Perfect Carb!---Almost.

[cdnus]

My holley 4160 style carb is almost pefect in all respects ( I run with a LM1 hooked up) except at low speed cruise.
The problem is at cruise 30 -50mph very little throttle is required and the F/A runs lean 15+,
I can improve this a little if I richen up the idle, but I don't want to do that as it idles nice now at 13.5-14.1 without excess fumes.
If I want to increase my speed slightly while cruising and just breath on the peddle a little, it goes even leaner, so I have to give it a little more (more than I want ) then it richens up to a perfect level. Then I'm going faster than I want to and have to slow down.
This takes place usually in the 1500-2300 rpm range, above that the ratio is usually OK. The F/A is within range in all other circumstances and the carb performs flawlessly otherwise.
I know there is 1 more adjustment in there somewhere that will cure this But I can't figure it out.
Any help would be appreciated as I don't like it running this lean while I am cruising--which is most of the time unfortunately due to our rediculous anti- racing laws.

Thanks Craig

[RicManSr]

You might want to try reducing the squirters in the carb. Mine was doing the same thing. I was running #29 squirter & changed it to a #31 & my problem went away.
HTH
Ricky

[jhv48]

Originally Posted by RicManSr

You might want to try reducing the squirters in the carb. Mine was doing the same thing. I was running #31 squirter & changed it to a #29 & my problem went away.
HTH
Ricky

Most recommendations would be to do the following first.

A) Open mixture screws slightly
B) Readjust butterfly positions
C) Raise float level slightly.
D) Make sure your squirters are operating as soon as the throttle moves. Some delay will cause a lean condition.

[RicManSr]

Originally Posted by jhv48

Wouldn't that further lean out the carb?

Most recommendations would be to do the following first.

A) Open mixture screws slightly
B) Readjust butterfly positions
C) Raise float level slightly.
D) Make sure your squirters are operating as soon as the throttle moves. Some delay will cause a lean condition.

Sorry , went from #29 to #31, I fixed it

[Rick Parker]

You can reduce the air bleeds slightly (will need some specific sizing) and it will richen the cruise mode for you which is what you are wanting to do. Contact a shop that modifies Holley Carbs, they will have the small brass bleeds in various sizes.

[Gaz64]

Or increase the idle feel restrictions in the metering block by .001-.002 and retest.
You'll end up with the mixture screws about 1/4 turn leaner to achieve the previous A/F ratio at idle.
This should make some difference in the off-idle transition A/F ratio.

Go up again if not enough, difficult to come back down.

[Jac Mac]

Have you tried going up/down on the secondary idle setting ( about 1/4 turn either way plus readjust primary to suit should be enough ).

Also a snail quadrant to give more progressive throttle control at small pedal% will help.

[cdnus]

Thanks guys,
the carb is so close I am leary of messing it up, the throttle control is so smooth & seamles I don't want to change anything to radical.
I raised the pimary float 1/2 turn so the level is now about 1/4-1/3 up the window. I have driven a few hundred miles like that & it has improved & now does not lean out & in fact richens up to the correct A/F when I breath on the peddle when cruising.
Better, but still runs lean while maintaining the slower cruise speeds, so I think I will try messing a little with the idle air bleeds. I have some blanks so I think I will try about a 10% reduction & see where that takes me.

Again Thanks everyone & keep the suggestions coming.

Craig

[Michael C Henry]

I'll be watching this tread. My car went through it's last emmissions test last year on a waver. My cruise hydrocarbon emissions were almost legal but my idle hydrocarbon emissions were over 10 and allmost 11 times the limit. I made some changes and had new primary metering blocks created with removable brass orifices to lean out the idle. I'm waiting to get the car through a frends computerized testing equipment to see where it stands now. I bought the brass screws and micro drills to manipulate the flows up or down once the portions are identified. I was also given a CNC machined holding fixture to hold the screws when drilling and facing.

[vector1]

the pics in your gallery the engine? nice.

looks like you're running a pcv valve in addition to the valve cover breather, if this is the case you're running air through the engine into the intake. plug the breather hole or pcv line and see if the afr is better.

the cleaner looks like it could have an effect also if the top is in too close proximity to the air inlet or choke horn or the well tubes.

my guess it is the first one.

[vector1]

Originally Posted by Michael C Henry

I'll be watching this tread. My car went through it's last emmissions test last year on a waver. My cruise hydrocarbon emissions were almost legal but my idle hydrocarbon emissions were over 10 and allmost 11 times the limit. I made some changes and had new primary metering blocks created with removable brass orifices to lean out the idle. I'm waiting to get the car through a frends computerized testing equipment to see where it stands now. I bought the brass screws and micro drills to manipulate the flows up or down once the portions are identified. I was also given a CNC machined holding fixture to hold the screws when drilling and facing.

drop your timing at idle and use a ported vacuum on the dist. or no vacuum advance at all. back in the 70's the vettes would run 6-8 deg. timing at idle to get around this, then set it back when your done playing with the dmv. tom kirkham has posted advance curve timing article lately in the forums that addresses this under the hei article.

[Bobcat]

Craig .... I`ll second the comment on the air cleaner possibly being too close to the vents on the carb . The top must be a minimum of 3/4" from the vents or it will cause all sorts of funky things to happen with the mixture .

Bob

[Michael C Henry]

In a perfect world or someday when I get things changed, I'm height challenged. If and when I find a buldge or scoop to get the air induction to the carbs corrected.
The breathes were a PCV cure that I cooked up after a foaming situation. I have a catch tank on the right wheel well with a K&N filter ontop. Air is filterd while being sucked into that tank then by way of the hoses to the valve cover breathers. I removed the rear manifold breather stack and installed a hose nipple that connects to a single PCV valve and then to the intake manifold plenium. That way filtered fresh air is pulled through the tank through the valvecover breathers downward into the lifter valley to help rather than hurt oil drainback Any thing produced is pulled into the intake and burn't and in the event of a catastrofic engine failure, system fluid would be captured in the catch tank.
There is no vacum advance it's a Mallory centrifigal advance distributor. I found that the more initial advance I dialed in the distributor the faster the engine idled. I had to back out the carb idle screws to keep the idle down to a realistic idle rpm level. I'm sure that the carb butterflys were open enough to expose the transition slots at idle before I adjusted the distrbutor advance upward.