All Small Six Which cylinder head?

[Otto]

but if it were me, I'd advance the timing by loosening the distributor hold down and gently tapping the distributor with the 1/2" open end wrench to move the vacuum can 1/4" in the advance direction. Lock down and try it. Keep doing this till pinging is heard, then go back 1/4" and you then know timing is perfect for those highway conditions.

I can certainly try this the next time I take it for a spin. It's easier to reach the distributor bolt from under the van than from the engine box, so I'll try to make a wrench.

When driving the van, I'm only applying light throttle right in the meat of the torque curve- It scoots along very well. If it wasn't burning more gas than a Buick station wagon towing a boat, I'd think it was running perfectly!

 

[Otto]

Fabricated a phenolic spacer and installed it on the engine under the carb. The aluminum adapter runs very cool when the engine is running, but when you shut it off it transmits a lot of heat up to the carb. Plus, the heat inside the small engine box is considerable. During an initial start up, the spacer seems to be blocking heat after turning off the engine- the aluminum is hot, but the spacer is not. A test drive will be the true test.

 

[Otto]

A test drive this evening was disappointing; I bumped up the timing like Frank described- advancing a bit at a time and listening for pinging. I tried this a few times and the doghouse’s Lizardskin thermal and sound application must work well because I couldn’t really hear the engine ping. With it being right next to me between the seats you would think it would be more noticeable.

I still didn’t see any more vacuum than the 10” Hg the gauge shows at any time during the drive except coasting. After I got home, I attached the timing light and measured 55* total mechanical advance as my last adjustment where before it was at 35*. All that timing was accomplished before 2000 rpm. Baffling.

After shutting the engine off at the end of the test drive, the aluminum adapter got very hot but the phenolic spacer and carb base was not. I’m calling that a win, so something went right.

 

[awasson]

My 200, with the weber 38/38, header and clay smith camshaft didn't so much ping on hard acceleration but there was a point somewhere around 2000 RPM if I had my throttle partially open and it had a little load when I could hear the ping if I was driving somewhere the sound could bounce like driving beside a tall road divider median with my windows down. I backed mine off a little at a time over a few sessions and now I think it's as good as it's going to get.

Initially, I was running mine with about 22° initial + 10° vacuum advance + 14° mechanical. After some tweaking occasionally during the first 1000 miles, I brought down the initial and am probably now closer to 15° initial. I will have to put my light on it and confirm that. Mine is all in sometime before 3000 RPM.

 

[Frank]

A test drive this evening was disappointing; I bumped up the timing like Frank described- advancing a bit at a time and listening for pinging. I tried this a few times and the doghouse’s Lizardskin thermal and sound application must work well because I couldn’t really hear the engine ping. With it being right next to me between the seats you would think it would be more noticeable.

I still didn’t see any more vacuum than the 10” Hg the gauge shows at any time during the drive except coasting. After I got home, I attached the timing light and measured 55* total mechanical advance as my last adjustment where before it was at 35*. All that timing was accomplished before 2000 rpm. Baffling.

After shutting the engine off at the end of the test drive, the aluminum adapter got very hot but the phenolic spacer and carb base was not. I’m calling that a win, so something went right.

Thanks for the update! Since you saw no power or vacuum improvement, put the timing back to 35* if you haven't already. Thanks for doing the test. It didn't pay off in your case, but now you know.

 

[Otto]

Thanks for the update! Since you saw no power or vacuum improvement, put the timing back to 35* if you haven't already. Thanks for doing the test. It didn't pay off in your case, but now you know.

10-4

 

[Otto]

My 200, with the weber 38/38, header and clay smith camshaft didn't so much ping on hard acceleration but there was a point somewhere around 2000 RPM if I had my throttle partially open and it had a little load when I could hear the ping if I was driving somewhere the sound could bounce like driving beside a tall road divider median with my windows down. I backed mine off a little at a time over a few sessions and now I think it's as good as it's going to get.

Initially, I was running mine with about 22° initial + 10° vacuum advance + 14° mechanical. After some tweaking occasionally during the first 1000 miles, I brought down the initial and am probably now closer to 15° initial. I will have to put my light on it and confirm that. Mine is all in sometime before 3000 RPM.

Thanks for your response, I did have a similar experience with hearing what I thought was some light detonation up a slight grade on light throttle with the AFR meter reading high 14, low 15s but it was very inconsistent. I'll set the timing back tonight and I have another experiment to try- I'll work on that.

 

[awasson]

@Otto, I put the light on mine this evening to see where my timing was. I have the original line on my damper and then added 2 more lines 14 degrees apart so I can see up to 42 degrees of timing. I put a white, yellow and amber line on each one so I could see them and quickly calculate my timing.

As I mentioned, I’ve been finessing the timing, idle speed and idle mix for the past 2000 miles and for the last couple of months I’ve been playing by ear and smell. It is no longer overly rich. It’s still a bit rich because it’s got a carb and not catalytic converter but it’s not horrifically bad. The timing I’ve been doing by ear and smoothness and it’s about as good as it’s ever been.

