Air Fuel Ratio Carb Tuning

[Scott06]

Ok so after a year of dialing the carbs on my GTO I'm going to move my AFR meter set up to my boat. Was hoping to get experience from folks regarding best AFR for marine applications.

Boat is a '04 Sea Ray 200 sport - 21 ft Bowrider,3500 # dry weight, large lake use
engine is a stock 5.0 ( I repowered from a 4.3) with a 4bbl intake( cast iron generic from Mich Motorz) and Edlebrock 1409 w 1/2" phenolic spacer, stock otherwise including TBV ignition. 1.81 ratio drive 21" pitch revolution 4. Best speed of 48 mph gps w 12% slip

Boat performs well most use is loaded watersports. Not looking for improved performance just to ensure I have good AFR and am not lean anywhere in the curve. Also I already owned the meter and lets face it I can't leave well enough alone...

So the real question what AFR ratio s should I target at idle (assumed 13.-14.0), cruise at 3k rpm or so (13-13.5?) and WOT (assumed 12.5 or so)? Are these good targets considering the load in the engine? Was hoping folks had good experience dialing things in.

And yes I did tweak the carb (two steps richer on primary step up rods, one step richer on step up spring, biggest accelerator pump nozzle) and engine shows no signs on plugs ( a tad rich looking) or via borescope on piston tops. Sometimes I get a touch of hesitation at WOT as I move through upper 3k rpms, really looking to see if that area is rich or lean ...

 

[itsathepete]

Sounds like an interesting experiment. Waiting to hear how it works. Does the AFR gauge need a certain temperature to operate like standard O2 sensors? Will water cooled exhaust cause a problem?

 

[Scott06]

Sounds like an interesting experiment. Waiting to hear how it works. Does the AFR gauge need a certain temperature to operate like standard O2 sensors? Will water cooled exhaust cause a problem?

Yes it goes through a heat up mode. It is a standard bosch wideband 4 wire sensor. The plate to stab it in goes between manifold and elbow. Innovate only recommends using it for tuning not constant placement as even though it is 'dry' there there the wet exhaust will shorten sensor life. Kit came with a plug to block off sensor port when not in use

I never used one until I set up the tripower on my GTO what a leap forward from plug reading. I my plugs looked rich but I found I had a lean spot in the transition circuit before main boosters took over. Interested to see what this is doing... I thought I had it well dialed in but last year I installed the 1/2" spacer to keep things cool for improve hot restarts ( fuel dribbles down into intake) and all of the sudden I'm running lean. Rebuilt he carb (6 years old) and it was completely clean ... fattened up step up rods and it went away, spring change improved the stumble in upper 3's so think I'm there...

 

[Rick Stephens]

Always wanted to do that, never did though. Hope you get a target answer. Might have to ask a marine engine builder.... or someone like Mike's Carburetor?

 

[Scott06]

Always wanted to do that, never did though. Hope you get a target answer. Might have to ask a marine engine builder.... or someone like Mike's Carburetor?

Offshore only has a bunch of info most of it targeted at more go fast boats with deeper investment level than we are running. Innovate motorsports has some info on their page.
Wasn't a bad tool I think less than $200 (one sensor only) , like the ignition analyzer (measures kV of spark) I bought a few years back I'm trying to get baseline numbers when everything is working well. ... the only issue is more info = more carb tear downs to play with jets....

 

[nola mike]

I'm dying to do this. Those numbers seem rich. Might try to see what the TBI models run at. Esp with the Holley sniper systems you might be able to find that out relatively easily

 

[Scott06]

So I was able to get this installed a few weeks ago and try things out. Only install issues I had was needing 1" longer bolts for the elbow as this 1" plate was sandwiched in...(stock is 5.75" long needed a 7" and trimmed off 1/4"), and the o2 sensor sits so close to the top of the manifold I needed to grind down the 3/4" pipe plug in the manifold top so the o2 sensor would fit... Harden could have made the plate a tad thicker..

Luckily the factory hardness that came with the gauge was long enough to get up to the cup holder by the helm which was convenient to stick the gauge in for a temporary install. This is the guide I was using for AFR targets- https://www.innovatemotorsports.com/tuning-a-marine-carb/

What I found surprised me as I was way too rich and lean at the same time... like low 11's nipping into 10's at WOT, cruise was like mid 12's. I had had a bog when mashing the throttle like pulling a skiier. AFR was going way lean (18-20 AFR) when hitting it and it was tough to recover when getting on a plane with a skiier. I had previously enlarged the accelerator nozzle to the biggest (.033?) and put the rod in the uppermost hole, plus went 2 steps richer in step up rods. What I saw on the AFR meter was way lean then way rich as the boosters responded to WOT. The engine pitch changed where it was very rich and stumbled, which I had mistakenly assumed was running lean...

