1991 Wagoneer - Basic Carb Tuning/Running Rich?

[Brynjminjones]

Hi All,

I've been spending the past month or so really trying to dial in the 2150 on my 1991 Grand Wagoneer.
It used to run dual-fuel on propane/gas, but all the propane stations around here recently closed so I've been forced to go back to just running gas.

I think I'm getting pretty close to having it sorted, but I think it's still running a little rich.

It starts and drives great, it runs beautifully smoothly at idle and it's got a good amount of power too.
It is generally as responsive as the fuel injected 4.0 in my XJ.

The trouble is that it's using more gas than I think it should, plus the plugs look a touch rich to me.
I know these things will never get any kind of MPG that can be classed as "good", but I'd like it to be as good as it can be as I drive it a lot and gas is stupidly expensive here.

Driving like there's an egg under the pedal at 55mph, I can't seem to crack 12 mpg.
In normal mixed driving (still driving gently) I'm getting 9-10 mpg.


Now for some details:

-Engine is a .030" over rebuild, with Melling MTA1 "RV" camshaft.
-Carb is the original 2150 with 1.21 venturis.
-It has #56 jets.
-Idle mixture is tuned for max. vacuum - 2 1/8 turns out on both screws.
-Idle speeds set to exact spec from FSM.
-Choke operates correctly and is fully open once warm.
-Timing is 14 at idle, 36 all in.
-Vacuum advance hooked up to ported vacuum.
-EGR present but disconnected.
-Charcoal canister not connected.
-No other emissions stuff.


So, my questions are:
1. Would you agree that I should be getting better gas mileage than I'm seeing?
2. Am I correct in thinking that this plug looks rich around the base ring?
3. If yes to those questions, what should I change next? I'm thinking of perhaps jetting down but don't know if that's the right thing to do.

Waggy Spark Plug by Brynjaminjones, on Flickr

Thanks in advance, sorry for the long post!

[wiley-moeracing]

The plug looks good, you can try and jet a smaller and see what happens, that mileage is about what it is supposed to be, you can try a free flowing exhaust system and intake to try and help.

[Brynjminjones]

Thank you, I did think that the plug looked mostly good, just a little too black around the base.

I've been doing a lot of searching on here lately and from what I've read, plenty of people seem to be getting 1-2mpg better than I am with the same carb.
I know I'm not going to manage much improvement, but I'm sure I should be able to squeeze something better out!

Even our '74 Ford F100 with a poorly tuned 390 and 2100 carb uses less fuel, and I'm not gentle on that thing at all!


I did some more research last night and read that disconnecting the charcoal canister will cause it to run a little rich with the stock carb - is that true?

I've been working on getting it reconnected this morning. First I had to fix a hole in the purge diaphragm so it will hold vacuum now.

I had a question on that too: There are two vacuum ports on the charcoal canister, the small one goes to ported and the other to the PCV manifold vacuum.
The ported one now holds a proper vacuum with a hand pump but the manifold one doesn't.
Am I correct in thinking that the manifold vacuum connection is basically a deliberate vacuum leak?

[Brynjminjones]

I've spent this morning working on this further.

On my first attempt I fixed the charcoal canister diaphragm with some silicone, but a little while later it started leaking again. I was possibly impatient in letting it set, but I still wanted to find a better fix.

I managed to get a used bicycle inner tube for free from a local bike repair place, and I've made a replacement diaphragm with that instead. I cut a large circle for the main diaphragm, then glued a smaller circle in the middle to replicate the thicker section.
It's not particularly pretty but it works perfectly!

Charcoal Canister Diaphragm 1 by Brynjaminjones, on Flickr
Charcoal Canister Diaphragm 2 by Brynjaminjones, on Flickr
Charcoal Canister Diaphragm Vacuum by Brynjaminjones, on Flickr




I've also replaced a load of the vacuum/vapor lines to the canister. I was sifting through my box of hoses when I realized how out of hand my collection has gotten lately. I'm guessing every Wagoneer owner probably has a similar collection hiding somewhere!

Mess of Hoses by Brynjaminjones, on Flickr



I've then gone back and adjusted my idle, it needed an extra 1/4 turn with the canister hooked up.
The Jeep is running and driving fantastically, so I'm looking forward to seeing if this improves anything.
I'm not expecting miracles but I get peace of mind knowing that things are set up right!

[wiley-moeracing]

You will not find 1 magical solution to better mpg other than buying a small jap car! You can make many small improvements to help but all will cost some money and what will the payback be? Try full synthetic oils in all components of drivetrain, free flowing headers and exhaust, free flowing intake, better ignition, higher tire pressure or better more fuel efficient tires, driving style, fuel injection, etc. and you may pick up 2-4 mpg. a lot of work and money and time for such little payback.

[rapom]

Maybe you can check, adjust your vacuum advance. At cruise it should be advancing your timing a lot more, 50 degrees plus, which really helps with fuel economy. May need to buy an adjustable vacuum advance.

[DarkMonohue]

Are you adjusting those figures for our little US gallons, or is that what you're seeing on imperial gallons?

I average about ten MPG (US gallons) in short around-town trips in my J20, also with a 360 and a 2150. It has deeper gears, bigger and knobbier tires, worse aerodynamics than your GW, and on top of all that, normal pump fuel in my area is 10% alcohol. All of those factors are disadvantages. Your GW should be doing better than my pickup. It won't be great by any means, but it should be better.

