Lean in Gear, but Good in Park.

A

Alibaba91

Active member
The air fuel ratio is good in park or neutral, but way too Lean when I'm in gear or holding the throttle. I'm talking off the charts, over 18:1. I feel like I need to get a bigger main jet (currently 61), but I want expert opinions before I start swapping jets.

65 Mustang 200 six cylinder coupe with C4 auto. I have an AEM wideband O2 sensor attached (blasphemy, I know), so I know exactly what my ratios are.

Freshly rebuilt Autolite 1100. Timing set with gun, idle speed with tach. Every part of fuel system except pump has been replaced.
 
What is your reading driving it at 20mph and at 40mph? What about your acceleration numbers? Have you tried adjusting your idle mixture screws? And double check for any possible vacuum leaks.
 
Tried checking for vaccum leaks with propane. Didn't find any.
Haven't taken it on the road since it runs so lean in drive.
Idle mixture screw is basically all the way out and I'm still lean in gear.
 
Have you verified the float level setting is correct? Have you tested the fuel pump pressure is in spec and did a fuel volume test? See below for more info on the Autolite 1100. If you have the mixture screw turned all the way out then the idle circuit passages may still be plugged up with some dirt or varnish or some other kind of crud. Jets won't control the idle, they only control the higher speed steady state cruse. Best of luck (y) :nod:

Autolite 1100 info & Settings
http://www.carburetor-blog.com/autolite ... arburetor/
 
"...to but proper equipment..."
nope.
U gota 1 or 5 gal bucket and a 'stop watch' (= volume)
AND
we usta 'lend' (deposit returned w/return of gauge) equp at AutoZone
(as do many of the big box auto prts stores). This gives measurements
to ck against specs for this Y/M/M'n engine (readily obtainable data).

Good Luck, let us know how U do ~
 
I would check engine vacuum with a gauge. It should be reasonably steady. Idk what vacuum should be, I’d guess at least 14 inches.

If you’re lean only at low idle, I agree with others your idle circuit may be plugged. Maybe time to at least clean and/or rebuild carb. wsa111 (Bill Ambler) is a carb expert and could help you if needed.

Thanks
Bob
 
What do you have the initial timing set??
Is the idle mixture screw adjustable. What i mean is it responsive to being lean when screwing in screw??
Is there excessive play in the throttle shaft.
Remove idle mixture screw & blow compressed air is the orifice. See of there is a change.
Replace the 61 main jet with a 64 or a 65 jet & road test @ 50-60 mph.
What are your readings??
 
You must log in or register to reply here.
Back
Top