I put the light on and to my immense surprise, it’s at 12 degrees initial. Timing is all in around 2,200-2,500 RPM or so. It runs as best as it ever has. I’m running Chevron 94 with zero ethanol.

 

[Otto]

There’s something I’ve always been curious about this marine carb since starting to make it work on my van’s engine. Since a boat’s engine primarily is intended to idle or run wide open, maybe mid throttle “driveability” wasn’t a critical concern. The issues with how the van runs is more fuel consumption rather than power production. The original engine for this carb was a 3.0L 4 cylinder and now it’s sitting on a 3.3L six. As the Mercarb (and 2G as well) is only adjustable via the idle mixture screw and main jets, there’s not much else that can be fine-tuned. Main jets and power valves for the Mercarb are unique and aren’t interchangeable with 2G carbs, but it appears the venturi clusters are.



Weber carbs have optional emulsion tubes that can be swapped to tailor a tune, the 2Gs and Mercarbs don’t have removable tubes and the venturi clusters package the emulsion tubes and air bleeds into one unit that has been engineered for a particular engine. I removed the venturi clusters that I have and compared them- they are labeled P, for a Pontiac carb; M= Mercarb, and C= Chevrolet. Spent some time gauging the holes in each cluster with torch tip cleaners as go/no go gauges to arrive at how each cluster measured.

Orifice	Pontiac 26958	Chevrolet 6635	Mercarb 442
Pump Shot	0.028"	0.031"	0.024"
Idle tube	0.028"	0.038"	0.028"
Inner Air Bleed	0.031"	0.024"	0.032"
Outer Air Bleed	0.041"	0.076"	0.061"
Emulsion Tube holes	0.047" all	0.055, 0.038, 0.028"	0.046, 0.038, 0.035"
E Tubes bottom hole	0.038"	0.047"	0.046"

I’m curious if either of the clusters I have could work better for improving low throttle fuel economy or could be sacrificed for experimentation. Maybe increasing an air bleed slightly or soldering up emulsion tubes and redrilling?

Do any induction scientists here on the Ford Six page think this approach could work?

 

[Frank]

Interesting that the tubes are not removable, first I've heard of that. My Rochester experience is with Q jet.
Since the carb is on a larger displacement engine it will tend richer by default. And, yes marine carbs are metered richer in the part-throttle cruise mode since marine applications see moderate to heavy loads at all times, there is no light-load cruise (accompanied by vacuum advanced timing) that allows the mixture to meter lean without overheating.

Modifying the air bleeds is more forgiving than modifying the emulsion tubes, less mixture change relative to the change in orifice.

The Chevy cluster is what I'd recommend trying without mods, if it will match up. I assume the Chevy cluster is from an automotive application.

 

[Otto]

I've heard that operating boat engines is like always driving a car uphill, so I can understand it might be set up a bit "fat" to avoid detonation or overheating- good point Frank. I guess my assumption was the carb would possibly run lean on a bigger engine, but you're saying it will run rich. That is not what I would expect. Could you elaborate on that please? I'm trying to wrap my head around it.

The extra clusters are from 2G applications from a Pontiac and a Chevy truck; that's as far as the clues the numbers yielded. I assume from V8 engines ranging from 300-400 cubic inches.

I also bought the Doug Roe book on Rochester Carburetors, so I'm reading through that.

 

[Otto]

I installed the Pontiac cluster on the Mercarb as a shot in the dark based on the similar orifice sizes and tried running the carb on the van’s engine. After setting the timing back to around 15* btc, it seems to run similar to before but initially idled a bit lean so I backed out the idle mix screw a bit. A test drive will tell the tale.
Still impressed with the phenolic spacer. After shutting the engine off and the engine heat migrating upwards, the aluminum adapter was blistering hot but the spacer and the carb base felt room temp. Seems like magic.

 

[awasson]

Hopefully you'll get some decent weather for a test drive. Today was nice for us, just above you. I think it's going to cloud over tomorrow but maybe Wed/Thurs will be decent.

Oh and yes, the thermal break that the phenolic makes is so effective that it's almost unbelievable. As you said, the adapter is blistering hot. My carb used to get hot like that as well. Now the carb stays cool. Around the mouth of the carb, it is cold when it's running but the rest of it is just cool and it stays cool even though the engine around it is blistering hot. Magic.

 

[Otto]

On a lark, I took the van for a test drive this evening. It was dry and we still had some daylight so why not? The AFR was vastly improved! Where it would previously read 11s and 12s, now it was mostly 14s and low 15s with some 13s under throttle. Idle and WO are still about 12.5.

Vacuum readings really didn’t read much over 12” Hg, but the engine ran well with no hesitations or flat spots- very smooth. But the objective with this was to improve fuel usage, so more testing will tell. We’re into the wet season here so more evaluation may have to wait.

Super happy to make tonight’s discovery!

 

[DON]

High of 73 and partly sunny today. Fla car show season is just getting started

 

[Otto]

High of 73 and partly sunny today. Fla car show season is just getting started

Lucky you! We've been experiencing stormy wet weather described as an "atmospherical river". Test drives will have to wait.