[DarkMonohue]

Anything new to report?

As I understand it, reading spark plug color for air-fuel mixture isn't really valid with unleaded fuel. Without a wideband oxygen sensor, you will never know the numbers, but you can still jet it by feel. If the 56 mains work well you can certainly drop down a size and see how it feels. If it gets too lean under light load it'll typically start to buck or surge. If it runs smoothly under light load then it's typically getting enough fuel. Someone will probably wring their hands in despair about being too lean under WOT, but I would wager there's a sufficient safety margin in the factory jetting.

Your vacuum advance can may have a set screw for adjustment, accessed by inserting an Allen key into the vacuum fitting. I don't remember how much adjustment is available but it may be worth looking into.

Something I failed to ask is how much time you're spending warming up the engine. That can burn more fuel than people realize, and it contributes zero miles to the miles-per-gallon equation.

[Brynjminjones]

Sorry, I totally missed your last post!

All my figures have been in US MPG. I've only had American cars so I'm very used to being on US forums

The figures you say you're getting are definitely better than mine. I just calculated my last tank (mostly short drives around town plus ~20 mins idling whilst I fiddled with idle mixtures) and I got 7.5 MPG!

The vacuum advance is set pretty well (I think). I've adjusted it so it basically drops out around the same time as the power valve comes in. I did this based on Ristow's post elsewhere on here.

I don't tend to warm the engine much. I fire it up, let it high idle for ~10-15 seconds, then kick the idle speed down and drive out of the garage so I don't get gassed!
Another minute whilst I open/close the gate then I drive off gently.

One thing I have thought is that maybe my choke isn't coming off quickly enough. It isn't connected to the electric heater so just relies on the heat pipes to warm up.
I have checked though and it is fully open by the time the engine gets to operating temperature, but maybe it could open a touch quicker?
I still wouldn't have thought that would be enough to ruin my MPG figures on long highway drives though.


I'd also just like to add that I know this thing won't ever get "good" gas mileage but if it's using more than it should, that's a sign to me that something isn't tuned right and it could be better!

[rang-a-stang]

...I've also replaced a load of the vacuum/vapor lines to the canister. I was sifting through my box of hoses when I realized how out of hand my collection has gotten lately. I'm guessing every Wagoneer owner probably has a similar collection hiding somewhere!

Mess of Hoses by Brynjaminjones, on Flickr
...

Facts! I have mine in a bag. Everytime I need one, I dump that bag on the garage floor and start sifting. It's amazing how often I have to crack out my vacuum pump to check lines, fittings, etc.

[babywag]

One thing on stock 2150 power valves...they're dual stage.
iirc 11.5 and 9.5??
If you put a vacuum gauge on it and watch it isn't hard to hit 11.5 even driving pretty mild.
Aftermarket parts are also of dubious quality these days, so a new valve may be out of spec.?
Ristow states Quickfuel power valves fit.
Stock jets are rich on them too, dropping a size can't hurt.

Didn't you have mystery gas spot on base of this carb?
Maybe a Holley 2bbl would be better than 30yr old carb.

[DarkMonohue]

All my figures have been in US MPG. I've only had American cars so I'm very used to being on US forums

The irony. My first car was an absolute sweetheart of an MGB and I spent a long time immersed in that world. Gotta build me another one someday before I get to old to enjoy it. Contrary to rumor, not all of the US is billiard-table flat, and there are plenty of good sports car roads over here.

Definitely get the choke working correctly. For my money, it's always best to fix the problems you know you have rather than outfox yourself thinking about whether they do or don't matter.

[Brynjminjones]

Rang-a-Stang, yup, that's exactly how I go through them as well! Dump them on the floor then fight them back into the box.
I've recently worn out my second hand vacuum pump from using it so much, maybe time to invest in one that isn't the cheapest from eBay!


Tony, funny you should say that as I'd also been wondering about the power valve.

I'm using a stock 2-stage power valve, like you said. I actually tested mine with my hand vacuum pump and it seemed to start opening somewhere around 8, fully open by about 2. That doesn't seem to coincide with what everything I've read says it should do, but I've tested it repeatedly.

With my "RV cam" I get vacuum at idle in gear of around 11 (neutral ~15), but I drove around with a vacuum gauge hooked up for a while and I can pretty effectively keep out of the power valve vacuum range whilst driving.

I've thought about ordering some Quickfuel valves like Ristow said. What kind of range would you go for? I was thinking somewhere around the 7 mark.

You're right that I did have a mystery gas spot, but I don't seem to have had any problems with fuel disappearing since the weather cooled down.


DarkMonohue, sounds great, I've never had the chance to drive an MGB but my mom had an MG Midget when she was younger that she adored.
Last time I was in the US we found some great driving roads, and they were a lot less crowded than the ones over here!

I think I will look into getting the choke heater working properly. I've been paranoid about all the fires I've read about so I've left the plug disconnected from the oil pressure switch, so no voltage gets to it.
I think I just need to add a fuse to that wire then hook it all back up.

[babywag]

If you have a cam should really ditch the 2bbl intake/carb.

[Brynjminjones]

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!)