I looked around a little bit to see if could find the answer myself because I feel stupid for asking but... Which way do I adjust the screws to make the mixture more RICH? Is it clockwise or counter clockwise? A lean carb makes the motor run hotter right? It's a q-jet on a stock 72 GS455 motor. Thanks,
MOST carbs will go lean with the screws turned "IN". Righty = Tighty, Lefty = Loose-y. Connect a vacuum gauge, adjust screws for highest vacuum at curb idle in gear, wheels blocked, park brake set, engine at normal operating temp. Re-adjust idle speed if needed. Then turn both screws LEAN 1/8-1/4 turn, just enough to "erase" about 1/2 inch of vacuum from the gauge. Going slightly lean will make almost no difference in the quality of the idle, but will make a DRAMATIC difference in the pollution coming out the tailpipe.
An excessively lean motor will run hotter, but in that case its dependent on the jets and rods since it would have to be into the main metering circuit rather then the idle circuit.
It is possible for idle or off-idle passages to be lean enough to cause over-heating, however, the engine will likely surge, or hesitate. The best way to adjust the idle mixture is with a tach, adjusting for the maximum idle. Counter-clockwise enriches the mixture (adding fuel), and the clockwise direction will lean the mixture, removing the fuel. The dwell and timing must be set first, allowing the throttle to be in the correct position in relation to the off-idle slot. If you are unfamiliar with this, I can explain further. Let me know... Ray
Yes, you can use a tach, and some people prefer that. I've found a vacuum gauge to be far more sensitive to change. Either way, find lean best idle, then adjust "slightly" leaner. You WILL NOT hurt the engine, you probably won't notice any idle quality difference, but the emissions come down dramatically. We all have to breathe...
I got my timing set (it's HEI so no dwell). I found out my vac advance was sticking in the advanced position. I sprayed some sylicone on it and I think I got it freed up. It got late real quick today so I didn't get to hook up the vacuum gauge. I plug this in to the manifold correct? Right behind the carb? Or do I plug it in to the full vac advance port on the carb? I'll let you know what I find with the vac gauge. Thank you all.
Hi Ray Sorry to hijack the thread but I would like to learn more about setting up the carb. I rebuilt mine this winter using the Doug Roe book and picked up a dwell/tach and already have a timing light. I set my mixture screws to where they were when I pulled the carb off but I'm sure they could be "tweaked". The timing/dwell/idle are all set but I would love to hear more on using my new found toy (tach) to really set it correctly. Thanks!
Yeah, you "can" set the idle mixture with a tach...but once you do it with a vacuum gauge, you'll never do it with a tach again.
