32/36 tuning guide?

[FiatFunk]

Hey everyone, Just got a genuine weber 32/36 DGEV that i will be installing on my 79 Spider. Stock motor except for the single plane manifold and the emissions stuff I've disabled. There probably is a tuning guide on here, but I couldn't find it. What do you guys like to run in those carbs?
Thanks

[geospider]

Great set up for a stock motor.
They come pretty set up. You do need to set the float. Can go to Redline or Pierce Manifolds )what I used) for the spec. This tends to be the part that messes with folks.
I run a smaller Primary Idle jet: I think a 50 (helps with setting the idle mixture.)
Idle mix screw: start at about 1 1/2 turns out from seated and adjust from there.

https://www.carburetion.com/Weber/adjust.htm

a link to Carbs unlimited: a good starting point.

geo

[FiatFunk]

Thanks for the tips Geo! Looking forward to getting er dialed in.

[18Fiatsandcounting]

In addition to Geo's info, the "average" jetting for a 32/36 DFEV on a 2L engine is around 135 or 140 for the main jets, and 165 or 170 for the air correctors. Each engine is different of course. So, a starting point could be:

Primary: 135 main, 165 air corrector
Secondary: 140 main, 170 air corrector

That should get you in the ballpark, and you can then fine tune for your particular engine. My method of tuning is pretty old school: feeling how the engine runs across the rpm range, spark plug color, and gas mileage.

-Bryan

[geospider]

agreed.

This is what is in mine:

Out of the box:

idle main air corr
primary: 60 137 165

secondary: 50 140 170

As I mentioned, I swapped a 50 for the primary idle jet as it was too rich. you will read that using a 47 idle jet is also used (Brad Artique suggestion) if having difficulty with idle mix.

Per Bryan (the feel thing): and this is how I have done it
When at idle: turn the idle mix screw out until is starts to run rough, then back in: should increase in rpm, until rough again, then back out to the smoothest idle. THEN set your idle speed.

[FiatFunk]

I finally got to looking at the new carb, these are the guts:

Primary: idle 60, main 140, air 170
Secondary: idle 50, main 140, air 160

Adjusting the float (plastic) i cannot quite get the 51mm height that is called for, it hits the power valve. I'm only getting 49mm, not perfect, is that enough to be a problem?

Thanks
Greg

[18Fiatsandcounting]

Adjusting the float (plastic) i cannot quite get the 51mm height that is called for, it hits the power valve. I'm only getting 49mm, not perfect, is that enough to be a problem?

That's probably fine. Not sure why you're hitting the power valve, but maybe your float isn't quite the same profile as the usual one.

After you get the car running, idle it for a few seconds and pull off the float cover and see how much gas you have in the float bowl. A little over 1 inch deep is what you want, anything much more or less than that and you probably need to adjust the float.

-Bryan

[FiatFunk]

Thanks Bryan. Seems like a strange problem to have. The car is currently sitting out on a freezing cold driveway, waiting for the lada diff to return from the machine shop, hopefully get that back in soon, then into the garage for the new carb, timing belt, ball joints, studded tires and a few other bits.
Greg

[jon8christine]

I've got a 32/36 tuning jetting question, so hopefully this is a good place for it. I upgraded to the 32/36 a few years ago when the engine was stock. I'm at 6,200' and at the time I ended up with 50s in the idle jets, 137, 140 in the main jets, and 180, 165 in the air correctors. The idle speed screw was about 1-1/4 turns in and the mixture screw was 1-5/8 turns out. It may not have been perfect, but ran fine.

I've since built the engine (8mm domed pistons 0.8mm oversized 10.4:1 compression, 1mm oversized valves, 40-80 cams, mildly ported head, headers and 2.25" exhaust, electronic dizzy) and am still using the 32/36. I've got the engine timed and setting the carb I ended up with the idle speed screw a half turn out if that. The mixture screw is 7/8 turn in and it idles at 1,100 rpm (which is too high, but turning the speed screw out makes it idle pretty rough.)

The Weber manual says if the mixture screw is less than 1-1/2 turns out the idle jet (assume primary but doesn't say) is too large (rich). It also says increasing air over the fuel jet is better and won't reduce power, but it may be talking about the main jet. I pulled a spark plug after a drive around town and it was black, but it's also too cold of a plug (NGK 9).

I guess I'm asking if you think I need to drop to something smaller than a 50 (I think 45 is the smallest) for the idle jets? Or perhaps continue to increase the air jets?

