MTFCA Forum

Hi all,
Looking at my Holley NH that I'm restoring, I noticed that the 2 drilled passages at the throttle plate are both showing while the throttle is closed (see pic). Is this normal? Should they both be exposed when the throttle is closed or should the throttle cover the inner one? Thanks.
John

Normal, and important to be in working order.



Holes are noted are for fast idle and slow engine speed D and E.

This may help?

The purists hate me for this but when I was rebuilding NH's I found that drilling out the brass plugs in the body and cleaning the passages behind them was very important. Just be careful not to drill the holes oversize when you are cleaning them.

The easy way to seal the plugs back up is to tap them 8-32 and put a little Allen head set screw in each hole. As I said, purists will scream that you should make tapered brass plugs, pound them in and cut them off and dress them to surface.

OK, whatever works for you. The Allen head set screws work for me.

Here's a somewhat better copy of the service bulletin drawing.

It shows one hole (E) inside the closed throttle and one outside (D), so your situation is not normal according to the drawing.


Here's the complete explanation from the service bulletin: The article has more about the rest of the NH.

John,
In your picture, for some reason the throttle butterfly is not closed all the way, you can see a small gap between the edge of the butterfly and the bore. It may be caused by either your idle adjustment screw or the butterfly isn't aligned properly. But the answer to your question is yes, when it is closed only one should be visible.
Bill

When the idle adjustment screw is adjusted for this opening, it is usually due to the idle passage being either restricted or blocked. If the carb must be adjusted to run at idle as in the picture. then this is the case

Showing with butterfly closed tight, only the one passage is exposed.

Showing slightly open like in your picture

Thank you so much Bill,
That hits it on the head. The adjusting screw was in too far. When I backed it out, the butterfly closed completely. Problem solved.
Thanks,
John