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xs650 > > Motorcycle Systems > > Fuel > > Pilot screw? |
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Hutzpah Full Member
Joined: Aug 21, 2008 Posts: 16 Location: Perth, Western Australia
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Posted: January 5, 2009, 5:07 am Post subject: Pilot screw? |
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Could someone please explain what the pilot screw is
and what its purpose is.
Its a very small adjusting screw on the side of the carb.
I have had the timing light on my bike and balanced the carbs with a newly
made manometer.
It starting real good when cold and running sweet on the road yet abit hard to start when hot any ideas?
Just starting to get my head into the mechanics of this bike.
Your help would be much appreciated.
Thanks
Hutzpah
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yamaman Support Staff
Joined: Jan 04, 2007 Posts: 1638 Location: Perth Western Australia
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Posted: January 5, 2009, 7:59 am Post subject: Re: Pilot screw? |
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Some useful reading here, cheers
www.mikuni.com/fs-tuning_guide.html
_________________ Its not enough to have an aim in life, you have to pull the trigger! |
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Retiredgentleman 650Rider Supporter
Joined: Mar 03, 2007 Posts: 2258 Location: Calgary, Alberta 1978 XS650 SE
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Posted: January 5, 2009, 12:51 pm Post subject: Re: Pilot screw? |
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The pilot screw (also called mixture screw and idle screw) is used to set the air/fuel ratio for engine operation from idle to about 1/4 throttle.
650garage.com has an excellent "Carb Guide", which you should read carefully. To adjust the pilot screw, you use something called the "dead cylinder method". It is explained very well in the carb guide. When you want to run the engine on just 1 cylinder for this adjustment, its important to make sure that the disconnected spark plug lead is grounded to a good ground on the bike. This prevents damage to your ignition sytem.
www.amckayltd.com/carbguide.pdf
www.iwt.com.au/mikunicarb.htm
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5twins Full Member
Joined: Aug 05, 2006 Posts: 1616
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Posted: January 5, 2009, 10:10 pm Post subject: Re: Pilot screw? |
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The pilot screws on the original CV carbs are true mixture screws - they regulate fuel flow not air. Opening them more will richen your idle circuit, closing them (screwing them in) will lean it.
The popular aftermarket Mikuni slide carb that many use on these bikes has an air screw - it meters air flow to the pilot circuit. It functions totally opposite from the fuel regulating screw on the CV carbs. Turning it out adds air and leans your idle circuit, turning it in cuts the air supply and richens the idle circuit.
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jpowell Full Member
Joined: Sep 04, 2008 Posts: 193 Location: Cincinnati, OH 1978 SE(special)
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Posted: January 5, 2009, 10:44 pm Post subject: Re: Pilot screw? |
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RG, I atemped this last year, but instead of pulling the wire off the plug, I pulled one wire at a time where the pig tail comes off the points. this way you're preventing one cylinder from firing, but leaving the plug attached so no damage can come. This probably is only possible with the stock points.
_________________ Jeff
78 Special
Cincinnati, OH |
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Retiredgentleman 650Rider Supporter
Joined: Mar 03, 2007 Posts: 2258 Location: Calgary, Alberta 1978 XS650 SE
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Posted: January 6, 2009, 12:49 am Post subject: Re: Pilot screw? |
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jpowell;
Yes, that would work fine when you have 2 individual coils. Lots of guys don't say what year bike they have when they ask qestions. Single coil dual output ignitions such as 80 to 83 must ground the unused spark plug/lead, so I simply generalize to be safe.
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Hutzpah Full Member
Joined: Aug 21, 2008 Posts: 16 Location: Perth, Western Australia
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Posted: January 6, 2009, 3:06 am Post subject: Re: Pilot screw? |
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"Lots of guys don't say what year bike they have when they ask questions."
Your dead right Retiredgentleman my bikes a 1979 xs650 Special.
A big thanks one and all looks like I've got a fair bit of reading to do.
Thanks
Hutzpah
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jayel 650Rider Supporter
Joined: Apr 16, 2006 Posts: 3417 Location: SE Iowa 1974 TX650A
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Posted: January 6, 2009, 9:48 am Post subject: Re: Pilot screw? |
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it's real easy guys, over on the left side is a box titled "Current Member Info" click on "My Account" under "My Account Tools" click on "My profile information" scroll down a bit to "My Location" fill in where you're at and what you got....
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_________________ all it takes is time and money -- Where are we going and why are we in this hand basket? |
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650skull Support Staff
Joined: Jul 19, 2007 Posts: 1186
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Posted: January 6, 2009, 5:00 pm Post subject: Re: Pilot screw? |
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I'm not sure that is what Hutzpah meant jayal..............it is a good idea to post what bike or bikes you have with your avatar but that is no indication exactly the make up of the bike.............The information that is recieved on this site has helped and saved people thousands of dollars i am sure, (how many mechanics now days could work on these and get it write without learning themselves and charging for the experiance), that's why it is important to know the the bike and the make up of it. If not then the answers given may be write for the question asked but wrong for the aplication..........As we all know the PO's may have mixed and matched any part of these bikes so saying what year the bike is may not help either..........SKULL
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xsleo Full Member
Joined: Oct 28, 2007 Posts: 1528 Location: Earlville NY
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Posted: January 7, 2009, 7:00 am Post subject: Re: Pilot screw? |
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yes mixed and matched parts are often found, giving a year and model of bike is a start. any info is better than no info.
_________________ "You live more in five minutes on a bike than most people do in there whole life"
'75 XS650B with a 79 dual disc front end, rear disk brake, Chrysler reg, Radio Shack rect, LED tail/ brake and turn signals. |
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650skull Support Staff
Joined: Jul 19, 2007 Posts: 1186
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Posted: January 7, 2009, 8:15 am Post subject: Re: Pilot screw? |
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xsleo! any info is better than no info.
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xsleo Full Member
Joined: Oct 28, 2007 Posts: 1528 Location: Earlville NY
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Posted: January 8, 2009, 5:23 am Post subject: Re: Pilot screw? |
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yes, any info such as year and model is better than no info at all. any info a person can give is helpful to us, so we can better help answer thier question.
_________________ "You live more in five minutes on a bike than most people do in there whole life"
'75 XS650B with a 79 dual disc front end, rear disk brake, Chrysler reg, Radio Shack rect, LED tail/ brake and turn signals. |
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