Issue was the accelerator pump linkage rod had some play in it. I bent it straight to keep some pump spring pressure on it which eliminated the delay in responding and the lean spot. Since I was adding too much fuel later in the rpm band I was getting a stumble between 3500-4000 rpm which was too rich...

Bottom line I tried it with step up rods 1& 2 (factory setting) steps leaner than where I was. Although the factory setting gave more text book AFR numbers it didn't feel as responsive and seat of the pants was better at one step richer (.065x .042) with the 7" pink step up springs. Also Idle and transition seemed better a tad richer 13-13.5. If I set the idle at 14 ish I got a lean rpm wander 1000-1500 rpm in no wake zones. 3000 rpm cruise I ended up around 13-13.5, WOT was 12.5 ish.

Only other odd thing I saw was if you cut back the throttle quickly it would go very rich, with the change in engine pitch.

Bottom line is except for the issue with accelerator pump linkage and nozzle upsizing on this engine the 1409 is pretty close out of the box. In retrospect I should have seen that the linkage to accel pump was sloppy...

 

[Rick Stephens]

Can you better define out of the box? What jets, springs and needles were installed? Then where did you end up?

I never had to do anything out of the box with the accelerator nozzle.

And I found that opening the secondaries for the last half only produced more noise, not more speed. So I never run past around 3/4 throttle. Did you find differently?

 

[Scott06]

Can you better define out of the box? What jets, springs and needles were installed? Then where did you end up?

I never had to do anything out of the box with the accelerator nozzle.

And I found that opening the secondaries for the last half only produced more noise, not more speed. So I never run past around 3/4 throttle. Did you find differently?

Out of the box aka stock 1409 has the following:
.098 primary jets, .068 x .047 step up rods with orange (5" vacuum) springs, .101 secondary jets.

I landed on :
Stock jets (.098/.101)
.065 x.042 metering rods (1 step richer both cruise and power)
Pink step up springs (7" vac)
.033" accelerator pump nozzle with pump rod in upper (richest) hole

I thought you had mentioned using a bigger nozzle in your tuning thread years ago... which is when I started on this... another six years I should have it nailed down...Maybe it was someone in your thread ...

Yes I do find the last 1/4 throttle helpful/useful as lightly loaded I can hit the limiter, and yes I end up with more noise as well.

I have a bigger engine -with 600 cfm on a 4.3 you can open the throttle but air flap above secondary's may not move open more due to lack of need for airflow ? I have never watched at WOT and close to upper RPM limit how far open the air flap is.

 

[nola mike]

That's awesome. I so want to do this, maybe next season. Got some pics of the setup, and what exactly you had to buy? I'm curious as to why @Rick Stephens has such different settings for his carb than mine with a very similar engine. I'm in the same situation with more noise than power up top (I do get a few hundred rpm). Change in sound is very noticable when the secondaries open.

 

[Rick Stephens]

Ah, I missed somehow that you were on a 5.0L. My understanding when I bought my 1409 was it was pre-cal'd for a 5.0L. So this now makes more sense.

Lisdexic.

 

[Scott06]

That's awesome. I so want to do this, maybe next season. Got some pics of the setup, and what exactly you had to buy? I'm curious as to why @Rick Stephens has such different settings for his carb than mine with a very similar engine. I'm in the same situation with more noise than power up top (I do get a few hundred rpm). Change in sound is very noticable when the secondaries open.

This is the sensor plate goes between manifold and elbow, you need 4 x longer bolts (6.75" long), plus a sensor of your choice
sensor plate-

O2 Spacer, Stock Mercury Riser Wet Joint

O2 Spacer, Stock Mercury RiserThis Unique 1" thick adapter plate provides an installation option for retro fitting a Oxygen sensor and or air fuel ratio gauge for tuning purposes Into Mercruisers most common Wet Joint style exhaust manifold systems. The

www.michiganmotorz.com

Sensor Kit - https://www.amazon.com/gp/product/B0184TSI84/ref=ppx_yo_dt_b_asin_title_o03_s02?ie=UTF8&psc=1

Kit has wiring between sensor and gauge plus power supply harness. I just took a spare supply fuse under the dash and unplug it when not in use.

I think what you and are seeing that you can open the throttle plates the last 1/4 but the air flap above the secondaries doesn't pull open more because a 4.3 doesn't need any more air, but not sure why the noise would change... Your jetting may be different if one has vortec heads vs pre vortec?

 

[nola mike]

This is the sensor plate goes between manifold and elbow, you need 4 x longer bolts (6.75" long), plus a sensor of your choice
sensor plate-

O2 Spacer, Stock Mercury Riser Wet Joint

O2 Spacer, Stock Mercury RiserThis Unique 1" thick adapter plate provides an installation option for retro fitting a Oxygen sensor and or air fuel ratio gauge for tuning purposes Into Mercruisers most common Wet Joint style exhaust manifold systems. The

www.michiganmotorz.com

Sensor Kit - https://www.amazon.com/gp/product/B0184TSI84/ref=ppx_yo_dt_b_asin_title_o03_s02?ie=UTF8&psc=1

Kit has wiring between sensor and gauge plus power supply harness. I just took a spare supply fuse under the dash and unplug it when not in use.

