Weber tuning/adjustment

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Joined: Tue Feb 26, 2019 12:51 am

Weber tuning/adjustment

Post by ftpiercecracker1 » Tue Feb 26, 2019 5:27 pm

85, 3A-C, 5spd

About 250k on the clock. Just finished installing the Weber kit, but having some difficulty dialing it in.

I also bought the recommended Holley regulator (1-4psi), but didnt have enough money to buy a gauge.

1.Is there a way to set the regulator to roughly the appropriate pressure without a gauge? Like, seat the screw and three turns out?

Also, on my distributor there are three vacuum ports. From what I've read, the lowest one is the vac advance and as such I have it plumbed to the vac advance on the carb.

I have read that one of the other two is supposed to be ran to the intake manifold. The problem the two remaining ports on my distributor are identical sizes, some people have said you can tell them apart by their size, but mine are identical. I dont know which should be plugged, ran to the manifold or whatever. I've swapped manifold vacumm back and forth during test drives but with the other issues I'm experiencing it's hard to tell if it helps.

2.Can someone post a picture depicting which port is which?

3.Where should the charcoal canister be hooked up? Vacuum wise.

4.The problem I'm experiencing when driving is a on and off type of stuttering under acceleration.

Put it gear, take off with moderate acceleration and the engine is smooth at first, then stutters rapidly, then is smooth, then stutters rapidly again.

Like it's running out of gas. It is not low on gas.

5.What should the plug gaps be? Recommended brand?


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My tercel:: '84 Tercel4wd w/extensive mods
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Re: Weber tuning/adjustment

Post by Petros » Tue Feb 26, 2019 8:03 pm

use NGK plugs, standard setting is .040" gap.

Usually the jets that come in the weber are proper for the 3ac engine, there are jet kits you can buy on line with a selection of differnt size jets you will need. Also,there is a thread in this forum on configuring the jets on the Weber to work on the 3ac engine, start from there.

sounds like the air emulsion jets are the wrong size, causes fuel starvation as certain engine speeds/fuel demands. but I am not an expert on Weber carbs, I have messed with them, but actually prefer the factory carb if it is working well and in good tune.

you have a low speed idle mixture screw, and two sets of both air jets (air emulsion tubes) and fuel jets for intermediate and high speed driving. the engine characteristics/fuel demand profile has to be matched to the carb by changing out the air and fuel jets on the carb for both the intermediate and high speed driving conditions (idle can be adjusted with the mixture screw). the ones recommended in the weber thread should get you close enough so it is derivable, and you can fine tune it by going one size up or down from there, and drive it for a tank or two of fuel (and keep records on fuel economy and acceleration power for each jet combo).

The fuel regulator does not need much, only 1-2 psi for the weber. if you back it out too far (too high fuel pressure) the carb will flood out. so you just want to set the lowest pressure above where you get stall out (fuel starved), and no more pressure that causes flooding. It seems just a little way above "0" is all you need.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
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Re: Weber tuning/adjustment

Post by xirdneh » Wed Feb 27, 2019 4:54 pm

the ports on the vac advance are the same size on outside (diameter) but if you look at the end one has a smaller hole (pinhole) and that one is for the high altitude compensation
Love those Tercell 4x4 wagons but they sure suffer from road noise.

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