Carb Cap Crisis

[Dr. Frankenstein]

I was putting the carb to my '79 GL1000 back together today and noticed this:
DSCN2024 by Dr. Frankenstein1, on Flickr

The opening you see is me putting a little pressure on the button to make it rise, and the red dot is so I can easily identify the faulty cap - here it is without the slight pressure on it - it's a pretty clean crack:
DSCN2026 by Dr. Frankenstein1, on Flickr

Is there a fix for this that doesn't take a lathe and other equipment I don't have...? I read in here that Pistol Pete has died, and his son may have shut down the rest of his former services including button replacement...I also read that some epoxy can solve the problem too.

[pidjones]

Honest, I'd try super glue making sure not to get any in the port.

[Dr. Frankenstein]

Would that work? I'd think the vacuum pressure would blow it out or something...

So epoxy is a viable option?

[cfairweather]

You need new buttons. I just sent you a PM.

[pidjones]

Vacuum pulls them down. They don't have to be super-strong, but the vent hole under them needs to be free. I would really trust a good super glue over epoxy for this. I have some spares, but they really should be matched to their pistons.

[Sidecar Bob]

I wouldn't trust any glue for that. And unless you have the tooling for installing the new buttons doing that is questionable too.

Here's what I did. 11 years later the carbs are still good so I'd call it a permanent fix.
https://www.ngwclub.com/forum/viewtopic ... 87#p437087

[Dr. Frankenstein]

Actually, I sent them off to CFairweather - and they came back GREAT! This guy knows his stuff:

From this - -
DSCN2026 by Dr. Frankenstein1, on Flickr

To THIS...!
DSCN2035 by Dr. Frankenstein1, on Flickr
(The 'white' on the cap there in the lower left is just light reflecting off the cap).

DSCN2037 by Dr. Frankenstein1, on Flickr

DSCN2039 by Dr. Frankenstein1, on Flickr

He does some beautiful work! The pics don't do it justice.

[Whiskerfish]

WOW!!

[Whiskerfish]

The one time I saw one of those caps actually fail was due to a backfire. Popped that sucker right off. I suspect that is how most get cracked

[gltriker]

The one time I saw one of those caps actually fail was due to a backfire. Popped that sucker right off. I suspect that is how most get cracked

agreed!
I spotted this *odd looking piece of something* on my garage floor in early April, 2018. Didn't know what it was or where it may have come from and left it laying there. Looked at it again and decided to set it on trike's right side floorboard.
Backing up now,
Trike had been hibernating for at least 3 months since my last attempt to start its engine on one of those unusually brief warm days, mid-Winter. May have been on New Years Day. The attempt was cut short at my wife's insistence. " It's too cold! "
The engine had been sputtering while cranking and I twisted the throttle open just to make some noise for her benefit. The engine snorted and popped several times. I felt bad that I had been so unthoughtful to the very cold engine.
Turned the key switch off, turned the fuel valve OFF and left it to resume hibernating.

20180421_165740_resized.jpg

April, 2018, I sat down beside trike to check its engine oil level before starting the engine . As you will note on the top of number 1 carburetor vacuum piston cap, something is amiss. hmmmmmm? I gradually recalled the snorting and popping engine event 3 months earlier and wondered if that *odd looking piece of something* on the right side floorboard actually belonged in that opening. Yep. fit perfectly.

20180421_165917_resized.jpg

Fortunately, the vacuum piston, itself, wasn't damaged!

[Dr. Frankenstein]

Yes, if I can get the floats set on this '78 here (with the new caps) , I want to go over the carbs on my '75 tomorrow; I still haven't explored my Really Bad Gas Mileage on the '75 yet, and I'm hoping I haven't popped one.

[redglbx]

My .02,

I used brass plumbing caps , 3/4” I think and used 2 part epoxy to glue them in place and as mentioned above care must be taken not to slop the epoxy around. Mine have been in for 20+ years, no problem!

That said, it’s not as simple as just gluing the new brass caps in because the caps control the slide travel by how high the slide goes, by the slide center pins hitting the inside the caps, and that’s what I believe is what breaks the nylon caps when the slide pins get slammed into the nylon caps probably due to backfires.

You want the slide to fully go up into the caps w/o the diaphragm hitting the inside the cap, you want the pin to stop the slide just short of the cap top. On mine I took some time and machined the copper plumbing caps to give the same exact travel for each cap & slide. That’s what I did ! Works great !

[Sidecar Bob]

Keihin designed the slides so that the shafts hit the inside of the cap before the skirts hit the insides of the caps and break and I think they intended the plastic caps to be something softer than the aluminum for the shafts to hit. (Note that GL1100 and CX/GL500/650 carbs have plastic bumpers in the ends of the shafts so that their caps don't need the buttons).
I believe that the shafts bounce against the buttons steadily at wider throttle openings. Over time exposure to UV in sunlight, heat from the engine and possibly even exposure to solvents &c used for cleaning causes the plastic that the buttons are made of become brittle and the shafts constantly tapping against them eventually cause them to develop tiny cracks.
At that point a real backfire (where it fires back through the carbs, not an afterfire in the exhaust) could cause the shaft to hit hard enough to break the cap but even without any such event the constant tapping can eventually cause the tiny cracks to develop into bigger ones and eventually break the cap completely.

In my case there was no backfire involved. The bike was running well and suddenly ran poorly. There had been a lot of talk about the buttons breaking on the forum at the time so I looked at my caps and found that the button on #1 was badly cracked and the others didn't look good. I found some washers that were a perfect fit around the bumps on the buttons and epoxied them on and epoxied nickles over them to cover the tops of the buttons. It looked nice but eventually they came off. I re-glued or replaced several of them over a couple of years and I do not recall any backfires.
In at least one case I was on the way to work, moving at a fairly steady pace and it suddenly started running rough. When I stopped for fuel near work I noticed that the nickle and part of the button was missing. When I got to work I put a couple of layers of foil duct tape over it to keep dirt out and it ran almost normally on the way home. I believe the epoxy just wasn't up to the constant tapping.
Shortly after that forum member kedanno posted that he had epoxied in freeze plugs to replace his. The last time he posted on the forum he still hadn't run his and that was 2014 so we'll probably never know whether the epoxy held but I didn't trust it so I used little bolts to fasten mine and only used epoxy to fill the cracks around the freeze plugs.

My measurements indicated that there was less than 1mm between the skirt and the cap when the shaft hit the original button and I had some HDPE sheet on hand that was the right thickness to stop them at just about the same place so I added discs of HDPE inside the freeze plugs for the slides to bump against.

[pidjones]

Remember also that the carbs original design was for a car. I don't know if the original caps were modified for the GoldWing, but the first float bowls still had vestigial fuel pump cavities.

[Gowing]

Remember also that the carbs original design was for a car. I don't know if the original caps were modified for the GoldWing, but the first float bowls still a vestigial furl pump cavities.

1966 Honda 600 car motor. You are right pidjones!