ZCar Forum banner
Status
Not open for further replies.
1 - 2 of 2 Posts

·
Registered
Joined
·
107,695 Posts
Discussion Starter · #1 ·
Can anyone advise me on correct or Successful jet settings for a L28 currently at 3.05 litres. It is set up with 3 mikuni 44s, a shorty intake manifold, Nissan Motorsports Header. Compression is about 9.5 with Rebello's 2nd hottest cam. Head has a medium level of porting. Electric fuel pump. I cant think of anything else that you might need to know. Problem is higher rpm performance, as it just levels out instead of coming on as I think it should. Engine is 200 miles old.
 

·
Registered
Joined
·
107,695 Posts
Discussion Starter · #2 ·
One piece of advice is to get a service manual or the weber book on carbs. The Mikuni/weber carb jetting is kind of a 2 stage operation. If your low to mid range performance is good then your main jets are prob. ok but your air correction jets are off. These act as gas brakes to help keep the fuel/air ratio constant as the RPM's go into the higher ranges as gas and air's density is different so this has to be regulated by the air correction jets. It's this setup that makes these types of carbs the best in the world and if you know these carbs well enough they will give fantasic performance through the RPM range. If you are going leaner at higher RPM's start going smaller with the air jets as it lets less air mixing to the gas at higher RPMs and the oppisite for richer. If you don't have the recomended jet setting here they are but when you change cams/exaust they may have to be played with till you get what your engine likes and don't quote me on this but with a freer flowing exaust and a engine that breaths better you have to go a bit richer in jetting but here's the stock jet sizes to start with:
Main 150
Air 200
Pilot 52.5 (when this is off the carb stumbles a bit off of idle)
These sizes are for a 34mm venturi on a 240Z.
For a L28:
Main 145
Air 200
Pilot 50
These do differ for engine setups though, Nissan's carb setup for built engines have a 180 main jet with a 250 Air so you can see there is a lot of range to play with.
Some folks don't seem to like the Colortune tool but after learning how to properly use it I found it to be a great tool for jetting these carbs and I also recomend you go to a motorcycle shop and buy a carb sync tool called a Manometer. It makes syncing these setups much betting/easier than that screwy unisync tool that motorsport sells and I can sync this setup in 10min with this tool so it's def. worth the 65.00 to 70.00 cost. I got a much better sync with a Manometer and Mikuni recomends it also. You just have to be a little carefull when using it, it has tubes with mercery that read vacume and if you hit a snap throttle you can suck the mercery out of it, it won't hurt the engine but you have to let the car run a bit to blow it out but it only happens when being careless when using the tool. Sorry about the lenght but I've been dealing with these carbs for quite some time and found these hints to help a lot so good luck. Note, you can also get a fair idea of jets by the spark plugs also so make sure you know how to read their colors after use...
 
1 - 2 of 2 Posts
Status
Not open for further replies.
Top