Fuel screw setting (pilot jet change)
Alright, thanks for my Trans-Atlantic friend Markus (a.k.a. Tweety), I be giving #48 pilots a try. While my bike runs flawlessly as it is, I have been known, on occasion, to experiment with new settings, all in the name of perfecting my beloved VTR. MY question, then, is the following:
- how much would one have to reduce the fuel screw setting to get an equivalent fuel flow with a larger #48 pilot (compared to stock 45). IN other words, if I am currently set at 2 5/8 turns out, what fuel screw setting would give me similar fueling with the 48 pilots in place? thanks all :) |
I love riddles? is this a riddle? beware the dwarf is my answer.
honestly I wouldn't change it. I didn't notice a lot of correlation between changing my pilots and a/f screw settings. I think the a/f is almost completely the idle circuit and the pilots are much more of the low end/needle impact. So I would say to slot your A/F screws, don't change them and get a motion pro right angle jobbie tool and then once you have it back on see if you can optimize anything at that point. I think you're more likely to find changes to just small on/off throttle transitions at the lower third of the throttle range. At least that has been my experience. And of course, never change more than one thing at a time - or you are sure to screw yourself up. I make that mistake over and over and over again. slotting the A/F screws and having that tool at least takes the worry out of it because you can adjust while idling which is ideal |
While Bill is correct, I have mine set at 2 turns out on the front and 2 1\8 turn out on the rear. They could be opened another 1\8 turn each but I don't have the tool and don't feel like pulling the carbs right now. ;)
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Hi gents,
my experiemntal streak was awakened by this posting by Tweety: "tune it with a slightly rich idle, a wee bit lower on power at the top end and you get a punch in the middle of the powerband that makes you ask yourself what you where doing before... The bottom then becomes clean and grunty, the middle has a much wider area where you get loads of torque and the top end rolls of further down than an IL4 but with a less sharp roll of... The middle of the powerband that felt "fine" before is now several steps beyond "fine"..." May try it (going to 48s). Worse case I go back to how it is now (as it's working fine; but one never knows what is left on the table unless you experiment a little) |
I certainly won't argue with tweety about tuning but not sure how much you can shift the powerband with merely carb changes aside from trying to get the ideal. In general the only thing that appears to matter much at WFO and high end is the main jets so not sure what relationship there is to the other things. I would just tune for the strongest midrange and the smoothest low end and transitions you can get. Agree you never know till you make a change on either side of perfect - thus make one change at a time.
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I have tried 48's but ultimately had to go back to 45's to get it to run right down low. This coincided with the change of my intake set-up. I was running 50's, but after change back to a K&N filter it was too rich and no amount of screw adjustment would get it right on the 50's or 48's.
Lots of factors involved in this of course, such as different exhausts etc, so 48's might be the go for you. As for the mixture screw position, I dunno if there is a straight answer to be found. I would start at about 1.75 turns out and experiment from there. |
I also went back to #45 pilots after experimenting with the larger #48. The difference in mixture screw settings between the 2, as best as I can remember, was probably 1~1.25 turns. I used the procedure for highest/smoothest idle while running. In both cases, after getting it just right, the engine will idle steadily at 1,000 rpm without ever dying. Pull in the clutch while downshifting, or at an intersection and it just idles perfect. There is a definite warm-up period involved though.
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rule of thumb i've always read was 3 turns.
tim |
Originally Posted by trinc
(Post 260703)
rule of thumb i've always read was 3 turns.
tim |
Originally Posted by mikstr
(Post 260681)
Hi gents,
my experiemntal streak was awakened by this posting by Tweety: "tune it with a slightly rich idle, a wee bit lower on power at the top end and you get a punch in the middle of the powerband that makes you ask yourself what you where doing before... The bottom then becomes clean and grunty, the middle has a much wider area where you get loads of torque and the top end rolls of further down than an IL4 but with a less sharp roll of... The middle of the powerband that felt "fine" before is now several steps beyond "fine"..." May try it (going to 48s). Worse case I go back to how it is now (as it's working fine; but one never knows what is left on the table unless you experiment a little) |
Originally Posted by 8541Hawk
(Post 260707)
The rule I've used is if you are 3 turns or more out, go to the next larger sized pilot jet. 1 turn or less out, go down 1 size. :)
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Originally Posted by 8541Hawk
(Post 260677)
...They could be opened another 1\8 turn each but I don't have the tool...
