insight on carb functions
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Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Wed Sep 09, 2020 11:43 am quote
After speaking with a few here on the subject of carb setup and breaking in a new motor,I thought it a good idea to be specific with the motor and setup.
- 20/20 Spaco 20d carb, and pulled the two , I think youíd refer to them as jets. The big one up top says 160 , the main body has a E3 and on the deep end of the main body the main jet says 118. The second jet which I think is the pilot jet says 50-120.
I searched a bit to find a break down of these carb for proper lingual but wasnít very successful , so my apologies.

- I also included a pic of the filter on the carb

- I have the BGM exhaust

-DR 180 top end and I think the only upgrade on motor is the Rich Nice crank which Iím pretty sure, anything but the top end is the pertinent information looked at.

-Ducati ignition and Pinasco Regulator.

-Looking back on old messages from the builder, the motor is timed at 20-21 btdc, retarded it a bit more than stock to keep motor running cooler.


I'm not sure why the carb was setup up the way it is other than the 118 is recommended for breakin and that the motor was benchtested to his soecifications which I trust, but I would like to get an understanding without having to be an annoyance to the builder as I know he is extremely busy.

So to start with could you's please explain what these jets represent , including the air corrector etc , kind of in laymans terms would help alot. I do know from experience the piolt jet is for low speed and main jet is for higher throttle opening ie hiway speeds.
P.S. I don't think I have enough time in my lifetime to both read and understand CM's highly technical Sidecar thread .
Thanks for the input
Lynn

sept 9 carb.jpg

sept 9 carb 2.jpg

sept 9 carb filter.jpg
blue fiber on filter

sept 9 blue carb filter.jpg

sept 9 main jet.jpg

sept 9 pilot.jpg

Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 61
Location: MA
Wed Sep 09, 2020 2:01 pm quote
The larger of the 2 jets consisting of 3 pieces is usually called the main stack. The 3 pieces from top to bottom are (1) the air correction (or just air) tube, (2) the emulsifier or mixing or atomizer tube, and (3) the main jet.

The smaller of the 2 jets consisting of one piece is the idle or pilot jet.

The idle jet controls fuel flow at idle and low rpm. The lower number corresponds to fuel and the higher number corresponds to air. Divide the higher number by the lower number to get a relative measure of richness (lower is richer).

The main stack controls fuel flow at mid to wide open throttle. The air tube meters air, the main jet meters fuel and the mixing tube combines them. The air tube and the main jet are pretty straightforward--a bigger number on the air tube means more air (leaner) and a bigger number on the main jet means more fuel (richer). To understand the mixing tube, you have to understand that the main stack sits in a well of fuel and the level of fuel in the well goes down as the throttle is opened up. The various mixing tubes have different hole patterns at different heights that feed air into the fuel as they are uncovered by the dropping fuel level in the well.

Your mixing tube is probably a BE-3, not an E-3. If that is correct, your jetting is pretty typical for your application.

I am attaching some pictures that help explain the mixing tube.

vivo_tech_jets_atomisers_01_zps134bc6b0.jpg

emulsifiers_4_87552.jpg

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Wed Sep 09, 2020 3:56 pm quote
Thanks kowalski , really well presented, Iíll have to read it a few times to really take it in and understand front to back but itís some very thorough information.
The Mixing tube does that indeed only say E3 but hard to tell there may be a B in front.

6055B260-4EAE-4A61-822C-84FFD8DC80FD.png

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Wed Sep 09, 2020 9:27 pm quote
Iím pretty sure the pilot let is determined by the air/fuel mixture screw but what about the main stack , what determines the size of the 3 pieces in the main stack (1) the air correction , (2) the atomizer tube, and (3) the main jet?
Well the main jet Iím sure is just a matter of doing a plug chop and seeing what the spark plug looks like , or does (1) and (2) play a part as well ?

Also I know my air cleaner is not the best and also has to be addressed and probably has an effect on the mix?
Enthusiast
2005 Stella 2T
Joined: 14 Jun 2020
Posts: 61
Location: MA
Thu Sep 10, 2020 4:37 am quote
That is a BE-3 mixing tube. You can tell because it has 4 holes in the midrange section (more air/leaner mix) where the E-3 only has 2 (less air/richer mix).

The mixture screw is used to fine tune the idle jet. One way to tell if you have the right idle jet is if the mixture screw is about 2 1/2 turns out when properly adjusted.

