Engine laying down ? Carb. Help?

[sparkyboyd]

 So I was running  127 Main jets. Then learned some of the guys I race with are running  117/120's so I went down to a 125 for a couple of races and everything Was good, then decided to try a 122.5,  15 laps into the 40 lap main engine started lay down, coming off the corners half way down the front and back stretch felt like I had 65% power and then would pick back up. After race talked to some of the guys, they said sounds like it's to rich. It was a humid cool night 62 degrees. When I got home I pulled the plugs and  they looked pretty white, like it was running hot. So for last nights race I went back to a 125 main. Car was good all day and most of the. Main. 10 laps to go after a coup,e of cation laps engine did the same thing. Plugs look hot again. So now I'm confused  125 main 160 air and air/fuel 4 1/2 turns out. What. Am I missing I want to run 120's or  122.5's any help would be greatly appreciated. -Brian

[racerrad8]

As the summer comes to a close and the temps fall you need to make the carbs richer because there is more usable oxygen in the air.

Also, do you know what needles you are running?
Why are you running the 160 air bleed?
What size is the pilot jet?

Why do you want to run 120/122.5 jets?

Randy - RPM

[VMS Motorsports]

I echo Randys question...why do you want to run leaner jets?
I want to run 135's, just can't til it gets colder and less humid

[sparkyboyd]

 Randy 120/122.5 would be leaner right? More power? Or do I have this backwards?  Air jet I was told to run a 160

[sparkyboyd]

Pilots  I'm not sure. I always based my main needle on air temp and humidity. I'm always learning

[VMS Motorsports]

The lower the jet, the leaner. Thus my comment of wanting to run a 135.
Remember, leaner also runs hotter

[sparkyboyd]

Ok,  I'll try a 127 for the next race. 

[Gimpster]

 Leaner jets are definitely hotter. It might be pointing to a clutch slipping issue because it is making the engine hotter with the leaner jets

~G~

[knoxracing]

The important factor as Randy brought up is you HAVE to know what needles you are using. Dropping in jet size will lean it out, too lean and you will destroy the motor. Some needles run best with 125- 127 mains and others with 117.5 - 120. Running a 117.5 with a redline needle could be a disaster.

[sparkyboyd]

Got yea, I am running a redline needle.

[Grape Competition Develop]

Comparing jet numbers without knowing the root diameter of your friends needles is dangerous.  Overall fuel flow is based on area of the needle jet oriface minus the area of the root of the needle.

You cant run jets that lean with Ray's deal unless you are above 5000' elevation.

Also, with your idle screws 4.5 turns out, you have lost control of fuel delivery at idle or closed throttle.  Run a smaller air bleed in the front of the carb to adjust that range.  142.5 or something similar.

[sparkyboyd]

 Thanks for all the help guys! One more thing I forgot, my engine temp never got above 210 degrees. Now I'm thinking I was running so lean the engine never had a chance to even get that hot, am I on the right track?

[knoxracing]

Head temperature would be the issue and detination would be the real problem, leading to piston and or valve damage. You may not really see it with your oil temp gauge. The spark plus would be the best indicator of lean conditions. Just remember not all jets and needles create a good combination for the 1200 / 1250.

[justfreaky]

Also; How and where were you measuring the temp? Gauge is likely not accurate.

Steve

[sparkyboyd]

Yes , I've read that in other post. Just the standard oil temp gauge. Still I think I'll go with the 127's next time. Again thank all you guys for all the help. Very appreciated -Brian.