autolite 1100 lean at higher RPM - carb tuning / jets?

[aribert]

I replaced the Holley 1908 (from a previous 170 engine) with an Autolite 1100 (P/N illegible). Car appears to run OK with the carb, other than much worse vapor lock as compared to the 1908).

I finally moved my Oxygen sensor & display (narrow band, heated) over from another car to the Falcon. Confirmed what I suspected - the carb is WAY lean at road speeds greater than 50 to 55 mph (unknown RPM, 3 spd trans, 3.2 rear axle ratio, 185R70-14 tires). The O2 gage goes blank (very lean) at about 55 mph. The plugs are now a very light grey in color. I hear knocking at harder acceleration in 2nd gear.

This is a manual choke/manual trans carb. What are my options? I am guessing that the main jet needs to be increased. I did not see any numbers on the main jet when I rebuilt the carb. What are some typicaly jet IDs? how much of a change in dia should I be contemplating - I expect to inch up on the final jet size. Anything other than the main jet to look into on this carb?

After having seized 2 previous engines (170 & 200, pistons swelled up in the bores) I am probably a bit hyper sensitive. I do know that the engine rattles more now that I have 2K+ miles on it (in my car, was told it had about 50K miles on it when I bought it and the lack of oil consumption tends to confirm that). TIA.

 

[Bort62]

There isn't much to control fuel flow in the 1100 other than the main jet.

Buy a set of numerical drill bits and get busy

 

[addo]

One really needs to know the RPM a bit. If it's approaching a practical limit in terms of carb or manifold CFM, I can imagine a pretty decent amount of turbulence at the carb mouth. What if this is affecting airflow/speed?

 

[BIGREDRASA]

No power valve in the 1100?

 

[aribert]

Thanks all. I did a bit of playing with the choke while on my latest freeway runs. Very easy to dial in the A/F using the choke. At 60 mph, the choke was about 3/16 out and at 70 mph the choke was about 5/16 out. But I do not want to have to apply the choke every time I jump on the freeway.

Bort: I already have the nuber drill bit set and have over drilled jets for Weber side drafts in my other 6 cyl car but there I had a good idea as to where I wanted to end up based on the jet numbering relating directly to the dia of the metering hole(s). Any suggestions as to how many thou oversize for a first drill attempt?

Addo: I would ***guess*** that the engine was at about 3600 to 3900. A couple of years ago I taped an inductive tach to the wiper arm and drove down the road recording the rpm to mph. But that info is logged into the car service log which is kept in my workshop garage (10 mile from home).

BIGREDRASA: There is a power valve but the carb rebuild instructions had a big disclaimer: DO NOT REMOVE (so I didn't). Is there something about the power valve that I should look into? I have another 1100 that I could pull the topcover (w/power valve) and swap in if it might help.

The accelerator pump has 2 settings high & low. I left it in the low position - am I correct in presuming that the high will give a bigger pump shot? I think I need a bit more accell pump but am interested in getting the steady state cruise dialed in first.

 

[BIGREDRASA]

Do you still have the old carb? What jets are in it?

Before tearing into anything, make sure you have no vacuum leaks. This is not uncommon after a carb change. Crank the idle up to around 1800 RPM (use the high speed idle cam on the choke linkage). Wave an unlit propane torch around all fittings, openings (such as throttle shaft), and mating surfaces. If the speed increases, you have a leak.

Make sure your PCV valve is not stuck open by shaking it, and maybe spraying it with carb cleaner. Maybe just change it anyway.

Another thing is to check that your fuel pump is putting out sufficient flow.

If none of that helps, maybe you can mod the power valve. For the life of me, I can't remember what the power valve on the 1100 looks like. If it has an accessible spring, maybe you can cut off part of it, and stretch the remaining portion.