1991 Wagoneer - Basic Carb Tuning/Running Rich?

[nograin]

That's about typical milage for mixed driving.
Only conditions I consistantly get over 12 mpg are long drives on highways without any stop lights and signs.

EGR may help help the milage slightly. Without it, there might be a little bit of efficiency to be found in slight tweaks to the mid to high timing. Simplest experiment will be if the vac advance can be brought in a little sooner to any effect. Any other experiments will be a fair amount of work.

[babywag]

Hi Tony,

The cam I've got is just a pretty mild Melling MTA-1. I chose it because I didn't care about top end power but just wanted a bit of a low-down torque boost.

I had thought that because it had little effect high up the rpm range, I should get by just fine with my standard carb.

What's the reason you think I need to upgrade? (Not meaning to sound argumentative by the way, genuinely wondering!)

generally speaking a 4bbl carb has smaller primaries which helps with fuel economy if you stay outta secondaries.
the stock 2bbl intake is kind of lacking.
these run very nice with small cam/intake/etc.

[Brynjminjones]

Nograin, that's a good point re. the timing. I have recently backed the vacuum advance quite a way off so there was no overlap between it and the power valve.

My power valve is a two stage though, and there never used to be any kind of pinging when the advance overlapped the first stage, so I might try bringing it in a little sooner again to see if that helps.

Tony, that's an interesting point on the 2 vs 4bbl. I would be tempted to swap, but I think if I were going to the trouble of buying a new intake manifold, I'd rather bite the bullet and get the Edelbrock Pro-Flo 4 kit.
I've been looking into it for a while now and it's the first time I've really been tempted by EFI!

I should also mention that I've recently got my electric choke heater working again. It hasn't really made a noticeable difference, but hopefully it might help on short journeys where the choke wasn't fully opening before.

[DarkMonohue]

Tony, that's an interesting point on the 2 vs 4bbl. I would be tempted to swap, but I think if I were going to the trouble of buying a new intake manifold, I'd rather bite the bullet and get the Edelbrock Pro-Flo 4 kit.
I've been looking into it for a while now and it's the first time I've really been tempted by EFI!

The idea of a packaged solution has its appeal, but they went and stuck it on a single-plane manifold. Great if you're running 7500 RPM at Santa Pod, but not for 99% of FSJs. Compared to a dual-plane (Performer, et al), you will see a reduction in torque and throttle response at the real-world engine speeds you actually use burbling around with the kids and the dogs in search of ice cream.

If they'd have built it around a dual-plane manifold, it wouldn't be as sexy to look at, but it would be a hell of a lot more useful to all of us here.

[wiley-moeracing]

The dual plain is a mute point if the injectors are injecting directly into the valve area like most new vehicles do. A dual plain will be beneficial when you have a aftermarket injection system with a injector set up on top of the intake.

[DarkMonohue]

The dual plain is a mute point if the injectors are injecting directly into the valve area like most new vehicles do. A dual plain will be beneficial when you have a aftermarket injection system with a injector set up on top of the intake.

I am going to have to disagree. Fuel distribution aside, the dual plane offers a big advantage in throttle response and cylinder filling at the speeds these things see. The Pro Flo system uses a race manifold with short, fat runners and a huge open plenum compared to the longer, smaller runners and much smaller (partially due to being divided) plenum that a street oriented dual plane manifold uses. The advantage may be more a result of smaller runners and plenum than of being a dual plane design, but the point remains.

That's all I want to say here in order to avoid derailing the thread any further.

[wiley-moeracing]

Would be happy to discuss further in private messaging, but agree to leave this off this post.

[Brynjminjones]

Thanks both for your input on that, it's something I wasn't aware of and will look into further if/when the time comes!

DarkMonohue, I'm impressed that you've heard of Santa Pod. Funny enough, I was actually there two weekends ago in my Wagoneer, not racing though!

Santa Pod Night by Brynjaminjones, on Flickr


I do have another issue I've spotted in the past few days related to fuel consumption, but probably not worth its own topic.

The fuel line into the front of my 2150 is definitely leaking gas. It's a steel line going into a brass fitting.
Gas is weeping along the threads of the steel line, so I don't think it's a leak from the carb body itself.

I've got it nice and tight but it won't stop. Any idea what can be done?

[wiley-moeracing]

Replace the gas line or remove and cut off the end a re-flare it.

[Brynjminjones]

Thank you. I've taken it off and found a little nick in the mating surface. I've sanded the surface smooth so hopefully it should be good now.


In other news, I think I've finally found why this thing is using too much gas!!!

