Weber 38 DGAS Tuning

[Joe Van Wagnen]

I am trying to dial in the main jets on my weber 38 dgas... here is the setup i have right now

Idle Jets 45
air corrector 170
emulsion tube f66
main jets 142


i warmed the engine up and then ran it at 3500 rpm's for 5 minutes and then shut it off and pulled plug #2 and took a pic... the color of the porcelin and the ground strap is tan to light brown
can you guys tell from the pic if the color is right??

also on the 38 dgas the primarys and secondaries are tied together and open and close together so i cant do much for checking the secondaries by them selves.... is it good enough to check them together??

Thanks!!

Joe Van Wagnen
71 2.4L GT

[Joe Van Wagnen]

here is another pic

Joe Van Wagnen

[RallyBob]

Difficult to see the coloring in a photo, but in general it looks a little bit lean. I suspect this is from your 2.4 Joe?

Based on some 2.0's and 2.2's I've had to rejet, I would think you'd need closer to 155 main jets and 175 to 180 airs. Might need 50 idle jets. With a DGAS you don't have to check primaries/secondaries separately.

Bob

[Joe Van Wagnen]

Bob

yes it is my 2.4L.... i have some 150 mains ill install them and then test again.... i have now figured out how to take a pic in macro mode so ill post a real close pic

Thanks

Joe

[Joe Van Wagnen]

Bob

i installed the 150 mains and retested... here is the setup now

2.4L 38dgas

Idle jets 45
air corrector 185 i have a 170 to install when the time is right
emulsion tube F66
Main Jets 150

the plug color is slightly darker brown than with the 142 mains

is it still too lean?? if so what would be a good group of mains to order to get it right??153,156,159??


Thanks

Joe

[Joe Van Wagnen]

Bob..

here is another view of the 150 mains jets

[RallyBob]

It seems to be a little better coloring, but again, it's difficult to tell on a computer screen. The area I can't see is deeper into the recess of the plug on the porcelain. This is a better indication, as the outer surface is easily obscured with carbon. With a 30X magnifier, you can see if there is any porcelain discoloration or glazing, plus you can tell if there is a leanness issue from deposits.

Generally, when you order jets for Webers, they are sold in increments of *5*. So you'd order 155, 160, 165, etc. An increase of your main jet from 142 to 150 gives a fuel passageway with about 11% more area (1.42 mm dia to 1.50 mm dia, area of 1.42 is 1.5836 mm2, the 1.50 is 1.7671 mm2).

Bob

[Joe Van Wagnen]

Bob

ill order 155 and 160 mains and 175 and 180 air correctors ( i have 185's and 170's)... then get back to the jetting

in the mean time ill read as much as i can on spark plug reading there is a bunch of information on the net about it... with pics


Thanks For your help!!

Joe Van Wagnen
71 2.4L GT

[Joe Van Wagnen]

Bob

i recieved the new jets for the 38 dgas... and while i was waiting i did a bunch of reading on how to read plugs.... more than one article sugested only reading new plugs and not to try to read old plugs... so i bought 4 more plugs and put a new plug in the #2 cylinder with the 150 and 155 main jets.... after running at 3000 rpm for 5-7 minutes i pulled the plugs and tried to read them with a 20 x lighted hand lens.... in both cases the only thing i could tell was that the plugs were alittle hot ( the color change on the ground strap was real close to base ring) and i couldnt tell anything about the mixture (couldnt see any color on the base ring or down toward the base of the ceramic) got any suggestions??? also i couldnt see any deposits on the ceramic

Joe

[RallyBob]

Sounds like it's still real lean. I obviously can't be there to help out, but can you tell if it runs better in general from the larger jets? Is throttle response better? Engine sound better? Are you just letting the car run in your driveway or are you actually driving it? You'll know right away if you're heading in the right direction with your jetting by actually driving it, the power difference will be very noticeable if it is in fact that lean.

I'd keep adding fuel until you see negative results. Incrementally of course. And for jetting purposes, there's no reason to put in all 6 screws on the top of the carburetor...two will do just fine. No need to hook up the choke also. This will reduce jet-changing times down to about 2 minutes.

Bob

[Joe Van Wagnen]

The Gt is still on jackstands until the ventilated rotors and calipers get here this week.... then ill be able to drive it

i noticed a big diffrence in throttle responce from the 142 to the 150 mains... i couldnt tell much diffrence when i installed the 155's
should i go back to the used plug (250 miles) and then run it on the road??

how long should it take to color up a new plug for reading?? i couldnt see hardly anything after five minutes on jackstands

i have a set of platinums i can install... are they easier to read??

Thanks!!

Joe

[RallyBob]

Plugs do take some time to color up (unless it's very rich). They will color up better on the road too. Leave out the platinums, they will give a 'false' reading, showing the engine is leaner than it really is. In fact, if you have a hi-po ignition, don't use the platinums at all. I have had the best results with Opels (street and race) with NGK u-grooves. Up to 9500 rpms.

I'd put the new plugs in the car, and go look for hills. Any long moderate hills that you can run in say, third gear, and maintain a partial engine load at a moderate rpms (4k or so) would be good. I had a favorite highway of mine near my old shop...great for testing in the lower gears for jetting (changed jets roadside). It was also low traffic, so I did a few impromptu top speed tests as well. That was mostly for evaluation of the fuel system (pump and fuel lines) and the air corrector sizing. BTW, don't hammer on your car if you have stock fuel lines. With that engine, a Weber carb and stock fuel lines (8mm or 5/16"), you'll empty the fuel bowl somewhere around the top of third gear. If you keep your foot in it, you WILL burn a piston. Upgrade to 3/8" fuel lines.

Bob

[ConreroGT]

Do you mean to have 3/8" lines all the way from the tank? I have my motor and tranny out right now. My engine will have dual webers when it gets put back in. I have 3/8 lines from the fuel pump to the carbs at the moment. (Should I go w/ an electric fuel pump also?)



-kyle

[RallyBob]

Originally posted by notavette Do you mean to have 3/8" lines all the way from the tank? I have my motor and tranny out right now. My engine will have dual webers when it gets put back in. I have 3/8 lines from the fuel pump to the carbs at the moment. (Should I go w/ an electric fuel pump also?)

If you have dual Webers, then the fuel line size is not an issue....you have two fuel bowls, and they're EACH larger than a downdraft Weber's fuel bowl. You'd have to have SERIOUS power to empty those out, even with 5/16" lines. I would use an electric pump, and a regulator just before the carbs...set to 3.5 psi.

Bob