Honda OEM carb info collection

[mousewheels]

Before the spring rush of carb questions, We will collect info members have captured in the past as well as new info. Then update the 'wiki as applicable.

--
Some info may be for fun, or to stimulate discussion First topic is one of those.

• Why did some carb bowls support two locations for the bystarter orifice?
• What would trigger Keihin to use one or the other?
• Do you have a carb bowl with the orfice installed in the lower casting location?
• Why did the SB50 move the bystarter orifice lower?

-- Fuel bowls and bystarter orifice placement --
Member lakehouse has been working on an Elite E (SB50) start&run issue. As part of troubleshooting, we got into a question. Is the fuel level in the carb bowl high enough to fill the auxiliary fuel bowl supplying the bystarter? Lakehouse reports a much different bystarter orifice location from models at mousewheels place. Here's photos and measurements:

1) Honda Express carb -- casting shows two possible locations for the bystarter orifice, on this carb, the higher one is used by Keihin.

Honda_Express_Bystarter_Fuel_orifice_location_1.JPG (33.1 KiB) Viewed 11845 times

Bystarter location from bottom of bowl ~ 0.75"

Honda_Express_Bystarter_Fuel_orifice_location_2.JPG (32.47 KiB) Viewed 11845 times

2) Honda Aero 50 carb (85-87 series) -- casting shows two possible locations for the bystarter orifice. Again, the upper location was chosen by Keihin.

Honda_Aero_Bystarter_Fuel_Orifice_location_1.JPG (33.16 KiB) Viewed 11845 times

Bystarter location from bottom of bowl ~ 0.72"

Honda_Aero_Bystarter_Fuel_Orifice_location_2.JPG (28.64 KiB) Viewed 11845 times

Honda Spree carb (unknown year) -- casting shows only one possible location

Honda_Spree_Bystarter_orifice_location_1.JPG (37.6 KiB) Viewed 11845 times

Bystarter location from bottom of bowl - 0.55 + 0.10 step up = 0.65"(see pic above, there is a raised floor on the bystarter orifice side of bowl)

Honda_Spree_Bystarter_orifice_location_2.JPG (33.98 KiB) Viewed 11845 times

Honda SB50 carb (member lakehouse provideds info) --
"Overall, the very inside bottom of the fuel bowl to the opening edge of the jet totals out to be 0.280". That's much different from the sister Spree bowl."

Also -- TODO: Check out 94-2001 Elite SA50...

[mousewheels]

-- Bystarter orifice size --
This is a small orifice and is a fuel metering orifice. A few have drilled out the orifice to un-plug, causing a too rich when cold issue.

An exact measurement is not yet made. However as a reference point a 0.010 wire will pass through, and useful to find a wire for cleaning. wiki link

[mousewheels]

-- Dirty float seats
If the seat is irregular, a new float needle may still seep or leak. Here's pics showing dirty seats.

Carbs_overview.jpg (161.19 KiB) Viewed 11839 times

Pic below illustrates the portion of contact between the float needle and seat

Float_needle_and_seat_a.jpg (23.33 KiB) Viewed 11835 times

From left to right - these close ups match the carbs above:

Float_seat_close_up_a.jpg (85.84 KiB) Viewed 11839 times

-- Resurfacing float seats
A popular method quoted is to use a Q-tip and polishing compound. Some use a sharpened wood dowel. What's working for you?

There is an aftermarket tool (note "Made in USA") tool being sold for Keihin carbs. I don't know that it fits our PA carbs, and at $100+ am not likely to 'buy to try'. Yet the idea sounds good. Anyone interested in making a seat reface tool? I'd pleased to pass clean seats to the microscope to present results here.

Keihin_seat_cutter_2.JPG (59.14 KiB) Viewed 11838 times

[ped]

thank you for posting this carb info. very helpful.

[mousewheels]

thank you for posting this carb info. very helpful.

Thanks ped



Carb Body changes:
Early Honda Scooters have rounded venture top/bottom. Later models changed to a 'v' shaped section at bottom and flattened out the top.

For the Spree, this change occurred in the 1986 model. That change led me to look at throttle needle and emulsion tube part numbers to see if a change was made there. None required.

Spree_Carb_Body_Change.jpg (55.05 KiB) Viewed 11788 times

Throttle Needle & Emulsion Tubes - Spree, Elite E
Part numbers varied over the years of Spree production and on to the similar Elite E. Note there were unique part numbers for 1984-86 restricted Sprees.

-- Part identification
It may be helpful to members (the ones with *boxes of mixed Spree carb parts* ) to collect identification information.

