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Old 09-30-2007, 09:04 AM   #1
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Carburetor Options

While this question is in regard to my latest acquisition, an 83 Tercel SR5 4WD, the answer may be more broadly applicable to other carb'd vehicles.

In short, faced with what seems to be poor fuel economy from the current carburetor, I have two upgrade options available: a 34mm DGEV dual throat, or a 32/36 DGEV dual throat.

I can't find any direct promotion for it, but I suspect that the 32/36 would deliver better economy AND more top end performance than the 34 would, but how much?

It would be a no-brainer to just get the 32/36, but there is a $150 price difference - which at my current annual mileage would take about 15 years to recoup at 1 mpg difference, but at 5 mpg difference would take 3 years to pay off. From a strictly financial sense with only 2500 miles driven per year, the extra $150 clearly is not worth it at only 1 mpg improvement. But this is a car that we will likely keep at least for another 5-10 years and might ultimately end up with many more annual miles put onto it. Obviously just doubling annual mileage strengthens the arguement for the more expensive carb significantly.

Would anybody like to offer any guesses or actual experience here?
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Old 09-30-2007, 02:50 PM   #2
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i'd have to look up the speciffics but i had my car's carb replaced with a similar one that was intended for a bigger engine... the only real difference where the size of the jets wich where slightly bigger on the new carb.. they did make the car feel a bit more powerfull but also made a bit better FE.... the difference isn't to great and i don't have any direct evidence to attribute the change to the carb alone, the old one was replaced because one of the adjustment screws had a worn sealing... it proved a free replacement carb (with a slightly different adjustment screw) was easter to gind than a tiny rubber ring... so FE improvement might be because the carb is actually adjusted better.... although the old always turned out "normal" FE for a 20 year old car
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Old 09-30-2007, 04:15 PM   #3
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Have you considered replacing your carb with a "throttle body injector" chamber, and then using something like a "mega-squirt" ( http://www.megasquirt.info/ ) to control the FI in the throttle body?

Of course, I haven't tried this myself, so this is all theory at this point (and therefore YMMV). However, I think the theory is sound, as a throttle body chamber looks to the engine as if it's just a smart carburetor. So in theory at least, just replacing the carburetor with a proper throttle body (with a proper engine computer running the throttle body's fuel injector) should keep the engine happy. And as an added bonus of this approach (especially from a FE standpoint), you should have complete control over your fuel map, vs being limited (like the rest of us) to just what fuel/air ratio some car maker wants to let you have in any given situation.
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Old 09-30-2007, 05:00 PM   #4
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I considered the EFI option, but it's a $1700 car at best that would require installing a mess of sensors and wiring. I'd be more interested in that option if an engine swap were part of the upgrade, but with 200k miles, it is still running clean and strong.

Supposedly either one of the Weber options available are an improvement over the stock carb fuel metering at idle and high load.
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Old 10-07-2007, 08:54 AM   #5
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Well it is definately looking like I have carb issues now. With not quite 200 miles on the car, it has already gone through more than 3/4 of a tank, which is only about 20 mpg in a car that should get closer to 30 - and I've been doing EOCs and short shifting the entire tank. I really can't justify the more expensive carburetor however, as I doubt the efficiency difference is really there.

I'm thinking that the biggest thing I can do to improve economy once I get it installed is to really lean out the idle. We'll see I guess.
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Old 10-07-2007, 06:13 PM   #6
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Have you considered that the weber will make the car more pleasant to drive. For $150 I'd almost do it just for the sake of the car running better. On another note, being that the car is carbed it would be very simple to swap to an LP conversion. Propane is clean burning and I've been told not anymore expensive to use than gas. There are quite a few drag racers that do turbo/propane combos in cheap cars that run very well.

Well its a thought.
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Old 10-07-2007, 08:47 PM   #7
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$150 is the price difference between the two different models. Regardless, the cheaper one is still only $249. I'll probably order it this next week.
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Old 10-08-2007, 07:06 AM   #8
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I guess it comes down to what I think my time is worth and where it will be best spent. A rebuild kit is about $50 vs. $249. So the question is whether it's worth $200 of my time to rebuild the stock one.

I do hate to throw useable stuff out! :P
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Old 10-09-2007, 09:06 AM   #9
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I have a 32/36 you can buy for $100. I had it running my hovercraft's Subaru 1600cc engine. I went back to the stock carb.

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Old 10-09-2007, 05:47 PM   #10
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Why did you go back to the stock one?

Regardless, I think I'm going to try the rebuild kit first just because I don't want to junk it. I'll see what happens with that and consider other options if necessary later on.

Thanks!
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