Installing a Carb Cap Kit

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cfairweather
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Installing a Carb Cap Kit

#1

Post by cfairweather »

Roger volunteered his great looking carbs caps for a test case using my new carb cap kit. The molds were designed using FreeCAD and I printed them using a Form 3+ SLA resin printer. I used 10K Rigid Resin for the mold and then used a plastic injection machine to inject acetal (POM). I am confident that Honda used Acetal for the original button because it is very tough plastic and the smell of a heated original smells exactly like acetal. After 40+ years, even this great plastic dries up and cracks. I believe my buttons will work as well as the originals. Old Fogey (John) has provided me with some helpful information and I greatly appreciate his help.

The kit will include most of the things you need to do the job and it will hopefully cost you about $50.00. I know that some probably think I am crazy for making them because it cost about $7500.00 for the equipment. Considering a mold from a plastic injection company would cost $5000.00 to $10,000.00, I think I did pretty good; however, I don't expect to recover my investment selling buttons. With the system that I have, I can make other parts.

Ok, back to the project...
Roger must have used a metal detector to find these carb caps :). They are currently getting a bath, so we will have to wait a day or so to get started on this adventure. I want to go through all the steps required to replace the buttons and use this thread to show people how to do it. Maybe some future expert can create a video. The kit will include four buttons, four seals, four 1mm nylon washers for the slide shaft and a button installation tool, You may question why include the four nylon washers and to make a long story short, install them because there is no downside in doing so. The slide will open completely with these installed and they will prevent metal-on-metal contact. More on these later but for now, let's take a good look at our carb tops:
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Old Fogey
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Re: Installing a Carb Cap Kit

#2

Post by Old Fogey »

Yep, I've had too many sets in for rebuild that look like that. With the owner insisting 'got to have those 'cos they are the originals!' to find out that the bike has been sitting outside with no cover for 40 years.
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robin1731
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Re: Installing a Carb Cap Kit

#3

Post by robin1731 »

Old Fogey wrote: Sun Feb 26, 2023 6:37 am Yep, I've had too many sets in for rebuild that look like that. With the owner insisting 'got to have those 'cos they are the originals!' to find out that the bike has been sitting outside with no cover for 40 years.
Then they expect you to make them perfect. I've had a few too.
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
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5speed
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Re: Installing a Carb Cap Kit

#4

Post by 5speed »

tagging...
1982 1100 standard. (sold)
1986 Yamaha FJ1200
2000 Yamaha Roadstar
1976 GoldWing. running but not on the road
1978 Goldwing. future cafe project.
2019 Can-Am ryker (boss's new ride)

2002 Shadow American Classic(sold)
1983 Shadow 500. (sold)
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Old Fogey
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Re: Installing a Carb Cap Kit

#5

Post by Old Fogey »

I had one guy practically in tears when I told him that his were basically scrap. I told him 'look, I have a set of 755As like yours, just finished that I can sell you'. 'But but but, they won't be original and I want the bike to be original'
'Listen if you don't tell anyone, I also will keep quiet! No-one will know' Eventually I did get through to him and he bought them. Something around two years later he came to me for a set of belts, which I though may be for that bike.
Nope, that bike had to be scrapped because the frame was rotten and the engine full of water.
Surprise, surprise.
And then, of course, he finds that 755As are not the right ones for the 78 he just bought (you know, the one with snapped belts!).
"Impossible Is Just a Level of Difficulty!..."
If I'd wanted you to understand, I would have explained it better! (Johann Cruyff)
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cfairweather
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Re: Installing a Carb Cap Kit

#6

Post by cfairweather »

