MTFCA Forum

Hi,
my 1921 Model T pickup generally runs OK, but the idle is nothing to write home about. It basicly can't go idle and when stopping for red for exampe, I have to either let it idle fast or be at the throttle all the time. The carburetor is a stock Holey NH.
Now, my 1914 Model T touring have an aftermarket carburetor - a Toquet - which I am very happy for and where the idle is really smooth and slow. I could restore the NH and probably get better results - but since the NH do not have a dedicated idle circuit in it, will I ever get the engine with the NH to go as smooth as the one with the Toquet carburetor? Or any other aftermarket as if the NH can't do it after a restore, I might as well be in the market for a new 3rd party carburetor for my pick-up.

The NH has an idle circuit. It has to do with the 2 small holes near the throttle plate. If you remove the brass plugs and drill out the small holes in the NH I think you'll be fine. A properly working NH will allow for a very nice idle.

Jerry VanOoteghem wrote: ↑

Wed Sep 06, 2023 8:38 am

The NH has an idle circuit. It has to do with the 2 small holes near the throttle plate. If you remove the brass plugs and drill out the small holes in the NH I think you'll be fine. A properly working NH will allow for a very nice idle.

This may be your main issue.
A worn sloppy throttle shaft also will cause the idle speed to vary as the butterfly jiggles around.
Keeps the carb from a consistent idle fuel supply.

"A properly working NH will allow for a very nice idle."

If there's a large amount play in the shaft it'll need attention. If it's really kind of minor there's a felt ring used on lawn mower throttle shafts that will do wonders in sealing it up. I've done it. It works. As to the idle circuit passages: no need to start out with drilling. At least not at first. A can of carb spray with the thin straw nozzle on it will give you a quick indication of the passages condition. If it blows through they're either clear or it's blown out some junk. If not drilling is your only other option.

OK, I'll plan for a proper full rebuild of the NH carburator then. Thanks!