I was playing around with it this evening, and decided to take the top off the carb and test how much vacuum it took to open/close the power valve.
I noticed straight away that the power valve in there didn't close as far as the one I've got on the shelf when vacuum was applied, even though they're supposed to be identical parts with the same rating.

I took the carb off and removed the power valve. Look what I found!

Broken Power Valve by Brynjaminjones, on Flickr


I don't know how well you can see in the photo, but the body of the power valve was splitting in half around the threads!
I remember when I installed it, it felt like I'd over-tightened it a touch so I left it as I was too scared to take it back out. It all makes sense now!

I applied vacuum to it, and even with it closed I could blow right through it.

That, on top of the fact that this power valve doesn't fully close, must be why I'm using a little more fuel than I'd have expected.

The funny thing is that because of the way it had failed, it held vacuum just fine so it seemed like nothing was wrong with it.

I'm not expecting miracles on the MPG front, but I should hopefully see a small improvement.
I'll report back after I've run a tank of gas through it

[Brynjminjones]

I've now put a tank of gas through it and we're up to 11mpg, mixed driving. That's getting closer to what I was expecting so I don't think I'm too worried now, not that that will stop me from obsessing over it!


The only concern I still have is about a slight hesitation that it now has on throttle tip-in. I'll describe what's happening...

When started from cold, it fires right up and idles great. Blipping the throttle brings it straight down to a lower idle and I can drive straight away.
The issue is that there is a hesitation on throttle tip-in when driving gently. If I accelerate harder it's barely noticeable at all, but of course I try not to do that on a cold engine.

Once the engine is completely up to temperature it pretty much completely goes away, but this takes somewhere around 10 minutes so isn't exactly quick. The choke fully opens in around 3 minutes so I don't know if it's choke related or not.

If I stop in a store for 20 minutes, when I restart the Wagoneer the hesitation comes back and will stay for another 5 minutes or so until the engine gets all the way back to operating temperature again.


Because there is no hesitation when the engine is FULLY warm, I assume that rules out the accelerator pump?
I thought it might be the choke cover setting, so adjusted it to stay on a little longer. It has improved the hesitation but also makes it run a little rich and lumpy after a couple of minutes. I feel like it might just be masking the issue.
I also thought about the choke pull-off, but surely that only affects it for about a minute before the choke starts moving?

The fact that this issue has come about since replacing the broken power valve suggests to me that the previous artificial rich condition was hiding this tuning issue, so I think it's a lean stumble rather than a rich one.


Any help on this would be much appreciated! I'm getting very close to having this thing dialled in - I've been driving it on propane for the last 3 years so have never driven it on gas long enough to discover these issues!

[Brynjminjones]

I think I may have this sorted!

I removed the accelerator pump yesterday and noticed the "button" was lightly corroded.
I've cleaned it up with some emery cloth to make it nice and smooth, then reassembled.

I didn't think it would do anything, but the last two days I've not had any hesitation problems at all!
It still drives a little "flat" when the choke is active but it's not a real hesitation. I guess I can't expect a carbureted engine to drive like fuel injection all the time!

Operating the accelerator pump by hand it seemed fine before, so I guess the corrosion must have been stopping it from moving smoothly with small throttle openings.

[rang-a-stang]

Awesome!! Well done!!

[MysticRob]

Just a quick FYI in general for MPG figures on any car, go to fueleconomy.gov and punch in the specifics on the vehicle you want to get MPG figures for. I've looked up many vehicles in the past and they're always very accurate. The powers that be a few years ago finally tweaked the algorithms to give MPG results based on real-world driving habits, not the make-believe figures we could never achieve (i.e. 55 MPH speed limits, etc).

Using a 1991 GW, your MPGs should be close to 10/11/12 for local/combined/hwy mileage.
Blame that on 4500 Lb weight, only 3 speeds in the ancient transmissions, and good old inefficient carburetion.

[Brynjminjones]

Thank you, it does give me some more confidence in my tuning to see that I'm actually getting the exact quoted figures!


I've now started playing with yet more stuff - I'm trying to reconnect the EGR.

I tested it by pushing up on the diaphragm whilst idling, and it nearly killed the engine (as I think it should).
I then hooked it up to vacuum and raised the rpms. I could feel the diaphragm moving so it looks like it might be working properly!

The only problem is that it has now introduced another part-throttle flat spot. Should I install a delay valve to help with that?


My other concern is about the CTO switch. I don't have any of these switches that still work, so I've hooked the EGR straight to ported vacuum.
Will this cause problems when the engine is cold?