carb problems

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maxco

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I need some help. I made some air box mads. Drilled, and re jetted. One size up on mains. one size up on pilots. It runs great at 5/8 to full., however 1/8 to 1/2 throttle it is very slow to build rpms in the mid range. What am I missing? needle needs to go up? How do you tell if you are too lean or too rich? what is the difference in how the engine responds? thanks
 
waaaahh ....wahhh...lean

blua blau blau ....rich

pull the enricher...giving more gas...you can tell that way.

You have also destroyed the resonace the box is designed for..so = less HP.
 
Put Duct Tape Over The Holes You Drilled/cut Out. If It Runs Good You Just Fixed Your Problem. Exactly How Did You Modify The Box?
Bob
 
air box mistake?

I read about this mod in the tech pages on this site. I followed it to the T. I am interested in why the descrepancy in thoughts. It said that done properly was a 2-3 H.P. gain on the dyno. any thoughts? thanks :letitsnow
 
the only thing the air box does is keep unwanted crap from getting sucked into the engine. tuned pipes have resonance...not air boxes. the more air & fuel you can pack into a motor the more h.p. you will make. my guess is the pilot is too rich. go back to stock pilot. all these sleds are rich from the factory. on ported srx's w/ cold air kit ( gutted air box ) i run stock pilots. my 835 srx w/ 38 mm carbs has 40 pilots. any bigger & it loads up. not only is my air box gutted but the top is cut almost completely out. also, & i can't stress this enough, get the carb vent hoses out of the belly pan & run them into the air box where they belong. that in itself will put a smile on your face when you pull the trigger.
bob
 
air box / carb vents

So you are saying even if we don't have gutted air boxes, that we should run teh vent lines up into the air box?

I have a 2000 SXr piped etc..

Thanks!
Steve
 
bufalobob said:
the only thing the air box does is keep unwanted crap from getting sucked into the engine.
Click to expand...
Incorrect statement,,if that was the case bob one could run open carbs and not have to worry about rejetting. The air box does make a difference,why would Yamaha state that in there jetting specs if it didn't matter?,leave the air box alone on a stock sled it's tuned for that application.

focus more on clutching you'll get more outa that.
 
i never said that jetting up isn't necessary?? when a air box is modified generally the only increase in jetting is to the mains & he already did that!!
bob
 
bufalobob said:
tuned pipes have resonance...not air boxes.
Click to expand...
i realize that, i was commenting mainly on this statement,not res but air flow,somebody reading this thread could get confused...clearing the water.
 
Why should the vent hoses go into airbox & what do you do with them, drill holes down near bottom & push them in?? Does it need anything on the end of hose.
 
you've got me confused. you quoted me in your first reply & i answered & then you post another quote & say that this is what you meant??? there is no resonance tuning to a yamaha air box. it's there to keep crap out of the motor & restrict under hood noise. if you let the motor breathe it will make more power. D&D has made a bunch of $$$ selling "bullseyes" which is an air box mod & works on most air boxes & increases h.p.
bob
 
vent tubes in the air box corrects the fuel flow difference caused by the difference in atmospheric pressure between the inside of the air box & the belly pan...which is where most vent tubes dangle on yamaha's ( except viper ). most other sled makers have the tubes already in the air box. you can feed them in any way you desire & you don't need anything on the ends.
bob
 
Thanks for the input, but back on task

I did the airbox mod, and as far as I know I did it correctly. I jetted the mains one size up. At that point in time I rode it, and It bogged really bad from 1/4 throttle to 1/2 throttle, but ran well at 5/8 to full. I posted on this site, and was told that it was a lean off idle bog caused by more air. So then I upsized the pilot jets, and it ran better, but was slow to build rpm's in the 1/4 to 1/2 throttle area. I checked the plugs at 1/2 throttle and I am not a machanic, but they had a cardboard colored electrode, a slight hint of white only at the very tip of the electrode. There was a little wet around the threads on only the third plug. they were all dark 3 threads down. I did a full throttle plug test, and the same readings. It seems to be well within a good looking plug (to my unpracticed eye). I feel compelled to add that I am jetted at 136.3 mains, 62.5 pilots, fuel screw 2 1/4 needle2.5. I have slp pipes. I ride at 10,000-12,500 feet above sea level. Temp range between -10-40 deg depending on the day. wheww thats a mouthful. Thanks for any and all input :letitsnow :letitsnow
 
bufalobob said:
you've got me confused.bob
Click to expand...
reread...i commented on your two statements above, whats to be confused about.

air box's are meant to be left alone is what I'm getting at....

Anyway.....getting back on topic, good luck maxco just watch plug color and you'll get it dialed in eventually wile your buds are out riding, lol
 
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maxco said:
I did the airbox mod, and as far as I know I did it correctly. I jetted the mains one size up. At that point in time I rode it, and It bogged really bad from 1/4 throttle to 1/2 throttle, but ran well at 5/8 to full. I posted on this site, and was told that it was a lean off idle bog caused by more air. So then I upsized the pilot jets, and it ran better, but was slow to build rpm's in the 1/4 to 1/2 throttle area. I checked the plugs at 1/2 throttle and I am not a machanic, but they had a cardboard colored electrode, a slight hint of white only at the very tip of the electrode. There was a little wet around the threads on only the third plug. they were all dark 3 threads down. I did a full throttle plug test, and the same readings. It seems to be well within a good looking plug (to my unpracticed eye). I feel compelled to add that I am jetted at 136.3 mains, 62.5 pilots, fuel screw 2 1/4 needle2.5. I have slp pipes. I ride at 10,000-12,500 feet above sea level. Temp range between -10-40 deg depending on the day. wheww thats a mouthful. Thanks for any and all input :letitsnow :letitsnow
Click to expand...

Seems like a lot of fuel for the altitude. I'm running benders with a pretty good port job on my wife's mountain max. At 8000'+ we ran 140's or 137.5's, Needles in the middle with both washers over the clip and 55 pilots. I've never ran SLP pipes, but you are putting quite a bit more fuel into the motor at idle and into the mid than we are. I also had to go to a .8 (or maybe .7) air jet in the mouth of the carb to cleanup a lean bog when whacking the throttle with the airbox mod.
 
air box mods...do increase power..are clutches meant to be left alone, what about gearing, jetting, porting, they will make your sled go much faster when done right.
i have been trail riding my sxr with airbod mods for 2 seasons with no troubles. my trail sxr did 116.1mph at the nbssr speed runs with airbox mod..i trail rode the sled to the races and rode back home.
 
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