another jetting question

[cr5004life]

I know u guys are probably sick of jetting questions, but im gunna ask anyway lol. Bike runs pretty good on the flat , plug is chocolate, but when i get on the hill (jericho sand mtn not sure the elevation) at wide open with load on it the bike falls on its face, just spits and sputters wont open up. I was told to drop a click on the needle and change the pilot up one size, Does this sound right to u guys?

thanks Cody

[ou812]

Not even close to being possible to answer. Why not try providing some info, what carb, what needle, what pilot and main jet, what method of riding did you use to check for plug color.

[iggys-amsoil]

True, however drop the main one or two sizes.

[cr5004life]

sorry guys i spaced the details, the main is 178 pilot is 55 and the needle is on the third click, the bike has pipe cool head port and polish boyesen rad valve an carb is bored to a 41 mm

[britincali]

Go down on the main.

[M.F.D.B.]

SPitting and sputtering definately sounds rich, but that main isnt very big. I would check your float level, sounds like it might be to high, causing a flood dependant on inclination level. A coco brown plug is right where you want to be, which also makes it hard to believe its too rich. If it runs good on the flats and not the hills id put money on a float issue...

[dannygraves]

down on the main, MFDB forgets his bike is weird and likes really fat mains, my cousins '92 blubbered with a 175, its been running a 172 since. also what oil ratio are you running, that makes a huge difference in jetting. When I was running 80:1 on a stock '86 motor I ran a 168 main. before I pulled my PWK I was running a 185 with tons of porting work and really high compression.
the way I like to jet if get everything really nice and fat to the point where it blubbers, then lean it out until its smoothe, that way you knowe you are on the rich side of running well. You can get more power if you get it really borderline lean, but riding the dunes like I do, that can be dangerous.

[AlisoBob]

carb is bored to a 41 mm

Boring the carb throws EVERYTHING out the window.

Forget any numbers, and just tune it until in runs good.

[M.F.D.B.]

X2!!

[dannygraves]

carb is bored to a 41 mm

Boring the carb throws EVERYTHING out the window.

Forget any numbers, and just tune it until in runs good.

oops, missed that part.
still, if it runs tits up until 3/4, then your main is the prob.

[M.F.D.B.]

carb is bored to a 41 mm

Boring the carb throws EVERYTHING out the window.

Forget any numbers, and just tune it until in runs good.

oops, missed that part.
still, if it runs tits up until 3/4, then your main is the prob.

You are loosing your touch...

The bike is running on the main jet (via the needle) starting at 1/8 throttle. He said it runs good in the FLATS but sputters on the hills. The only thing that changes in that situation is the float level. Increased LOAD isnt going to make a bike start sputtering, generally its the other way around. A bike that sputters in the flats will often clear out once it hits the hills do to increased load/heat in the motor...

[dannygraves]

Boring the carb throws EVERYTHING out the window.

Forget any numbers, and just tune it until in runs good.

oops, missed that part.
still, if it runs tits up until 3/4, then your main is the prob.

You are loosing your touch...

The bike is running on the main jet (via the needle) starting at 1/8 throttle. He said it runs good in the FLATS but sputters on the hills. The only thing that changes in that situation is the float level. Increased LOAD isnt going to make a bike start sputtering, generally its the other way around. A bike that sputters in the flats will often clear out once it hits the hills do to increased load/heat in the motor...

uhm, I'm gonna have to disagree with you on both points there, the main only comes into play at about 3/4 when the needles position in relation to the carb housing created less fuel flow resistance than the diameter of the main jet.
Load will create more vacuum which in turn will pull more fuel out of that main.
when i was working on that mikuni it was running great at home on the street because there was never enough load for the mix to become a big issue, then we made it out to the hill and my needle was way lean and my main rich. You have to get it out in the environment it will be run in and start from scratch. I still think swapping a main a few times to see if it improves is the best starting point and if going either direction on the main doesn't show an improvement on WOT performance, I would suggest checking the float level, inspect the carb for blockages, or leaks and pull the reeds and inspect them, those boyesen rad valve reeds bust petals all the time, they run too harsh an angle and for the reeds and bend too far. This is why I personally prefer the vforce design...

[M.F.D.B.]

http://www.keihin-us.com/am/_media/pdf/slide_valve.pdf

We are both wrong, the main starts at 1/4 throttle, come over and rub my feet bitch...

[dannygraves]

ya, but up until 3/4 it will make a tiny bit of difference that would barely be noticeable, WOT is where it really makes any real difference.

[britincali]

When are people gonna understand that every motor is different and likes different timing/jetting??????

GO LEANER ON THE MAIN

[dannygraves]

When are people gonna understand that every motor is different and likes different timing/jetting??????

GO LEANER ON THE MAIN

thats exactly what I've been saying.

[CR480R]

ya, but up until 3/4 it will make a tiny bit of difference that would barely be noticeable, WOT is where it really makes any real difference.

I agree... I rode a bike once that had the main jet fall completly out... it was ridable until about 3/4 throttle..

[AlisoBob]

ya, but up until 3/4 it will make a tiny bit of difference that would barely be noticeable, WOT is where it really makes any real difference.

X2

[M.F.D.B.]

Im still trying to figure out how the main jet chainges sizes on its own dependant on inclination angle...

[AlisoBob]

The Angle of the Dangle = The Heat of the Meat

Everyone knows that...

[britincali]

Im still trying to figure out how the main jet chainges sizes on its own dependant on inclination angle...

It doesnt its called load

[dannygraves]

load=vacuum
vacuum=higher fuel velocity=more fuel coming out of the same size hole

[M.F.D.B.]

load=vacuum
vacuum=higher fuel velocity=more fuel coming out of the same size hole

Load decreases vacuum, try again...

Lower vocuum DECREASES velocity (less suction) thats why they invented accelerator pumps and not accelerator SUCKERS...

Higher load equals higher heat, which means the motor needs more fuel. Like I said before, unless my bike respnds completely inversly then everyone elses, the higher the load/heat the leaner the bike gets. So, if it doesnt sputter in the flats (little load) but sputters on the hill (higher heat in the meat) why would this be do to the main jet and not the float??

[lewisclan]

I am jumping in with MFDB

[M.F.D.B.]

I am jumping in with MFDB