As most of you know my Scrambler has been acting really crappy as of late. It has been rebuilt twice and continues to have a lean midrange. I have done everything including: changing carbs, cleaning carbs, changing needles, shaving needles, changing clip positions and pilot/main jets. Always 200 degrres too hot in midrange no matter what! I checked for airleaks around the engine and intake manifold while the quad was idling with spray starter fluid. No change in revvs.
Is there something I may have overlooked?
Should i tear her apart once again?
Where else could air get in? Near the recoil starter? Oil injection plate?
Could my 39mm carb or the HPD porting be defective?
Could the 12:1 Billet Head mess up the temps?

So much money and so many hours to have such a small detail screw everything up! [img]i/expressions/face-icon-small-sad.gif[/img]

 

Sounds like your using a EGT? Could the probe or gauge be bad? Sounds like everything has been done. You may need another pair of eyes looking at it. Get a buddy to spend a few hours with you and see if two heads are better than one. Is it running bad, or just hot in the mid-range? Mid-range as you already now is controled by the Needle Jet, so it almost has to be there. If it was an air leak, you would think it would be there at Idle, Half & Full throttle. Sorry I can't give you a fix all answer but I hope you find it soon, for your our mental health.
Good Luck

 

Have you cut down or removed the brass stop pin in the bottom of the float bowl ? This will give you more float drop, and will allow more fuel flow into the bowl, if the fuel level is dropping too quickly for the needle & seat to keep up with. Have you checked the fuel tank vent ? You may be to the point that the vent hose is too small to properly vent the tank.
If richening the needle has no effect on EGT, the fuel flow is probably limited.
If all else fails, call Darryl @ HPD.

 

It maybe your fuel is becoming a little aerated due to vibrations at that engine speed range? Is there a dampner on that model that mounts under the carb attached to he transmission or some thing?
Charlie

 

The only other place air could be getting in (assuming you have checked the obvious like cylinder head base gasket etc.) would be crank shaft seals. They can be real buggers to catch and can cause lean conditions at certain RPMs. Something to look at anyway.

 

Thanks guys.

Capt, What exactly does this brass pin look like? Could you give me a detailed description.(very detailed because I am not that mechanically inclined but very visual...) The only thing I did so far in the carb was align the two black plastic floats. They were not "parallel" with the base of the carb like Mike at HPD described to me. I will try something about the fuel vent next time I ride...but it is only bad in the midrange?!?!


NewDSlover, The guage seems fine because the other levels are fine, WOT and 1/4 seem good.Right around HPDs' specs. It seemed to be running good with the "normal" settings except the lean midrange. Last week I did a plug check and it did "read" lean in the midrange.

Charlie, There is a small rubber piece that is bolted to the quad under the carb. Once again I do not think it's the vibrations because it only runs lean in midrange.

Trailboss450, Where exactly do I look for that specific leak? Would it not affect the other throttle ranges also?

 

I you look inside the flopat bowl, you'll see a solid brass pin that limits the amount of float drop. Remove about 1/8th inch from the top of it. Test ride it and see if it changes EGT.
I modified the bumper under the carb, cutting part of it out to give more clearance. I could see that the carb was riding on part of the bracket and beginning to tear up the aluminum.

 

Xplor, I'm starting to get stress from your quad not running like its supposed to! LOL! When yo get the midrange problem fixed i bet that thing will FLY!!!!

 

It will work eventually! It must! It has to! That way I can sell it for a smaller/lighter quad for my wife.[img]i/expressions/face-icon-small-happy.gif[/img] Tomorrow I start removing parts one by one in order to "maybe" find something defective...starting with the 12:1 Billet Head. I will run it between operations. If all else fails HPD will get another call to have them check the porting to be sure it wasn't botched! [img]i/expressions/face-icon-small-frown.gif[/img]

 

Xplor, dude your gonna sell that highly modified Scrambler that you've spent countless hours on modifying? I understand that you wanna get somethin lighter for the wife, and i figure that the Raptor will then be your main ride. But dude i have a feeling your gonna miss that Scrambler a hell of a lot when it is gone! LOL!!!!