Mid range stumble

[piglet74]

My friend has a 2006 Blaster with a mild port job, full FMF system, carbon tech reeds, 290 main jet, stock needle, K+N and no lid.
It has the slightest miss or stumble in the mid range which a normal rider would ride right through under acceleration but his silly daughter rides around right in this flat spot and is complaining no end.
I have tried every clip position and air screw adjustment with little or no luck. Everything is spotlessly clean and unblocked in the carb. It has got slightly better with the clip in the top position on the needle and the airscrew about 3 turns out.
Would a Dynojet kit help?

 

[MrTwoJay]

Try putting airbox lit back on, or cover holes, if drilled, with tape.

Check for air leaks around reedbox/carb.

Is the filter clean? And oiled properly?

Try doing a plug chop at the problem range??

You will have to determine if it is a bog or stumble (rich or lean issue)

 

[motoman159]

The air screw seems way to far out at 3 turns.

 

[Larry's Shee]

If you look at dyno graphs of 2s, alot have a bit of a dip part-way up the "hill" Even perfectly tuned motors have this dip. Need to train her a little more.
Know what you're saying as to "riding through it", LOL, even at my age I'm either on the gas or the brake thinking this is going to hurt.
2s pacemaker FTW !!

 

[gizzy2014]

do u have a exhaust leak right off the cylinder?? i had a drop off really bad in the mid and that was my problem, sealed that up and it was good to go

just put that "ultra copper" gasket maker on the mating surfaces, you can get it for like $8-9 at auto parts stores

 

[Blaaster]

A #290 main and the needle at the lowest setting and the screw out 3 turns, with the stated mods, screams lean to me, and you are trying to mask a flooding problem.

How is the float setting?

 

[piglet74]

A #290 main and the needle at the lowest setting and the screw out 3 turns, with the stated mods, screams lean to me, and you are trying to mask a flooding problem.

How is the float setting?

Thanks for all the advise.
Blaaster, are you saying there could be two problems?
The carb is loading up the cylinder in the mid range and with the needle dropped all the way down this is trying to stop or slow down the fuel overload?
I have checked the float level and it seems to be within normal levels.
The problem has decreased as I lowered the needle but I cannot lower it any more. It seems if I could get that needle down a poofteenth more all would be perfect.
When the needle is in the middle slot and the airscrew is 1 3/4 out this thing is unridable.

 

[speedyslyder]

do you have allllllllllll of the carb parts in there?

 

[piglet74]

do you have allllllllllll of the carb parts in there?View attachment 9197

Absolutely!

 

[98blaster]

My opinion is that it could be due to the porting an the pipe, i dont really know how to explain it easily, its kinda like a built car engine with radical cam an its has like a slight stumble at the rpm range were its about to come into the cam, i guess its the point were the porting an the pipe are starting to match the pulses, my blaster does it right at a certain point like its tryin to hit powerband but has like a stumble if you hold it right at a certain rpm were its kinda in an out of hitting powerband. Id try a read spacer to see if it moves the stumble spot up or down from her sweet spot she like to ride it at

 

[Blaaster]

How sure are you that it is a stock needle?

I cannot ever remember an FMF pipe needle ever being other than middle slot or one richer.

That's why I thought flooding.

 

[Larry's Shee]

https://www.google.com/search?q=yam...IHwCg&ved=0CAcQ_AUoAQ&biw=1440&bih=721#imgdii=_

Won't hurt to experiment with trying to tune it finer. A plug chop/plug read at that specific throttle opening might help. Might have to drag brake to keep a load on it.
Depending on how deep you want to go on the tune, might be a different needle, might be more.
Also consider a gear or tire change so the speed/throttle opening will be different.

 

[gizzy2014]

How sure are you that it is a stock needle?

I cannot ever remember an FMF pipe needle ever being other than middle slot or one richer.

That's why I thought flooding.

my needle is in the middle and i have FMF

 

[piglet74]

Well I have it now perfect.
It had a stock needle. Just to give it a try I put in a new Dynojet 660 Raptor needle I had laying around. Middle clip position, 2 turns out on the airscrew.
If this nitwit shiela can't ride it now, I give up. It was perfectly rideable before but now there is no excuse. It is a neighbours quad and we have had a bit of a falling out over it. You know what they say"do someone a favour and they will never forgive you"

 

[Larry's Shee]

Four pokes are good for something
Must have missed the part that it wasn't your quad.
At least it's all good now.