As far as selecting the components for the main stack, I am still figuring that out myself. They are all interrelated and there is some overlap with the idle jet to consider too. The biggest enigma is how the air tube and the mixing tube interrelate. It seems to me that the air tube isn't that critical because the air still has to pass through the mixing tube. Nonetheless, people put a lot of emphasis on air tube size, so I'm probably missing something. In any event, as I said before, your 160/BE-3/118 is pretty typical for a 177 cylinder kit. Beyond that, I will have to defer to Jack and the other jetting gurus here.

You are right that yours is not the best air filter. The easiest thing to do is replace it with a Piaggio air filter that comes with holes in the "heart section" already drilled. That is supposed to flow more air and may require a larger main jet to compensate.
bodgemaster
63 GL, 76 Super (x 2), 74 Primavera (x 2), 06 Fly 150
Joined: 26 Sep 2013
Posts: 5481
Location: So Cal
Thu Sep 10, 2020 7:36 am quote
Lynn, its good to get smart about how SI carbs work and how to fine tune the jetting.

But this is a Gick-built engine, right?

Jon knows his stuff. He bench tested it and supplied you with jets suited to the build.

If thereís a specific running issue youíre having, Iíd give him a shout. Iím sure heíd be happy to help you sort it out.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Thu Sep 10, 2020 9:13 am quote
Kowalski wrote:
That is a BE-3 mixing tube. You can tell because it has 4 holes in the midrange section (more air/leaner mix) where the E-3 only has 2 (less air/richer mix).

The mixture screw is used to fine tune the idle jet. One way to tell if you have the right idle jet is if the mixture screw is about 2 1/2 turns out when properly adjusted.

As far as selecting the components for the main stack, I am still figuring that out myself. They are all interrelated and there is some overlap with the idle jet to consider too. The biggest enigma is how the air tube and the mixing tube interrelate. It seems to me that the air tube isn't that critical because the air still has to pass through the mixing tube. Nonetheless, people put a lot of emphasis on air tube size, so I'm probably missing something. In any event, as I said before, your 160/BE-3/118 is pretty typical for a 177 cylinder kit. Beyond that, I will have to defer to Jack and the other jetting gurus here.

You are right that yours is not the best air filter. The easiest thing to do is replace it with a Piaggio air filter that comes with holes in the "heart section" already drilled. That is supposed to flow more air and may require a larger main jet to compensate.
Thankyou for the insight, I did kind of figure the pilot jet is directly related to the mixture screw, not enough room to adjust with the mixture screw and a larger pilot jet is needed, thats kind of the only technology that works on all makes of carbed bikes, I have done my own jetting on Harley's kawasaki's and british bikes. Its this main stack that has me intrigued , I will have to do more research , gotta be something out there.
Yes I agree on the air cleaner, I will be leaving it off the carb.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Thu Sep 10, 2020 9:15 am quote
SoCalGuy wrote:
Lynn, its good to get smart about how SI carbs work and how to fine tune the jetting.

But this is a Gick-built engine, right?

Jon knows his stuff. He bench tested it and supplied you with jets suited to the build.

If thereís a specific running issue youíre having, Iíd give him a shout. Iím sure heíd be happy to help you sort it out.
Yes it was built by Gick, but that was back in 2013 so time to pull the rip cord , he has other things to do. Its just like the welding and the painting, had to learn it to understand before I could do it myself, thats just me.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Thu Sep 10, 2020 10:03 am quote
During my research today I came across this video on youtube.


https://www.youtube.com/watch?v=06m3450pTps&list=PL7SWwzc0TBDYXhXvfkw6UQSaoR5m9l5hN&index=55&t=0s
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Fri Sep 11, 2020 11:11 am quote
Question: is there going to be much noticeable difference between a 55/120 and a 50/120 idle jet? At what number is there a big noticeable differnce?
Thanks
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Fri Sep 11, 2020 2:05 pm quote
I got around to adjusting my shifter cables today, used Voodoos bundgie cable and vise grip method. Shifts much better.
I also pulled the crappy blue mesh air filter out of the carb, amazing improvement, actually hit 50 mph and seemed to want to keep going but Iím respecting the breakin period. Much easier to keep it off wot now.
Hooked
1970 180 Rally, 1980 P150X and P200E
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Location: George, South Africa
Sun Sep 13, 2020 1:55 am quote
While you are at it, drill out the section in the air filter directly above the jets. Use a 5mm and 8mm drill. That also makes a big improvement.
Ossessionato
1963 VBB2T
Joined: 07 Nov 2012
Posts: 2284

Sun Sep 13, 2020 4:59 am quote
danie wrote:
While you are at it, drill out the section in the air filter directly above the jets. Use a 5mm and 8mm drill. That also makes a big improvement.
I had a blue fiber air filter in there , I removed the air filter completely. I noticed an improvement immediately.
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