All Small Six Car Lean with Open Air Cleaner

This relates to all small sixes

Alibaba91

Active member
Car is a 1965 Mustang with a 200 six, auto trans, stock load-o-matic dizzy and autolite 1100.
When I use the stock air cleaner, the car runs perfectly. Idle is smooth and air fuel ratio is perfect as measured by a wide band O2 sensor. When I switch to an open element air cleaner, the car runs lean no matter how far I back out the mixture screw.
This tells me that the stock air cleaner is restrictive, and I can likely get more power of I can get enough fuel for the open air cleaner to run properly. What can I do here to get more fuel iinat idle?
 

B RON CO

Famous Member
Supporter 2021
Supporter 2018
Hi, what are the wideband readings with and without the air cleaner, at idle, cruise, and WOT?.
Is the idle nice and smooth?
Does the mixture screw change the way the engine runs when you turn it in and out? The mixture screw and idle circuit have no effect after the throttle is opened a little.
What is the idle RPM? Maybe the throttle plate is not closed enough.
Good luck
 

bubba22349

Top Poster
Staff member
VIP
Supporter 2021
Supporter 2019
REDLINE 10K
You could try going two jet size bigger that will likely help it. X2 changing the mixture screw has little effect other than for just the idle circuit if you get much more than a range from 3/4 to 1 1/2 turns out you have other problems. Good luck
 

Alibaba91

Active member
I'm doing the jet change for sure. Jet size will fix everything except the idle though, no?
Is there anything I can do to fix the idle circuit? Float adjustment, drilling out any passages, etc. Idk feeling in the dark a bit here.

The reason I care about idle is that when it runs so lean, it overheats really quickly. So I need to address the lean condition at idle specifically.
 

bubba22349

Top Poster
Staff member
VIP
Supporter 2021
Supporter 2019
REDLINE 10K
Yes going a little higher setting on the float level might help (don't go much past the factory spec though). It could help also to check out the fuel pressure that your fuel pump has too. Use a thicker carb base gasket or stack some or you can make an insulator out of a plastic cutting board if it's overheating. How much base timing are you running? Are the carb internal fuel passages clean?
 

Alibaba91

Active member
I've tried three carbs, including a new one, so I don't think cleanliness is an issue.
I think I have 12° in it right now, as measured by timing gun.
I have to install that fuel pressure gauge I have lying around...
Why would stacking gaskets help? I thought they overheating caused the violin condition was due to what happens in the combustion chamber and not like heat soak to the carb.
 

bubba22349

Top Poster
Staff member
VIP
Supporter 2021
Supporter 2019
REDLINE 10K
Excellent on the cleansess! 10 or 12 degrees is a good place to start, some have found they also had good results with 14 or as much as 16 degrees with a LOM Distribitor. Those to seem to be good so far than. Stacking the carb base gaskets provides insulation from heat soak Ford started using these thick carb base gaskets around 1974 if not earlyer they made some really nice ones the thickest are those from the late 1970's to end of production of 1983. Trouble is some of them might not fit (so check them out against your stock carb gasket though as some of the gaskets will have sloted base insert and the can fit both sizes) the early six engines have a narrower carb base bolt spacing. The later model 200's and 250's six's used a wider carb bolt spacing, I use them on everthing myself since I have almost always lived in hotter areas. Our small six'es now days will often suffer from heat soak in the hotter climates because of the newer fuels we have plus also with the carb setting right on top of the hot exhaust. If you have one of the stock type aluminum carb spacers be sure to also check out the bottom gasket or replace with a new one if you haven't already. The heat soak maynot be a problem for you in your area or currently this time of year with the cold but this is a very common problem for many there art other ways to fight it too with a different three outlet fuel filter or a return fuel line. You could also do a simple fuel volume test in place of the fuel pressure test. If you want to increase the flow into the stock log head it helps to open up the carb mounting hole to 1 3/4 inch too. With your new open elimate air filter how does the steady state cruise speed mixture read? If after you have tried the float level setting and checked for proper fuel volume / or pressure then your right to think about drilling out the idle passages or better yet going with a little bigger carb like an Autolite 1101 off a 223 Ford Six, they used them on the 1963 or 1964 models. Best of luck
 

Alibaba91

Active member
Thanks, that makes sense. I haven't driven the car enough to know if heat soak to the carb or vapor lock is an issue. Will see this summer. (I'm in NJ)

Steady state gets a bit lean depending on the amount of throttle I give it. I'm definitely gonna change out the jet to address that. I'll adjust the float to address idle at the same time. Fingers crossed. I'd really rather not get into drilling out idle passages unless I can get access to some proper machining equipment.

If I change out carbs entirely, I might go big and do a 2v conversion, or EFI with the sniper 1100 at that point.
 
Last edited:
Top