

Ok, cool.  I didn't know that, and that's why I suggested the cleaning kit; I bought one and am really pleased with it.

[gs500ey]

Scatch. Too bad i dont think I will be able to work on it till beggining april. But I can check to see if it is too high. What level should it be off hand?

[scratch]

Level with the floatbowl gasket surface (or a little below, I try for below because I don't want to flood the eng).

[gs500ey]

Got it thanks:

http://www.bbburma.net/FloatHeight.htm

Yea it sounds like a flooding situation, well we'll see.