How to: Clean & Overhaul Seca II Carburetors (BDS26 carbs)

Maintenance, repair, troubleshooting, etc.
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radare
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Mon Jan 30, 2012 1:51 pm

I finally received all of the parts from Bike Bandit and so today I've sat down to assemble the carburetors.

I will reference "silicone" throughout this post. What I mean by silicone is a silicone based protectant. I am using Black magic's Tire Shine. I use it on o-rings and seals to help assist in assembly:
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Starting with a clean bare carb body, the first step will be to install the butterfly shafts.
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I am using new butterfly shaft seals. They are Yamaha P/N 256-14997-00.
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Coat the new seals with silicone protectant and slide them in place. The proper orientation is with the lip facing outward:
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This is the correct sequence for installing the butterfly and shaft. This is the #4 carburetor (rightmost cylinder):
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Lubricate the shaft with silicone protectant, slide the spring onto it and slide it through the seal and into the carburetor. Be careful not to scratch the carb body when sliding in the butterfly shaft. Fit the plastic spacer and clip in the c-clip. When properly installed, this is the correct orientation for the spring:
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Slide the brass butterfly into position and carefully set it into the carburetor. Be very careful; the butterfly is not round and can wedge itself into the body:
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Coat NEW screws with threadlock blue and fit them. The screws are stainless steel, M3 and are 5mm long. I found them at my local Ace Hardware. The threadlocker is used to keep the screws from backing out and being sucked into the engine:
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With the butterfly installed, turn your attention to the fuel deliver side. Begin by installing the valve seat:
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Install a new o-ring and coat it with silicone protectant. Press the seat into the hole in the carb body and fit the screw. Tight is tight-enough when tightening the screw:
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Thread in the pilot jet and seat it (I'm using a new #20 jet):
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Here is the proper sequency for the main jet and holder:
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Coat the new o-ring with protectant and install the main jet holder. Tighten it lightly using an 8mm wrench. Thread in and seat the main jet (I'm using a new #100 jet (sized for 5k feet elevation)):
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This is the correct sequence for the emulsion tube:
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Slide the tube in from the topside of the carb (where the diaphragm sits) and align it with the tab in the carb body. Fit the washer and then thread in the acorn nut. Lightly tighten the acorn nut (they are very soft and known to twist off).:
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Slide in a NEW needle valve and fit the floats. Slide the float pivot pin into place:
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Fit a new float-bowl gasket and lightly coat it with protectant:
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Install the float bowl and tighten it firmly:
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Prepare the slide/diaphragm for installation by folding the diaphragm back:
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Slide the slide into place and press the diaphragm seal into it's channel. Keeping it in this channel may be tough and will likey require more than two sets of hands:
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Fit the spring and install the top cap. Tighten the screws securely:
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Here is the proper sequence for the enrichment circuit plunger:
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Lubricate the plunger and it's sealing surface with protectant and slide it into place. Fit the spring and then the securing nut. Lightly tighten the nut:
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Here is the proper sequency for the pilot needle screw:
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Lubricate the o-ring with protectant and install the needle. Thread the pilot screw all the way in and lightly seat it. Back it out the number of turns you noted on disassembly.

That's one carb assembled (the rightmost or number 4 carb):
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Continue assembly with the other three carburetors in like manner. Assembly of the carb bank will follow shortly.
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1Oldman
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Mon Jan 30, 2012 2:57 pm

Am curious as to why you didn't set your float heights at this time? Where did you end up getting the o-rings for the main jet? Great write up, beautiful job. :kudos:
Better to be over the hill than under it.
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radare
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Mon Jan 30, 2012 3:00 pm

1Oldman wrote:Am curious as to why you didn't set your float heights at this time? Great write up, beautiful job. :kudos:
I will be. I prefer to set them wet and so I'll do the assembly instead of a carb at a time. I should probably add the procedure for bench setting the float height though and then add the wet procedure. Good advice 1Oldman!
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radare
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Mon Jan 30, 2012 11:51 pm

When assembling the remaining carbs, here's the appropriate sequence and alignment for installing the butterfly shafts:

Carb #3:
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Carb #2:
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Carb #1:
Image
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radare
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Mon Jan 30, 2012 11:55 pm

Continuing with assembling the carburetors onto the rack.

