I am looking for a zenith HP5a sidedraft carb. If anyone has one in complete decent condition that they would consider selling please contact me. Thanks!
I have several. I spent the day today working on two of them. Have them ready to go back together in the morning. These are sold but I have 3 or 4 more. Stan Howe 406-949-3448 email@example.com
Are you making adjustable main jets for these? Do they require modifying the body of the carb? I'd sure be interested in one for the 5A on my speedster if it were an easy (no brainer) install.
Yes, I will be standing at the lathe for an hour or two this afternoon because I really need to get one done before I leave tomorrow and get an HP5A in the mail.
Answer to your question. No modifications necessary. I replace the bottom plug under the main jet with an adjuster and the main jet itself with a reworked jet to allow for more fuel flow and the adjustment of that flow.
I also make one for the idle mixture, which stops the annoying stumble and slobber at idle and stops the plugs from fouling if somebody drilled the idle jet for richer idle.
Installation is about 5 minutes. Unscrew the plug and the jet. Install the new jet with the gasket. Install the new plug and gasket with the adjuster. Start engine and adjust the mixture. $150 each or $275 for a set of main jet and idle adjusters including postage. I like to have the original plugs back as a core if they are in good condition.
I have them available for the 5A, 4A and 4U, S4BF and can make them for about any other Zenith or other carbs with fixed size jets.
Here is one in an HP4S. Same design, 5A is slightly larger.
Just put the one I was working on today in a box for tomorrow's mail. Thought I'd post a couple photos of my new design for the adjustable main jet. Slightly smaller and no threaded connection between the carb plug and the adjuster.
Also, since it is now machined as all one unit with the threads as the reference location rather than a threaded piece screwed in to the drilled and tapped hole in the plug it should center exactly on the hole in the jet for finer adjustment.