jet sizes Z1A with Vance and Hines header..

[Texwing]

Well tonight I finally had a chance to pull the pods and carbs on my stock (i think) 1974 Z1A 900, and also replaced the the pods with the stock air box and check the jet sizes in the carbs.

The jet sizes I found were 115 mains and 17.5 secondaries, I would welcome comments on anyone else running the same set up (stock air box, vance and hines 4 into 1 header) as to jet sizes since i think this must be a common set up.

I would like to tell all how its running with the stock air box on, but for some reason I have lost no. two cylinder. I had the bowls off of two to switch them as the previous owner had them mixed up where the gas drains were pointed the wrong way, I swapped them and one of the bowl gaskets was trying to drag against the float, perhaps causing the problem, although there was gas in the bowl, and fire at the plug. Oh well, the next time I pull the carbs I would like to have the jets ready is someone can suggest the right sizes...

[Jeff.saunders]

The Z1A came with two different sets of carbs - the early style have a drain plug with a 17mm hex head directly under the main jet, the later style a brass drain screw angled to the side.

The main jet would normally be around 117.5 or 120.0. The pilot jet will differ based on whether you have the early or late carbs - #20 versus #22.5.

With the pilot jet they are a different series, so you do need to know what you have...

[Texwing]

Thanks for the reply, these are the later style side drain carbs which appear to be correct for the engine serial no 40,xxxx. I wonder when and why smaller the mains and pilots would be smaller than stock, although I will say that the brass jets were new and shiny looking, so perhaps later model carb kits were used that contained smaller sized jets. In any case I would appreciate a good starting guess for my set up, stock engine, stock air box, vance and hines 4 into 1 header, and i will go about rounding up the brass.

[DrKayak]

I have the same Z1b carbs on my kz900. They came with 117.5 main and 17.5 pilot jets. I'm running pod filters and a Header w/stock baffle. When I bought the bike it had sat since 1999. After 2 cleanings I was still starved for fuel at idle and low throttle. Pluss the PO had the air screws all the way in. Which was running it as rich as possible. I ordered #20 pilot jets. After seeing new #20 it was clear my 17.5 jets were still clogged.

With new coils it starts instantly with #20 pilot. IMO it pulls plent hard at full throttle with 117.5 mains. I'm getting 40-45MPG commuting at 75-80MPH. I'm real happy with the MPG so I will not go to bigger jets for more power.

It smells a little rich at idle. I plan to try going back to new 17.5 pilot jets some time. IMO for the price of new pilot jets and the tiny holes you have to get clean I would just relace the pilots on a restore project.

[Texwing]

Thanks for the info DrKayak. The Clymer manual says Z1A carbs should have 20 pilots and 112.5 mains, Z1B's 17.5 pilots, same 112.5 mains. So, for some reason, after going to pods and a 4 into 1, my PO must have upped the mains to 115 but reduced the pilots to 17.5, since the brass looks new I suspect it may have been the brass in a 76 carb kit. Plugs look gassy and rich, but I am having a big stumble at about 3 to 4 thousand rpm, starts good, pulls good under full throttle. Anyway, Its looking like the best plan is to go back through the carbs and make sure they are really clean (they look clean, but who knows) before doing much else.

[DrKayak]

I could see clogged pilot causing a stumble at that RPM. I cleaned mine twice and the bike ran worse after each cleaning. The third time I pulled the carbs. I just replaced the pilot jets for less than $10.. The new #20 pilot did the job.

I also found when I replaced the plugs one of the new plugs was dead. I ended up replacing the coils thinking a new plug could not be bad. In the end with 4 good plugs, new coils, and new pilot jets the bike runs like new. Starts instantly. I have over 1,500 miles on it since the restore.

[Texwing]

OK. I think I must have misread Jeff S. earlier post since what he said would then make perfect sense, not for stock, but to accommodate the 4 into 1 header. His comments: "The main jet would normally be around 117.5 or 120.0. The pilot jet will differ based on whether you have the early or late carbs - #20 versus #22.5." Since I have the late carbs, (as you do, i think, the side drain models) that would seem to mean the 22.5 pilots (I think my z1a cams are different from the KZ's), and I think I will try the 117.5 mains since I still retain the stock airbox (I replaced the pods that came with it) and will have just the 4 into 1 header as the only mod. Thanks for the help, I am looking forward to getting it running right. I also see that the needle heights can be adjusted as well on these carbs, and I am not sure when that gets introduced into the carb tuning mix....