I found two Holley NH Straight Through Carb bodies and would like to know the differences. I have attached some pictures (not very good ones).
One body has a threaded hole by the nameplate. What type plug goes in this hole?
Is one for 26-27 and one earlier? Are there parts that are unique to these carbs? Bowls of a different shape? Needle valves of different length like Simmons?
I will be happy to post other pictures if needed. I did a search but may not have used the appropriate search words.
Thanks for the help.
Dennis, NH straight through carbs were only factory equipment in the early 20's (1920-21, I think). They wouldn't have come on a 1926, even a pre-vaporizer car. I couldn't see the tag plainly on the one on top, but both tags appear to say Holley.
Dennis to answer your question a brass screw goes into the air bleed that you were asking about .I attached a link where they talk about it on the forum. As for the differences I believe the one on the right is the earliest version of the 1920 nh and sometime later they changed the design a little and moved the id plate to cover the air bleed. Someone smarter than me will probably tell you when. The throttle and choke arms were originally cast brass so those must have been changed out through the years. Hope I helped.
That's great information. I love learning something new every day.
Further to Micol's post, the brass screw is a hex piece, drilled from the bottom and through the sides to act as a vent piece. The later version puts the plate over the vent hole, cheaper to produce. On our Canadian sourced cars I have found cast steel choke arms on the earlier type, but not brass ones.
Yours may vary.
Allan from down under.
My '21 Canadian built car has a straight through fitted and has been on the car from new. It has steel choke and throttle arms and I'm 99% certain they haven't been changed.
I think the throttle and choke arms may be a carry over from the G.
Someone may have mentioned this before, but notice how straight through carburetors tags seem to be upside-down.
Tom, interesting observation.
The link posted above by Micol shows an ad from Oct 1921 with a side drain bowl. The diagrams posted by Martin Vowell http://www.mtfca.com/discus/messages/506218/535364.html?1429643760 show a center drain starting in 1920.
Did Holley produce two designs of the NH - sway back and straight through - for several years, and if so, for what period of time? Would they have used both a center drain and a side drain bowl during the same time frame?
Does anyone have a clear picture of the air bleed screw or know where I can get one?