Pilot screw


28 replies to this topic
  • dldavis_66

Posted January 30, 2008 - 08:33 PM

#1

Gosh...I've always had a problem understand carbs: this jet, that jet, this screw, that screw, everywhere a screw screw:bonk:

Anyways, The Pilot screw is a.k.a Idle Mixture Screw, right???

When turned clockwise(cw) fully and seated/closed , that means that there is no air getting....uh somewhere??? So that means a rich fuel mixture???

Turning ccw adds air and leans the mix???:busted: :worthy: :ride:

I just read if the Pilot screw is near the back of the carb then it controls the air and if it is near the front it controls the fuel. So, which is the back and which is the front of the carb. According to the diagram the front is the inlet side and the back is the outlet. So, in other words, the front of the carb is facing the back of the bike???? And the back of the carb hooks up to the intake manifold????

Geeze....I feel so stoooopid:banghead:

  • resurrection

Posted January 30, 2008 - 08:45 PM

#2

On some bikes they control fuel.
If your example controls air your correct.Very small amounts mostly noticable at just off idle.Or maybe at closed after you chop the throttle.

  • martinfan30

Posted January 30, 2008 - 09:20 PM

#3

If the screw is between the throttle slide and engine, its a fuel screw(typical on 4 strokes). If the screw is between the air filter and throttle slide its an air screw(a 2 stroke thing).

  • Denn10

Posted January 30, 2008 - 09:34 PM

#4

screwing in makes it richer yes and out leaner, this works in conjunction with your pilot jet. It can also tell you if your pilot is off as if you need it maxed in or out you have a pilot thats off.

  • dldavis_66

Posted January 30, 2008 - 09:35 PM

#5

If the screw is between the throttle slide and engine, its a fuel screw(typical on 4 strokes). If the screw is between the air filter and throttle slide its an air screw(a 2 stroke thing).


Thanks again.

So, then, that means when the Pilot screw is turned cw(when carb is upside down) all the way closed there is little or no(??) fuel going to the venturi at idle to 1/4 throttle, right???

  • martinfan30

Posted January 30, 2008 - 10:13 PM

#6

Yes.:busted:

  • dldavis_66

Posted January 30, 2008 - 10:46 PM

#7

I used a little hack saw blade to cut away the limiter tab on the bowl without having to take it off the bike again. I closed the Pilot the reopened it 2 1/2 turns as DynoJet instructed. That is where I had it initially after taking it off the bike and putting in the new jet and needle.

When I first started it up yesterday night after the revamp, it started up fine on half choke. When I unchoked it the engine died, idle set too low. No big deal. Started it up again with half choke, turned up the idle, unchoked and it idled fine on its own. Gunned the throttle a bit. BIG LOUD POP. Figured it was too lean so I turned the Pilot out maybe a 1/4 turn. Gunned it again. Sounded significantly better, still just a wee bit of popping on decel. Took it for a spin. Ran really good. Acc was excellent. Decel was quicker than I anticipated, prolly cuz of the bigger holes in the Slide. Some minor popping and burping here and there, pretty much the same as when carb was stock.

Took it to work this morning. Again, it ran really good. However, I was going down the freeway about 70 - 75 mph. Had to slow down, traffic conjestion up ahead. Backed the throttle down all the way, BIG LOUD POP, again, at least half way through the decel. During lunch, turned the Pilot another 1/4 turn out, maybe a little more, for a total of 3. Test drove it, pretting quiet, no popping at all. Same good pick up. I'm thinking 3 might be a little too rich for the idle with every thing else stock, but with K&N filter, White Bros Pipe and Snorkel removed...not sure. Bike runs good though.

Picked up 2 IMS Smog-removal kits for $30.00 on my way home from work. Will be installing one on the new bike soon.

Any comments or other recommendations??? I already know about Hi Comp piston and HotCam, Port and Polish. Gotta wait till I get the other bike done first.

  • cleonard

Posted January 30, 2008 - 11:21 PM

#8

The fuel screw is one of the places that crud gets stuck and is hard to get out. If you still have problems take the screw out and blast the passages out with carb cleaner.

  • weskc35k

Posted January 30, 2008 - 11:45 PM

#9

In is leaning it out,out is enrichening it on the 650R carb.

  • sploogemonkey

Posted January 31, 2008 - 04:41 AM

#10

Always be careful not to lose the rubber o-ring that resides under the spring where the fuel screw is. If you use carb cleaner to blow out the passage and then follow up with a blast of compressed air, you can blow the o-ring out of the carb.

Also, when you reinstall the o-ring/spring combo, make sure that the o-ring is properly seated between the spring and carb body.

Never torque down the fuel screw too hard to seat it. The needle tip of the fuel screw is precision tapered to match the orifice in the carb, and over tightening it can potentially wear a groove in the brass needle and alter the fuel delivery.

Your carb is your friend.:busted:

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  • scalejockey

Posted January 31, 2008 - 05:03 AM

#11

and.... If you need to go more than 3 turns out you need to go 1 larger on the pilot the pilot.(but make sure the pilot is completly clean first by running a fine wire through it.)

  • Denn10

Posted January 31, 2008 - 03:32 PM

#12

In is leaning it out,out is enrichening it on the 650R carb.


OK which bike is this for? two different answers so we need clarification, i may be wrong so wanna make it clear.

  • jetfuel

Posted January 31, 2008 - 03:38 PM

#13

He recently posted up looking for a edelbrock for his "L" so I'm guessing he is still playing with the stock one first..

  • Denn10

Posted January 31, 2008 - 03:44 PM

#14

thats what i thought but is there a difference in L to R for what screw does? in/out rich/lean ??? im not 100% sure so i dont wanna quote wrong.

  • martinfan30

Posted January 31, 2008 - 05:26 PM

#15

thats what i thought but is there a difference in L to R for what screw does? in/out rich/lean ??? im not 100% sure so i dont wanna quote wrong.


Then dont quote at all!LOL


J/K :busted:

  • Denn10

Posted January 31, 2008 - 07:12 PM

#16

Then dont quote at all!LOL


J/K :busted:


SHUT UP JACKOOO

OK heres what i found in my book, for 650L "high altitude adjustment, turn the pilot screw clockwise (in) 1/2 turn" If you turn in for high elevation thats making the mixture leaner so in must be lean and out rich.

  • Denn10

Posted January 31, 2008 - 07:13 PM

#17

In is leaning it out,out is enrichening it on the 650R carb.


TY for clearing that up!! now we can :busted:

  • dldavis_66

Posted February 04, 2008 - 07:58 PM

#18

Hey Denn...Is that really you in your avatar pic??:worthy:

J/K:thumbsup:

Yeah...I shoulda been a little more clearer with what bike I was talking about.:busted:

  • martinfan30

Posted February 04, 2008 - 09:10 PM

#19

Yea, thats him.

  • danny v

Posted February 04, 2008 - 09:33 PM

#20

Nice to see you two at it again.Being a moderator has not changed you at all,that is cool !Hey denn any new ideas on the mods for your ''L'' :busted:
I am still messing with my jetting,not happy yet. Did you guys say to run a new plug after a jet change to see if it is too rich? I still think I might be a little rich at mj160,pj65 2 1/2 out at sea level.WB E-series with 12 discs/uni ?

Danny





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