Begin by assembling the fuel-rail connector tubes. These supply fuel between the four carbs. Fit a new seal to each side of the tubes. The seals are P/N 3EN-14997-00. You will need 6 of them for the assembly. Fit the new seals onto the brass tubes:
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Coat the seals with protectant and connect the #4 and #3 carburetors:
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When pressing the carburetors together, don't forget to install the vent tubes. I forgot them and had to add them after the fact:
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Carefully flip the carbs over and install the throttle spring:
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Install the upper brace and it's four screws. This will keep the carbs from pulling apart:
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Repeat the same process with the #1 and #2 carbs:
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Fit new seals to the fuel supply tube:
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And install it to one of the carb pairs:
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Fit the two pairs of carbs together and install the upper brace to hold them together:
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Flip the carb assembly on it's top and install the lower brace. Before securing the brace, position the fuel supply connector so that it is between the #2 and #3 carbs as shown:
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Install the throttle synch spring between the #2 and #3 carbs:
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Lubricate the enrichment rod with protectant and slide it in place. Position each of the actuator arms in place as the rod slides through and secure them with their lock screws:
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Install the enrichment knob bracket:
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Lay the carb assembly on the fuel bowls and install the throttle cable stop:
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Finish by laying the carb assembly on it's top and installing the throttle stop screw:
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There are a couple post-assembly adjustments that are recommended: Setting the float height and bench-syncing. I'll cover these shortly. Stay tuned!
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radare
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Fri Feb 03, 2012 10:20 am

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radare
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Thu Feb 16, 2012 12:47 am

The replacement main jet o-rings are Yamaha P/N 1AE-14227-00. You'll need 4 of them and they sell for $4 each, plus shipping :o.

Before installing them, I measured them with calipers. Here's the dimensions:
Image

They are o-rings with a square cross section. I do not believe that this square cross section is absolutely needed and a standard o-ring should work fine. Using these measurements, I've found a cheap alternative that sould work well.

McMaster Carr P/N 9262K511 which sells for $5.00 for a bag of 100 o-rings.

If you don't want to give Yamaha $20 or more for these little o-rings, I'd highly recommend picking up a pack of 100 from McMaster Carr and keeping them on your shelf for future use.
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radare
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Thu Feb 16, 2012 1:19 am

The dimensions for the pilot screw o-ring are as follows:

Image

These O-rings are unavailable individually from Yamaha and you have to buy the pilot screw assembly for $6 each plus shipping.

McMaster Carr sells an eqivalent o-ring, P/N 9262k441 for $12 for a bag of 100.
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1Oldman
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Thu Feb 16, 2012 1:21 am

radare wrote:The replacement main jet o-rings are Yamaha P/N 1AE-14227-00. You'll need 4 of them and they sell for $4 each, plus shipping :o.

Before installing them, I measured them with calipers. Here's the dimensions:
Image

They are o-rings with a square cross section. I do not believe that this square cross section is absolutely needed and a standard o-ring should work fine. Using these measurements, I've found a cheap alternative that sould work well.

McMaster CARR P/N 9262K511 which sells for $4.50 for 100 o-rings.

If you don't want to give Yamaha $20 or more for these little o-rings, I'd highly recommend picking up a pack of 100 from McMaster Carr and keeping them on your shelf for future use.
Or "C" you can buy an o-ring kit and have all you'll ever need.
http://www.amazon.com/O-RING-ASSORTMENT ... 734&sr=8-1
Better to be over the hill than under it.
User avatar
radare
Site Founder
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Posts: 8638
Joined: Mon Nov 07, 2011 12:42 pm
Region:: Rocky Mountains
Motorcycles:: '92 XJR600, '92 Seca II
Location: Denver, CO
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Mon Feb 27, 2012 10:07 am

Routine Replacement Parts Needed for Carb Cleaning:

Full Disassembly:
If you are going to do a full disassembly and cleaning, which entails removing the butterflies, seperating the carburetors from the rail and soaking the disassembled parts in a chemical cleaner, you should purchase and replace the following (this is the type of cleaning you'd do on carburetors that had sat for a few years or if the bike had carburetor related running issues):

Partial Disassembly (Routine Cleaning):
If you are going to partially disassemble the carburetor to clean out the bowl, jets and enrichment circuit (i.e. spray carb cleaner through the jets and circuit), but are not going to remove the butterflies or seperate the carburetors from the rail, you should purchase and replace the following (this is a typical maintenance style cleaning):
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