• Needles have unique numbers we can use to id them.
• Emulsion tubes have no markings, but may differ by location, size or number of air holes.

Spree_Elite_E_Needle_Sets.JPG (43.21 KiB) Viewed 11788 times

[mousewheels]

Aftermarket Jets
Main jets fitting Gurtner carbs also fit Keihin PA carbs. They are available in sizes to 118.

Finish is not as smooth as Keihin, but they are inexpensive. This Naraku set of a dozen (incrementing by '2' from 74 to 96) was just under $23 before shipping at External link to racingplanetusa.com

Gurtner_Jets_2_sm.jpg (76.18 KiB) Viewed 11777 times

[mousewheels]

Bystarter clone comparison
Here is one more clone to compare. To allow direct comparison photo positioning was controlled.

Summary -
Neither clone is same as OEM

• Clone 1's fuel metering needle differs in length and taper.
• Clone 2 is too short when cold, and when hot extended only to about 0.40" at the air valve. Note 0.42" is the cold position for the OEM bystarter. Clone 2 will always be in the enrich state

-- Photos
Reference OEM bystarter: Aero 50
Clone 1 is from Wincycles. It is a couple years old, current model may be different
Clone 2 is unknown origin

Bystarter_Compare_1..jpg (110.79 KiB) Viewed 11703 times

Bystater_Compare_2.jpg (75.52 KiB) Viewed 11703 times

[mousewheels]

Aftermarket carb rebuild kits
Buyer beware: Watch for components which differ from OEM

Kit on the left:

• Longer float needle and a float with a metal hinge.
• User may need to tweak the float level by bending a tab on the hinge

Kit on the right:

• Main jet is a mushroom head (incorrect part)
• Bowl gasket is incorrect
• Float valve is metal tipped, and with use will wear the softer carb body

[mousewheels]

-- Bystarter closing - time lapse --
This is an AF16 bystarter connected to a 12v dc bench supply. It displays ~20x faster than actual speed, frames were taken 1 every 10 seconds.

-- Over travel
Normally, after hitting bottom, a spring driving the air valve takes up the extra extension. However in the photo sequence, the bystarter is not clamped down. Thus after the air valve hits bottom, the bystarter body is pushed out of the carb.

[Wheelman-111]

Greetings:

All hail Mr. Mouse, and quite possibly the most comprehensive and helpful post EVER! Cool time lapse, too. You must really, really love these scooters and your brother enthusiasts. Wow!
I am speechless except for the following question: (Spoiler alert - JOKE!!)
You don't have a girlfriend, to you?

Sinceriously, awesome post Dawg. You're the best.

[mousewheels]

Thanks Wheelman!

I am speechless except for the following question: (Spoiler alert - JOKE!!)
You don't have a girlfriend, to you?

Mrs Mouse would stop saying 'cheese'

[mousewheels]

Watching the bystarter makes a person wonder how expanding wax creates the long extension.

For example, a candle burning has wax level with the sides while burning, and only a slight depression once the wax cools.

-- Pic from our 'wiki' of a disassembled bystarter showing the actuator

Bystarter_Actuator_assembly.jpg (37.99 KiB) Viewed 11590 times

-- Annotated Cutaway

Bystarter_actuator.jpg (97.5 KiB) Viewed 11590 times

[GSX1400]

Terrific topic!
In my favourites. Thanks for the research and all the typing.

[mousewheels]

-- Clone bystarter seal --
OEM bystarters have no seal between the brass air valve and fuel needle. Many Clones do.

An issue may arise from the clone and it's seal. The seal may prevent the bystarter from fully closing. The leaves some of the air path flowing air *but* the fuel section is sealed. This may cause the engine to run lean or die when the bystarter warms up.

The photo below shows the OEM bystarter has a recess between the needle and air valve sides. The clone has a recess, but it's nearly filled by the rubber seal

Bystarter_front_view.jpg (75.8 KiB) Viewed 11510 times

An issue with this clone is the rubber seal contacts the bystarter fuel pickup tube before the air valve is closed.

Bystarter_Clone_with_seal.JPG (61.92 KiB) Viewed 11510 times

With the clone's seal removed, the air valve can be observed fully closed

Bystarter_Clone_after_seal_removed.JPG (47.78 KiB) Viewed 11510 times

[GSX1400]

That could explain a question or two I was asking...
http://www.hondaspree.net/phpBB3/viewto ... &start=120

Question :
When doing the air pressure test as per the Honda Shop Manual (uploaded here : many thanks for putting this online guys) when the engine is hot (bystarter completly closed), should it be air tight or what is an acceptable leak when doing the pressure test?