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its a right angle screw driver that is usually gear driven so you can rotate the action head by turning the handle. Motion pro sells one. You have to be sure to get the D-shaped adapter - to fit the AF screw head. It still doesn't work that great and you are better to slot the screws next time carbs are off so you can use a straight screw driver tip instead. works better.
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Thanks again.
My bike runs more than fine as it is but one never knows if there is some improvement left untapped unless I try it. (BTW, this line of reasoning, I am told, is a sure sign of OCMD, lol). Given the minimal cost involved and the fact taht I have the carb removal routine down to a fine art, I will give this a try in the near future. cheers |
According to the Factory Pro website:
Rule of thumb.... If you go 1 size larger or smaller on the size of the pilot jet, you will change the fuel screw ~1.5x richer or leaner to retain the original idle mixture - |
thanks, that is precisely what I was looking for :)
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Originally Posted by residentg
(Post 260724)
I need to get to this at some point. My bike runs ok as it is, so no real rush. What "tool" are you referring to - a screwdriver won't do it? If I need a special tool I want to order it before I tackle this job. Thank you. JB
http://www.motorcyclecarbs.com/Pilot...ools_C2297.cfm |
Would this one work:
http://cgi.ebay.com/ebaymotors/CARBU...motiveQ5fTools The ad notes it doesn`t work on Hondas but I fail to see how it differs from anything else so long as the head shape fits (virtually same as Motion Pro whch makes no similar exception)... |
Originally Posted by mikstr
(Post 260752)
Would this one work:
http://cgi.ebay.com/ebaymotors/CARBU...motiveQ5fTools The ad notes it doesn`t work on Hondas but I fail to see how it differs from anything else so long as the head shape fits (virtually same as Motion Pro whch makes no similar exception)... |
Thanks again bud. So are Honda alone in using the D shaped screw head then?
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Originally Posted by mikstr
(Post 260756)
Thanks again bud. So are Honda alone in using the D shaped screw head then?
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Decided to bring this thread back to life....sorry. I've been reading much of the threads concerning the D shaped screws to have my eye balls bulge outta my head. One thing I have never found is the methode used to notch/groove the screw to use a screw driver.
After driving the '98 for a few years, never did anything to it, but simple maintenance. But with this one, I have begun to suffer form OCMD, like most of my fellow Hawkers. That being said, I now have my carbs on my work table, and, unless I am brain dead, the only way I see to groove the screw is with my dremel. However, this will also damage the housing around the screw itself. Question : Is there another, cleaner way that I'm over looking to groove the screw ? Hawk, being the undisputed carb expert, perhaps you may sheed some light for me....:cool: |
If I can recall, I just used a hemostat/tweezer to turn it out and dremeled a slot
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Thanks nath. So if I understand, the screw is pretty loose and not jamed
in the housing. It should turn easy ? |
oh yeah, it turns easily. Turn it out with a tweezers and clamp a little vicegrip or pliars on the tweezer if you can't squeeze it tight enough.
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Thanks Nath, I'm on it tonight.:thumbsup:
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Originally Posted by Jack Flash
(Post 345786)
Thanks Nath, I'm on it tonight.:thumbsup:
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Originally Posted by Jack Flash
(Post 345786)
Thanks Nath, I'm on it tonight.:thumbsup:
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Thanks Tweety. I had begun thinking about that before playing
with it to make sure I know where I am, and where I need to go. I did the TPS earlier this week, and made sure I took precise readings before playing with it. I was at 900omhs, so, I knew where I need go before removing it. |
I just saw this. Not sure if it would work but hand adjustable would be sweet
Parts & Accessories - Cycle Gear - Motorcycle Gear and Motorcycle Accessories |
Originally Posted by Jack Flash
(Post 345802)
Thanks Tweety. I had begun thinking about that before playing
with it to make sure I know where I am, and where I need to go. I did the TPS earlier this week, and made sure I took precise readings before playing with it. I was at 900omhs, so, I knew where I need go before removing it. |
Originally Posted by smokinjoe73
(Post 345806)
I just saw this. Not sure if it would work but hand adjustable would be sweet
Parts & Accessories - Cycle Gear - Motorcycle Gear and Motorcycle Accessories found this guide to carb tuning: http://keihincarbs.com/tips/gate.html |
Originally Posted by twist
(Post 345807)
If you are really anal you can mess with it a long time and even attach the balance tool so to get both just right. Unfortunately, weather, temp, and all those factors will affect the tune from day to day so it never stays the way it was set up but the changes aren't really all that noticeable unless it's a track bike.
