Author Topic: Drilled out (welch?) plug in carb?  (Read 1079 times)

Offline TimS-Orby

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Drilled out (welch?) plug in carb?
« on: September 10, 2025, 02:37:53 PM »
Hi All,
I'm still tinkering away on my CB500k2. I'm about to swap out the US bars for the lower European type, to deal with the short cable issue we spoke about a while ago. I'm pretty sure I'll prefer the lower bars too.
However, this is about somethin' else!
I got a 'bargain' on good old Ebay. A complete carb assembly for my bike. I thought it was worth having a spare assembly in stock, especially as the inlets on my carbs are pretty chewed up.
All seemed well until i opened the float bowls. As per the photo below, it seems someone has drilled out on of the (welch?) brass plugs in one of the carbs, and replaced it with a screw! Yeah! Looks like they had a good old go at the other one in there too.
Hmm... does this render this carb useless? Can the plug be replaced? Will this foreign body actually work?

Other than that everything else with the carbs seems potentially good, and they are in much better shape than those currently on the bike, with that one exception!
Any advice much appreciated.
Regards,
Tim.

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Offline taysidedragon

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Re: Drilled out (welch?) plug in carb?
« Reply #1 on: September 10, 2025, 03:37:53 PM »
I would be concerned about how long that screw is. Does it crush or interfere with the jet underneath? Some investigation required.
Gareth

1977 CB400F
1965 T100SS

Offline TimS-Orby

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Re: Drilled out (welch?) plug in carb?
« Reply #2 on: September 10, 2025, 03:55:33 PM »
AFAIK there is no jet under there. From what I've read these plugs cap the end of airway drillings creating the internal passageways, drilled during manufacture. Although I may be wrong.
I've carefully removed the screw and the threaded parts has been cut down to around 4mm. Looks like the hole has been properly tapped, so that's something. I'm wondering about replacing the screw with a set screw, with maybe a spot of JB weld over the head of it just for good measure.
Not sure if that's a viable solution.
I suppose I should see how things look after a thorough clean and blow-out.
T
Edit: Perhaps I misunderstood... No, it's not interfering with the lower part of the pilot jet there.
« Last Edit: September 10, 2025, 03:57:52 PM by TimS-Orby »

Offline taysidedragon

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Re: Drilled out (welch?) plug in carb?
« Reply #3 on: September 10, 2025, 07:49:55 PM »
If the screw is not interfering with the jet or the float movement you could put it back in or use a short grub screw. Use some threadlock to stop it coming out.
Gareth

1977 CB400F
1965 T100SS

Offline Bryanj

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Re: Drilled out (welch?) plug in carb?
« Reply #4 on: September 10, 2025, 08:44:40 PM »
I agree, as long as it seals and interfeers with nothing its fine

Offline Murf

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Re: Drilled out (welch?) plug in carb?
« Reply #5 on: September 12, 2025, 11:16:28 PM »
I like it it’s doing the job,  it’s plugging up the hole.
As long as no air or fuel can get past it and it’s not blocking anything important, then I can’t see it is doing any harm.

I guess it’s just another example of POs interesting repairs😂
Could be worse they might have used chewing gum.

Offline K2-K6

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Re: Drilled out (welch?) plug in carb?
« Reply #6 on: September 13, 2025, 11:05:39 AM »
I guess it’s just another example of POs interesting repairs😂
Could be worse they might have used chewing gum.

Strangely enough ..... I started work in a summer job years ago for a small plant hire company, the owner of which plugged rusty fuel tank holes with just this and it is resistant to petrol  :) pretty effective and durable too.

He moved like and wore a hat like David Carrdine character in King fu .... one of my learning "grasshopper" moments in life  ;D

Offline deltarider

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Re: Drilled out (welch?) plug in carb?
« Reply #7 on: September 13, 2025, 11:48:17 AM »
I've heard this about soap.

Offline K2-K6

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Re: Drilled out (welch?) plug in carb?
« Reply #8 on: September 13, 2025, 12:10:40 PM »
Horrible to chew that though ... soap that is  :)

Offline Orcade-Ian

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Re: Drilled out (welch?) plug in carb?
« Reply #9 on: September 13, 2025, 01:50:02 PM »
The chap who delivers our heating oil, always has a bar of soap in the cab.  If a customer has a leaking tank, he rubs soap on the leak and it stops instantly.  We had a leak at the outlet joint on ours and I tried it and it worked.  I was then able to pump the tank nearly empty into an IBC, fix the leak and put the oil back in - all 800 litres of the precious stuff.

Ian

« Last Edit: September 13, 2025, 01:52:14 PM by Orcade-Ian »

Offline taysidedragon

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Re: Drilled out (welch?) plug in carb?
« Reply #10 on: September 13, 2025, 03:14:31 PM »
The chap who delivers our heating oil, always has a bar of soap in the cab.  If a customer has a leaking tank, he rubs soap on the leak and it stops instantly.  We had a leak at the outlet joint on ours and I tried it and it worked.  I was then able to pump the tank nearly empty into an IBC, fix the leak and put the oil back in - all 800 litres of the precious stuff.

Ian

Will Carb-olic soap work on carb leaks? 😂
Gareth

1977 CB400F
1965 T100SS

Offline Oddjob

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Re: Drilled out (welch?) plug in carb?
« Reply #11 on: September 13, 2025, 03:29:45 PM »
My doctor told me I needed more carbs in my diet but they hurt my teeth.
Kids in a the back seat cause accidents.
Accidents in the back seat cause kids.

Offline Orcade-Ian

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Re: Drilled out (welch?) plug in carb?
« Reply #12 on: September 13, 2025, 03:41:05 PM »
Wahey! Back on form Ken - was it you who stole Bob Monkhouse's Joke Book?  Keep 'em coming!

Ian

 

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