Big Gun jetting question!!!

[BassGin3]

I just put on a full race big gun exhaust with a K&N air filter and outerwear, 160 main jet, needle one up from the bottom (was in the middle stock and now it's down one more to the 2nd from the bottom) and a 40 pilot jet. It feels like it's got more torque low end but the top end seems like it decreased alot. What i was thinking is that since it's colder out and whatnot, i should try a 165 main and possibly raise the needle to the last spot, all the way down. The motor doesn't sound like it's bogging at all so i don't think it's too much fuel, but does anyone with a big gun race exhaust feel like it's slowed down the holeshot ability?

[WickedRider]

try going up a size on the main jet .

[cals400ex]

if you are running the airbox lid on, i would go down on the main depending on elevation and temp. what elevation you at?? what is the temp? i wouldn't recommend moving the needle farther than the 4th position. the big gun gained torque but didn't seem to do much of anything in midrange to top speed for us.

[BassGin3]

I'm not sure of the elevation, but i'm located in Tewksbury, MA. the temp this time of year is usually no more than 35 or 40, so pretty cold. The big thing i noticed is that it rev's fine, but just doesn't seem to have the top end power.

[cals400ex]

did you put anything else on besides the filter and exhaust at that time?? i say go down and try a 155 or so.

[MIKE400EX]

Mine liked a 165 main with a 42 pilot, and the needle clip one groove down from the middle --- that's when I just had the full BigGun, K&N and no air box lid. We have about he same weather conditions. Oh, you may want to invest in some ear plugs for the neighbors too...LOL

[BassGin3]

MIKE400EX, did it feel like the bike lost any top end power when you put these mod's on?

Another general question, how does the bike feel when it's running too rich and when it's running too lean??? I've heard that when it's running lean, it rev's fine but the power's just not there. That's pretty much what mine feels like on the top end.

[Toadz400]

Originally posted by BassGin3
MIKE400EX, did it feel like the bike lost any top end power when you put these mod's on?

Another general question, how does the bike feel when it's running too rich and when it's running too lean??? I've heard that when it's running lean, it rev's fine but the power's just not there. That's pretty much what mine feels like on the top end.

meh, i think that's just how Big Gun is....i have a slip-on and i feel like i have no top end power, but i also run a 14t front sprocket....oh well, i ride a lot of woods and don't need the top end, if i want to ride something fast i ride my banshee....

[ewalker302]

When I jetted my 400 I started 1 size up from stock. That worked good, so I tried the next size. It was too rich.

In my experience, (400 w/pipe, filter)---(when too rich) I could feel a major decrease in power coming out of a turn--getting back on the gas.
It just didn't want to rev with the larger jet.

:bandit:

[cals400ex]

Originally posted by ewalker302
When I jetted my 400 I started 1 size up from stock. That worked good, so I tried the next size. It was too rich.

In my experience, (400 w/pipe, filter)---(when too rich) I could feel a major decrease in power coming out of a turn--getting back on the gas.
It just didn't want to rev with the larger jet.

:bandit:

i agree. i think a 165 is too big. i don't know if everyone is using dynojets or keihin jets so that makes a difference too.

[BassGin3]

I'm not sure how to tell the difference between the dyonjet's and keihin jets. The jet's I used have a little mishaped star beside the number, i think they're keihin but not sure.

[ewalker302]

Originally posted by BassGin3
I'm not sure how to tell the difference between the dyonjet's and keihin jets. The jet's I used have a little mishaped star beside the number, i think they're keihin but not sure.

The star is a K for keihin.

dynojets are short & use an extention piece on the main.

:bandit:

[BassGin3]

The only thing i think is that since i'm running with a stock airbox lid and 160 main, it's craving more air and fuel on the top end??

[cals400ex]

Originally posted by BassGin3
The only thing i think is that since i'm running with a stock airbox lid and 160 main, it's craving more air and fuel on the top end??


like ewalker and myself said, we think it is craving more air or less fuel. a rich mainjet will hurt your top speed. by the way, you didn't happen to take out your jet needle holder when removing the mainjet did you?? the needle jet holder is the piece that the mainjet skrews into.

[BassGin3]

Naww, i tried to leave that undesturbed. I just unscrewed the old main jet out. I was thinking that i might just try taking off the airbox lid with the jetting i have now and seeing if that works. Any other idea's?

[chucked]

Originally posted by BassGin3
Naww, i tried to leave that undesturbed. I just unscrewed the old main jet out. I was thinking that i might just try taking off the airbox lid with the jetting i have now and seeing if that works. Any other idea's?
i just got a big guns on my 400 last monday, i did notice that it was slower but then i readjusted the throttle screw so it opened the carb all the way up on the thumb throttle and it was fast again.

[ewalker302]

In my opinion/experience you are still going to be too rich even with the lid off, & just a pipe & filter.

Bigger dosent' always mean better
(when it comes to main jets that is)

For me starting out stock or a little lean then going up one size at a time makes it easier to tune than starting rich and going down.

Just a better reference point IMO

There is a big difference between having the bike running good, and having it tuned perfectly, or as close as you can get.

:bandit:

[cals400ex]

Originally posted by BassGin3
Naww, i tried to leave that undesturbed. I just unscrewed the old main jet out. I was thinking that i might just try taking off the airbox lid with the jetting i have now and seeing if that works. Any other idea's?

go ahead and try that. if it seems to run better with the lid off, your probally a little rich with the lid on. you still may be rich with the lid off though. if the jet needle holder was turned in, this will make your bike slower too. that is why i asked. a improperly adjusted throttle cable will also hurt your speed.

[BassGin3]

I put a new plug in and rode around for a while with that, trying to open it up alot (airbox lid still on). I compared it to the pictures of the plugs in the tech section, and it looked like it was running ok. It had just a little black around the outside and a slight light grey to the top. This was after riding around for about 45 minutes, trying to run mostly open on the main jet. I've heard that you can tell alot about the engine from the plug, is this still true with all the new technology??

[chucked]

look on the thumb throttle assembly, how far is the cable adjustment screw in?

[ewalker302]

You can tell a lot more about it by riding it than looking at the plug.

:bandit:

[BassGin3]

I've adjusted the throttle assembly so there's just a tiny little bit of play in the throttle, rather than a larger amount of slack like there was before. I think this helped, but it's snowy here so it's hard to tell when the tires are hooking up with full power. I'll have to hit some paved streets to find out more.

[chucked]

Originally posted by BassGin3
I've adjusted the throttle assembly so there's just a tiny little bit of play in the throttle, rather than a larger amount of slack like there was before. I think this helped, but it's snowy here so it's hard to tell when the tires are hooking up with full power. I'll have to hit some paved streets to find out more.
im getting my dyno tuned within the next few weeks after my dyna ignntion comes in, ill let you know how I ended up jetting it,

[BassGin3]

thanks