Jetting Weber DCOE for 948 and 1275 cc

[twas_brillig]

Jetting Weber DCOE for 948 and 1275 cc

Further to my Dec. 12/08 note requesting help in “Jetting a Weber 45 DCOE for a stock 1275 cc", I’ve listed what is currently in the 40 DCOE on our stock 948 cc Bug-Eye (it’s been a reliable set up for several decades, but not a lot of miles at our 3600 ft. elevation) immediately below, plus the Haynes Weber recommendations, and then thoughts from "scubabatdan”

Stock 948 cc; goose-neck manifold:
30 mm = Choke
4.5 = Aux Venturi
135 = Main Jet
175 = Air correction Jet
F2 = Emulsion Tube
45 = Pump Jet
45F9 = Idle Jet 45F9
?? = Ex.Valve (there were absolutely no markings on this one; I pulled the same thing out of the 45 DCOE that prompted this whole escapade, and it had a number but no joy on this one in the 40)

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What the Haynes Weber Manual recommends for all Mk. 1, 2, & 3 Sprites and Mk 1 & 2 Midgets, which I believe are the 948 and 1098 cc engines:

32 mm = Choke
5.0 = Aux Venturi
1.40 = Main Jet
1.80 = Air correction Jet
F16 = Emulsion Tube
0.40 = Accelerator Pump Jet
0.45F6 = Idle Jet
.50 = Accelerator pump inlet valve with exhaust orifice


What the Haynes Weber Manual recommends for Sprite Mk 4 and Midget Mk 3s (1275 cc engine):

34 mm = Choke
3.5 = Aux Venturi
1.30 = Main Jet
1.75 = Air correction Jet
F2 = Emulsion Tube
0.50 = Accelerator Pump Jet
0.5F9 = Idle Jet
.50 = Accelerator pump inlet valve with exhaust orifice

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And what scubabatdan (2008-12-15 21:28:47) was good enough to advise of in response to my earlier cry for help:

Here is a setup for a stock 1275 DCOE45
33mm = Choke
3.5 = Aux Venturi
155 = Main Jet
185 = Air correction Jet
F2 = Emulsion Tube F2's are made for top end according to the weber plant
50 = Pump Jet
45F9 = Idler Jet 45F9
50 = Ex.Valve
Might be a good place to start...

Here is what I have in my DCOE40 for my 1275:
30mm = Choke
4.5 = Aux Vent
120 = Main Jet
190 = Air correction Jet
F16 = Emulsion Tube
40F8 = Idler Jet
35 = Pump Jet
Plugged = accelerator pump discharge

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The carb I’ve got that I’d like to put on the forthcoming 1275 currently has:

33 mm = Choke
3 = Aux Venturi
1.35 = Main Jet
1.65 = Air correction Jet
F16 = Emulsion Tube
0.35 = Accelerator Pump Jet
0.50F9= Idle Jet
.50 = Accelerator pump inlet valve with exhaust orifice

I think I’ll follow scubabatdan’s advice and just bolt ‘er on and see what happens….

 

[twas_brillig]

Re: Jetting Weber DCOE for 948 and 1275 cc

Dang! forgot to mention that Haynes suggests a single 45DCOE; my 'future' carb is a 45DCOE. And I built a table of all the above info, but couldn't figure out how to add it and have it readable.

Doug

 

[twas_brillig]

Re: Jetting Weber DCOE for 948 and 1275 cc

I found my "Tuning the A-Series Engine" by David Vizard and he has a chapter on Webers. For a stock 1275, he suggests:

45 DCOE
35 mm = Choke
4.5 = Aux Venturi
150 = Main Jet
180 = Air correction Jet
F2 = Emulsion Tube
40 = Accelerator Pump Jet
50F2 = Idle Jet


Doug
1960 bug-eye: running
1960 bug-eye: project
1962 AH 3000 BJ7: running

 

[RonMacPherson]

Re: Jetting Weber DCOE for 948 and 1275 cc

Don't forget your elevation. At that altitude you may want to go two sizes smaller on the fuel(main jet) for a start.