[Bosco2]

I'm trying to re-jet my 32/36 DGEV to run a bit richer (per emissions testing its at 1.18% CO at 2500 rpm). I'm not sure I understand the connection between the main jets and the air correction jets. My carb had 130 (pri) and 150 (sec) mains and 170 (pri) and 180 (sec) air corrections. I just put in a 140 (pri) main and changed the airs to 160 (pri) and 170 (sec) as from what I could see after searching the archives on here those air correctors seemed high. The car ran alot better, much smoother and stronger thru the rpms. Today as my son left for school I could see visible smoke (that I hope is fuel and not oil) swirling around the rear of the car as he drove down the street. Should I have just stopped after I put in the 140 main or should I have just brought down the airs to 160/170 and left the main jet alone?
Kinda lost.

 

[tekenaar]

32/36 DGEV mains and airs "tuning"

First, you're running strictly on the primary up to 2/3rds of throttle opening on that particular carb, which is most of the time on a DD. Second, what's your altitude there? Third, what are your pri/sec idles?

From what you've said about running stronger through the gears, it's the right direction, but may just need a little fine tuning now. Your original 130/170 primary and 150/180 secondary were a quite bit on the lean side and that's why you saw the improvement with the change to 140/160 pri and 150/170 sec, which richened things up considerably.

Mains are fairly self-explanatory, increase to richen, but airs are there to emulsify (aerate) the fuel flow and work opposite from mains, i.e. decrease to richen mixture (less air to fuel ratio). Once you've established the fuel component requirement of the engine, you then fine tune it by aerating it more or less (changing fuel/air ratio), understand?

You two-stepped the primary (130/170 to 140/160) and one-stepped the secondary (150/180 to 150/170), both richer. Increasing the mains by 10 richens the mixture ratio much more than decreasing the airs by 10, it's not a one-to-one ratio. That's why you "fine-tune" with airs.

I would leave secondary alone for now, but change primary air back to 170 to lean out primary "power" mixture somewhat and see what that does. That'll probably take care of the "smoking", but retain your new-found power.

 

[Bosco2]

Thanks for that explaination.....exactly what I was looking for. Will try just that as soon as my son gets home from school.

altitude here is 2100 ft. and I'll have to check the idles....I changed them awhile back to get my idle adjustments within the specs given on Redline's (I think) website.

Mike D.

 

[Bosco2]

The idles are 60 (pri) and 50 (sec). I didn't have another 170 air jet so I put them back to the original 170 (pri) and 180 (sec). It still runs very well and when revving it in the garage/driveway I don't see any smoke.

Thanks again for your explaination.

 

[tekenaar]

Idles and secondary tuning

The idles are 60 (pri) and 50 (sec). I didn't have another 170 air jet so I put them back to the original 170 (pri) and 180 (sec). It still runs very well and when revving it in the garage/driveway I don't see any smoke.

Thanks again for your explaination.

Try swapping primary and secondary idles after testing on your current 140/170 pri and 150/180 sec setup . . . you may need to buy a 55 idle and go to 55pri/60sec idles for further transition (just off-idle) fine tuning, but should be very close now.

You need to fully open the secondary and see how engine behaves under load, through the gears. That will tell you how the engine likes the secondary mixture. If you need to richen up the secondary slightly (bog, lag, hesitation, struggling), I would suggest changing the air back to 170, buy another.

 

[Bosco2]

Ok. I'll try the different idle jets. This morning it was smoking again as my son left the driveway but I was wondering if it was possibly due to the fact it had been idling for a few minutes with the choke engaged JUST prior to him leaving. hmmm

Also......how does a secondary "idle" jet fit into this scenario....I 've always wondered?? In my limited carb logic it seems only the primary would need be involved at idle or lower rpm.

Thanks for addressing my issues.
Mike

 

[tekenaar]

Ok. I'll try the different idle jets. This morning it was smoking again as my son left the driveway but I was wondering if it was possibly due to the fact it had been idling for a few minutes with the choke engaged JUST prior to him leaving. hmmm

Also......how does a secondary "idle" jet fit into this scenario....I 've always wondered?? In my limited carb logic it seems only the primary would need be involved at idle or lower rpm.

Thanks for addressing my issues.
Mike

Remember that on cold startup, not only are you running rich (choke on) but you're also heating up and vaporizing any condensation that always collects in your crank case and exhaust system on cool down. Between these two items, it will "smoke" a bit more than after complete warm-up . . . all cars do that. As long as it stops after warm-up, I wouldn't worry about it and don't think it is a "symptom" of any carb jetting anomaly.

As I've said NUMEROUS times before, "idle jet" is just a Weber naming convention and describes only HALF of its true function. I had explained the actual function in another thread here. Read this to help you understand the "idle" jet's importance in both barrels, i.e. idle AND transition fuel mixture in the primary, transition fuel mixture in the secondary . . . Without this, you'd get a HUGE BOG just as the secondary begins to open! Remember, this is a progressive carb and barrels open sequentially, not synchronously (simultaneously).

