Topic: Weber carb set-up

[Tintop]

Stock petcock should be OK, but something larger won't hurt.

[BPellerine]

I run stock petcock as well.billp

[scottly]

My bike used the stock petcock originally, but with the Seeley gas tank, it was only possible to switch from on to off or reserve by lifting the rear of the tank. The stock petcock should flow enough fuel, but there may be a difference in hose size, depending on which flavor of fuel inlets you have on your carbs.
My support is connected to the rear side of the carbs, under the stack mounting nuts. The top of the support is bolted to a rubber lined clamp that fits over a horizontal cross tube on the Seeley frame; not sure if this would work with a stock frame.
Note the two vertical grooves in the carb tops: these were caused by the air box mounting tabs rubbing against them. The MPD manifold with short hoses may mount the carbs closer to the motor? I only had to slightly tweak the tabs to clear the back of the carbs.
 

[Greggo]

Even with brand new boots, getting them situated was a real PITA.  The spacing was just not right any way I twisted them.  I ended up mounting the boots to the RC manifold, wrestling those onto the motor, then mounting the carbs onto the manifold once the clamps were all tightened.   

[RAZZ]

HI
Spring is comming and I finally had some time to take a close look at my Weber Carbs  after layiong a year in the shelf searching for a manifold and now I got one. I have a MPD one piece manifold, Im gona use the Webers on a stock 736ccm K6 engine, with at Dyna ignition and “power arc” coils and a MAC 4-2-1 header with a 2,5” Stainless reverse cone megaphone muffler  on ( with DP killer, I have neighbours)
IM thinking, IM” in the right area “regarding chokes and jetting, but you guys have any adwise for jetting corrections  before I start running them ?? Maybe 105  or 110 main jets and 180 Air correction jets ?? or
I have following parts inside:
Start jet 150 / 85-F9
Idle jet: 45 F9
Emulsion tube: F9
Main jet: 100
Air correction jet: 225
Accelerator pump jet:  35
Intake and discharge valve for accelerator circuit : 50
Needle valve 1,75
Float hight aproxx 11 to 12 mm
AUX venturi : 4,5
Chokes 28 mm
Thanks
Razz

[RAZZ]

one small correction

I have F16 Emulsion tubes (not F9)

thanks

/ Razz

[scottly]

I would start with the 105 mains, and 180-190 air correction jets, and you may be able to go as small as the 100 mains you already have, given the 28mm chokes, 4.5 aux, and F16 emulsion tubes. The only thing that stands out about your setup as it is are the large 225 air correction jets.
BTW, the Power-Arc coils may not be compatible with the Dyna ignition; I would recommend tuning the carbs using standard type coils. Then, if you change something with the ignition and have issues, you will know it's ignition related.

[PeWe]

+2
make sure that ignition is OK before carb jetting procedure! Risk for a huge waste of time.... I have wasted a lot...

[RAZZ]

Hi

I need some help troubleshooting a very high idle, I have just mounted my webers with new 105 main jets and 185 air corrector jets - my problem is, the bike starts in very high rpms +3000 rpms (ii let it run for + 1 sek. and then I stop it  due to Cold engine and no oilpressure) I have tested that the throttle plates Closes and i have tried to open and and close for the idle mixture screws, checked that the throttle levellers don't touches anything - I have 45 F9 idle jets in( can see others uses the same size) - is the float height wrong ? or do i need smaller Idle jets ?or have I put something together wrong or??

 I need some adwise here, thanks

R

[BPellerine]

maybe your cable is too tight,mine started like that first time ,idle screws were too high,they are very sensitive on a motorcycle vs a car.bill

[Tintop]

are you using the 'chokes'?  if not, are they closed?

[scottly]

Some of the Webers have an additional idle air bypass adjustment screw, which I first learned of through Tintop's experience with his sidecar rig. This screw allows air to by-pass the throttle blades, even if they are fully closed. IIRC, they are mounted just inboard and slightly behind the normal idle mix screws, and have a lock-nut. If your carbs have these screws, loosen the lock-nuts and turn the screws all the way in; note how far out they are from fully seated for future reference. 

[RAZZ]

hi

thank guys for our input

the cable is checked and it is Loose

I have choke on, but i assume that they are closed with a Loose cable


I found out I have idle air bypass adjustment screws on my carbs..  I thought they where some sort of venturi Lock screw or so..haha I will Lock in to them in the next days

I found this info regarding the subject: http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm

Again thanks

[RAZZ]

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[BPellerine]

nice choke cable setup!bill

[scottly]

The cold start "choke" on Webers is also a by-pass system; when operated, it allows air to bypass the throttle valve, picking up fuel from the starter jets. I've never bothered with it; with accelerator pumps a twist of the wrist is all that's needed.

[754]

Sometimes when really cold, i would pull the left choke by hand while kicking it over, then work the throttle till it warms a bit.. But usually a squirt or two then play with throttle to keep it going.
 If i were to build a choke though, i would make a knob with a shaft portion, and a pin drilled thru it at 90 degrees. Then fit that into a bushing with a few notches, so you can pull the knob and turn it to go in the notches. The knob is fit to a cable to allow it to twist.
 What I also used, a piece of inner throttle cable about 10 inches long, with a end still on it. Insert from left side , passing thru both choke arms, then clamping down on it. Now when you pull it by hand both chokes go on.

[scottly]

I have fitted an extra idle speed screw on the outside of the left carb; I use it to speed up the motor during warm-up, then back it off until the idle speed is controlled by the inboard screws. BTW, it's #$%*ing nice to have an electric starter again after all these years of kick-only,despite the weight!

[754]

 E Starter..aka..the Girl Button..

[scottly]

Frank, you've said you can "kick-start" a 750 by hand; after you try that on my 836 this August, let's see if you still call it a Girl Button.

[seanbarney41]

ha ha...I call the kickstart the poser lever

[BPellerine]

despite the weight,still very nice to have the button option!bill

[Bill/BentON Racing]

Well, I've cranked a few by hand....think it would take Atlas to crank my current build by hand.....lol.

[PeWe]

No oil pressure?? 3000rpm should ensure pressure. My carbs ( Not Weber) idle 2000 up to 3000 rpm after a while on choke. Idle low rpm when cold cannot be healthy

[DB Durf]

Thanks guys, Scotty especially! I have just begun the process on mounting up a new set of sidedrafts on my bike (cough cough DOHC) but the work you all have done will help me a lot. Just finished my intakes and cable stuff and now looking to do the jetting.

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