My experience is with Kart racing, two stroke engines. 125cc shifter karts, and 125cc clutch driven karts. Once at the track, temp, humid, and barometric pressure is what I read, and jet accordingly. Carb veturi's are between 28mm to 34mm according to race category, and I can tell you air screw mixture is pretty stable, and barely need to play with this. Once again, I am not sure the V-Twin is going to feel it if you play with it on a daily basis, but then again, I may be wrong. Four stroke is different then two stroke engines. Silencer volume and design affects enormously a two strock engine. Even the type of driver, will determine a portion of the jetting I will provide in order to have the engine run right....but now, I'm out of line with this. |
Originally Posted by Jack Flash
(Post 345870)
I am probably getting ahead of myself, but, I don't think playing around with the air screw mixture on a daily basis will provide any satisfactory gain. I will set mine as per 8541Hawks suggestion, fine tune from there, and forget about it.
My experience is with Kart racing, two stroke engines. 125cc shifter karts, and 125cc clutch driven karts. Once at the track, temp, humid, and barometric pressure is what I read, and jet accordingly. Carb veturi's are between 28mm to 34mm according to race category, and I can tell you air screw mixture is pretty stable, and barely need to play with this. Once again, I am not sure the V-Twin is going to feel it if you play with it on a daily basis, but then again, I may be wrong. Four stroke is different then two stroke engines. Silencer volume and design affects enormously a two strock engine. Even the type of driver, will determine a portion of the jetting I will provide in order to have the engine run right....but now, I'm out of line with this. BTW, got a cool boost joint today. Cheers!! |
Originally Posted by twist
(Post 345875)
+1 there really is no reason to mess with the air mixture but the initial setting or if something is changed in the intake or exhaust. Best to set it and leave it, maybe that's why it has a "D" shaped screw to begin with?
BTW, got a cool boost joint today. Cheers!! In my case, with altered pipes, jets, air box, filter,etc., you're on your own. The way I use to get in the ball park is to take it to an extreme point one direction, see how it runs, then take it to the other extreme and see what happens. One extreme will usually be obviously worse. Tweak accordingly. Then, to get it right on, get or make the tool and adjust while idling. |
[QUOTE=twist;345875
BTW, got a cool boost joint today. Cheers!![/QUOTE] Happy it got to you in timely fasion. It is a cool piece. I now have to get one for mikstr, he wants one also. :thumbsup: Nath, I ended up using a flat head precision screw driver, and applying pressure on the flat portion of the D shaped screw, slowly got it to budge. Once it began moving, the rest was easy. Once off, dremeled the head and tested with my tool, it works perfectly. I do have the 90 deg. screw driver for this job, so, I set at 2 1/4 front, and 2 1/2 rear as per suggested many times. Once the white sh**....eh....snow clears next spring, I'll be able to fine tune as you mentioned. |
Originally Posted by Jack Flash
(Post 345906)
Happy it got to you in timely fasion. It is a cool piece. I now have to get one for mikstr, he wants one also. :thumbsup:
Nath, I ended up using a flat head precision screw driver, and applying pressure on the flat portion of the D shaped screw, slowly got it to budge. Once it began moving, the rest was easy. Once off, dremeled the head and tested with my tool, it works perfectly. I do have the 90 deg. screw driver for this job, so, I set at 2 1/4 front, and 2 1/2 rear as per suggested many times. Once the white sh**....eh....snow clears next spring, I'll be able to fine tune as you mentioned. |
Originally Posted by twist
(Post 345907)
question: joint has a small hole in it and not wide open like the OEM piece. How will that affect tuning? If the rear has a larger opening than the front will that be enough to make a difference? Drill it out to same ID as OEM?
As for the OEM, part, I've never seen it, so I do not have a reference for you. And, I've always used that with the TecMate calibration tool. |
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