 

[Bosco2]

So a smaller numbered idle jet would result in a leaner mixture......unlike the air correctors?

 

[RallyBob]

A smaller numbered idle jet will result in a leaner transition from the 'true idle' (air/fuel mixture adjusted by idle mixture screw) into the main circuit (main jet). The idle mixture can still be adjusted via the idle mixture screw, but there is a leaner 'window' or range of motion you can adjust within.

Air correctors work opposite the idle and main jets....the higher the number, the leaner they get. And air correctors work in approximately a 3:1 ratio relative to a main jet. It'll take about three changes in size with an air corrector to make the same percentage difference in mixture as a main jet.

 

[Bosco2]

Thanks Bob,

I jetted this thing a bit richer and now I'm trying to lean it back (a little at a time) to no black smoke...yet still run as well as smooth and strong as it does now.

 

[Bosco2]

32/36 Dgev

Today I noticed that my car loses rpm....sorta like a rev limiter....at about or just under 6000rpm (at the yellow to red zone on the tach). Otherwise it seems to run fairly well. I'm thinking its a jetting problem on the secondary side. It's currently set-up (I think....lost my sheet with the jet settings) as Idles 55(pri), 50 or 45 (sec)......Mains 140 (pri), 150 (sec)....Airs 170 (pri) 180 (sec). I guess I still don't understand whether I should be changing the secondary idle jet size slightly (like maybe 50 to a 55) or changing the airs on the secondary (from 180 to 170). Which would affect the biggest difference??

 

[RallyBob]

The secondary idle jet will affect the response when the secondary barrel is opened. It won't affect the high rpm power at all.

Have you determined whether the engine is lean or rich at high rpms? Probably a good idea before you make any major changes.

 

[Bosco2]

i'm not sure if its lean or rich.........it was quite lean when last checked at the state emissions station.......ive since bumped the main primary from 130 to 140, reduced the idle from 60 to 55. and on the secondary I think I might have reduced the idle from 50 to 45 but im not sure. It seems richer...but i dont have a way to test it at my home.

 

[tekenaar]

Higher altitude too, right?

Today I noticed that my car loses rpm....sorta like a rev limiter....at about or just under 6000rpm (at the yellow to red zone on the tach). Otherwise it seems to run fairly well. I'm thinking its a jetting problem on the secondary side. It's currently set-up (I think....lost my sheet with the jet settings) as Idles 55(pri), 50 or 45 (sec)......Mains 140 (pri), 150 (sec)....Airs 170 (pri) 180 (sec). I guess I still don't understand whether I should be changing the secondary idle jet size slightly (like maybe 50 to a 55) or changing the airs on the secondary (from 180 to 170). Which would affect the biggest difference??

The secondary idle jet will affect the response when the secondary barrel is opened. It won't affect the high rpm power at all.

Have you determined whether the engine is lean or rich at high rpms? Probably a good idea before you make any major changes.

Bob is spot on . . . as always. You're at higher altitude there, right? You're very close to being dialed in from what you're saying here. Just a bit more "fiddlin"!

I'd leave the secondary air at 180 and richen secondary main to 155 first. Then, if you still need a bit more at the top end, back off secondary air to 175.

 

[Bosco2]

Thanks Bob and Otto.

I think I'll fiddle with the secondary idle to try and cure a slight lag when the secondary throttle opens... and move the secondary main to 155 (which should get me to at least redline).

 

[tekenaar]

Secondary "idle"

Thanks Bob and Otto.

I think I'll fiddle with the secondary idle to try and cure a slight lag when the secondary throttle opens... and move the secondary main to 155 (which should get me to at least redline).

Didn't want to address too many things at once, but thought you were a little "light" on the secondary idle as well . . . maybe 50 or 55 is more like it. Remember, this ONLY helps in the secondary transition area between closed throttle to where main/air mixture begins.

 

[Bosco2]

I appreciate that...I had been wondering if it needed a little transition enrichment due to the slight bog when moving to the secondary. I'm trying to move it up slowly as I have a state emissions test looming in late March and (besides an idle test) they do a test at close to 2000 rpm, sustained over a couple minutes (it seems). From what I gather on here, that rpm will include operation of the secondary idle jet. Other than looking at plugs I have no way to analyze the mixture. At this point they are tan and dry after warming-up the engine (and the sprint manifold) completely.

The one concern I do have is that upon initial morning startup it leaves a fairly large exhaust "fan" of carbon/water deposits on my garage floor....but I'm going with the idea that this is due soley to a cold engine and the choke being engaged.......and once warm (given the plug condition) it is running somewhat within the realm of "nearly correct".