Running lean after engine swap

[nola mike]

Finally splashed my 3.7L --> 4.3L swap today. A few issues remain, but the biggest is that I'm running lean. Seems to run fine up until about 2500 RPM, but starts surging after that and eventually starts backfiring if I push it. Doesn't matter if I ramp up slow or fast. Interestingly, it gets on plane without stumbling badly. Doesn't do it smoothly, but doesn't backfire either. Again, I can hammer it or go slowly, and it planes ok. Plug after chopping and running at around 2500 rpm is attached.

The block is an '01, with the peripherals from an '89. I put on a new manifold, 4 bbl Edelbrock 1409. Carter electric fuel pump.

Carb was setup per Rick Stephens guidance, running basically the same setup:

.095 (part#1426) primary jets
.092 (part#1425) secondary jets
.065" x .057" (part number 1461) meter rods
7" pink step up springs

Problem is i have NO idea where the issue is. It can literally be anywhere in the fuel system, since everything past the gas tank is new or new to me.

1. Old (ish) gas. No water in the filter, but it wasn't nice and clear either. I put in 5 gallons (27 gal tank) of fresh before going. I don't think this is it, but I'm going to go out with a jerry can next.

2. Carb. Oy. Bought the carb used, so strike one. A bit of a crap shoot on how to set it up, but used the jetting and metering that a few others have used with success. But it's never been used on this boat. Strike 2.

3. Fuel pump. It was only putting out 2.5-3 psi when installed. No idea if it's running out of gas (ha ha) at higher rpm. No easy way to tee a gauge into my hard line to see what it's doing when I'm running, though I don't know what I'd be looking for anyway. 2.5 psi and lean condition might be enough to get yet another new pump, right? I'll need to put together a rubber line for testing, but it will have to wait till I get home.

Any other suggestions welcome. Should I swap in some larger jets? Fatter springs? The edelbrock tuning guide is set up for a 5.0 which is allegedly too rich for this motor. I'm not sure which order I should start swapping things, a 4bbl carb is new territory for me.

 

[Lou C]

Have you had a look at your anti siphon valve? That can restrict fuel flow if corroded. What about the pick up tube in the tank? Ever have this problem with the old engine or no?
was the 1409 totally cleaned out?

 

[nola mike]

No, didn't check any of the fuel system, but no problems with the old engine. The 1409 looked clean but I didn't do it myself. I'll run it on a Jerry can tomorrow, that will take everything before the pump out of the equation.

 

[Rick Stephens]

Popping and surging at 2500 RPMs is not yet even near secondaries. So primary jets and or needles is the place to approach this. You can fool with needles by just changing to stronger springs, which richens up the mix by holding the needles open against more vacuum. Use smaller diameter or shorter needles. Or you can drop in a couple notches richer main jets.

What parts do you have on hand that were pulled out?

 

[nola mike]

It's tough to know what to change. Stiffer springs, shorter needles (although they have a diameter dimension as well), fatter Jets... I only have what came with the carb, which I assume is stock. I couldn't read the numbers off the Jets. I think I'll try to just throw in the stock stuff and see what happens. I should run rich. If that happens I know I have a carb tuning issue. If not, then I might need to investigate the fuel pump.

Edit: I also have a full set of springs

 

[Rick Stephens]

Need a headset:



Do one thing at a time. Need to read the calibration manual so you know how the 1409 works, then go after the specific things that are noticeably lean or rich. I would strongly recommend you take this in a organized fashion. FLoat level, fuel pressure, primary jets, springs, needles. Probably in that order.


Shorter or skinnier needles are richer.

Stronger spring is richer

Larger jet, of course.

 

[kenny nunez]

Have you checked the float level? Also the inlet screen.

 

[nola mike]

No inlet filter, the float is correct. Rick Stevens , the manual is less helpful since I'm not starting from stock. I just don't know which part of the system to adjust first. This might be enjoyable if I wasn't so over this project.

 

[Rick Stephens]

Float level, fuel pressure, primary jets, springs, needles. Probably in that order.

And you won't tag me with someone else's name spelling ;^)

 

[Rick Stephens]

A more complete answer: the carburetor being not 'stock' matters not at all as far as following the manual goes. How the carburetor works is the important part of the manual, the changes made to the carburetor add up no matter where the start point is. The approach should be to address the worst symptoms one at a time and see how those changes effect things. Then you can narrow in on tiny final adjustments. All adjustment have a fairly narrow focus, yet have wider ranging effects, a main jet change for instance will effect things from soon after cracking the throttle up through WOT. While needles and springs are much more narrow in effects.

Your description of surging and apparently running lean at 2500 RPM makes me think you are mid-range in the primaries. That puts you right in the main jets for the primaries for making your adjustment. You do not change multiple items as that will make changes across a wider spectrum - a potentially frustrating experience as you fix it at 2500 only to screw it up at 1800 RPMs.

It took me several calibration trips when I did my 1409. I took parts and pulled the top off the carb while sitting mid-lake. Next trip, after receiving different jets, needles and springs, didn't have to pull the top since I made changes in jets and needles in the shop and only changed the springs on the water. I did not spend near as much time trying to calibrate the secondaries. Still not sure it is just right as it doesn't increase engine power output throughout the opening of the secondaries. Gets noisier but doesn't appear to add speed. Not sure if that is a calibration problem or just the motor not being capable of using all the CFM available. I never run WOT except maybe once a season for a couple minutes. Cruising solely on primaries is much more efficient and a more relaxing way to boat, for me at least. And more especially for her bossness.

