4 bolt su weather affects idle?

[Mark Maras]

 Thanks. If you notice a slight lag at the onset of acceleration (possible because you leaned it out a bit) you may want to try using 20 wt. oil. It will richen the mixture when you first hit the gas.

[kully 560]

mark if I am not mistaken turning the screws out will run richer I turned them out a 1/4 turn more

[Mark Maras]

 That's right. Out is down and rich, In is up and lean. We'll avoid the terms clockwise and anti-clockwise. Nice that you were able to clear it up with a 1/4 turn. In post #2 I wasn't sure if it was too rich or lean. I thought it was probably too rich (I assumed the plugs were a tan color) so my suggestion at that time was to lean it "Up a half turn".The choke test confirmed it wanted to run a bit richer. Congrats on getting it idling properly.

[kully 560]

Mark thank for the help !! I let you know tomorrow how far out the mixture screws are . I also remember spending some time setting up the floats I think they should be good.

[kully 560]

hi Mark, I check the turns down on both carbs and the front was 2 3/4 turns down and the rear was 2 1/2 turns down . so I set both at 2 5/8 turns down and re balanced  both carbs and it  runs perfect now. I guess the previous setting was a 1/4 turn up lean and maybe that is why the weather was affecting the idle [some days richer when warmer and some days leaner when cooler] thanks again for the advise on checking with the choke as far as being to lean . also it looks like my floats are set perfect .kind regards

[jonathanrussell]

I will share a couple of things with you that you can think about and potentially try out. I do think SU carbs are sensitive to temperature. They are also prone to fuel percolation in the float bowls. When the weather is below about 55 degrees I move the air cleaner to the winter setting which pulls air from the warm area around the exhaust manifold. If you have headers you may want to figure out how to direct the winter air duct to the area around your headers for cooler weather (assuming you have a winter/summer air cleaner housing). On 80+ degree days, I disconnect the winter duct and run a duct from the air cleaner round winter port through the hole in the radiator support so cool air gets pulled from in front of the radiator (so, in this case I set the air cleaner to winter). On fall and spring days between 60 and 80, I use the normal summer mode where air gets pulled from the under-hood area.

Also, I was having idling in traffic problems at the start of summer this year. I have an electric fuel pump and I only run ethanol free fuel. After lots of trial and error, I solved the problem by wrapping pretty much every inch of my stock (but ceramic coated) exhaust manifold with the product in the link below. I also wrapped the float bowls. I haven't had idle problems in the heat again. Here is the product I used, though there are lots of ways to accomplish with headers. 

Heatshield Armor

As mentioned above, your plugs look great and your carb float setting must be pretty spot on....key in my opinion to getting these carbs to work right.

 

 

[Stanley]

The car runs best at correct air/fuel ratio. High altitude has thinner air so a leaner mix is required. High temperature also has thinner air, so leaner mix required. Cold air is dense so richer mix is required. There's a graph in the carb tuning section of the manual that shows altitude and temperature vs initial number of turns down at the mix nuts. So on a hot day in Denver you'd want a lean setting. On a cold day at sea level you'd want a rich setting. Dunno if that affects your issues.

Edited September 3, 2019 by Stanley

[kully 560]

thank for the suggestion Jonathanrussell I will keep that in mind about the heat shield.I know the headers put out a lot of heat and that is also been on my mind. I went with the jet hot headers as it is supposed help with the heat but it still gets hot anyway . I do not  drive the z when it is to hot out as I removed the a/c 20 years ago,and with only 2 open windows as you know these cars can get hot on the inside. now my 1971 air cleaner does not have the ducts for summer or winter modes  and I all ways thought about bringing the air in from the front of the car so as to try to decrease the heat in the engine area. but I do not know if the su carbs have enough suction to pull the air from all the way from the front of the car back to them.  so now  when you drive the z  will it be like ram air and run to lean and maybe run to rich at idle? right now as of today the z is running great if not perfect but the temps today were in the mid to upper 70s. the next hot day I will take it out and see it being a 1/4 turn lean was my problem.the plugs were a little more on the white side then the pictures I posted but the tips still had a tan color to them . it ran great off line ,mid range ,top end , I never thought about it being lean at idle! maybe one day I look into the header wrap also but the jet hot headers look so nice!

[kully 560]

Stanley mine was the opposite ! I balanced the carbs on a cool day early summer and it idled great ran fine . then on a hot humid day it idled poorly but ran great, I have all ways balanced several time a year as weather changed .maybe it was just a little on the lean side the hole time for a  smooth idle. for the mixture adjustment I used the color tune ,I also tried to  used the lifting pins on the sides of the 4 bolt su carbs to raise the piston a little for the change in rpms but my engine never really reacted  like the ones you see on u tube so that is why I all ways went with the color tune for the readings. I was originally around 2 1/4 turns down approx. now both are 2 5/8 turns down and much better all around.