View Full Version : Poor gas mileage help.

03-17-2008, 10:27 PM
The 1g has been running REALLY well for the past month or so. It's got good power, the car starts right up for me and it's smooth and quiet at idle.

Last two times I've been at the gas station, I've measured my mileage at about 24mpg. It sucks because I expect to get better mileage than my 2g got with the same carb on it. I'll admit I'm a bit heavy-footed, but even the 2g got 28mpg with an even heavier foot.

I double-checked the timing, and it's advanced just slightly more than the recommended setting. It seems to run better this way, and I run premium fuel anyways.

I have one symptom that seems weird to me, and that's the catalytic converter ticks a lot after I shut the car off. I'm not sure if it's getting too hot or if it's due to a bad mixture or what, and if it's just another symptom of bad jetting possibly... Or if maybe it's shot and time to gut it... I mean replace it with a "high flow" version. Any ideas?

03-18-2008, 08:01 AM
Are you using the mail jeep carb? Did you ever post your jet sizes in the jet size thread for that one?
There is an old parts house here that has ooodles of carbs, new rebuilt. I got a carb kit for this other weber and the top hat gasket is too small and after talking to them some more they had several versions of the 5200, the one you have.. does it have third extra booster helper in the venturi? This one did for that small engine like the one you got yours off of. The one for the vega looks pretty servicable and I may get one, 65 bucks!
As to the concern, yep you may need to tinker some on that carb, float level first.

03-18-2008, 08:18 AM
You can run a bit more base advance with the mods you have, you might also try backing the throttle screww all the way till the throttle plates are shut. It still should run but very low rpm.. then try and adjust your mixture screw (not past two turns out from bottom, and do not bottom out the screw hard into the seat it will ruin it) Then bring up your base throttle stop idle to around 600 rpm and set your timing . That gets you a good base point to start tweaking from. Get as much advance you can without detonation, then go back and readjust the carb settings.
What kind of air filter housing are you using btw?

03-18-2008, 10:53 AM
I'm using the actual Weber that was on my 2g. Not the 5200. I wanted to run something on this car that I knew would work out of the box to minimize potential problems. I posted the jet sizes I found on that thread, too.

I've played with the base mixture on the Weber and got it set up like you suggested. It's well within limits, so I think the idle jetting is okay. I downsized the air corrector jet on the secondary barrel because it seemed that the car was leaning out up top, bit of power loss after 5000RPM. That helped that a bit. Seems to run really nice now is the wierd thing. Spark plugs don't show signs of excessive lean or rich... But I'm guessing that could still be an issue.

I'm kinda not thinking that jetting is my problem. What's your opinion on that catalytic converter noise?

I'm using a stock Weber air filter. Not the short one that comes with the carb, but a taller one that is just like it. I might try cleaning it and see if that helps...

You can pick up rebuilt 5200's from a few places. All good and ready to go. I think Clifford Performance sells them. Or whoever that company is that specializes in domestic inline 6 engines.

03-18-2008, 12:01 PM
ticking exhaust shields are somewhat normal, but you may want to shoot an infrared thremometer at that to see how hot it is. glowing red is a dead giveawayv:wave:
yep I saw your jet sizes on that thread, just wondering what was in the other one you have.

03-18-2008, 12:33 PM
ticking exhaust shields are somewhat normal, but you may want to shoot an infrared thremometer at that to see how hot it is. glowing red is a dead giveawayv:wave:
yep I saw your jet sizes on that thread, just wondering what was in the other one you have.

Oh the jet sizes in the Weber?

03-19-2008, 03:30 AM
Oh the jet sizes in the Weber?

the sizes of the brass in the holley you have, just curious.

03-19-2008, 08:46 AM
Oh the idle jets. Yeah I haven't pulled them out yet. Waiting to get a fuel pump for the 2g since it died and I'm short on money for a couple weeks. I wanted to see if it would run at all in its original configuration... I'll check it out later this week.

So what all do you suppose could be problems that I can check out to fix my mileage?

1) Jetting
2) Mixture setting
3) Timing
4) Catalytic converter

Anything else that could possibly be doing it? Any gaskets or pieces in the carb that could be not functioning properly?

03-20-2008, 02:44 AM
i did my first ever mileage calculation and got around 30mpg, and i've been quite economical. with the bigger carb and heavier foot you're running, it doesnt seem as horrible on fuel as i thought it might be...

03-20-2008, 03:43 AM
you should be getting a whole lot more than 24 mpg even gassing it every now and then.
Some areas to check/ ensure the timing belt is not a tooth off, double check your tdc mark that you are using the right one. I know you have already:)
It could be a leaking power valve in the carb, jetting wrong for the displacement as well. Make sure your vacuum advance works correctly if you have it.
Wheel alignment, tire pressure n all that. Check that air filter element sometimes those just get so grimmy they dont even wash out well anymore, you can tell that easy by seeing if you pick up ten or so rpm at idle just by taking it off.
REcheck valve lash adjustments..

make sure the e brake is off ?? LOL.


03-20-2008, 08:15 AM
Thanks for the input. I'll give the valves a thorough lashing... ;) Check the clearances for sure.

I'm beginning to think it might be the wrong jetting, since the carb was off of my other car. They're both "1.8 liter" engines, but this car is a 1751 while the other is an 1827. So almost 100cc difference. I'll tinker some more tomorrow on my day off and see what I find.

03-20-2008, 08:24 AM
what all did you do to the head, was is a cvcc and you converted it right?

03-20-2008, 09:01 AM
It's a stock cylinder head. I was going to do the EL conversion to get rid of the CVCC and bump compression... but the cylinder head I got was for the wrong year so I never did it.

This cylinder head, I had rebuilt with parts from two cylinder heads. Full valve regrind, head was resurfaced, cam was reground to stock specs due to the usual wear, and they told me they adjusted the valves to the correct spec, but I haven't readjusted them yet or even checked them for that matter...