I think what you and are seeing that you can open the throttle plates the last 1/4 but the air flap above the secondaries doesn't pull open more because a 4.3 doesn't need any more air, but not sure why the noise would change... Your jetting may be different if one has vortec heads vs pre vortec?

My jetting is actually a bit fatter than stock (don't remember exactly). Plugs looked perfect when I pulled them a few weeks ago, but like you're seeing that only gives me an average. I feel a touch sluggish out of the hole and I think I should top out better than 48 mph (which is the same as my 3.7). Guess I can have someone driver while I look at the secondaries, but I'd be shocked if that noise wasn't the secondaries opening. Presumably the 4.3 can use the airflow, esp with vortec heads, since merc and vp put the 4bbl on them. FWIW Michigan motorz uses the stock settings on their crate 4.3 motors (1409, vortec heads, same as mine).
So $300 for something that is almost completely useless except that it's cool...sign me up.

 

[Scott Danforth]

Just catching this thread now.

I am toying with pulling my H-pipe cross-over and modifying it for an AFR meter unless I can find a thread in small diameter Wide-Band O2 sensor where I can drill in-situ...... as I am currently trimming my AFR by tweaking the air bleeds and the emulsion bleeds on the Holley.

 

[Scott06]

Just catching this thread now.

I am toying with pulling my H-pipe cross-over and modifying it for an AFR meter unless I can find a thread in small diameter Wide-Band O2 sensor where I can drill in-situ...... as I am currently trimming my AFR by tweaking the air bleeds and the emulsion bleeds on the Holley.

On my gto i used a clamp on bung that goes over the exhaust pipe, but they were rusty pos pipes nit what u have but it would save you pulling it to weld in a bung. Needs to be upstream of water dump in…

 

[Scott Danforth]

@Scott06 I have about 5/8 of an inch between the marmon clamps and the end of the ring. So I would need a mini O2 sensor with an m10 thread or smaller, or I have to bore thru the inner and outer water jacket, weld up the inner and outer tubes to the stainless bung

Not enough room to run a sandwich spacer.

Should have added them when I fabbed the exhaust

 

[Scott06]

My jetting is actually a bit fatter than stock (don't remember exactly). Plugs looked perfect when I pulled them a few weeks ago, but like you're seeing that only gives me an average. I feel a touch sluggish out of the hole and I think I should top out better than 48 mph (which is the same as my 3.7). Guess I can have someone driver while I look at the secondaries, but I'd be shocked if that noise wasn't the secondaries opening. Presumably the 4.3 can use the airflow, esp with vortec heads, since merc and vp put the 4bbl on them. FWIW Michigan motorz uses the stock settings on their crate 4.3 motors (1409, vortec heads, same as mine).
So $300 for something that is almost completely useless except that it's cool...sign me up.

Not surprised that you have to go fatter on a smaller displacement engine. I would suspect you get less strong of a vacuum signal in the booster and pull less fuel. Mich motorz 1409 on the 4.3 , 5.0, and 5.7 partial engines. the air flap ( maybe not officially eddy Terminology) allows the carb to only supply needed air for engine size Similar to qjets secondaries But controlled different.
its not completely useless, to me its a maintenance tool. Once the stab in is there if you have an run ability issue down the road you can compare to baseline. It was really helpful on my gto setting up the tripower.

if you have vortec heads you should be around 220 hp vs what you had with the 3.7. I assume the 4.3 added 150 lbs of weight maybe more Which is working against you. can you trim out fully without prop blowing out? I picked up 3-4 mph top end because the revolution 4 can bite when fully trimmed out

 

[nola mike]

if you have vortec heads you should be around 220 hp vs what you had with the 3.7. I assume the 4.3 added 150 lbs of weight maybe more Which is working against you. can you trim out fully without prop blowing out? I picked up 3-4 mph top end because the revolution 4 can bite when fully trimmed out

I don't think I'm fully trimmed out, and I think I'm stern heavy. I have a 4 blade that I'm going to give another shot. I have a prop thread open but everyone is suggesting 3 blades.

 

[nola mike]

its not completely useless, to me its a maintenance tool. Once the stab in is there if you have an run ability issue down the road you can compare to baseline. It was really helpful on my gto setting up the tripower.

Definitely not completely useless, that's tongue in cheek. It's running "good enough". Nobody but me would spend the amount of time (>>money) on an essentially worthless boat. This carb tuning by reading tea leaves is barbaric.

 

[Scott Danforth]

This carb tuning by reading tea leaves is barbaric.

However it builds knowledge that most people can not comprehend