tripple weber jet sizes and adjustment

[willybowden]

Hi, I have a 77 formerly fuel injected L-28 with tripple weber 40dcoe's. The engine ran rich before with some weber dgv32/36's also. Excellent exhaust, later model distributor. I know its way too much fuel for this engine. It'll blacken a set of plugs really fast. I just dont know how to correct the problem, or if it can be corrected. Chokes, jets, cam? It'll run fine, until it fouls out a set of plugs every 20 miles putting it around. Any help would be appreciated. Hey does anyone want set of tripple webers? .

[gogriz91]

There's some goo dinfo here if you search for it, another place to check would be hybridz.org there's a post specifically about jetting your triples.

[willybowden]

I know it was a vague question, but this car has been aggravating me for years. Its way to beautiful to sit doing nothing because of this. Hell, I built it myself from 3 different cars. I'll do some research. Just didnt know if anyone here had a simular configuration.

[Babalouie]

40DCOEs will be just fine, that's what I run on my L28. First step is to see what you have got.

Remove the round covers on top of the carbs, and unscrew the main jet and emulsion tube.

The main jet is at the bottom...

...and the corrector is at the top.

The choke size is a little tricker to find....it'll be cast into the front of the choke tube, which is behind the "pillar" in this pic...this is looking right down the throat of the carb from the air filter side. Easy to see if you have the carb out and sitting on your bench, not so easy to find if you're just leaving the carb on the motor and messing around with flashlights and mirrors

The jet/corrector sizes are a matched set with the choke size, so you won't know if your jetting is in the ballpark until you obtain the choke size you currently have. As a rough rule of thumb, most ppl say that the main jet should be 4x the choke size, and the corrector should be 40-50 bigger than that. In my case, the chokes were 32mm and 125mains and 175 correctors (I swapped out the 220s in the pic above) and turned out to be optimum after some dyno tuning, so the rules of thumb are pretty much on the money IMHO.

At the end of the day your jetting could be perfectly correct, but the carbs are just out of tune. But verifying your current hardware is a good place to start.

Edited March 29, 2010 by Babalouie

[Walter Moore]

Babalouie, that is one cool post.

[willybowden]

Hell yeah, thanks a million. I had the emullsion tube out the other day, I believe the main jet said 130. I'll check on the chokes asap. It's a bone stock 77 model L-28, dont know if this matters. Thanks again!

[ChrisZ]

Pretty nice write up, maybe you could make one more explaining the basic setting at first start up, and how to adjust after that.

Would be a good sticky if so.

Chris

[willybowden]

Other than the Chokes, main jets, and air correctors, are there any other componets like idler jets or something odd like that. Seems like it really loads up at idle, but has always been gassy and fumy. Gonna pull em off and check the choke size asap.

[Babalouie]

Pretty nice write up, maybe you could make one more explaining the basic setting at first start up, and how to adjust after that.

Would be a good sticky if so.

Chris

This first step is just to see what Willy's got to work with. If the jetting is wrong, then there is no point trying to tune around it until we address it. But sure, once we we ensure that the jetting/hardware is all in the ballpark, then we'll look at the tuning.

Other than the Chokes, main jets, and air correctors, are there any other componets like idler jets or something odd like that. Seems like it really loads up at idle, but has always been gassy and fumy. Gonna pull em off and check the choke size asap.

Yup. You see those two smaller brass screws next to the main/correctors (under the round cover)? Those are the idle jets, and you can just unscrew them to have a looksee. They seem to be quite forgiving though, so anything from 45 to 55 seems to work just fine.

Try this check for now: see those big screws with the spring? That's the idle mixture screw and there's six of 'em in total.

Now the way it works is that from idle to 3000rpm the idle circuit is doing all the heavy lifting. So the fuel is coming thru the idle jet and the mixture is set by the idle screw.

Between about 2500rpm and 3000rpm the idle circuit fades out and the main circuit (that's the main jet) blends in. At the top end, the main jet is still providing the fuel, but left to its own devices it will be too rich, so the corrector compensates by allowing some air to bleed in at the top end to balance things out.

So above 3000rpm the mixture is purely set by the jet/choke sizing. Below 3000rpm, the fuelling is set by the size of the idle jet, however, you also have that idle screw mechanism to fine tune it. From what you described, you're fouling the plugs at low rpm so it probably isn't your main jet/corrector/choke that's at fault (just the same...you really should pull one carb out to see what you got).

Anyway...back to the idle screw...get a screwdriver and very gently with fingertip pressure, turn it clockwise and count how many turns before the screw bottoms. The more turns (out) it is, the richer the idle setting. Take a pic of one of the carbs if you could, but if yours is an early carb (made in Italy, it will say Bologna Weber Brevitatta), then a rule of thumb is that one turn from bottom is about right. For a later carb two turns is more like it. A quarter turn too rich and it will blacken the plugs a little, a half turn too rich and they'll be quite black. So see what you got, pull the idle jet and read the size, then count the number of turns the idle screws are currently at. If your idle jet is too big, then you might find that the ideal setting is less turns out than the rule of thumb and vice versa. But let's see what idle jets you got, and how many turns the screws are at. If the idle screw is out by miles then we can cover how that is adjusted.

BTW it could be an ignition fault we're dealing with too...if the spark is weak the plugs will foul. But we should at least eliminate the carbs as a cause.

Edited March 30, 2010 by Babalouie

[ChrisZ]

You sure seem to know your way around Webers, i don't know of how much of it that is the same for Dellorto's but i am in the learning stage, being that i am putting on my triples as i write this, so i will follow your write up.

I allways learned that ignition should be solved before carburation, am i wrong.

What is your user name on Auszcar, i assume you are a member there.

Chris

[Babalouie]

You sure seem to know your way around Webers, i don't know of how much of it that is the same for Dellorto's but i am in the learning stage, being that i am putting on my triples as i write this, so i will follow your write up.

I allways learned that ignition should be solved before carburation, am i wrong.

What is your user name on Auszcar, i assume you are a member there.

Chris

Well the car I have right now is the first one I've had with multiple Webers, I'd never tuned carbs before and like Willy, I had to learn. There is actually a lot of info on the 'net but even so it does seem quite daunting. But in the end it's not actually that difficult at all to understand IMHO....it's maybe hard to visualise at first, that's all.

But you're right about the ignition, in the sense that if you have a problem with the ignition, you will drive yourself crazy trying to diagnose the issues from the carb-side. We went NUTS playing with the carbs, even going to the extent of swapping out a borrowed set of carbs, only to discover that a fault with the ignition wiring was not giving the coil a full serve of juice Once we fixed a couple of loose connections the engine fired up like a champ

But...for the time being let's see what we got with Willy's carbs. For all we know, he's got early DCOEs, but a well-meaning previous owner read on the 'net that the ideal idle setting is two and a half turns out on the idle screws (not realising that only works on later carbs) and hence it's way too rich and he's just a few turns of a screwdriver away from a decent tune

Oh and no I'm not on ausZcar...because I don't have a Z My Nissan product starts with an "S"

Edited March 30, 2010 by Babalouie

[ChrisZ]

Yeah i need to find a write up on the basic cettings for Dellorto's, got a new ZX dizzy and new wires so i'm ready to fire them up soon

Chris