After installing new pipes I now have back firing when I crack the throttle. Also idle seems a bit shaky. I looked all over the net and cannot find exactly where the idle adj screws are. Is there a separate screw for each carb? Anyone have a clear pic pointing out where this/these screws are? I was going to start here before checking into jetting (ugh!)
Announcement
Collapse
No announcement yet.
carb tune ?
Collapse
X
-
Hey, Rob -
Do you mean the idle speed adjustment screw? If so, there is only one, and it is located facing up between carbs 2 and 3 on the airbox side of the carbs.
Based on your signature, I'm assuming you have the early '78-'79 carbs.Marco
Current bikes:
1979 Yamaha XS Eleven Special (SF)
1979 Honda CBX
2002 Kawasaki ZRX1200R
Rest in Peace, Don Glardon (DGXSER) 1966-2014
WE MISS YOU, DON
-
The crackle can be reduced by adjusting each of the four air screws on the carbs. Each carb has one. I always get my two bikes confused but I'm sure someone will post about whether to screw them in or out. I believe the mixture needs to be richened slightly. The popping is caused by the mixture being too weak.
The air screw on the left carb can be seen in this pic. It has a spring round it to stop it moving...
Last edited by James England; 09-04-2014, 08:26 AM.XS1100F 1980 European model. Standard. Dyna coils. Iridium plugs. XS750 final drive (sometimes). Micron fork brace. Progressive front springs. Geezer regulator/rectifier. Stainless 4 into 2 exhaust. Auto CCT (Venturer 1300) SOLD. New project now on the go. 1980 European model.
Comment
-
did you install new exhaust gaskets?
If you did not then that could be a source of the backfiring. I had the same problem. Once I bought new gaskets it disappeared. If you used new ones with the new pipes then the problem may be elsewhere.2 - 80 LGs bought one new
81 LH
02 FXSTB Nighttrain
22 FLTRK Road Glide Limited
Jim
Comment
-
Backfiring, or poppingbfrom lean-ness? You'll need to check your plug color and adjust accordingly. Clockwise is rich, CCW is lean. Don't chase your tail confusing the idle screws with the mixture screws (very easy to do rushing). After you get your plugs looking tan, sync your carbs (Morgan Carb Tune works great- thought that's what the thread was about).1979 XS1100F
2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.
Comment
-
Originally posted by James England View PostThe crackle can be reduced by adjusting each of the four air screws on the carbs. Each carb has one. I always get my two bikes confused but I'm sure someone will post about whether to screw them in or out. I believe the mixture needs to be richened slightly. The popping is caused by the mixture being too weak.
The air screw on the left carb can be seen in this pic. It has a spring round it to stop it moving...
81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.
Comment
-
Prisoner6...I have a 79 special. So that I know,....the idle speed and air screws are different right? Not to confuse things more,...the jets are a whole other tuning adjustment....right?
I've called 2 different bike shops and when I mention what bike I have they get all flustered..."4 carbs....whoa!"....lol. Guess I have to learn to tune on my own!Rob - 79 SF
Comment
-
Originally posted by mrhammer2u View PostPrisoner6...I have a 79 special. So that I know,....the idle speed and air screws are different right? Not to confuse things more,...the jets are a whole other tuning adjustment....right?
I've called 2 different bike shops and when I mention what bike I have they get all flustered..."4 carbs....whoa!"....lol. Guess I have to learn to tune on my own!81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.
Comment
-
BTW, they'd REALLY be at a loss if it where a Honda Vaulk 1500 with SIX carbs.81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.
Comment
-
Originally posted by mrhammer2u View PostPrisoner6...I have a 79 special. So that I know,....the idle speed and air screws are different right?Originally posted by James England View Post
To answer your question ... Yes, they are different, but there is one big caveat ...
First, as I said in my earlier post (see post #2), there is only one idle speed adjustment screw.
Now, look at the photo above. That screw with the red arrow pointing to it is the Idle Mixture Screw, or PILOT Screw.
As James said, each carb has it's own PILOT screw. Adjusting these screws controls the air/fuel mixture at idle/low speeds.
The way the PILOT screws control the mixture is (as motoman said) by controlling the amount of FUEL, not air, allowed into the mixture.
A good rule of thumb to remember is this: When the PILOT screws are on the front of the carbs (engine side, like our XS's), they control/meter the fuel.
When they are on the rear of the carbs (airbox side), they control/meter the air.
Clear as mud, right?Marco
Current bikes:
1979 Yamaha XS Eleven Special (SF)
1979 Honda CBX
2002 Kawasaki ZRX1200R
Rest in Peace, Don Glardon (DGXSER) 1966-2014
WE MISS YOU, DON
Comment
-
Yes, sorry...fuel screws not air screws! I slipped into Triumph Bonneville mode on that one. I'm not sure re my XJR...I think they are fuel screws too, not air....XS1100F 1980 European model. Standard. Dyna coils. Iridium plugs. XS750 final drive (sometimes). Micron fork brace. Progressive front springs. Geezer regulator/rectifier. Stainless 4 into 2 exhaust. Auto CCT (Venturer 1300) SOLD. New project now on the go. 1980 European model.
Comment
-
Well,
To be truly correct NOW since we've seen the sawed in half views of the carbs, the PILOT screws are actually FUEL/AIR screws since the air is being mixed into the fuel flow path after the PILOT JET, and BEFORE the pilot screw...so what you're metering is both fuel and air...albeit still mostly fuel...just ATOMIZED a bit, and it's then getting mixed/atomized with MORE air when it hits the carb intake throat going into the intake manifold.
But for a simplistic view, yes, it's still a fuel metering screw.
T.C.T. C. Gresham
81SH "Godzilla" . . .1179cc super-rat.
79SF "The Teacher" . . .basket case!
History shows again and again,
How nature points out the folly of men!
Comment
-
A Waste
Originally posted by mrhammer2u View PostAfter installing new pipes I now have back firing when I crack the throttle. Also idle seems a bit shaky. I looked all over the net and cannot find exactly where the idle adj screws are. Is there a separate screw for each carb? Anyone have a clear pic pointing out where this/these screws are? I was going to start here before checking into jetting (ugh!)
If you have a problem or question about your bike, feel free to ask us here. We're here to help. And we normally do not charge that much either (LOL).1981 XS1100H Venturer
K&N Air Filter
ACCT
Custom Paint by Deitz
Geezer Rectifier/Regulator
Chacal Stainless Steel Braided Brake Lines
Chrome Front Rotor & Caliper Covers
Stebel Nautilus Horn
EBC Front Rotors
Limie Accent Moves On In 2015
Mike
Comment
-
Originally posted by TopCatGr58 View PostWell,
To be truly correct NOW since we've seen the sawed in half views of the carbs, the PILOT screws are actually FUEL/AIR screws since the air is being mixed into the fuel flow path after the PILOT JET, and BEFORE the pilot screw...so what you're metering is both fuel and air...albeit still mostly fuel...just ATOMIZED a bit, and it's then getting mixed/atomized with MORE air when it hits the carb intake throat going into the intake manifold.
But for a simplistic view, yes, it's still a fuel metering screw.
T.C.
Don't want to confuse him in any way ...Marco
Current bikes:
1979 Yamaha XS Eleven Special (SF)
1979 Honda CBX
2002 Kawasaki ZRX1200R
Rest in Peace, Don Glardon (DGXSER) 1966-2014
WE MISS YOU, DON
Comment
Comment