Step 1: Clean the carbs and remove the old buttons. I am sure everyone has their own way of taking these out but I used a lathe to get the bulk of the plastic out. Then I used a small pair of diagonal cutters to snip the remainder of the ring.
Once it is cut, you can sometimes easily pull out the remainder. If I get desperate, I use a heat gun to melt the plastic so I can then use a craft knife to cut the ring, then it will pull out. I am sure someone else has a better way.
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Step 2: Polish the caps and the shaft hole. It is best to do the polishing before you install the caps (if desired). I usually make them look like chrome, but just did the minimum amount on these. Polishing the shaft hole is highly recommended before you install the cap. I use a Dremel tool with a small buffing wheel on it but if you choose this method, be careful not to have any metal to metal contact. The safest way to get the brass shinny is to put a bit of Mothers Metal Polish (or some similar product) on a Q-Tip and lightly coat the shaft. Then get a clean micro fiber cloth and twist it into the hole. No matter how you polish this hole, do a very good job getting it perfectly clean and shinny. These are now prepared for buttons:
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Last edited by cfairweather on Wed Mar 01, 2023 10:47 pm, edited 1 time in total.
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Old Fogey
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Re: Installing a Carb Cap Kit

#7

Post by Old Fogey »

You will find on many of the caps that the groove under the lip has a dried up something (never been too sure whether is the remains of some sealant, that's the most likely, or possibly fuel residue. Whatever it is, it needs to be cleaned out thoughly.
"Impossible Is Just a Level of Difficulty!..."
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cfairweather
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Re: Installing a Carb Cap Kit

#8

Post by cfairweather »

I am glad Roger sent me his caps as this has helped convince me to increase the diameter of my buttons. One of his caps had a larger rim diameter and my button was too easy to press in. I did have a slightly larger size that I installed in that cap, so I was able to complete his set. Unfortunately, I will have to go back to the original style seal with a larger button. Back to the instructions…

Step 3. Polish the slide shaft using Mothers Metal Polish or another similar polish. I use a micro fiber cloth and push a corner of the cloth into the well and then turn the slide. After that consider installing the optional nylon washers. There is a wide side of the washer and I recommend installing the wider side face down. The washer is to prevent metal-to-metal contact if the rod is unable to be stopped by the button. If the depth of the shaft hole to the bottom of the button exceeds about 44.80 mm, the slide will be stopped by the washer instead of the button. Normally, the button will stop the slide, but there have been numerous cases where slides have cracked due to due to metal-to-metal contact. This could be because the button cracked or totally failed. If the slide shaft depth to the bottom of the button is too deep and the rod is unable to contact the button, you will also have metal-to-metal contact. The nylon washer is insurance and I actually prefer using it as a stop instead of the button because the load is spread across a larger area with the washer. I have determined the ideal depth of the shaft to the bottom of the button is about 44.70mm. If you have that depth, the washer and the button are probably going to make contact, which is ideal. The load is then spread across a larger area, the washer and the button. Also, installing the washer allows the slide to fully open, so I don't see any downside of using it. It is totally up to you if you want to use it or not.
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Step 4. Make sure the slide will operate very smoothly. You should be able to drop the slide into the cap and hear a thud with no resistant. Also make sure the tiny vacuum hole is open. Push a paperclip into the hole to insure it is open.

