Carb Tuning

It’s been about 400 miles since the rebuild. The weather hasn’t been cooperating, so only 400 miles. Enough time though to do a plug check.

The engine is running smooth, clean, and quiet and has great throttle response. But it doesn’t have much go and is very lean. The engine was built really tight – very tight. The heater will blow warm air in about 45 seconds after start up. It runs fine throughout the rpm range, but simply doesn’t have much pick up.

My tuning is starting with the carb jetting. Other factors will be adjusted when I get the plugs / jetting closer, like timing and advance.

Below you’ll see a plug pic showing the classic signs of leanness, clean, no deposits, and the insulator is red/pink from lean running.



I purchased a jet kit for the 32/36 DGEV, part number 701 DGV 4 (for 4 cylinder engines). It comes with 3 larger stages of jets, including the Primary Idle, Air/Corrector, Main Jet and Pump Jets.

Below is a schematic of the Webber 32/36 with the jets circled.



I’ll post plug pics as I go through the jetting options.

Stay Tuned

Russ

Cool info, if you can list the actual jet and air bleed sizes that came with that kit it would be great. I'll see if I can find a better diagram and put the info in the tech section.

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Now I’m getting somewhere! The Jet Kit addresses the Primary circuits with minor changes to the Secondary circuits. Stage I was an improvement and showed just how lean it was running. It was an improvement but I was quick to go to Stage II.

With Stage II, I can now at least accelerate onto the entrance ramp with some confidence. I used a larger Main Jet on the secondary along with the other changes to the Primary circuits. The engine is running much cooler too.

I will put a couple of hundred miles on it then do another plug check. I suspect it’s still running lean. Gas mileage on tank one was 18.56mpg and on the second tank 21.56mpg, so the engine is loosening up. I will be curious to see what the mileage is with the larger jets, although it had to be done.

Stage III includes Single and Double Pump Jets along with larger Main Jets for both Primary and Secondary circuits. I suspect that I could easily go several more sizes up on both circuits before the blubbering starts. That ported / polished head along with the headers and exhaust made a huge difference. I may even toy with the idea of a 38 DGS and jet is down just to see how that works.

I will put together a table of Jet sizes of each stage and stock sizes to post them in a few days. In the mean time, it’s looking up!

Russ

Double pump jets?? The webers only have one accelerator pump, you can drill out the accelerator pump nozzle to inject into both venturi but unless you have a 34/34 or a 38 where both the primary and secondary open at the same time, all you will be doing is puddling fuel all over the place. By the way, larger is not always better on the accelerator pump nozzles, a smaller nozzle will have more pressure behind it and will spray/mist the fuel better when you hit the gas. I used to have a large one in mine, don't know what size it was, I put one from a Pinto in there which had an opening that was like half the size and my truck went from almost stalling when I punched it to flat out hauling .

You really need atleast an air fuel meter on there if you expect to half way decently tune it, or atleast hook a voltmeter to the O2 sensor and run it around a bit while recording readings.

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I think the jet kit includes a Double Pump Jet to use as the next step. You’re right that this carb is a Single Pump.

Reading plugs is a bit old school, but is a way to gauge the mixture nonetheless. I use this technique on bikes with fine results. Normally, I would get several sets of good ol’ NGK plugs to read each jet change. I might go ahead and get those, because reading new plugs is easier. Bike carbs are easier for me to understand, having worked on them many years. Auto carbs are a bit of a new experience.

Auto carbs have the basic three circuits, idle, mid and main. They go about it in a different way, though. I was half tempted to put 4 batwing-slide, 34mm, CV mikuni carbs on, or side draft Webbers, but the linkage and intake manifold would have been very costly.

I’m not using an 02 sensor, because the CPU is removed. I intend to put it on a dyno in the future just to see where I ended up. There is a dyno here in town that can hold an rpm and take readings at various rpms. In the mean time, I’ll continue with larger jets until I get blubbering and then back off a step or two. Then, I’ll work on the single power jet and the timing / advance. Step by step and note all changes is a way “old school” to make changes to jetting. It is time consuming, but that’s ok.

One of the changes that has had an impact is the high output Accel coil with iridium spark plugs. I’m sure the coil is over kill (90kv) with such low compression, but that should let me add some timing. It sure helps with starting with just a touch on the key and it fires up instantly.

Russ

Lol, if you're just running the performance can type or ecoil there is no way you're putting 90kv out unless you're running dual coils, and even if so 60kv is more than enough to do the job. I would drop the Accel coil and get something else, everyone I've known to get one including myself has had it go bad in relatively short amount of time. You arn't gaining any power out of the plugs the main purpose out of the different plug materials is to increase longevity of the plug and keep spark resistance lower over a longer period of time. If you where running the engine on like 15 lbs of boost or spraying nitrous or something there may be some benefits to using them that are worth the cost, but if you're changing you're plugs when you should, they arn't doing anything.

Plug reading will always be a great tool, the race team I worked for even with their millions of dollars worth of equipment hooked up to the engine on the dyno would still pull the plugs out and look at them under a microscope after any run on the dyno or a few practice laps. Under normal street driving it can only give you a general reading though. It cannot tell you at what rpm's you're lean, or rich or tell you if the power valve is opening right when it should. For the price of a couple sets of plugs, especially if you're using iridium, it's worth it to keep you're O2 sensor in there and get an air/fuel gauge.

One thing to do as soon as you can is to increase you're plug gap .005" - .010" over stock. With the extra power from the coil the system isn't going to be able to use all the power it's putting out. I know this as a fact from running my truck with an Accel coil and low impedance wires on an ignition scope. When the transistor in the magnetic pickup closes to turn on the primary circuit all the unused power creates a spike which overheats the ignition coil.

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w/ weber 32/36 pacesetter & 260 cam
jetting currently is:
140/145 main
f50/f50 em tube
165/165 air corr
60/50 idle
runs well; perhaps this info is helpful
curious what combo of jets u find best
wonder what others r running

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87 b2000 w/body change
webber;260cam;polished ports & pacesetter

Here is the result of my Jetting. It is now drivable and has decent acceleration. Now, I need to put more miles on and do the next plug check. Per the Jet Kit instructions, I’m right in the middle of the “sweet spot”. The two adjustments the kit keys on are the Idle Adjustment Screw and the Idle Air Adjustment Screw. Not much was done on the Secondary side and the transition from idle to full throttle is smooth.

Next step will be playing with the timing advance and up the secondary jets a bit, maybe play with the single power jet too.

Modifications
2.2L with 2.0 head with mechanical rockers
Ported / Polished Head
Pacesetter Ceramic Coated Header
Webber 32/36 DGEV Progress Link Carb
High flow Catalytic and Flowmaster Series 60 Muffler
Electric Fan
Accel High Output Coil
8.2mm Plug Wires
Iridium Plugs

I have about 500 miles on it now and it is enjoyable to drive. I look forward to more miles, but wonder what the jetting may do to mileage.

First tanks of gas 18.5mpg and the second tank 21.56mpg.

Russ