[Nut124]

I would not worry too much about how many turns the idle mixture screw is open. Changing the idle jet from 50 to 45 is a huge change. The fact that Weber did not bother to make idle jets in smaller increments is because nobody really cares about precise idle mixture. A bit rich always runs good. Lean, not so much. And at these low speeds, fuel economy is not really a factor. As long as you do not flood or foul plugs, move on to tuning the top end.

The air corrector jets have nothing at all to do about the idle circuits. These are for the main circuit only. The idle circuit has its own, a pressed in one-size-fits all air jet. No-one ever messes with those.

How did you come to determine you static CR was 10.4? Is this based on head, piston dome volume measurements?

The NGK9 plug is way too cold. The plug selection or recommendation is not determined by the specs or parts of your engine but the actual use case. For regular daily driving, no sustained hot rodding, use the factory spec NGK6. For autocross or track days, use NGK7. For full out endurance racing use the NGK9.

The NGK9 plug is useless in terms of reading it for A/F mixture.

Reading plugs is hard anyway. Performance engines often run rich at idle and low load, which quickly makes plugs black or dark, in seconds. WOT top end mixture is what matters. For at load plug reading, run under (high) load for some time, long enough to clean the idle fouling, then turn off ignition, get off the gas and coast to stop, pull plugs, safely at a HWY exit ramp.

[jon8christine]

Got some NGK7s to install after checking cylinder compression later today. The 10.4:1 compression ratio came from Vicks website where I bought the domed pistons. They are 0.8mm oversized.

The AFR sensor is currently in the #2 cylinder runner (not ideal I know, but I figured it would be a good enough starting point until I got the bung welded on further down ... The instructions say 18" from the head. I think I remember seeing a picture with yours mounted their as well nut. Did you see a big change when you put it further down where it should be?

For tuning the main circuit (without a dyno trip) are you just using the AFR gauge to get into the mixture range you want? Do you mostly do that by adjusting the air correctors or fuel or both?

[jon8christine]

Guess one should actually check his jets before posting them. Must have made a change and not written it down. My jets when running the carb before I built the engine and subsequently how it sits now are:
Pri idle - 60
Sec idle - 50
Pri main - 137
Sec main - 140
Pri air - 165
Sec air - 160
Pri emulsion - f66
Sec emulsion - f50

Knowing that, I swapped out the 60 for a 50 I had on the primary idle. Now I just need it to get above freezing so I can run it.

[Nut124]

Your jetting looks like factory jetting, which should work OK.

Did you get a cranking compression number?

I have two AFR sensors; an old narrowband in the header and the wideband in the final Y.

I think you are running the same 8mm dome piston as I am. depending on whether your head has been surfaced and gasket thickness I think your SCR could be way over 11. I would try to get the cranking compression test done to get some more info.

Assuming your SCR is on the high side, I would try to avoid running any lean as it will increase cylinder temps. I hear these engines make best power at 12.5 AFR. I do not like to see anything above 13.5 at load for fear of detonation. At low speed cruising I will be OK with 11-13 AFT. I do not like running in the 10's but with the IDFs it seems unavoidable.

Get a good weber manual. My IDFs have 3 operating modes. Yours have this times two so it seems a bit confusing.

First, the primary idle jet and the idle mix screw control mixture at low speed, low load. This could be up to 30mph. At idle and very low speeds it is mainly the mix screw. Once the primary plate opens to the progression holes, the idle jet determines the mixture. Next the primary main circuit kicks in. I do not know at what point the secondary kicks in. The secondary seems to have the same 3 modes.

Im thinking under hard acceleration and at speeds above 80 the secondary rules.

I would be tempted to do testing where I disable or disconnect the secondary to see how far the engine can run on the primary alone. This would help in assessing which barrel to adjust.

[jon8christine]

Engine compression testing today yielded the following:

PSI No throttle. WOT
1. 155. 160
2. 154. 160
3. 140. 148
4. 154. 157

Not sure what's going on with cylinder 3, but they all seem good and not too high based off what I've read.

[Nut124]

Have you guys seen this:



A common manifold carb like the 32/36 D should work pretty well with factory jetting in any application. Unlike an IR setup, like my dual IDFs, common manifold carbs see pretty much continuous flow and apply fuel accordingly. In an IR IDF application the air flow thru each carb is not continuous, but stops completely during the compression and combustion phases. Tuning of these IR carbs is affected by cams, static compression etc.

If your 32/63 D engine feels sluggish, I would check:
- carb float level
- fuel pressure under load
- ignition timing and curve
- cranking compression (cam timing)
- cam timing

If you engine seems to run out of legs, plumb a fuel pressure gauge right next to the carb and run the hose/gauge under the hood to where you can see it while driving. Watch fuel pressure under load. If it drops, loaded fuel filter, gunked up lines, bad pump...