Gas mileage issues, '86 BRAT

[TomRhere]

Haven't looked into anything yet, but will be heading outside in a bit to start checking things over.

 

Problem I'm having is way lousy gas mileage for the last 2 weeks or so. I filled the tank this last Tuesday, and only drove 200 miles before gauge showed less than 1/4 tank, took a shade over 9 gallons to fill it on Friday. That ain't good at all....

 

Been awhile since I've done a full-to-empty run in it, but that tank got me 322 miles before I chickened out and bought gas. So I know I can do better than what the last 2 tanks have gotten me.

 

Bit of history of maintenance done in the past month;

11-23, new tires 185/70R-13's same as what was on it.

re-adjust rear brakes, adjust clutch.

11-27; new oilpan gasket, new valve cover gaskets along with adjusting the valves, new disty cap & rotor, plugs and wires are less than 6 months old, did an oil/filter change, new OEM PCV valve.

12-7; replaced altenator, swapped battery cables out for heavier gauge ones.

 

This is an '86 BRAT GL 4spdD/R, Weber carb on an EA-82 carb intake on an older solid lifter engine (mileage unknown), no ASV, stock Y-pipe into a XT6 mid-pipe, no muffler. Timing is at 10*, doesn't seem to like the factory setting of 8*.

 

It's been running real good until the last 2 weeks, still seems like it's running good, no smell of raw or un-burnt gas, doesn't chug or lope like it's flooding or running rich, still has plenty of giddyup to it going down the road. No miss while running at any RPM.

 

Kinda thinking I may have gotten the valves abit tight, but not sure. Set them to the middle of the range they give in the book, just like I've done each time I've adjusted them.

 

BRAT rolls easy, I can push it on a flat surface while sitting in the seat and putting one foot on the ground, so I don't believe there's any dragging brakes. Goes straight down the road with no pull to either side.

 

Just looking for ideas that I may have over looked. Can't really recall how she did last Winter, but the temps might have some play in this. It's been in the teens or low 20's for the past couple weeks, so yea, maybe so.

[Frank B]

Check that the choke isn't closed a little. Is the engine getting up to temp? If the thermostat is stuck open and the engine never reaches operating temp, the mixture could be too rich. You don't have a gas leak do you? I'd say pull the plugs to see if they are black, brown or white. Brown is better. Oh and is this place that you filled up a regular stop for you? Could have gotten a bad mix. These days with all the ethonal blends, just a little water in the fuel and it seperates and turns to goo. That ethonal will rot in the tank and run like crap in the engine. It could be as simple as bad gas. Try that before digging too deep.

[TomRhere]

Yeah, the choke opens fully and within the proper time frame.

 

Engine gets up to temp, normal time frame there. Runs just below 1/2 on the gauge, never above that. Good heat from heater/defroster, windshield clears of frost within 5 minutes of starting engine. Running a 195* OEM T-stat.

 

Haven't pulled plugs yet. Just came in for a hot cup of coffee. Cold, windy and rainy out there, Brrr....

 

No gas leak that I can find, no smell of gas around vehicle, other than from carb after engine was ran, warmed up, shut off.

 

Hmm,,, could be the gas as I did fill the tank at the other station on my trip to/from work. Bought gas there before though, don't recall any issues. But,,, could've been the delivery they got that week.. Dunno.

Have a BP and a Mobil that I normally stop at, and Tuesday was the BP, been mostly the Mobil though.

 

Wife thinks it's from doing the 5 minute warmup in the AM and when leaving work. I really can't see where that would account for that much change in the mileage. Filled it Tuesday morning, filled it again Friday night, so that's roughly a 1/2 hour total warmup run. That's almost one trip to work, time wise, running at 55 MPH, it does it's warmup at 1100 RPM's. Just can't see it burning that much gas..... Even with the choke being on for part of that run time.

Edited December 14, 2008 by TomRhere
added more text

[Wirebrush]

Temps play a huge part for two reasons. First the choke is on longer using more gas and second, the lube in the engine, trans, and diff get very thick and take a lot of power. This is very pronounced in cars like the Brat because of the extra diff in the rear soaking up power and the fact that there is very little power to begin with. My Brat will actually move forward in neutral when temps are very low due to the viscosity of the trans fluid. The best thing you can do is to have the gear lube and trans fluid replaced with a good synthetic and have a block heater installed.

[TomRhere]

Well,, the plugs look good. Can't really tell color but they're light in color. This cold I have is affectting my vision somewhat, so color hues are iffy at best.

 

Think I'm done playing out in the rain/wind/cold today...

 

May just chaulk this up to iffy gas and cold temps, as I really didn't find anything obviously wrong. 22 MPG sucks when you drive 64 miles a day.

 

Thanks for the input......

[Wirebrush]

Depending on where you live many refiners add alchohol to the gas in the winter as well to prevent water accumulation and possible gas line freezing. Unfortunately the 10% alchohol mixture also reduces gas mileage by 10%.