Jetting troubles?

[gb blaster]

So I bought this new fmf pipe. Finally installed it after I had problems with stripped bolts. Went riding on a 280 main. I was riding to the track and it was riding fine. Got on the stretch of clearing and decided that I was going to open it up a bit. Everytime I hit higher gears or higher rpm's it bogs down terribly like almost shuts off so I stopped in the woods changed my plug ( it didn't look that bad even but it seemed almost as tho I fouled my plug. ) road it all the way thier from where I was at I hit higher gears but left it at low rpms got there fine. Then I road all day even had my buddies riding it an no one had trouble with it at all. Went to take it home and once I hit the stretch again and tried to open it up past half throttle the bike did it again died completely and wouldn't start for like 20 kicks. Finally got it started went half throttle the rest of the way home fine.

So my question is what causes top end bog, I figured with the new 14/40 gearing I would have some dam topend.

No I haven't plugged chopped I no I need to and will be doing it this weekend. But Im almost certain I'm pretty darn close maybe one jet size rich my buddy runs the same set up at the same spot and everything.

 

[89blaster89]

topend bog is caused by the main jet, try a 270

 

[Blaaster]

So I bought this new fmf pipe. Finally installed it after I had problems with stripped bolts. Went riding on a 280 main. I was riding to the track and it was riding fine. Got on the stretch of clearing and decided that I was going to open it up a bit. Everytime I hit higher gears or higher rpm's it bogs down terribly like almost shuts off so I stopped in the woods changed my plug ( it didn't look that bad even but it seemed almost as tho I fouled my plug. ) road it all the way thier from where I was at I hit higher gears but left it at low rpms got there fine. Then I road all day even had my buddies riding it an no one had trouble with it at all. Went to take it home and once I hit the stretch again and tried to open it up past half throttle the bike did it again died completely and wouldn't start for like 20 kicks. Finally got it started went half throttle the rest of the way home fine.

So my question is what causes top end bog, I figured with the new 14/40 gearing I would have some dam topend.

No I haven't plugged chopped I no I need to and will be doing it this weekend. But Im almost certain I'm pretty darn close maybe one jet size rich my buddy runs the same set up at the same spot and everything.

You should plug chop before you wreck the motor, if you have not done so already.

FMF calls for a #260.

I do not know your other mods, but if you have the lid off the airbox, are using a different air filter and running premix, you could be way too lean with a #280 main.

 

[gb blaster]

Yeah I guess I'll just try to chop it with the 280 in their and see what happens I guess the only way to find out for sure.

 

[Wifesblaster]

If you read FMF jetting specs it clearly shows they use a 260 main. This is using premix at 32:1 and with the airbox lid removed. We use a 270 because we are at sea level. We plug chopped our bike in the winter and it was a perfect cardboard color. If you are using anything higher than a 280 on a stock bore/stroke unported motor you are WRONG! You are either covering up an air leak or your bike is running rich. Like I said we tested at sea level in the winter with a K&N air filter no need to be any richer. I know bikes vary a little bit, but not that much. If anything you might be at a 260 if you ride at high elevation.

Type in yamaha blaster and year. Under comments you will see it says snorkel removed.

Rider Support - Jetting Center - FMF Racing

 

[gb blaster]

Thanks man. I'm gonna drop to a 270 chop see where I'm at! But I'm planing for port work this weekend. The port work an head mod would mean a little richer jet anyways or porting has no impact on jetting?

 

[Wifesblaster]

I'm not sure about stock carb jetting on a ported motor. We runn bigger carbs on our ported motors. Our blue bike has a clean up home port job on it. We raised the exhaust port 1mm. I don't know if the boost ports affect jetting though.

 

[yungbuc18]

It sounds like wifes blaster knos wat he's talkin about

 

[Blaaster]

FMF with stock 26mm carby at sea level.

FMF only = #260.
A/market air cleaner + 1 or 2 sizes. Depending on what type.
Airbox lid off + 2 sizes.
32:1 premix + 1 size.
Cold weather + 1 or 2 sizes.

Any changes in breathing will change jetting requirements.

Porting affects the breathing, you make the choice and then plug chop to confirm.

 

[Wifesblaster]

FMF with stock 26mm carby at sea level.

FMF only = #260.
A/market air cleaner + 1 or 2 sizes. Depending on what type.
Airbox lid off + 2 sizes.
32:1 premix + 1 size.
Cold weather + 1 or 2 sizes.

Any changes in breathing will change jetting requirements.

Porting affects the breathing, you make the choice and then plug chop to confirm.

I beg to differ. I know changes in intake and exhaust warrant a jetting change. FMF recommends a 260 with the air box lid off. So if I put on a FMF exhaust, removed air box lid, installed K&N air filter, and jetted in 30 degree weather I would close with a 330? I disagree because we have two bikes with those exact mods. They are both cardboard color in the winter after a proper plug chop.