MTFCA Forum

So I got my fancy rebuilt motor back for my 1915 Canadian Touring, put it in, attached the carburetor and although it worked fine before, leaked like the dickens from the top of bowl and drain valve plug assembly. Figured likely a float or needle issue so I took it apart. All seemed well so I put it back together and it would not get tight. Turns out the threads on the carb were bad enough to destroy the threads on the plug and now the carb is useless. Is there a tool for chasing the carb threads or rethreading to a new size? Is there a fix for this?

What carburetor, (make, model...)?

... threads on the carb ...

Which threads?

...it would not get tight

What would not get tight?


Post pictures, please.

Holley NH Threads on bottom plug and bottom of carb where plug goes in no good....

Took me a while to get photos. I was developing the film, but my wife showed me how to do it with her phone! Who knew?

Thread sizes on the NH carb. Drain assembly into the carb housing is 9/16” - 24 thread.



Your carb body seems rather rusted, best fix is a better unit to rebuild. A good one looks like this:

A helicoil kit for that size thread and a replacement carb body are about the same price. Buy the kit and you'll never use it again and your carb will still be a rusted core no matter how well it's cleaned. Buy a good pristine core and never question yourself.

I know what I'd do.

You have a new engine that is relying on a good carburetor...what will YOU do?

Thanks for the input. Yep - Working on another carb I found in the pile, although not that much better, it has decent threads. I'll give it a go if I can just get the darned float seat out...

Really appreciate the forum.

Wobbly Dave wrote: ↑

Sat Feb 21, 2026 8:54 pm

Thanks for the input. Yep - Working on another carb I found in the pile, although not that much better, it has decent threads. I'll give it a go if I can just get the darned float seat out...

Really appreciate the forum.

Is the advice for this to heat the body to red, then allow to cool before trying to extract the seat?

PorkChops wrote: ↑

Sun Feb 22, 2026 6:20 am

Wobbly Dave wrote: ↑

Sat Feb 21, 2026 8:54 pm

Thanks for the input. Yep - Working on another carb I found in the pile, although not that much better, it has decent threads. I'll give it a go if I can just get the darned float seat out...

Really appreciate the forum.

Is the advice for this to heat the body to red, then allow to cool before trying to extract the seat?

I have not done a lot of carburetors, but I've done a few and I've never had to do that, and I never would. Assuming that nobody has already destroyed the slot, it's not that hard to get the seat out with a tool properly sized to fit the slot, and some penetrating oil. I believe Scott Conger makes a proper tool for this.

Jerry VanOoteghem wrote: ↑

Sun Feb 22, 2026 7:51 am

PorkChops wrote: ↑

Sun Feb 22, 2026 6:20 am

Wobbly Dave wrote: ↑

Sat Feb 21, 2026 8:54 pm

Thanks for the input. Yep - Working on another carb I found in the pile, although not that much better, it has decent threads. I'll give it a go if I can just get the darned float seat out...

Really appreciate the forum.

Is the advice for this to heat the body to red, then allow to cool before trying to extract the seat?

I have not done a lot of carburetors, but I've done a few and I've never had to do that, and I never would. Assuming that nobody has already destroyed the slot, it's not that hard to get the seat out with a tool properly sized to fit the slot, and some penetrating oil. I believe Scott Conger makes a proper tool for this.

I am sure to get criticism for this, but typically I work on bottom of the barrel parts and living in the rust belt with a non existent budget means the parts I work on are usually fairly bad. If I get a nice clean part it feels like cheating but I take it when I can.
I also often get handed part that others have already failed on.
I modified a screwdriver many years ago to fit the stock seat perfectly and it works great on the ones that are not pre-mutilated.

All fasteners hold in place (don't loosen up) through a combination of rotating friction or stretching of the fastener like a spring or a spring in the assembly like a lock washer. Sometimes a digging in type lock is used in special circumstances like serrated nuts etc but this is generally a more modern style giving more rotating friction. The bendix bolt with its tab generally serves to act like safety wire or cotter pins in areas where there is no clearance. Loctite works by increasing the rotating friction.
Safety wire and cotter pins only keep fasteners from coming apart if they do move and are not strong enough to prevent all possible rotation.
The exception to this is on low or no torque fasteners like spindle nuts and those are secured with oversized (fatter than normal) cotter pins.
If you want to prove this for yourself then grab your wrenches and loosen or unbolt fasteners without removing the safety wire or cotter pins.

On the carburetor inlet seat and the spray nozzle these are installed with a fiber paper gasket underneath to seal them.
When I run into a stuck seat or spray needle I light the carburetor on fire in a convenient way (torch, campfire, shop stove, charcoal grille etc).
Brass melts at about 1700 degrees F and iron melts at about 2800 degrees F so stay away from those temperatures.
I am assuming this is an iron body carburetor.
When you burn out the fiber gasket then you make a small gap between the parts.
That gap reduces the rotating friction massively and it typically is finger tight after that.
The body is cast iron and if it can not take the heat it was failing or cracked already and going to fail on you anyway.

After you get it out, inspect the threads and gasket surface to see if they are still good for service.
Also check for previously hidden cracks or patches in the inlet fitting thread area.
Bad threads or gasket surface are fixable but usually not worth it.
Mike

Thanks all for your input. Tried making a tool from a screwdriver this morning after several heating/penetrating oil sequences. Still no luck. So rather than totally destroy the seat insert, I may hand it off to someone who has more experience with these and use it as a good core - the only good one I have!

Wobbly Dave wrote: ↑

Sat Feb 21, 2026 8:54 pm

Thanks for the input. Yep - Working on another carb I found in the pile, although not that much better, it has decent threads. I'll give it a go if I can just get the darned float seat out...

Really appreciate the forum.

I rebuild quite a few NH's. I NEVER try to remove seats or jets before heating with a concentrated oyx/acetylene flame on the casting over the threads. Cherry red. Let cool completely. This burns off the varnish & the expansion/contractions loosens the threads. Both pieces remove with ease. I do this to salvage the pieces with NO knackering to the screw slots. I have had a few really nasty rusted carbs that needed the blue wrench twice before relenting.

Looks like you've already got a handle on the situation, but if not either get yourself another NH body to rebuild, or better still, get yourself a Holley G carb, proper for a 15.

Follow speedtinc's advice. I have been doing it that way for many years as well. It WORKS and does not damage anything.

Wobbly Dave wrote: ↑

Sun Feb 22, 2026 11:44 am

Thanks all for your input. Tried making a tool from a screwdriver this morning after several heating/penetrating oil sequences. Still no luck. So rather than totally destroy the seat insert, I may hand it off to someone who has more experience with these and use it as a good core - the only good one I have!

I made my tool out of a cold chisel. Nice, hard steel and thick enough to fit the seat once the end of the chisel is ground to a nice and square, with flat sides. The hex body of the chisel makes grabbing with a wrench very easy as well. I'm not opposed to using heat, as I seemed to state earlier, I just don't get things as hot as some others do.