It should be fun calibrating. I get it that your boat repair mental fix was completed months ago. Just have to recapture that joy for a little longer.Imagine how the fishing is going to be next year with all the bugs worked out.

 

[nola mike]

Thanks for the continued help, Rick Stephens (I blame iboats for the last tag). Been reading more about this and searching the forums. Surprisingly few posts on working combos on this motor, and I couldn't find anybody using .098 primaries. I'd like to follow the edelbrock guide, but the metering rods I went with aren't on the table. It doesn't look like I have a step in between stock and what I'm running. I'm going to go back to stock and confirm that it runs rich (or perfectly!). Also may try to call edelbrock and see what they recommend as a starting point. If I'm rich, I guess I'll have to get a set of metering rods. On the chart, the closest point is #8, with a leaner power setting. So..IDK. #1 is only one step richer at cruise. Windy today, not sure if I'll be able to get back out. What's the advantage of a 4bbl if you're not getting more power when the secondaries open?

 

[Rick Stephens]

What's the advantage of a 4bbl if you're not getting more power when the secondaries open?

Not very damn much advantage. However, a 4 barrel running on the primaries is more efficient at midrange throttle settings than a 2 barrel with the larger venturis.

 

[nola mike]

1. Opened the secondaries today. They sound pretty sweet.
2. Swapped in the stock primary jets as well as metering rods. Also put in plain springs by accident (thought they were the stock setup).

So no more backfiring. I was able to get to 3500 rpm before I backed off. Secondaries open at that point. Did about 5 miles at 3200 rpm. Plugs *still* look lean (well,#5 is the only one I checked). But really smooth. Definite hesitation when I hit the throttle, and it's slower out of the hole than it should be. I'll need to spend more time and pay attention to this stuff. I'm still afraid to do a wot run. I may put the .101 secondaries back in before I attempt it. Fwiw, I hit 41 mph @3200 rpm, so I don't know if my tach is off or if this thing is going to hit mid 50's when I'm dialed in (which is possible).

What's the next step? I assumed I'd be putting out a smoke screen with this setup, and going richer seems wrong, but the plugs don't lie. I'm just wondering if I can rule out the rest of the fuel system at this point. I don't know why I'm so far off from your setup Rick Stephens.

​​​​​​​Pics are #5 plug from both sides

 

[Rick Stephens]

Yup, plugs don't lie. Those pulled on the water when you did a quick shutdown after the 3200 RPM run?

Any chance you have an intake leak?

Hesitation when you hit the throttle can be throttle pump or need of stronger springs. When you hit the throttle, the vacuum drops and the springs push the needles up. The stronger the springs are, the longer the needles stay up. As vacuum builds back up the vacuum pulls the needles back down leaning the mixture.

 

[nola mike]

Yeah, those were pulled on a quick shutdown. I did another run at 3k today and pulled #4, looked similar. Intake leak? Idk, anything possible. All new gaskets, everything lined up and torqued to spec, so no reason to think that. I'm still confused by power and cruise mode. I'm thinking I tune my plugs to cruise mode, and then the springs to immediate throttle response, and power mode to prolonged acceleration? Not sure where acceleration pump comes into play v springs. So many variables. Wondering if I should buy a tuning kit? I think I need fatter cruise springs? I also can't set the idle mixture. I can turn them all the way in and it will stumble, but I turn out 4 turns without a change. I have them both at 1 ½ now. Need a better tach, i can't detect a 40 rpm drop by ear

 

[nola mike]

Ordered a shop tach, and 3 sets of rods, .065*.047, .063x.047, and .065x.037. going to swap out yet another fuel pump to take that out of the mix, though if that were were the issue I wouldn't expect a jet change to make any difference. Thursday or Friday.

Also found that my flame arrester doesn't fit. Trying to find a replacement. Looks like the pn is 805298A1, but that comes up as a rochester carb when I search for it. Anyone know the correct number, or preferably something cheaper to use?

 

[Scott Danforth]

I would check your anti siphon valve.

 

[nola mike]

I would check your anti siphon valve.

Because of the symptoms or the low psi? Initial symptoms with the smaller jets started immediately after starting the boat, and the pressure was measured running on a jerry can. But yeah, easy enough to rule out.

 

[Scott Danforth]

I would pull the end cover off the carter fuel pump and look at the vanes. you could have debris in one of them, thus the low output pressure.

something is taking your pumps out.

 

[Rick Stephens]

Ordered a shop tach, and 3 sets of rods, .065*.047, .063x.047, and .065x.037. going to swap out yet another fuel pump to take that out of the mix, though if that were were the issue I wouldn't expect a jet change to make any difference. Thursday or Friday.

Also found that my flame arrester doesn't fit. Trying to find a replacement. Looks like the pn is 805298A1, but that comes up as a rochester carb when I search for it. Anyone know the correct number, or preferably something cheaper to use?

The flame arrestor that came on my QuadraJet equipped motor fit the 1409, if that is any help. Also any arrestor made to fit a Weber will fit.