Step 5. Prepare arbor press area. Have everything you need arranged for easy access. See the picture below for ideas.
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Step 6. If you want to measure the hole with calipers, the size should be about 25.50mm. If you don't have calipers, place the button on top of the cap and see it the edge will go into the hole at least ¼ to 1/3 of the way. If not, use a craft knife and run the blade around the hole ONE time. Hold the knife at a 45 degree angle to create a bevel to make it easier to push the button into the hole. Then, place the button in the hole and recheck to see if it will go in ¼ to 1/3 of the way. If not, trim again, but only one time around. It does not take much at all to make the hole big enough. Old Fogey gave me this tip of using the craft knife and it works great.
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Step 7. Now you are ready to add epoxy to the groove. Only a small amount of epoxy is needed. Do not put too much or you will plug the vacuum hole. Mix only enough JB Weld Plastic Bonder for one button at a time. You only need enough to fill the groove. Use a toothpick to mix the epoxy and then work a small amount into the groove. Then use rubber gloves and run your finger around the groove to remove excess epoxy. Go to the next step quickly and get the button pushed in because we want the epoxy to settle around the button. Nothing sticks very well to acetal, but this epoxy does pretty good. It will definitely create a seal and help hold it in place. Old Fogey prefers using Gorilla glue but if you choose to use that stuff, be very careful because it expands a lot. I found that epoxy bonds better to acetal but it is your choice. Install the seal.
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Step 8. Make sure the button is even all the way around as it sits in the hole. Then place the button press tool on top of the button. Use the curved edge for the first press. The curved edge allows the button to give a little as you press it in. Once the button is in, turn the press tool over and press again to make sure it is fully seated. Wipe off any excess epoxy if it comes out the top. Then, verify the vacuum hole is open. One way to do this is to inset a finger over the hole inside the cap and then suck air through the shaft hole and then remove your finger to see if the pressure changes. You could use a vacuum pump too. I also run a paperclip through the hole and if any epoxy is on the paperclip. If so, you used too much epoxy. You may be ok, but double check to see if air freely flows. If it is blocked, simply knock out the button using a large flat head punch and do the procedure over again. It is easy to clean up the mess and start over so don’t get upset, you will be fine. If you damage a cap, I will have individual caps available for about $10.00 each.
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Step 9. Place the cap on a flat surface, right side up, so the epoxy can settle and cure.

Step 10. Repeat for the rest of the caps.
Last edited by cfairweather on Thu Mar 02, 2023 2:19 pm, edited 2 times in total.
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Re: Installing a Carb Cap Kit

#9

Post by Fred Camper »

Love the details, yet hope to never have to do this. But getting 50 years out of a plastic button says someday...
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1977 GL1000 BADDOG (April 2012 BOTM)
1976 LTD - '993 LTD...and so it begins'

You should remember that it's peace of mind you're after and not just fixing the machine. R.Pirsig
cfairweather
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Re: Installing a Carb Cap Kit

#10

Post by cfairweather »

Final results:
20230227_114059.jpg
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Re: Installing a Carb Cap Kit

#11

Post by CYBORG »

Looks great
1978 custom GL1000
1977 custom with 1200 engine
1985 gl1200
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robin1731
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Re: Installing a Carb Cap Kit

#12

Post by robin1731 »

CYBORG wrote: Tue Feb 28, 2023 10:15 pmLooks great
I agree
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
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Fred Camper
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Re: Installing a Carb Cap Kit

#13

Post by Fred Camper »

Ready for shipment. Nice to have the trial done.
Proud member of the NGW Cartel (Rochester MI)
1977 GL1000 BADDOG (April 2012 BOTM)
1976 LTD - '993 LTD...and so it begins'

You should remember that it's peace of mind you're after and not just fixing the machine. R.Pirsig
cfairweather
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Re: Installing a Carb Cap Kit

#14

Post by cfairweather »

Almost, but the trial revealed I need a slightly bigger diameter. I have fine tuned my design and made a new mold today, but I need to make some buttons with it and install them into a few caps. Old Fogey is sending me his last button that came from Pistol Pete, so I can compare it to my design. I may make changes after I see it, but I think it is almost ready to go as is. I have based my design on the original with some improvements. For example, most of the originals crack where the plastic is very thin. The plastic on mine is thicker at that same point. I will cut one in half and show everyone what I am talking about tomorrow if I have time. Also, I need to make sealing rings. I made the last ones on my 3D resin printer but I may create a mold and inject these or come up with a better way to make them. They will be available soon. Thanks for your interest in this project.
cfairweather
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Re: Installing a Carb Cap Kit

#15

Post by cfairweather »

On my last post, I mentioned that I tried to improve on the original design. Take a close look at the picture below. Compare the thickness of the original button to my button (the white one). Notice the original has a thin point at the corner of the cavity and the rounded part of the button top. Compare that spot with my button and you will notice the plastic is a bit thicker. I did this by chamfering the edge of that corner and also by taking some of the curve out of the top side.
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Last edited by cfairweather on Wed Mar 01, 2023 10:53 pm, edited 1 time in total.
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